Re: [Emc-users] Micro-switch repeatability

[Dave Cole]

On 2/22/2016 9:15 AM, andy pugh wrote:
> On 17 February 2016 at 17:14, Dave Cole  wrote:
>> Prox switches are just the opposite.   Most are even waterproof.
>> Prox switches are becoming very cheap.   Someplace is trying to sell me
>> some for about $10 each with a cable.
>> I've used Prox switches on very expensive machines for homing and limits
>> and they just work.   No call backs.
> Those must be the expensive ones :-)
> http://www.ebay.co.uk/itm/390880485798 as a random example, that's about $5.
>
> NPN work better with parports and mesa cards (not sure about Pico).
> They almost all need a >5V power supply, but NPN ones look like a
> switch-to-gnd to 5V logic, so that isn't a problem.
> I run mine at 12V because it is convenient.
>
> Note that they come in a variety of diameters and detection distances,
> and that there are two types. The one in the link above will _not_
> work if embedded in an iron casting. This type, where the threaded
> portion reaches right to the end (called "shielded") will work in that
> situation.
> http://www.ebay.co.uk/itm/121776227835
> These have a shorter detection distance.
> I have recently been tending to use these embedded into the machine
> out of harms way and picking up on drilled holes in the slideways as
> targets. I do try to find non-bearing surfaces, of course.
> There are two here:
> https://picasaweb.google.com/108164504656404380542/HarrisonMill#5989135693933177186
>
> There is also an alternative mounting style that might be very
> convenient for an extruded-frame machine:
> http://www.ebay.co.uk/itm/121766473917
>

>>Those must be the expensive ones :-)

Yes, but the ones I buy are extra shiny.  :-)
Seriously, the 12 mm ones that I spec out most often are about $18 with a quick 
connect plug on the back end.   The cord with the connector is another $9-$20 
depending on length.  All of the ones I have seen die have been due to customer 
tweaking or abuse, or extreme corrosion.  In general, if the plastic projects 
from the end of the metal shell, it is an unshielded prox.

Dave




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Re: [Emc-users] Micro-switch repeatability

[andy pugh]

On 17 February 2016 at 17:14, Dave Cole  wrote:
> Prox switches are just the opposite.   Most are even waterproof.
> Prox switches are becoming very cheap.   Someplace is trying to sell me
> some for about $10 each with a cable.
> I've used Prox switches on very expensive machines for homing and limits
> and they just work.   No call backs.

Those must be the expensive ones :-)
http://www.ebay.co.uk/itm/390880485798 as a random example, that's about $5.

NPN work better with parports and mesa cards (not sure about Pico).
They almost all need a >5V power supply, but NPN ones look like a
switch-to-gnd to 5V logic, so that isn't a problem.
I run mine at 12V because it is convenient.

Note that they come in a variety of diameters and detection distances,
and that there are two types. The one in the link above will _not_
work if embedded in an iron casting. This type, where the threaded
portion reaches right to the end (called "shielded") will work in that
situation.
http://www.ebay.co.uk/itm/121776227835
These have a shorter detection distance.
I have recently been tending to use these embedded into the machine
out of harms way and picking up on drilled holes in the slideways as
targets. I do try to find non-bearing surfaces, of course.
There are two here:
https://picasaweb.google.com/108164504656404380542/HarrisonMill#5989135693933177186

There is also an alternative mounting style that might be very
convenient for an extruded-frame machine:
http://www.ebay.co.uk/itm/121766473917


-- 
atp
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http://www.ifixit.com/Manifesto

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Re: [Emc-users] Micro-switch repeatability

[Dave Cole]

I understand your situation.
In light of what you said you might want to go with Prox switches and 
forget about mechanical microswitches.
My reason is this:  Small cheap mechanical microswitches are very easy 
to break and hard to mount, protect and adjust.
Prox switches are just the opposite.   Most are even waterproof.
Prox switches are becoming very cheap.   Someplace is trying to sell me 
some for about $10 each with a cable.
I've used Prox switches on very expensive machines for homing and limits 
and they just work.   No call backs.

Dave

On 2/17/2016 11:10 AM, Bertho Stultiens wrote:
> On 02/17/2016 04:28 PM, Dave Cole wrote:
>> The other approach to take is to forget about home switches and do a
>> touch off on the work or the stops by using a probe.
> Yes, you are right. That would be a good solution.
>
> I may just want to clarify... The whole discussion is not about the
> correct or best way to do this. My implementation target is a cheap
> router and a lot of not-so-experienced operators.
>
> However, the speculative and inquisitive mind got hold of me when
> thinking about the switches and started to question the switches. The
> micro-switches for themselves are actually interesting how they behave.
>
> My thoughts here were more like, why pay a lot of money if cheap stuff
> can do the trick. Is there data on the cheap stuff as to prove that the
> expensive stuff is better. If the cheap stuff works well, or works
> badly, then that would be a nice insight if documented with data.
>
>
>> Mount the probe in in the spindle and touch off on the stops or the
>> workpiece to obtain a zero position.
>> There are some relatively inexpensive probes for sale.
>> Most homing systems I have used on machines are not that accurate.
>> Homing only positions the spindle or carriage to the machine, and not
>> the workpiece.
> The point of homing, in the application at hand, is not about perfect
> accuracy. It is to make sure that the machine is in a known state.
>
> The mounting/unmounting of a probe in the spindle will be a challenge
> for non-experienced operators.
>
>
>> If you clamp the workpiece against a stop and there is a spec of grit or
>> a rough edge or interference then super accurate homing becomes useless.
>> Referencing to the workpiece is usually what people usually really want
> You are right that the work-piece is the actual reference and that it
> takes precedence when actually performing the work. However, from what I
> saw on the old router at the hackerspace, we want to automate the
> machine boundaries. At least we can make the machine not run past its
> ends. Having a (home-) side more accurate than simple end-stops is just
> a bonus.
>
> Doing proper touch-off on the work-piece or calibrating the work-piece
> position is a story that merits a whole thread for itself, I guess.
>
>

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Re: [Emc-users] Micro-switch repeatability

[Chris Albertson]

OK could be the optical switch sonly used for self-calibration when the
printer is first powered up.  Still the little things are very accurate.  I
bought some a while back, I think a bag of them for $5 on eBay.

Does the printer need to do a SLOW home one each line?  I thought the
advantage of an optical switch was that there was not physical contact and
you can blow through them at any speed.  Simply note the encoder count as
you pass.  This would mean it self corrects for any missed steps.   We
would need the firmware source code to really know for sure and even then
different printers might be different.

I've used these to build a motor shaft encoder, you need two per shaft for
quadrature.  With a mother spinning at a couple thousand RPM and over a
dozen slots on the disk you get a decently fast pulse rate.  The device
would handle a very high speed, certainly no need to slow down and bump.
In fact I wonder if the slow pass the printer makes is not for some kind of
backup mechanical switch?


In any case anyone with a machine tool and a dial indicator could rig up a
test and determine for themselves the specs for a mechanical or optical
switch. Just watch on the dial where the switch trips and repeat a few
dozen times.

On Tue, Feb 16, 2016 at 8:40 PM, John Dammeyer <jo...@autoartisans.com>
wrote:

> I believe they only use the home switch to figure out where the end of the
> printer is.  Once established for page of printing it's not used to
> reference until perhaps the next page and probably not even then.  From
> then
> on the positioning is based on the motor steps.  Just think if they had to
> do a slow homing operation on every line.
>
> John Dammeyer
>
>
> > -Original Message-
> > From: Chris Albertson [mailto:albertson.ch...@gmail.com]
> > Sent: February-16-16 6:34 PM
> > To: Enhanced Machine Controller (EMC)
> > Subject: Re: [Emc-users] Micro-switch repeatability
> >
> >
> > Look at how inkjet printers work.  They need to trip a home switch so
> that
> > each line of sprayed ink lines on to better then 1/1000th of an inch.
> They
> > use a low cost optical device.  There is a slot cut in a plastic block.
> > One one side is a LED on the other a light detector.  The look at each
> > other through a pin hole.  They are very reputable and you can get then
> for
> > free from salvaged printers.   One trick is to modulate he LED's light at
> > about 30KHz and use an RC filter on the detector so as to be insensitive
> to
> > absent light.   The plastic block the interrupts the beam is just a
> simple
> > square, no slot or hole.  If you have to buy a new one the cost is about
> $1.
> >
> > On Tue, Feb 16, 2016 at 6:46 AM, Roland Jollivet
> <roland.jolli...@gmail.com>
> > wrote:
> >
> > > On 16 February 2016 at 14:46, Bertho Stultiens <ber...@vagrearg.org>
> > > wrote:
> > >
> > > > On 02/16/2016 01:38 PM, Nicklas Karlsson wrote:
> > > > >>>> It seems that the micro-switches are well suited for the
> purpose,
> > > but
> > > > I
> > > > >>>> guess some hard (unbiased) data has yet to be gathered (outside
> of
> > a
> > > > mill).
> > > > >>> The alternatives seem to have the same problems of repeatability.
> > > Using
> > > > >>> a hall sensor or optical one will give the same problems.
> > > > Micro-switches
> > > > >>> are at least inherently mechanically constrained.
> > > > >> Indeed, unless you can crush them. There must be a
> run-into-the-wall
> > > > >> protection, as mentioned earlier, to prevent killing your switch.
> > > > >
> > > > > Pass over the switch might be possible?
> > > >
> > > > No. The datasheets I've read all say the same that you must activate
> the
> > > > plunger straigt on. Any angle will give you bad performance. Any
> > > > sideways stress on the plunger can kill the plunger assembly.
> > > >
> > > > The only alternative is to use a level-based micro-switch. That,
> > > > however, will probably make it less accurate. Especially when you
> move
> > > > over it side-ways. The angle of attack is too small with respect to
> the
> > > > travel distance.
> > > >
> > > > --
> > > > Greetings Bertho
> > > >
> > > >
> > > >
> > > That's not true. Use a switch like this
> > > <
> > > http://uk.rs-online.com/web/p/microswitches/1031645/?searchTerm=103-
> > 1645

Re: [Emc-users] Micro-switch repeatability

[Bertho Stultiens]

On 02/17/2016 04:28 PM, Dave Cole wrote:
> The other approach to take is to forget about home switches and do a 
> touch off on the work or the stops by using a probe.

Yes, you are right. That would be a good solution.

I may just want to clarify... The whole discussion is not about the
correct or best way to do this. My implementation target is a cheap
router and a lot of not-so-experienced operators.

However, the speculative and inquisitive mind got hold of me when
thinking about the switches and started to question the switches. The
micro-switches for themselves are actually interesting how they behave.

My thoughts here were more like, why pay a lot of money if cheap stuff
can do the trick. Is there data on the cheap stuff as to prove that the
expensive stuff is better. If the cheap stuff works well, or works
badly, then that would be a nice insight if documented with data.


> Mount the probe in in the spindle and touch off on the stops or the 
> workpiece to obtain a zero position.
> There are some relatively inexpensive probes for sale.
> Most homing systems I have used on machines are not that accurate.  
> Homing only positions the spindle or carriage to the machine, and not 
> the workpiece.

The point of homing, in the application at hand, is not about perfect
accuracy. It is to make sure that the machine is in a known state.

The mounting/unmounting of a probe in the spindle will be a challenge
for non-experienced operators.


> If you clamp the workpiece against a stop and there is a spec of grit or 
> a rough edge or interference then super accurate homing becomes useless.
> Referencing to the workpiece is usually what people usually really want

You are right that the work-piece is the actual reference and that it
takes precedence when actually performing the work. However, from what I
saw on the old router at the hackerspace, we want to automate the
machine boundaries. At least we can make the machine not run past its
ends. Having a (home-) side more accurate than simple end-stops is just
a bonus.

Doing proper touch-off on the work-piece or calibrating the work-piece
position is a story that merits a whole thread for itself, I guess.


-- 
Greetings Bertho

(disclaimers are disclaimed)

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Re: [Emc-users] Micro-switch repeatability

[Dave Cole]

The other approach to take is to forget about home switches and do a 
touch off on the work or the stops by using a probe.
Mount the probe in in the spindle and touch off on the stops or the 
workpiece to obtain a zero position.
There are some relatively inexpensive probes for sale.
Most homing systems I have used on machines are not that accurate.  
Homing only positions the spindle or carriage to the machine, and not 
the workpiece.
If you clamp the workpiece against a stop and there is a spec of grit or 
a rough edge or interference then super accurate homing becomes useless.
Referencing to the workpiece is usually what people usually really want

Dave

On 2/17/2016 7:52 AM, Bertho Stultiens wrote:
> On 02/17/2016 04:28 AM, Gregg Eshelman wrote:
>>> I'm now considering to take an old CD player and move the
>>> laser-assembly onto several micro-switches at different speeds. The
>>> laser-assembly is sub-micrometer accurate (CD track-separation runs at
>>> 1.5...1.6 um) and generally uses a simple stepper.
>> They don't get that accuracy with the stepper. The lens is suspended on
>> springs and uses magnetic coils for fine positioning radially for
>> tracking and vertically to focus.
> You are right. I was overly optimistic and too eager to use something on
> my desk. It is a darn difficult task to make something accurate.
>
> I did a wholy unscientific test on a no-name micro-switch with my
> calliper (0.01mm resolution) and was looking at about -0.01/+0.05mm
> variability. Most of that variability was most likely caused by me not
> holding the switch firmly enough.
>
> However, it does show that the activation of the switch is pretty
> consisent. It looks like a +/-0.01mm repeatability is readily in that
> switch (if not better), which again seems to align pretty well with
> other's experience.
>
>

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Re: [Emc-users] Micro-switch repeatability

[Bertho Stultiens]

On 02/17/2016 04:28 AM, Gregg Eshelman wrote:
>> I'm now considering to take an old CD player and move the
>> laser-assembly onto several micro-switches at different speeds. The
>> laser-assembly is sub-micrometer accurate (CD track-separation runs at
>> 1.5...1.6 um) and generally uses a simple stepper.
> 
> They don't get that accuracy with the stepper. The lens is suspended on 
> springs and uses magnetic coils for fine positioning radially for 
> tracking and vertically to focus.

You are right. I was overly optimistic and too eager to use something on
my desk. It is a darn difficult task to make something accurate.

I did a wholy unscientific test on a no-name micro-switch with my
calliper (0.01mm resolution) and was looking at about -0.01/+0.05mm
variability. Most of that variability was most likely caused by me not
holding the switch firmly enough.

However, it does show that the activation of the switch is pretty
consisent. It looks like a +/-0.01mm repeatability is readily in that
switch (if not better), which again seems to align pretty well with
other's experience.


-- 
Greetings Bertho

(disclaimers are disclaimed)

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Re: [Emc-users] Micro-switch repeatability

[Gregg Eshelman]

On 2/16/2016 9:40 PM, John Dammeyer wrote:
> I believe they only use the home switch to figure out where the end of the
> printer is.  Once established for page of printing it's not used to
> reference until perhaps the next page and probably not even then.  From then
> on the positioning is based on the motor steps.  Just think if they had to
> do a slow homing operation on every line.

They use a linear or rotary encoder. HP's mostly use a spring tensioned 
plastic strip behind the carriage, with optical sensors straddling it.

Others use a thin plastic disk on one of the shafts in the drivetrain.

A common cause of problems with the linear type is ink fog on the strip. 
Cleaning gently with a bit of damp paper towel folded over the strip can 
often fix problems where the printer wants to slam the carriage against 
the ends. You have to start the printer up then pull the power cord 
after it takes the carriage out of its parked position. That's so you 
can slide it to be able to clean the whole strip.

Cleaning the disk encoders involves taking the printer apart. Some 
printers seem to be designed to be serviced, the higher end HP inkjets 
used to have a panel on one end for easy removal of the 'dock' so the 
nozzle wipers, priming system and waste ink sump and absorber could be 
pulled out and cleaned.

Other printers, well, they *can* be taken apart but the case may not 
look so pretty after reassembly.


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Re: [Emc-users] Micro-switch repeatability

[John Dammeyer]

I believe they only use the home switch to figure out where the end of the
printer is.  Once established for page of printing it's not used to
reference until perhaps the next page and probably not even then.  From then
on the positioning is based on the motor steps.  Just think if they had to
do a slow homing operation on every line.

John Dammeyer


> -Original Message-
> From: Chris Albertson [mailto:albertson.ch...@gmail.com]
> Sent: February-16-16 6:34 PM
> To: Enhanced Machine Controller (EMC)
> Subject: Re: [Emc-users] Micro-switch repeatability
> 
> 
> Look at how inkjet printers work.  They need to trip a home switch so that
> each line of sprayed ink lines on to better then 1/1000th of an inch.
They
> use a low cost optical device.  There is a slot cut in a plastic block.
> One one side is a LED on the other a light detector.  The look at each
> other through a pin hole.  They are very reputable and you can get then
for
> free from salvaged printers.   One trick is to modulate he LED's light at
> about 30KHz and use an RC filter on the detector so as to be insensitive
to
> absent light.   The plastic block the interrupts the beam is just a simple
> square, no slot or hole.  If you have to buy a new one the cost is about
$1.
> 
> On Tue, Feb 16, 2016 at 6:46 AM, Roland Jollivet
<roland.jolli...@gmail.com>
> wrote:
> 
> > On 16 February 2016 at 14:46, Bertho Stultiens <ber...@vagrearg.org>
> > wrote:
> >
> > > On 02/16/2016 01:38 PM, Nicklas Karlsson wrote:
> > > >>>> It seems that the micro-switches are well suited for the purpose,
> > but
> > > I
> > > >>>> guess some hard (unbiased) data has yet to be gathered (outside
of
> a
> > > mill).
> > > >>> The alternatives seem to have the same problems of repeatability.
> > Using
> > > >>> a hall sensor or optical one will give the same problems.
> > > Micro-switches
> > > >>> are at least inherently mechanically constrained.
> > > >> Indeed, unless you can crush them. There must be a
run-into-the-wall
> > > >> protection, as mentioned earlier, to prevent killing your switch.
> > > >
> > > > Pass over the switch might be possible?
> > >
> > > No. The datasheets I've read all say the same that you must activate
the
> > > plunger straigt on. Any angle will give you bad performance. Any
> > > sideways stress on the plunger can kill the plunger assembly.
> > >
> > > The only alternative is to use a level-based micro-switch. That,
> > > however, will probably make it less accurate. Especially when you move
> > > over it side-ways. The angle of attack is too small with respect to
the
> > > travel distance.
> > >
> > > --
> > > Greetings Bertho
> > >
> > >
> > >
> > That's not true. Use a switch like this
> > <
> > http://uk.rs-online.com/web/p/microswitches/1031645/?searchTerm=103-
> 1645
> data=636F3D3126696E3D4931384E525353746F636B4E756D6265724D504E266C
> 753D656E266D6D3D6D61746368616C6C26706D3D5E5C647B337D5B5C732D2F2
> 55C2E2C5D5C647B332C347D2426706F3D313426736E3D592673743D52535F5354
> 4F434B5F4E554D4245522677633D4E4F4E45267573743D3130332D3136343526
> > >,
> > where the roller is almost directly over the plunger.
> > Then, use a wiper with an edge set at about 70deg. When this approaches
> the
> > switch, the angled edge will cause full travel over less than 1mm. After
> > that, overtravel will have no effect.
> >
> > I've never seen a travel limit switch used head-on in a machine. It's a
> > ticket to disaster.
> >
> > Regards
> > Roland
> >
> >

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> >
> 
> 
> 
> --
> 
> Chris Albertson
> Redondo Beach, California
>

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Re: [Emc-users] Micro-switch repeatability

[Gregg Eshelman]

On 2/16/2016 6:47 AM, Bertho Stultiens wrote:

> The micro-switches look like they can manage at almost no cost. But then
> my curiosity got in my way on how far you actually can go with the
> cheapo method. I'm now considering to take an old CD player and move the
> laser-assembly onto several micro-switches at different speeds. The
> laser-assembly is sub-micrometer accurate (CD track-separation runs at
> 1.5...1.6 um) and generally uses a simple stepper.

They don't get that accuracy with the stepper. The lens is suspended on 
springs and uses magnetic coils for fine positioning radially for 
tracking and vertically to focus.


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Re: [Emc-users] Micro-switch repeatability

[Chris Albertson]

Look at how inkjet printers work.  They need to trip a home switch so that
each line of sprayed ink lines on to better then 1/1000th of an inch.  They
use a low cost optical device.  There is a slot cut in a plastic block.
One one side is a LED on the other a light detector.  The look at each
other through a pin hole.  They are very reputable and you can get then for
free from salvaged printers.   One trick is to modulate he LED's light at
about 30KHz and use an RC filter on the detector so as to be insensitive to
absent light.   The plastic block the interrupts the beam is just a simple
square, no slot or hole.  If you have to buy a new one the cost is about $1.

On Tue, Feb 16, 2016 at 6:46 AM, Roland Jollivet 
wrote:

> On 16 February 2016 at 14:46, Bertho Stultiens 
> wrote:
>
> > On 02/16/2016 01:38 PM, Nicklas Karlsson wrote:
> >  It seems that the micro-switches are well suited for the purpose,
> but
> > I
> >  guess some hard (unbiased) data has yet to be gathered (outside of a
> > mill).
> > >>> The alternatives seem to have the same problems of repeatability.
> Using
> > >>> a hall sensor or optical one will give the same problems.
> > Micro-switches
> > >>> are at least inherently mechanically constrained.
> > >> Indeed, unless you can crush them. There must be a run-into-the-wall
> > >> protection, as mentioned earlier, to prevent killing your switch.
> > >
> > > Pass over the switch might be possible?
> >
> > No. The datasheets I've read all say the same that you must activate the
> > plunger straigt on. Any angle will give you bad performance. Any
> > sideways stress on the plunger can kill the plunger assembly.
> >
> > The only alternative is to use a level-based micro-switch. That,
> > however, will probably make it less accurate. Especially when you move
> > over it side-ways. The angle of attack is too small with respect to the
> > travel distance.
> >
> > --
> > Greetings Bertho
> >
> >
> >
> That's not true. Use a switch like this
> <
> http://uk.rs-online.com/web/p/microswitches/1031645/?searchTerm=103-1645=636F3D3126696E3D4931384E525353746F636B4E756D6265724D504E266C753D656E266D6D3D6D61746368616C6C26706D3D5E5C647B337D5B5C732D2F255C2E2C5D5C647B332C347D2426706F3D313426736E3D592673743D52535F53544F434B5F4E554D4245522677633D4E4F4E45267573743D3130332D3136343526
> >,
> where the roller is almost directly over the plunger.
> Then, use a wiper with an edge set at about 70deg. When this approaches the
> switch, the angled edge will cause full travel over less than 1mm. After
> that, overtravel will have no effect.
>
> I've never seen a travel limit switch used head-on in a machine. It's a
> ticket to disaster.
>
> Regards
> Roland
>
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Re: [Emc-users] Micro-switch repeatability

[TJoseph Powderly]

agreed
a near home switch
and
a home switch

fanuc called the near hone a 'decel switch'
tomp

On 02/16/2016 10:42 PM, Kurt M. Sanger wrote:
> When we were building high resolution printers we would use an optical
> switch looking at a rotary flag in series with a linear switch to define
> home.  We repeated well within ten thousandths of an inch.
>
> Kurt Sanger
>


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Re: [Emc-users] Micro-switch repeatability

[Ed]

On 02/16/2016 06:46 AM, Bertho Stultiens wrote:
> The only alternative is to use a level-based micro-switch. That, 
> however, will probably make it less accurate. Especially when you move 
> over it side-ways. The angle of attack is too small with respect to 
> the travel distance. 


I use roller lever switches bought from DigiKey on my CHNC lathe on a 
pass by setup. That lets me have the limit switches past the home and 
not have to worry about crashing the switch. Repeatability was about 
.0003 inches before the Index pulse was implemented, now within a tenth. 
Use a fairly steep ramp and you get better results.

Ed.


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Re: [Emc-users] Micro-switch repeatability

[Kurt M. Sanger]

When we were building high resolution printers we would use an optical 
switch looking at a rotary flag in series with a linear switch to define 
home.  We repeated well within ten thousandths of an inch.

Kurt Sanger

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Re: [Emc-users] Micro-switch repeatability

[Bertho Stultiens]

On 02/16/2016 03:15 PM, TJoseph Powderly wrote:
>> I heard rumors here a while ago about micro meter accuracy switch
>> but I guess it might be a little bit expensive.
> my-com switches, 1um guaranteed. every good german wedm uses them
> and high end japanese
> my-com
> yes expensive   paeng maak!  but damn accurate

Yes, 10um ... 5um version starts at about $200, the 1um version is
between $800 and $1500 (depending where you look and what manufacturer).
Actually, the high-side of the price knows no limit.

The whole machine cost $1500 (used) and is about $3500 new. I /could/
install switches more expensive than the machine, but I guess that it
would be slight overkill, not much, but just a teensy bit of overkill.

Hence the humble inquiry into cheapo micro-switches ;-)


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Re: [Emc-users] Micro-switch repeatability

[TJoseph Powderly]

my-com switches, 1um guaranteed. every good german wedm uses them
and high end japanese
my-com

yes expensive   paeng maak!  but damn accurate
tomp

On 02/16/2016 02:53 PM, Nicklas Karlsson wrote:
> I heard rumors here a while ago about micro meter accuracy switch but I guess 
> it might be a little bit expensive.
>


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Re: [Emc-users] Micro-switch repeatability

[Bertho Stultiens]

On 02/16/2016 02:01 PM, Lester Caine wrote:
>> Indeed, unless you can crush them. There must be a run-into-the-wall
>> protection, as mentioned earlier, to prevent killing your switch.
> 
> The problem on the Taig is while one hits the end stop one end, you come
> out of the nut the other ;) But while stalling the motors looses
> position, it's not a particular problem from the safety point of view.
> Unless you put a finger in the way ...

The router here is constrained at both ends, so that would be fine.
Stalling will be an issue.

Regarding fingers, well, I'm not sure about some of the would-be
operators ;-)

We do have a sign stating "KillBot Machine" and other large graphic and
descriptive words of how you will die when mismanaging the machine.


> I've been looking to fit slotted sensors as limit switches to prevent
> problems at both ends of the table, with a flag on the bed which goes
> through the sensor (so no crush problem), and this is fine for limiting
> things, but it's repeatability is somewhat suspect for use as a home
> position. I was seeing 0.1mm drift depending on various factors, but not
> being desperate for it I did not investigate further.

Optical sensors are problematic for repeatability unless you have very
good ones (like encoders).

That said, general accuracy of 0.1mm would be sufficient for most of the
things done on the machine (simple woodwork).

The machine itself is rated at 0.02mm repositioning, so a 0.01mm homing
repeatability is more than enough.

The micro-switches look like they can manage at almost no cost. But then
my curiosity got in my way on how far you actually can go with the
cheapo method. I'm now considering to take an old CD player and move the
laser-assembly onto several micro-switches at different speeds. The
laser-assembly is sub-micrometer accurate (CD track-separation runs at
1.5...1.6 um) and generally uses a simple stepper.


-- 
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Re: [Emc-users] Micro-switch repeatability

[Lester Caine]

On 16/02/16 12:26, Bertho Stultiens wrote:
>> The alternatives seem to have the same problems of repeatability. Using
>> > a hall sensor or optical one will give the same problems. Micro-switches
>> > are at least inherently mechanically constrained.
> Indeed, unless you can crush them. There must be a run-into-the-wall
> protection, as mentioned earlier, to prevent killing your switch.

The problem on the Taig is while one hits the end stop one end, you come
out of the nut the other ;) But while stalling the motors looses
position, it's not a particular problem from the safety point of view.
Unless you put a finger in the way ...

I've been looking to fit slotted sensors as limit switches to prevent
problems at both ends of the table, with a flag on the bed which goes
through the sensor (so no crush problem), and this is fine for limiting
things, but it's repeatability is somewhat suspect for use as a home
position. I was seeing 0.1mm drift depending on various factors, but not
being desperate for it I did not investigate further.

-- 
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Re: [Emc-users] Micro-switch repeatability

[Bertho Stultiens]

On 02/16/2016 01:38 PM, Nicklas Karlsson wrote:
 It seems that the micro-switches are well suited for the purpose, but I
 guess some hard (unbiased) data has yet to be gathered (outside of a mill).
>>> The alternatives seem to have the same problems of repeatability. Using
>>> a hall sensor or optical one will give the same problems. Micro-switches
>>> are at least inherently mechanically constrained.
>> Indeed, unless you can crush them. There must be a run-into-the-wall
>> protection, as mentioned earlier, to prevent killing your switch.
> 
> Pass over the switch might be possible?

No. The datasheets I've read all say the same that you must activate the
plunger straigt on. Any angle will give you bad performance. Any
sideways stress on the plunger can kill the plunger assembly.

The only alternative is to use a level-based micro-switch. That,
however, will probably make it less accurate. Especially when you move
over it side-ways. The angle of attack is too small with respect to the
travel distance.

-- 
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Re: [Emc-users] Micro-switch repeatability

[Nicklas Karlsson]

> On 02/16/2016 12:42 PM, Lester Caine wrote:
> > On 16/02/16 10:21, Bertho Stultiens wrote:
> >> It seems that the micro-switches are well suited for the purpose, but I
> >> guess some hard (unbiased) data has yet to be gathered (outside of a mill).
> > 
> > The alternatives seem to have the same problems of repeatability. Using
> > a hall sensor or optical one will give the same problems. Micro-switches
> > are at least inherently mechanically constrained.
> 
> Indeed, unless you can crush them. There must be a run-into-the-wall
> protection, as mentioned earlier, to prevent killing your switch.

Pass over the switch might be possible?

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Re: [Emc-users] Micro-switch repeatability

[Bertho Stultiens]

On 02/16/2016 12:42 PM, Lester Caine wrote:
> On 16/02/16 10:21, Bertho Stultiens wrote:
>> It seems that the micro-switches are well suited for the purpose, but I
>> guess some hard (unbiased) data has yet to be gathered (outside of a mill).
> 
> The alternatives seem to have the same problems of repeatability. Using
> a hall sensor or optical one will give the same problems. Micro-switches
> are at least inherently mechanically constrained.

Indeed, unless you can crush them. There must be a run-into-the-wall
protection, as mentioned earlier, to prevent killing your switch.


> I do look at the kit available and wonder if simply adding scale bars
> locked to the table aren’t a sensible compromise here? You have an
> absolute on on the machine which can be used not only to define a home
> position, but also to add limits based on the actual job? Which could be
> used where the natural home position IS in the middle of the work piece.
> I'm not talking about a set of inputs that are used as part of any
> closed loop control, but simply as has been done in the past, a check
> that particular points are in the right place. It could be used to
> measure the current backlash between the motion elements and the base
> machine, with a 'calibrate' cycle as part of the home process?

The point of the switches is not to be correct in perfection. The
background here is that the router is located at the local hackerspace,
where many will have access to the machine. Not all have the same
experience and a run-into-the-wall can be expected from a novice. Well,
an experienced person might just hit the wrong button too ;-)

The router has currently end-stop switches, but none on the other end of
the axes. I'd like to have the controller limit the movement such that
it will stop the machine when running into the wall. This will not
prevent hitting anything with the spindle.

Using a "proper" home (0,0,0 position) will not only make it a lot
easier to recover from an error, but, it allows the machine to be shut
down. Especially the "shut down" is important because it is not expected
that this machine runs 24/7, but mere hours at a time, losing its
position in space every power-cycle.

The natural home, as you say, is the work piece. But that is just an offset.


> Cheap Chinese readout bars can be used as one can easily compensate for
> the latency between readings, and I know in essence you are discussing
> the provision of a 'hardware' zero point on the axis, but as a cross
> check that the machine has not missed steps, or a flexible means of
> moving the machine to a fixed position to recover after a collision or
> stall it has merit?

You are right. It is a hardware zero point. Losing steps is my least
worry at this moment, but it surely has crossed my mind. It is, as you
say, the collisions I am (slightly) worried about. And then, the
power-cycling of the machine.

It is mostly a balance of how much it'll cost and how much I can prevent
problems when many different operators with different experience and
volatile g-code handle the machine. The machine was cheap, so investing
perfection is a bit off.


-- 
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Re: [Emc-users] Micro-switch repeatability

[Bertho Stultiens]

On 02/16/2016 12:39 PM, Dave Caroline wrote:
> I originally searched for a switch with data and a local distributor
> had some movement specs of the plunger, I got some but unfortunately
> that distributor no longer lists the item. but it is a Patterson V4
> type microswitch, the .tw website of theirs is not easy to read
> though. One day I might fit them

Most micro-switches avalable from electronics pushers have datasheets.
Most of those datasheets do have "activation distance" (plunger depth
for activation) and hysteresis values.

However, they are specified with only one decimal (in mm). That leaves a
lot of wiggle-room.

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Re: [Emc-users] Micro-switch repeatability

[Lester Caine]

On 16/02/16 10:21, Bertho Stultiens wrote:
> It seems that the micro-switches are well suited for the purpose, but I
> guess some hard (unbiased) data has yet to be gathered (outside of a mill).

The alternatives seem to have the same problems of repeatability. Using
a hall sensor or optical one will give the same problems. Micro-switches
are at least inherently mechanically constrained.

I do look at the kit available and wonder if simply adding scale bars
locked to the table aren’t a sensible compromise here? You have an
absolute on on the machine which can be used not only to define a home
position, but also to add limits based on the actual job? Which could be
used where the natural home position IS in the middle of the work piece.
I'm not talking about a set of inputs that are used as part of any
closed loop control, but simply as has been done in the past, a check
that particular points are in the right place. It could be used to
measure the current backlash between the motion elements and the base
machine, with a 'calibrate' cycle as part of the home process?

Cheap Chinese readout bars can be used as one can easily compensate for
the latency between readings, and I know in essence you are discussing
the provision of a 'hardware' zero point on the axis, but as a cross
check that the machine has not missed steps, or a flexible means of
moving the machine to a fixed position to recover after a collision or
stall it has merit?

-- 
Lester Caine - G8HFL
-
Contact - http://lsces.co.uk/wiki/?page=contact
L.S.Caine Electronic Services - http://lsces.co.uk
EnquirySolve - http://enquirysolve.com/
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Re: [Emc-users] Micro-switch repeatability

[Dave Caroline]

I originally searched for a switch with data and a local distributor
had some movement specs of the plunger, I got some but unfortunately
that distributor no longer lists the item. but it is a Patterson V4
type microswitch, the .tw website of theirs is not easy to read
though. One day I might fit them

Dave Caroline

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Re: [Emc-users] Micro-switch repeatability

[Bertho Stultiens]

On 02/16/2016 07:53 AM, Nicklas Karlsson wrote:
> I heard rumors here a while ago about micro meter accuracy switch but
> I guess it might be a little bit expensive.

Well, yes. The "real" switches which are /specified/ with repeatability
values of about 0.005mm are in the order of $200...$300 per unit from
what I found. The ones specified at 0.001mm are about an order of
magnitude more expensive. Even specified 0.010mm repeatability switches
are in the $100 class range.

This is a cheapo - not-too-good, not-too-bad - used router (bought for
$1500). Using expensive homing switches is like upgrading your bicycle
to run a formula 1 race ;-)


It looks like micro-switches will do just fine if the speed is
controlled. Maybe it would be a good idea to have a two-stage trip, as
mentioned. Proximity to home and then a home switch. Then you can
control the mechanics a bit better.


On 02/16/2016 03:00 AM, John Alexander Stewart wrote:
> I did some tests, plotted the results, etc, at:
> http://cnc-for-model-engineers.blogspot.ca/2015/06/home-switch-repeatability.html

Those numbers are not /that/ good if you think about it. At least not in
comparison to /significantly better than 0.001"/, what others report.

I had seen you graph while searching the net, but asked the question
here anyway because you already said that there might be some problems
with the measurement.


> I think my major issue was the mounting for my dial indicator, and
> if you do read the article, I did some tests with my new mill, and 
> results are the same or better. I was *totally* surprised at how well
> they worked.

Your graph does seem to indicate some kind of bias. However, it is hard
to tell whether it is a mechanical feature or your measurement setup (as
you mention).

However, when we get into these kinds of distances, simple temperature
and moisture changes are a factor too. Especially with (mechanical)
electronics involved.


It seems that the micro-switches are well suited for the purpose, but I
guess some hard (unbiased) data has yet to be gathered (outside of a mill).


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Re: [Emc-users] Micro-switch repeatability

[Gregg Eshelman]

On 2/15/2016 11:53 PM, Nicklas Karlsson wrote:
> I heard rumors here a while ago about micro meter accuracy switch but I guess 
> it might be a little bit expensive.

What about the Hall effect or optical sensors that are options with 
generic electronics parts kits for 3D printers?

BTW, Mattel is soon to release a 3D printer called Thingmaker, operated 
with a smartphone app to print out toys designed using snap together 
parts downloaded from Mattel. It has an auto-locking cover and the hot 
end retracts to a shielded area so kids can't get their fingers on 
anything hot.

Price supposed to be around $300. If it's any good I'll bet there will 
be hacks to use other software with it within days of first sale.


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Re: [Emc-users] Micro-switch repeatability

[Nicklas Karlsson]

I heard rumors here a while ago about micro meter accuracy switch but I guess 
it might be a little bit expensive.

On Tue, 16 Feb 2016 07:41:41 +0200
Roland Jollivet  wrote:

> As others will advise, a slotted disc directly on the stepper is your best
> option. It's the finest resolution you'll achieve for a low cost. Here
> 
> is a typical example I found on the net, although I'd make the cut-out just
> one quadrant.
> 
> Regards
> Roland
> 
> 
> On 16 February 2016 at 02:02, Bertho Stultiens  wrote:
> 
> > On 02/16/2016 12:53 AM, Dave Cole wrote:
> > >> Has anyone numbers on the repeatability of "normal"
> > >> micro-switches?
> > >>
> > >> Micro-switches are (relatively) cheap and mostly not too shabby,
> > >> but I have a not seen any hard data on repeatability (other than
> > >> datasheets saying that they are made for repeatability).
> > >
> > > If you have a marker pulse on an encoder you can use a cheap home switch
> > > and back off to the marker pulse.
> >
> > Yeah, but it is a cheap stepper system, so no encoders there.
> >
> >
> > --
> > Greetings Bertho
> >
> > (disclaimers are disclaimed)
> >
> >
> > --
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-- 
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Re: [Emc-users] Micro-switch repeatability

[Gene Heskett]

On Monday 15 February 2016 21:35:29 TJoseph Powderly wrote:

> Gene
> an improved home routine would add a solenoid and piping to clean the
> switches

Ohmygawd. ROTFL. TomP, you kill me with your logic.  Of course that would 
work, but this toy lathe, no matter how much lipstick you put on it, is 
still a pig. :)

> no more "wheres the dang non-osha gun gone today?"
> tomp

And mine is for damned sure non-osha.  And you can buy it yet today if 
you recognize what all is in the blowmold pack in the 8 dollar bin.

Cheers, Gene Heskett
-- 
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Genes Web page 

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Re: [Emc-users] Micro-switch repeatability

[TJoseph Powderly]

most commercial cncs have encoder home morks ( Z phase)
and they have what users often miss-call a 'home' switch

its really a 'close to home,  slow down you fool' switch

so the velocities during the home 'stretch' ( between 'nearhome' and home)
are always controlled

the distance between those should be
governed by distance, max velocity + safety margin
btw proxes have trip distance and trip time, see specs from mfctr
want really good switches? look for swiss My-com  guaranteed 1um
seem Baumer owns them now ( Baumer is big prox company in Euro-tania )
tomp

On 02/16/2016 10:05 AM, Gene Heskett wrote:
> On Monday 15 February 2016 19:11:10 Jack Coats wrote:
>
>> I saw some prox sensors ebay (china trash) that folks on 3D printers
>> are using for automatic bed leveling compensation.  They are about
>> $2.50/ea delivered, others are $10 if you want a better quality.
>>
>> Their repeatability is good,
> But hows the velocity vs trip point?  Do they lag at the higher speeds,
> or pre-trip at higher speeds?  Never played with any, but could be
> cajoled if these elcheapo's turn crappy before their time.
>> If using switches, please check the brand.  Microswitch and possibly
>> Cherry make great switches.  Some others are 'problematic' to be kind.
>>
>> Enjoy.
>>
>> On Mon, Feb 15, 2016 at 5:57 PM, Gene Heskett 
> wrote:
>>> On Monday 15 February 2016 18:44:00 Bertho Stultiens wrote:
 Hi,

 I'm looking for an on-the-cheap way to do reasonable homing. Usual
 switches for the purpose cost a lot. The machine only has a
 repeatability of 0.02mm, so it may just be a waste to use too
 accurate (expensive) switches.

 Has anyone numbers on the repeatability of "normal"
 micro-switches?

 Micro-switches are (relatively) cheap and mostly not too shabby,
 but I have a not seen any hard data on repeatability (other than
 datasheets saying that they are made for repeatability).
>>> I am using some micro-mini roller lever junk I got for 6 bucks a bag
>>> of 10 from ebay.  Repeatability according to my dials is well within
>>> .001" even with crap switches.  Its a "dry' circuit, so as long as
>>> the contacts are clean, there's very little other wear.  MMMV after
>>> a long time, but its not beem noticable in 6 months now.
>>>
>>> Cheers, Gene Heskett
>>> --
>>> "There are four boxes to be used in defense of liberty:
>>>   soap, ballot, jury, and ammo. Please use in that order."
>>> -Ed Howdershelt (Author)
>>> Genes Web page 
>>>
>>>
>>> 
>>> -- Site24x7 APM Insight: Get Deep Visibility into Application
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>
> Cheers, Gene Heskett


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Re: [Emc-users] Micro-switch repeatability

[TJoseph Powderly]

Gene
an improved home routine would add a solenoid and piping to clean the 
switches
no more "wheres the dang non-osha gun gone today?"
tomp

On 02/16/2016 10:11 AM, Gene Heskett wrote:
  I paint brush or air hose the swarf from in front of it before I 
command a home,


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Re: [Emc-users] Micro-switch repeatability

[Gene Heskett]

On Monday 15 February 2016 19:37:43 Bertho Stultiens wrote:

> On 02/16/2016 01:16 AM, Len Shelton wrote:
> > We in fact see about 2-3 tenths of a thou repeatibility with a slow
> > approach on cheap chinese snap switches.
>
> Just like what others seem to report.
>
> Is that on direct activation or using an positional offset on a lever?
>
> Using a lever seems like introducing a variable due to spring forces.

Possibly so.  The reason for the roller tipped lever here is so I can go 
on by it without any damage.  Same swtch is used for z on my lathe, but 
x is a teeny teeny button that is mounted to trip about 5 thou before x 
hits a solid stop on the backaway motion.  I paint brush or air hose the 
swarf from in front of it before I command a home, but haven't managed 
to damage it in at least 2 years now.  Pay no attention to that faint 
knocking sound, it just my knuckles on my head. :)

Cheers, Gene Heskett
-- 
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 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page 

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Re: [Emc-users] Micro-switch repeatability

[Gene Heskett]

On Monday 15 February 2016 19:11:10 Jack Coats wrote:

> I saw some prox sensors ebay (china trash) that folks on 3D printers
> are using for automatic bed leveling compensation.  They are about
> $2.50/ea delivered, others are $10 if you want a better quality.
>
> Their repeatability is good,

But hows the velocity vs trip point?  Do they lag at the higher speeds, 
or pre-trip at higher speeds?  Never played with any, but could be 
cajoled if these elcheapo's turn crappy before their time.
>
> If using switches, please check the brand.  Microswitch and possibly
> Cherry make great switches.  Some others are 'problematic' to be kind.
>
> Enjoy.
>
> On Mon, Feb 15, 2016 at 5:57 PM, Gene Heskett  
wrote:
> > On Monday 15 February 2016 18:44:00 Bertho Stultiens wrote:
> > > Hi,
> > >
> > > I'm looking for an on-the-cheap way to do reasonable homing. Usual
> > > switches for the purpose cost a lot. The machine only has a
> > > repeatability of 0.02mm, so it may just be a waste to use too
> > > accurate (expensive) switches.
> > >
> > > Has anyone numbers on the repeatability of "normal"
> > > micro-switches?
> > >
> > > Micro-switches are (relatively) cheap and mostly not too shabby,
> > > but I have a not seen any hard data on repeatability (other than
> > > datasheets saying that they are made for repeatability).
> >
> > I am using some micro-mini roller lever junk I got for 6 bucks a bag
> > of 10 from ebay.  Repeatability according to my dials is well within
> > .001" even with crap switches.  Its a "dry' circuit, so as long as
> > the contacts are clean, there's very little other wear.  MMMV after
> > a long time, but its not beem noticable in 6 months now.
> >
> > Cheers, Gene Heskett
> > --
> > "There are four boxes to be used in defense of liberty:
> >  soap, ballot, jury, and ammo. Please use in that order."
> > -Ed Howdershelt (Author)
> > Genes Web page 
> >
> >
> > 
> >-- Site24x7 APM Insight: Get Deep Visibility into Application
> > Performance APM + Mobile APM + RUM: Monitor 3 App instances at just
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Cheers, Gene Heskett
-- 
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 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page 

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Re: [Emc-users] Micro-switch repeatability

[Gene Heskett]

On Monday 15 February 2016 19:08:34 Bertho Stultiens wrote:

> On 02/16/2016 12:57 AM, Gene Heskett wrote:
> > I am using some micro-mini roller lever junk I got for 6 bucks a bag
> > of 10 from ebay.  Repeatability according to my dials is well within
> > .001" even with crap switches.  Its a "dry' circuit, so as long as
> > the contacts are clean, there's very little other wear.  MMMV after
> > a long time, but its not beem noticable in 6 months now.
>
> That is interesting. That would be better than 0.0254mm, which is in
> the order of the machine step-size.
>
> I'd seen some reports on the net of repeatability in the order of
> 0.005mm (~0.0002"), but the problem is that "hard" data is not
> available. It is difficult to decide on anecdotal evidence.
>
> However, it seems that you have the same experience and the cheap
> micro-switches are really good after all (that is, of course, a
> relative statement of really good).

Yes it is, I tried to use them in the motor reversal and limit switch 
control of the jig flipper I had rigged to tip in and out a stopper that 
a board whose end was about to be carved was being located by it, < a 2 
amp load.  They were good for perhaps 20 or 30 cycles doing that.  So I 
replaced them once, and then kept a screwdriver handy so I could reach 
over and give it some brogan maintenance when it miss-behaved.  Then 
that part of the project was finished, so I tore down that jig & stored 
it up in the other shed.  Hopefully I'll never use it again in this 
lifetime.

OTOH for dry,logic level contacts, they've been fine.

And since I've hit a roadblock in mahogany carving for lack of a cutting 
tool that should arrive this friday or saturday, so I am back to making 
an alu coated floor as I carve out a camera mount for this mill, which 
will supposedly be removable and re-installable without spending a 
couple hours recalibrating the machine.  Dovetail joints etc.

Looking a bit fugly on one side as I was pushing the tool too hard and 
too deep, so it walked sideways about 30 thou, amazingly without 
breaking a 1/4" 4 flute SC mill.  The text in the MDI command line is so 
small I missed a missing decimal point, so I sat down and wrote a 2 loop 
nested proggy to do it in 40 LOC.  Worked just fine. Tommorrow I need to 
drill & tap a few 3mm holes to serve as camera aiming adjustments & then 
it will be about ready for use. But if I see that guy Murphy that wrote 
all those laws about how things can go wrong, coming my way, he's dead, 
stone cold dead. ;-)

Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page 

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Re: [Emc-users] Micro-switch repeatability

[John Alexander Stewart]

Bertho;

I did some tests, plotted the results, etc, at:

http://cnc-for-model-engineers.blogspot.ca/2015/06/home-switch-repeatability.html

I think my major issue was the mounting for my dial indicator, and if you
do read the article, I did some tests with my new mill, and results are the
same or better.

I was *totally* surprised at how well they worked.

John.
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Re: [Emc-users] Micro-switch repeatability

[Jack Coats]

I saw some prox sensors ebay (china trash) that folks on 3D printers are
using for automatic bed leveling compensation.  They are about $2.50/ea
delivered, others are $10 if you want a better quality.

Their repeatability is good,

If using switches, please check the brand.  Microswitch and possibly Cherry
make great switches.  Some others are 'problematic' to be kind.

Enjoy.

On Mon, Feb 15, 2016 at 5:57 PM, Gene Heskett  wrote:

> On Monday 15 February 2016 18:44:00 Bertho Stultiens wrote:
>
> > Hi,
> >
> > I'm looking for an on-the-cheap way to do reasonable homing. Usual
> > switches for the purpose cost a lot. The machine only has a
> > repeatability of 0.02mm, so it may just be a waste to use too accurate
> > (expensive) switches.
> >
> > Has anyone numbers on the repeatability of "normal" micro-switches?
> >
> > Micro-switches are (relatively) cheap and mostly not too shabby, but I
> > have a not seen any hard data on repeatability (other than datasheets
> > saying that they are made for repeatability).
>
> I am using some micro-mini roller lever junk I got for 6 bucks a bag of
> 10 from ebay.  Repeatability according to my dials is well within .001"
> even with crap switches.  Its a "dry' circuit, so as long as the
> contacts are clean, there's very little other wear.  MMMV after a long
> time, but its not beem noticable in 6 months now.
>
> Cheers, Gene Heskett
> --
> "There are four boxes to be used in defense of liberty:
>  soap, ballot, jury, and ammo. Please use in that order."
> -Ed Howdershelt (Author)
> Genes Web page 
>
>
> --
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>



-- 
><> ... Jack

The Four Boxes of Liberty - "There are four boxes to be used in the defense
of liberty: soap, ballot, jury and ammo. Please use in that order."
"Whatever you do, work at it with all your heart"... Colossians 3:23
"Anyone who has never made a mistake, has never tried anything new." -
Albert Einstein
"You don't manage people; you manage things. You lead people." - Admiral
Grace Hopper, USN
"The most dangerous phrase in the language is "We’ve always done it this
way"-- Admiral Grace Hopper, USN
"Tell me and I forget. Teach me and I remember. Involve me and I learn." -
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Re: [Emc-users] Micro-switch repeatability

[Steve Traugott]

I also remember someone, could have been at reprap.org or cncrouterparts.com,
doing repeatability tests, and getting similar surprisingly consistent
results with cheap switches.

On Mon, Feb 15, 2016 at 5:04 PM, Len Shelton  wrote:

> We don't use levers, we activate the plungers directly. The key is to
> design the switch mount such that a physical stop would prevent wrecking
> the plastic switch on a rapid jogs ooops.
>
>  >Len
>
>
>
> On 2/15/2016 6:37 PM, Bertho Stultiens wrote:
> > On 02/16/2016 01:16 AM, Len Shelton wrote:
> >> We in fact see about 2-3 tenths of a thou repeatibility with a slow
> >> approach on cheap chinese snap switches.
> > Just like what others seem to report.
> >
> > Is that on direct activation or using an positional offset on a lever?
> >
> > Using a lever seems like introducing a variable due to spring forces.
> >
>
>
>
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Re: [Emc-users] Micro-switch repeatability

[Len Shelton]

We don't use levers, we activate the plungers directly. The key is to 
design the switch mount such that a physical stop would prevent wrecking 
the plastic switch on a rapid jogs ooops.

 >Len



On 2/15/2016 6:37 PM, Bertho Stultiens wrote:
> On 02/16/2016 01:16 AM, Len Shelton wrote:
>> We in fact see about 2-3 tenths of a thou repeatibility with a slow
>> approach on cheap chinese snap switches.
> Just like what others seem to report.
>
> Is that on direct activation or using an positional offset on a lever?
>
> Using a lever seems like introducing a variable due to spring forces.
>


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Re: [Emc-users] Micro-switch repeatability

[Bertho Stultiens]

On 02/16/2016 01:16 AM, Len Shelton wrote:
> We in fact see about 2-3 tenths of a thou repeatibility with a slow 
> approach on cheap chinese snap switches.

Just like what others seem to report.

Is that on direct activation or using an positional offset on a lever?

Using a lever seems like introducing a variable due to spring forces.

-- 
Greetings Bertho

(disclaimers are disclaimed)

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Re: [Emc-users] Micro-switch repeatability

[Len Shelton]

We in fact see about 2-3 tenths of a thou repeatibility with a slow 
approach on cheap chinese snap switches.

 >Len



On 2/15/2016 6:08 PM, Bertho Stultiens wrote:
> On 02/16/2016 12:57 AM, Gene Heskett wrote:
>> I am using some micro-mini roller lever junk I got for 6 bucks a bag of
>> 10 from ebay.  Repeatability according to my dials is well within .001"
>> even with crap switches.  Its a "dry' circuit, so as long as the
>> contacts are clean, there's very little other wear.  MMMV after a long
>> time, but its not beem noticable in 6 months now.
> That is interesting. That would be better than 0.0254mm, which is in the
> order of the machine step-size.
>
> I'd seen some reports on the net of repeatability in the order of
> 0.005mm (~0.0002"), but the problem is that "hard" data is not
> available. It is difficult to decide on anecdotal evidence.
>
> However, it seems that you have the same experience and the cheap
> micro-switches are really good after all (that is, of course, a relative
> statement of really good).
>


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Re: [Emc-users] Micro-switch repeatability

[Bertho Stultiens]

On 02/16/2016 12:57 AM, Gene Heskett wrote:
> I am using some micro-mini roller lever junk I got for 6 bucks a bag of 
> 10 from ebay.  Repeatability according to my dials is well within .001" 
> even with crap switches.  Its a "dry' circuit, so as long as the 
> contacts are clean, there's very little other wear.  MMMV after a long 
> time, but its not beem noticable in 6 months now.

That is interesting. That would be better than 0.0254mm, which is in the
order of the machine step-size.

I'd seen some reports on the net of repeatability in the order of
0.005mm (~0.0002"), but the problem is that "hard" data is not
available. It is difficult to decide on anecdotal evidence.

However, it seems that you have the same experience and the cheap
micro-switches are really good after all (that is, of course, a relative
statement of really good).

-- 
Greetings Bertho

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Re: [Emc-users] Micro-switch repeatability

[Bertho Stultiens]

On 02/16/2016 12:53 AM, Dave Cole wrote:
>> Has anyone numbers on the repeatability of "normal"
>> micro-switches?
>> 
>> Micro-switches are (relatively) cheap and mostly not too shabby,
>> but I have a not seen any hard data on repeatability (other than
>> datasheets saying that they are made for repeatability).
>
> If you have a marker pulse on an encoder you can use a cheap home switch 
> and back off to the marker pulse.

Yeah, but it is a cheap stepper system, so no encoders there.


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Re: [Emc-users] Micro-switch repeatability

[Gene Heskett]

On Monday 15 February 2016 18:44:00 Bertho Stultiens wrote:

> Hi,
>
> I'm looking for an on-the-cheap way to do reasonable homing. Usual
> switches for the purpose cost a lot. The machine only has a
> repeatability of 0.02mm, so it may just be a waste to use too accurate
> (expensive) switches.
>
> Has anyone numbers on the repeatability of "normal" micro-switches?
>
> Micro-switches are (relatively) cheap and mostly not too shabby, but I
> have a not seen any hard data on repeatability (other than datasheets
> saying that they are made for repeatability).

I am using some micro-mini roller lever junk I got for 6 bucks a bag of 
10 from ebay.  Repeatability according to my dials is well within .001" 
even with crap switches.  Its a "dry' circuit, so as long as the 
contacts are clean, there's very little other wear.  MMMV after a long 
time, but its not beem noticable in 6 months now.

Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page 

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Re: [Emc-users] Micro-switch repeatability

[Dave Cole]

If you have a marker pulse on an encoder you can use a cheap home switch 
and back off to the marker pulse.

Dave

On 2/15/2016 6:44 PM, Bertho Stultiens wrote:
> Hi,
>
> I'm looking for an on-the-cheap way to do reasonable homing. Usual
> switches for the purpose cost a lot. The machine only has a
> repeatability of 0.02mm, so it may just be a waste to use too accurate
> (expensive) switches.
>
> Has anyone numbers on the repeatability of "normal" micro-switches?
>
> Micro-switches are (relatively) cheap and mostly not too shabby, but I
> have a not seen any hard data on repeatability (other than datasheets
> saying that they are made for repeatability).
>
>

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