Re: [Emc-users] Floating plasma torch - asking to share experience

[Viesturs Lācis]

2012/11/16 Jeshua Lacock :
>
> Just my 2¢
>
> I think if the axis itself doesn't have any intentional backlash, you could 
> mount the torch with a stiff spring.
>
> In normal operation you won't have any backlash from the spring (only if it 
> hits the work piece).

That means that this spring has to be implemented somewhere between
ballscrew nut and Z axis itself. Or I need additional linear
rails/slides for the torch itself.

I came up with a solution, it will take a day or two to implement,
then I might share some pics.

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Re: [Emc-users] Floating plasma torch - asking to share experience

[Jeshua Lacock]

On Nov 13, 2012, at 2:39 PM, Viesturs Lācis wrote:

> 2012/11/13 Peter C. Wallace :
>> 
>> You can sense ferror or PID output (on a torque mode drive)
>> on a voltage mode drive like the 7I39, ferror (and a slow move
>> against a resiliant stop) is probably the best route for
>> "switchless" limit sensing
> 
> Thank You!
> I better will try to make a mount for torch, where it can slide a
> little and attach a small switch to it.
> I might use this option, if everything else fails, because moving
> rigidly attached torch into material does not sound very encouraging
> and I am not sure that client will understand that too :)

Just my 2¢

I think if the axis itself doesn't have any intentional backlash, you could 
mount the torch with a stiff spring.

In normal operation you won't have any backlash from the spring (only if it 
hits the work piece).

My 3D printer table is actually mounted on springs, and in normal operation the 
springs do not adversely affect the quality. 

The springs primary function is to allow the table to be leveled by tightening 
a bolt on each corner, but I have seen the springs allow it to compensate for 
extra ooze. Without the springs the stepper motors will lose position, with the 
springs the table just brief lowers to compensate for the extra material.


Cheers,

Jeshua Lacock
Founder/Engineer
3DTOPO Incorporated

Phone: 208.462.4171


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Re: [Emc-users] Floating plasma torch - asking to share experience

[Viesturs Lācis]

2012/11/13 Peter C. Wallace :
>
> You can sense ferror or PID output (on a torque mode drive)
> on a voltage mode drive like the 7I39, ferror (and a slow move
> against a resiliant stop) is probably the best route for
> "switchless" limit sensing

Thank You!
I better will try to make a mount for torch, where it can slide a
little and attach a small switch to it.
I might use this option, if everything else fails, because moving
rigidly attached torch into material does not sound very encouraging
and I am not sure that client will understand that too :)

-- 
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If you can't fix it, you don't own it.
http://www.ifixit.com/Manifesto

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Re: [Emc-users] Floating plasma torch - asking to share experience

[Peter C. Wallace]

On Tue, 13 Nov 2012, Viesturs L?cis wrote:

> Date: Tue, 13 Nov 2012 22:12:33 +0200
> From: "[UTF-8] Viesturs L?cis" 
> Reply-To: "Enhanced Machine Controller (EMC)"
> 
> To: "Enhanced Machine Controller (EMC)" 
> Subject: Re: [Emc-users] Floating plasma torch - asking to share experience
> 
> 2012/11/13 Peter C. Wallace :
>>
>> It should be noted that this should be possible with any torque mode servo
>> and some HAL magic.
>
> Peter, could You, please, explain in little more detail, how do You intend 
> that?
> This machine has 4 servos, including Z axis, driven by 2 pieces of 7i39LV.
>
> The way I see is that there are 2 setting for PID loop - one should be
> relatively soft (command for probing move would be "select" for mux2
> components, which would change the PID parameters) and Z axis ferror
> pin should be watched and "torch has touched material" event would be,
> when ferror exceeds a certain value, for example, 0,5 mm. Or am I
> thinking in wrong direction?
>
> -- 
> Viesturs
>
> If you can't fix it, you don't own it.
> http://www.ifixit.com/Manifesto

You can sense ferror or PID output (on a torque mode drive)
on a voltage mode drive like the 7I39, ferror (and a slow move 
against a resiliant stop) is probably the best route for
"switchless" limit sensing


>
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Peter Wallace
Mesa Electronics

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Re: [Emc-users] Floating plasma torch - asking to share experience

[Viesturs Lācis]

2012/11/13 Peter C. Wallace :
>
> It should be noted that this should be possible with any torque mode servo
> and some HAL magic.

Peter, could You, please, explain in little more detail, how do You intend that?
This machine has 4 servos, including Z axis, driven by 2 pieces of 7i39LV.

The way I see is that there are 2 setting for PID loop - one should be
relatively soft (command for probing move would be "select" for mux2
components, which would change the PID parameters) and Z axis ferror
pin should be watched and "torch has touched material" event would be,
when ferror exceeds a certain value, for example, 0,5 mm. Or am I
thinking in wrong direction?

-- 
Viesturs

If you can't fix it, you don't own it.
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Re: [Emc-users] Floating plasma torch - asking to share experience

[Marius Liebenberg]

Karl
Most good THC equipment give you three signals of importance.
1: The Arc good signal - tells you that the system has pierced and is 
ready to move
2: Torch up - tells you the torch is too low
3: Torch down - tells yo the torch is to high

Simple bit of logic will sort out the THC loop I think.



On 2012/11/13 12:34 AM, Karl Schmidt wrote:
> Controlling arc distance has been used as an example of one of the 
> hardest things to put in a control loop. The interaction is non linear 
> and chaotic.  For cutting most sheet material, I would set it up to 
> start at some sane distance and have a long, filtering time constant 
> in the loop with some dead-band hysterisis - might want to throw away 
> out of range samples.
>
> Trying to do a lot of fancy math to linearize the loop will lead to 
> frustration.
>
>
> 
>  
>
> Karl Schmidt  EMail k...@xtronics.com
> Transtronics, Inc.  WEB 
> http://secure.transtronics.com
> 3209 West 9th Street Ph (785) 841-3089
> Lawrence, KS 66049  FAX (785) 841-0434
>
> True wisdom is knowing what we don't know;
> There are many things that we can be certain of if we are willing to 
> think, but
> true maturity is being comfortable with the idea that there are 
> unknowable things.  -KPS
>
>
> 
>  
>
>
>

-- 
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Marius D. Liebenberg
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Tel: +27 12 743 6064
Fax: +27 86 551 8029
Skype: marius_d.liebenberg
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Re: [Emc-users] Floating plasma torch - asking to share experience

[Yishin Li]

On Tue, Nov 13, 2012 at 9:14 AM, John Thornton  wrote:

> But not practical for touch off on thin material...
>
> There's a digital probe signal attached to the plasma head. For thin
material or dry plasma cut, we use digital probe.

-Yishin
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Re: [Emc-users] Floating plasma torch - asking to share experience

[Tom Easterday]

I think it would work fine,  you can set the torque and velocity quite low.  I 
think I could touch off on cardboard if I had to :-)
-Tom

On Nov 12, 2012, at 8:14 PM, John Thornton wrote:

> But not practical for touch off on thin material...
> 
> 
> On 11/12/2012 6:30 PM, Peter C. Wallace wrote:
>> On Mon, 12 Nov 2012, Tom Easterday wrote:
>> 
>>> Date: Mon, 12 Nov 2012 19:13:15 -0500
>>> From: Tom Easterday 
>>> Reply-To: "Enhanced Machine Controller (EMC)"
>>>     
>>> To: "Enhanced Machine Controller (EMC)" 
>>> Subject: Re: [Emc-users] Floating plasma torch - asking to share experience
>>> 
>>> 
>>> On Nov 12, 2012, at 5:56 PM, Yishin Li wrote:
>>> 
>>>> On Tue, Nov 13, 2012 at 1:06 AM, Marius Liebenberg
>>>> wrote:
>>>> 
>>>>> I have seen many alternative solutions that all end up being scraped and
>>>>> redone to floating head.
>>>>> It is my opinion that the only good and maybe better alternative is the
>>>>> capacitive sensing THC system. The simpler the solution the lesser the
>>>>> troubles:)
>>>>> 
>>>>> The plasma head we worked with is rigid type. We use the torque feedback
>>>> of the Z-axis servo motor to decide if it is hitting the plate. We called
>>>> it analog probing. It is useful for underwater plasma cutting. Here's the
>>>> video:
>>>> http://youtu.be/amnozqEhRYE
>>> 
>>> Very nice.  This is a feature of Granite servo drives 
>>> (http://granitedevices.com/index.php?q=servo-drive-vsd-e).  It is called 
>>> homing to a hard stop.  We use it on our plasma machine to home the X and Y 
>>> axes which are driven by Granite VSD-E drives .  We have it torque limit 
>>> the servo motors and slow the velocity until the axis runs into a door stop 
>>> (literally) that we placed at the end of travel.  When the ferror reaches a 
>>> settable max it then backs up to the index pulse of the encoders.  Very 
>>> accurate homing, no switches/wiring required.  I never thought of using it 
>>> to do touch off for the torch, but why not?
>>> 
>>> -Tom
>>> 
>> It should be noted that this should be possible with any torque mode servo
>> and some HAL magic.
>> 
>> 
>> Peter Wallace
>> Mesa Electronics
>> 
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Re: [Emc-users] Floating plasma torch - asking to share experience

[John Thornton]

But not practical for touch off on thin material...


On 11/12/2012 6:30 PM, Peter C. Wallace wrote:
> On Mon, 12 Nov 2012, Tom Easterday wrote:
>
>> Date: Mon, 12 Nov 2012 19:13:15 -0500
>> From: Tom Easterday 
>> Reply-To: "Enhanced Machine Controller (EMC)"
>>  
>> To: "Enhanced Machine Controller (EMC)" 
>> Subject: Re: [Emc-users] Floating plasma torch - asking to share experience
>>
>>
>> On Nov 12, 2012, at 5:56 PM, Yishin Li wrote:
>>
>>> On Tue, Nov 13, 2012 at 1:06 AM, Marius Liebenberg
>>> wrote:
>>>
>>>> I have seen many alternative solutions that all end up being scraped and
>>>> redone to floating head.
>>>> It is my opinion that the only good and maybe better alternative is the
>>>> capacitive sensing THC system. The simpler the solution the lesser the
>>>> troubles:)
>>>>
>>>> The plasma head we worked with is rigid type. We use the torque feedback
>>> of the Z-axis servo motor to decide if it is hitting the plate. We called
>>> it analog probing. It is useful for underwater plasma cutting. Here's the
>>> video:
>>> http://youtu.be/amnozqEhRYE
>>
>> Very nice.  This is a feature of Granite servo drives 
>> (http://granitedevices.com/index.php?q=servo-drive-vsd-e).  It is called 
>> homing to a hard stop.  We use it on our plasma machine to home the X and Y 
>> axes which are driven by Granite VSD-E drives .  We have it torque limit the 
>> servo motors and slow the velocity until the axis runs into a door stop 
>> (literally) that we placed at the end of travel.  When the ferror reaches a 
>> settable max it then backs up to the index pulse of the encoders.  Very 
>> accurate homing, no switches/wiring required.  I never thought of using it 
>> to do touch off for the torch, but why not?
>>
>> -Tom
>>
> It should be noted that this should be possible with any torque mode servo
> and some HAL magic.
>
>
> Peter Wallace
> Mesa Electronics
>
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Re: [Emc-users] Floating plasma torch - asking to share experience

[Peter C. Wallace]

On Mon, 12 Nov 2012, Tom Easterday wrote:

> Date: Mon, 12 Nov 2012 19:13:15 -0500
> From: Tom Easterday 
> Reply-To: "Enhanced Machine Controller (EMC)"
> 
> To: "Enhanced Machine Controller (EMC)" 
> Subject: Re: [Emc-users] Floating plasma torch - asking to share experience
> 
>
> On Nov 12, 2012, at 5:56 PM, Yishin Li wrote:
>
>> On Tue, Nov 13, 2012 at 1:06 AM, Marius Liebenberg
>> wrote:
>>
>>>
>>> I have seen many alternative solutions that all end up being scraped and
>>> redone to floating head.
>>> It is my opinion that the only good and maybe better alternative is the
>>> capacitive sensing THC system. The simpler the solution the lesser the
>>> troubles:)
>>>
>>> The plasma head we worked with is rigid type. We use the torque feedback
>> of the Z-axis servo motor to decide if it is hitting the plate. We called
>> it analog probing. It is useful for underwater plasma cutting. Here's the
>> video:
>> http://youtu.be/amnozqEhRYE
>
>
> Very nice.  This is a feature of Granite servo drives 
> (http://granitedevices.com/index.php?q=servo-drive-vsd-e).  It is called 
> homing to a hard stop.  We use it on our plasma machine to home the X and Y 
> axes which are driven by Granite VSD-E drives .  We have it torque limit the 
> servo motors and slow the velocity until the axis runs into a door stop 
> (literally) that we placed at the end of travel.  When the ferror reaches a 
> settable max it then backs up to the index pulse of the encoders.  Very 
> accurate homing, no switches/wiring required.  I never thought of using it to 
> do touch off for the torch, but why not?
>
> -Tom
>

It should be noted that this should be possible with any torque mode servo
and some HAL magic.


Peter Wallace
Mesa Electronics

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Re: [Emc-users] Floating plasma torch - asking to share experience

[Tom Easterday]

On Nov 12, 2012, at 5:56 PM, Yishin Li wrote:

> On Tue, Nov 13, 2012 at 1:06 AM, Marius Liebenberg
> wrote:
> 
>> 
>> I have seen many alternative solutions that all end up being scraped and
>> redone to floating head.
>> It is my opinion that the only good and maybe better alternative is the
>> capacitive sensing THC system. The simpler the solution the lesser the
>> troubles:)
>> 
>> The plasma head we worked with is rigid type. We use the torque feedback
> of the Z-axis servo motor to decide if it is hitting the plate. We called
> it analog probing. It is useful for underwater plasma cutting. Here's the
> video:
> http://youtu.be/amnozqEhRYE


Very nice.  This is a feature of Granite servo drives 
(http://granitedevices.com/index.php?q=servo-drive-vsd-e).  It is called homing 
to a hard stop.  We use it on our plasma machine to home the X and Y axes which 
are driven by Granite VSD-E drives .  We have it torque limit the servo motors 
and slow the velocity until the axis runs into a door stop (literally) that we 
placed at the end of travel.  When the ferror reaches a settable max it then 
backs up to the index pulse of the encoders.  Very accurate homing, no 
switches/wiring required.  I never thought of using it to do touch off for the 
torch, but why not?

-Tom


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Re: [Emc-users] Floating plasma torch - asking to share experience

[Yishin Li]

On Tue, Nov 13, 2012 at 1:06 AM, Marius Liebenberg
wrote:

>
> I have seen many alternative solutions that all end up being scraped and
> redone to floating head.
> It is my opinion that the only good and maybe better alternative is the
> capacitive sensing THC system. The simpler the solution the lesser the
> troubles:)
>
> The plasma head we worked with is rigid type. We use the torque feedback
of the Z-axis servo motor to decide if it is hitting the plate. We called
it analog probing. It is useful for underwater plasma cutting. Here's the
video:
http://youtu.be/amnozqEhRYE

-Yishin
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Re: [Emc-users] Floating plasma torch - asking to share experience

[Karl Schmidt]

Controlling arc distance has been used as an example of one of the hardest 
things to put in a 
control loop. The interaction is non linear and chaotic.  For cutting most 
sheet material, I would 
set it up to start at some sane distance and have a long, filtering time 
constant in the loop with 
some dead-band hysterisis - might want to throw away out of range samples.

Trying to do a lot of fancy math to linearize the loop will lead to frustration.



Karl Schmidt  EMail k...@xtronics.com
Transtronics, Inc.  WEB 
http://secure.transtronics.com
3209 West 9th Street Ph (785) 841-3089
Lawrence, KS 66049  FAX (785) 841-0434

True wisdom is knowing what we don't know;
There are many things that we can be certain of if we are willing to think, but
true maturity is being comfortable with the idea that there are unknowable 
things.  -KPS




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Re: [Emc-users] Floating plasma torch - asking to share experience

[Jim Coleman]

I like it when pros weigh in.  The machine I used (it was in a production
environment) didn't have any floating mechanism that I could see, but then
again I wasn't at all impressed by that machine.  It's homing sequence
would get you within a repeatability of 2 inches or so in both X and Y,
resuming a stopped cut was a headache of rehoming over and over till it
chose the right spot.  I do wish I had experience with a machine of higher
quality, I'd probably think better of plasma tables.  I developed a disdain
for it, having to bend the parts and keep holes located consistently
relative to a bends, and keep overall part widths consistent while bending
with opposite sides of the burnt parts against the press' stops.

Jim

On Mon, Nov 12, 2012 at 12:06 PM, Marius Liebenberg
wrote:

> I concur with Andy. Some of us use plasma cutter on a daily basis in
> production and some of us (Me) do consultation to sort out machine
> problems on a daily basis. From experience and seeing many good and many
> bad machines, the best production solution is a floating head that will
> detach when run into a job.
> I have seen many alternative solutions that all end up being scraped and
> redone to floating head.
> It is my opinion that the only good and maybe better alternative is the
> capacitive sensing THC system. The simpler the solution the lesser the
> troubles:)
>
>
> On 2012/11/12 06:08 PM, andy pugh wrote:
> > On 12 November 2012 16:00, Jim Coleman  wrote:
> >> Is the reason behind the floating head so there won't be damage if the
> head
> >> hits an object while cutting, like a warped part sticking up?  I'm
> having
> >> trouble grasping why it's needed.
> > While cutting you can measure the head-to-work distance using the arc
> voltage.
> > However, to start cutting you need to have the head at the correct
> > height then strike the arc.
> >
> > The idea is to use the head as a probe, lower to find the work, raise
> > to the correct height, strike the arc then continue to cut while
> > adjusting height based on arc voltage.
>
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Re: [Emc-users] Floating plasma torch - asking to share experience

[Marius Liebenberg]

I concur with Andy. Some of us use plasma cutter on a daily basis in 
production and some of us (Me) do consultation to sort out machine 
problems on a daily basis. From experience and seeing many good and many 
bad machines, the best production solution is a floating head that will 
detach when run into a job.
I have seen many alternative solutions that all end up being scraped and 
redone to floating head.
It is my opinion that the only good and maybe better alternative is the 
capacitive sensing THC system. The simpler the solution the lesser the 
troubles:)


On 2012/11/12 06:08 PM, andy pugh wrote:
> On 12 November 2012 16:00, Jim Coleman  wrote:
>> Is the reason behind the floating head so there won't be damage if the head
>> hits an object while cutting, like a warped part sticking up?  I'm having
>> trouble grasping why it's needed.
> While cutting you can measure the head-to-work distance using the arc voltage.
> However, to start cutting you need to have the head at the correct
> height then strike the arc.
>
> The idea is to use the head as a probe, lower to find the work, raise
> to the correct height, strike the arc then continue to cut while
> adjusting height based on arc voltage.
>
>

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Re: [Emc-users] Floating plasma torch - asking to share experience

[Jim Coleman]

What about, instead of it actually floating, if you were to soften the
structure a little so it could handle the impact of hitting on the probe
operation?  I'm envisioning the torch mounted on rubber standoffs
resembling the body mounts to a car.  I'd think they could allow enough
flex to keep from breaking stuff, but be rigid enough for accurate cutting,
as accurate as plasma can be.  Again I'm not all that familiar with plasma
tables and their results, I know that the one I ran occasionally and bent
parts from every day, would be doing great to give 1/16 inch repeatability
cutting 13g steel.

Jim

On Mon, Nov 12, 2012 at 11:14 AM, andy pugh  wrote:

> How I would do it:
>
> Use a trapezoidal screw and a delrin nut.
>
> Allow the nut to float axially in its housing, with a microswitch to
> detect when it has moved.
>
> Normally the head hangs on the nut. When the head touches then the nut
> slides down in its housing, operating the microswitch. (Use the probe
> G-code)
> back off to the required height + the known actuation distance and
> start the arc.
>
> I think I would use a leaf-spring suspension to supply the required
> angular constraint on the nut.
>
> --
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> If you can't fix it, you don't own it.
> http://www.ifixit.com/Manifesto
>
>
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Re: [Emc-users] Floating plasma torch - asking to share experience

[Jim Coleman]

Ok so I should have re-read the first message in this thread before sending
that.  I now see the OP is looking for a way to handle the overtravel from
decel on the Z axis after the probe has touched.  I'm guessing that just
probing slow enough to be able to stop quickly is less than desirable
because of the amount of time it will take for probing before every cut.

How far will the head overshoot at probing speed once the probe event
occurs?  Is the machine too rigid to just handle the flexing while the axis
decelerates?  Do people regularly use automated probing on a mill to set
tool length to work surface, or is it only done on a special pad to absorb
any overshoot?  When I worked running Haas and Fadal machines we just
jogged by hand while sliding a gauge block back and forth until it hit snug
to set length offsets, and the Hitachi-Seiki had a special "tool setter"
that was set on the table and the machine probed down to it's surface.  I
would guess there was some give to the surface on that device.

Jim

On Mon, Nov 12, 2012 at 11:00 AM, Jim Coleman wrote:

> Is the reason behind the floating head so there won't be damage if the
> head hits an object while cutting, like a warped part sticking up?  I'm
> having trouble grasping why it's needed.  Again, I have very little
> experience with plasma tables, being limited to the one machine my former
> employer had.  That machine had a "rigid" Z axis with the plasma torch
> coupled with a device that used air pressure to hold the assembly in
> place.  If the head crashed into a raised part, it would knock the 2 parts
> off from each other and the torch side would fall loose within the
> constraints of the other side of the housing and trigger an error on the
> control.  To reset the head you had to pull it outward and lift slightly to
> reform the seal and the head would stick back in place.  It took some tries
> before getting it to seal and stick, before you developed "the touch".  The
> mechanism was maybe 4 inches square, with the joining interface itself
> appearing to be round.  A very similar machine can be seen at
> http://www.plasma-automation.com/mod_fabricatorHD.html and the page has a
> link to a slightly better image of their "collision protection" but they
> don't seem to provide many details.  When the machine touched off, it
> appeared to use some form of conductivity to probe the surface.  Holding a
> piece of steel off of the surface of the table and letting the head touch
> it wouldn't trigger the probe, until it pushed the steel down to the
> surface of the table.  If it was strictly capacitance based, it seems it
> would trigger as soon as it touched, unless a human body holding onto a
> piece of scrap doesn't have enough capacitance to set it off.
>
> I'm sorry if I'm completely missing the point of wanting the floating
> head, I'm trying to comprehend the need.  At first I thought the intention
> was for the head to just ride the surface of the workpiece and not use THC,
> but now I see that THC is to be implemented for cut height so I'm a little
> lost.  Unless the float will replace the need for an electronic probing.  I
> hope someone can clear up my confusion, and sorry if all of this is
> irrelevant.
>
> Jim
>
> On Mon, Nov 12, 2012 at 7:17 AM, andy pugh  wrote:
>
>> On 12 November 2012 11:32, Les Newell  wrote:
>>
>> > I have been thinking about this for some time and a while back I came up
>> > with a very different design to all of the others I have seen. First of
>> > all, you don't need or want a ball screw on Z. Z doesn't need to be
>> > hugely accurate. It needs reasonable resolution and it needs to be dirt
>> > resistant.
>>
>> Are double-helical racks available? It seems to me that those would
>> give good location in a number of degrees of freedom, and allow direct
>> stepper control.
>> (Google) I can't find any. It would be reasonably expensive to make as
>> an injection moulding, though relatively expensive to hob.
>>
>> --
>> atp
>> If you can't fix it, you don't own it.
>> http://www.ifixit.com/Manifesto
>>
>>
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Re: [Emc-users] Floating plasma torch - asking to share experience

[andy pugh]

How I would do it:

Use a trapezoidal screw and a delrin nut.

Allow the nut to float axially in its housing, with a microswitch to
detect when it has moved.

Normally the head hangs on the nut. When the head touches then the nut
slides down in its housing, operating the microswitch. (Use the probe
G-code)
back off to the required height + the known actuation distance and
start the arc.

I think I would use a leaf-spring suspension to supply the required
angular constraint on the nut.

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Re: [Emc-users] Floating plasma torch - asking to share experience

[andy pugh]

On 12 November 2012 16:00, Jim Coleman  wrote:
> Is the reason behind the floating head so there won't be damage if the head
> hits an object while cutting, like a warped part sticking up?  I'm having
> trouble grasping why it's needed.

While cutting you can measure the head-to-work distance using the arc voltage.
However, to start cutting you need to have the head at the correct
height then strike the arc.

The idea is to use the head as a probe, lower to find the work, raise
to the correct height, strike the arc then continue to cut while
adjusting height based on arc voltage.


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Re: [Emc-users] Floating plasma torch - asking to share experience

[Jim Coleman]

Is the reason behind the floating head so there won't be damage if the head
hits an object while cutting, like a warped part sticking up?  I'm having
trouble grasping why it's needed.  Again, I have very little experience
with plasma tables, being limited to the one machine my former employer
had.  That machine had a "rigid" Z axis with the plasma torch coupled with
a device that used air pressure to hold the assembly in place.  If the head
crashed into a raised part, it would knock the 2 parts off from each other
and the torch side would fall loose within the constraints of the other
side of the housing and trigger an error on the control.  To reset the head
you had to pull it outward and lift slightly to reform the seal and the
head would stick back in place.  It took some tries before getting it to
seal and stick, before you developed "the touch".  The mechanism was maybe
4 inches square, with the joining interface itself appearing to be round.
A very similar machine can be seen at
http://www.plasma-automation.com/mod_fabricatorHD.html and the page has a
link to a slightly better image of their "collision protection" but they
don't seem to provide many details.  When the machine touched off, it
appeared to use some form of conductivity to probe the surface.  Holding a
piece of steel off of the surface of the table and letting the head touch
it wouldn't trigger the probe, until it pushed the steel down to the
surface of the table.  If it was strictly capacitance based, it seems it
would trigger as soon as it touched, unless a human body holding onto a
piece of scrap doesn't have enough capacitance to set it off.

I'm sorry if I'm completely missing the point of wanting the floating head,
I'm trying to comprehend the need.  At first I thought the intention was
for the head to just ride the surface of the workpiece and not use THC, but
now I see that THC is to be implemented for cut height so I'm a little
lost.  Unless the float will replace the need for an electronic probing.  I
hope someone can clear up my confusion, and sorry if all of this is
irrelevant.

Jim

On Mon, Nov 12, 2012 at 7:17 AM, andy pugh  wrote:

> On 12 November 2012 11:32, Les Newell  wrote:
>
> > I have been thinking about this for some time and a while back I came up
> > with a very different design to all of the others I have seen. First of
> > all, you don't need or want a ball screw on Z. Z doesn't need to be
> > hugely accurate. It needs reasonable resolution and it needs to be dirt
> > resistant.
>
> Are double-helical racks available? It seems to me that those would
> give good location in a number of degrees of freedom, and allow direct
> stepper control.
> (Google) I can't find any. It would be reasonably expensive to make as
> an injection moulding, though relatively expensive to hob.
>
> --
> atp
> If you can't fix it, you don't own it.
> http://www.ifixit.com/Manifesto
>
>
> --
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Re: [Emc-users] Floating plasma torch - asking to share experience

[andy pugh]

On 12 November 2012 11:32, Les Newell  wrote:

> I have been thinking about this for some time and a while back I came up
> with a very different design to all of the others I have seen. First of
> all, you don't need or want a ball screw on Z. Z doesn't need to be
> hugely accurate. It needs reasonable resolution and it needs to be dirt
> resistant.

Are double-helical racks available? It seems to me that those would
give good location in a number of degrees of freedom, and allow direct
stepper control.
(Google) I can't find any. It would be reasonably expensive to make as
an injection moulding, though relatively expensive to hob.

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Re: [Emc-users] Floating plasma torch - asking to share experience

[John Thornton]

That does sound like a lot of work when a simple acme screw and plain 
bearing slides do the trick.

http://gnipsel.com/shop/plasma/z-axis-02.xhtml

John

On 11/12/2012 5:32 AM, Les Newell wrote:
> If you want to go with the auxiliary slide idea you can often pick up
> short linear slides off eBay for peanuts. Bolt on your torch, add a
> switch and the job is done. I have some nice 100mm long THK rails here
> that I bought for this purpose.
>
> I have been thinking about this for some time and a while back I came up
> with a very different design to all of the others I have seen. First of
> all, you don't need or want a ball screw on Z. Z doesn't need to be
> hugely accurate. It needs reasonable resolution and it needs to be dirt
> resistant. Plasma generates a lot of very fine abrasive dust that gets
> everywhere and will wreck ball screws fairly quickly. My plan is to use
> a simple winch. Think of a drum with a coarse thread machined into it.
> Wind some flexible wire or heat resistant cord on the drum and control
> it with a stepper or servo. This is simple, dirt tolerant and provides
> good enough accuracy. Run the wire over a pulley at the top of the Z
> axis to lift the torch. The weight of the torch and slide should provide
> enough tension.
>
> For touch sensing, mount the pulley on a spring loaded arm with a hinge
> at one end and a switch at the other. As the weight comes off the cord
> the pulley will lift and trip the switch. Alternatively you can have a
> fixed pulley and a separate spring loaded pulley and switch to measure
> the cord tension.
>
> The main problem I can see with this setup is the possibility of the
> cord coming off the drum. This can happen if the cord goes slack. There
> are a few ways to get around this. One is to add some guides so there
> isn't room for the cord to lift out of the grooves. Another is to stop
> the machine if the touch sensing switch trips and you aren't seeking the
> top of the work. This is worth doing no matter what touch off mechanism
> you use.
>
> I have used the grooved drum setup for position measurement and have had
> very few problems with the cord coming off. After initial calibration
> they maintained surprisingly good accuaracy.
>
>> I dont think your idea is a good practical idee for a production
>> machine. The torch does touch off thousands of times and the loose nuts
>> will wear out in no time. There is nothing wrong with a well designed
>> floating head and in my opinion it is the best possible pactise to date.
> I can't see why the nut would wear. There is very little load on it when
> it moves on the pins. Instead of bolts you may want to use hardened pins
> as they can be made a better fit and will wear less.
>
> Les
>
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Re: [Emc-users] Floating plasma torch - asking to share experience

[Les Newell]

If you want to go with the auxiliary slide idea you can often pick up 
short linear slides off eBay for peanuts. Bolt on your torch, add a 
switch and the job is done. I have some nice 100mm long THK rails here 
that I bought for this purpose.

I have been thinking about this for some time and a while back I came up 
with a very different design to all of the others I have seen. First of 
all, you don't need or want a ball screw on Z. Z doesn't need to be 
hugely accurate. It needs reasonable resolution and it needs to be dirt 
resistant. Plasma generates a lot of very fine abrasive dust that gets 
everywhere and will wreck ball screws fairly quickly. My plan is to use 
a simple winch. Think of a drum with a coarse thread machined into it. 
Wind some flexible wire or heat resistant cord on the drum and control 
it with a stepper or servo. This is simple, dirt tolerant and provides 
good enough accuracy. Run the wire over a pulley at the top of the Z 
axis to lift the torch. The weight of the torch and slide should provide 
enough tension.

For touch sensing, mount the pulley on a spring loaded arm with a hinge 
at one end and a switch at the other. As the weight comes off the cord 
the pulley will lift and trip the switch. Alternatively you can have a 
fixed pulley and a separate spring loaded pulley and switch to measure 
the cord tension.

The main problem I can see with this setup is the possibility of the 
cord coming off the drum. This can happen if the cord goes slack. There 
are a few ways to get around this. One is to add some guides so there 
isn't room for the cord to lift out of the grooves. Another is to stop 
the machine if the touch sensing switch trips and you aren't seeking the 
top of the work. This is worth doing no matter what touch off mechanism 
you use.

I have used the grooved drum setup for position measurement and have had 
very few problems with the cord coming off. After initial calibration 
they maintained surprisingly good accuaracy.

> I dont think your idea is a good practical idee for a production
> machine. The torch does touch off thousands of times and the loose nuts
> will wear out in no time. There is nothing wrong with a well designed
> floating head and in my opinion it is the best possible pactise to date.

I can't see why the nut would wear. There is very little load on it when 
it moves on the pins. Instead of bolts you may want to use hardened pins 
as they can be made a better fit and will wear less.

Les

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Re: [Emc-users] Floating plasma torch - asking to share experience

[Jeshua Lacock]

Here is an "intelligent" solution:

http://www.cnc4pc.com/Store/osc/product_info.php?cPath=70&products_id=330


Cheers,

Jeshua Lacock
Founder/Engineer
3DTOPO Incorporated

Phone: 208.462.4171


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Re: [Emc-users] Floating plasma torch - asking to share experience

[Viesturs Lācis]

2012/11/10 Roland Jollivet :
>
> Are you talking about what's happening in this video?
>
> http://www.youtube.com/watch?v=HZlV4dUuvMI

Yes, the idea is exactly what I meant, it is just that wrong
application mentioned in title... :)

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Re: [Emc-users] Floating plasma torch - asking to share experience

[dave]

Hi Viesturs,

Nothing I envision is ever as simple or as good as I would hope: but
here goes:

Torch is attached to Z with a cylinder that slides in a close fitting
tube. Movement is limited in the -Z direction by a collar. 
Close fitting tube can be clamped to restrict movement of the torch. 
So: raise torch to easily clear work
unclamp torch which now slides to the collar limit and closes switch
-Z until torch touches work (switch changes state)
clamp tube
raise torch to working level.

I hope this makes sense. I'm certain someone can or already has come up
with something simpler. 

Good luck. 

Dave 



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Re: [Emc-users] Floating plasma torch - asking to share experience

[Viesturs Lācis]

2012/11/10 Marius Liebenberg :
> I have a very simple design that you just bolt onto the Z plate. If you
> have access to a cnc router or mill, it is a quick job to make. Let me
> know if you want to use the design

Thank You, I would appreciate few pictures just to understand the concept!

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Re: [Emc-users] Floating plasma torch - asking to share experience

[Marius Liebenberg]

I have a very simple design that you just bolt onto the Z plate. If you 
have access to a cnc router or mill, it is a quick job to make. Let me 
know if you want to use the design

On 2012/11/10 05:06 PM, Viesturs La-cis wrote:
> 2012/11/10 Marius Liebenberg :
>> I dont think your idea is a good practical idee for a production
>> machine. The torch does touch off thousands of times and the loose nuts
>> will wear out in no time. There is nothing wrong with a well designed
>> floating head and in my opinion it is the best possible pactise to date.
> Ok, thanks, I will once again think over my approach!
> The thing is that the floating head has to be designed and
> manufactured, but I already am over the project deadline, while giving
> a nut freedom to move some 10 mm in axial
> direction can be set up very quickly. But risk of wearing out the
> ballscrew nut from outside is not something nice to have...
>
> Can anyone share some nice and simple floating head design?
>
> 2012/11/10 Jim Coleman :
>> I know that the big commercial machine I interacted with at my previous job
>> would run over diamond plate and run it's head up and down to maintain the
>> distance from the surface without actually touching the surface.  I'm
>> guessing it had to do with it's current/voltage sensing feedback.  I did
>> not follow the THC module that the guys here were working on years ago, I'd
>> bet those threads have alot of info regarding the subject, how it works and
>> how to implement it. I would think that just riding the surface on a
>> floating head would be rather stressful to the mechanisms involved.  Then
>> again I doubt you'll want your machine to be running every possible second
>> it can, 10 hours a day 5 days a week.
> It is just for probing move to find material surface, then retract and
> start piercing. I intend to use plasma tip voltage feedback for
> maintaining the torch height during cutting process.
> I guess that some kind of capacitance sensor might be used for this
> probing purpose, but I have dealt with them only once and actually do
> not know, where to get one for a reasonable price.
>

-- 
Regards / Groete

Marius D. Liebenberg
MasterCut cc
Cel: +27 82 698 3251
Tel: +27 12 743 6064
Fax: +27 86 551 8029
Skype: marius_d.liebenberg
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Re: [Emc-users] Floating plasma torch - asking to share experience

[Marius Liebenberg]

What I did not mention and took for granted that everybody knows is that 
you nee a THC with the floating head. The THC does the work to keep the 
torch at the correct cutting and piercing height.
There are various systems but most of them look at the arc voltage to 
determine how high the torch must ride.

On 2012/11/10 02:44 PM, Jim Coleman wrote:
> I know that the big commercial machine I interacted with at my previous job
> would run over diamond plate and run it's head up and down to maintain the
> distance from the surface without actually touching the surface.  I'm
> guessing it had to do with it's current/voltage sensing feedback.  I did
> not follow the THC module that the guys here were working on years ago, I'd
> bet those threads have alot of info regarding the subject, how it works and
> how to implement it. I would think that just riding the surface on a
> floating head would be rather stressful to the mechanisms involved.  Then
> again I doubt you'll want your machine to be running every possible second
> it can, 10 hours a day 5 days a week.
>
> Jim
>
> On Sat, Nov 10, 2012 at 1:20 AM, Marius Liebenberg
> wrote:
>
>> I dont think your idea is a good practical idee for a production
>> machine. The torch does touch off thousands of times and the loose nuts
>> will wear out in no time. There is nothing wrong with a well designed
>> floating head and in my opinion it is the best possible pactise to date.
>> I do call out service to cnc machines as part of my income and most of
>> the problems that I attend to re badly designed or built mechanics on
>> machines. Sometimes the electronics are not good but mostly mechanics.
>> I will leave you with his idee - Because a thing works once does not
>> mean it will work well forever.
>>
>>
>> On 2012/11/10 02:51 AM, Tom Easterday wrote:
>>> Perhaps a drawing or something?  I am not following what you are
>> proposing.  Sounds like you are talking about having a set up where the
>> z-axis ball nut (and hence the whole z-axis) is "sloppy" and can move
>> 10-15mm up/down?  While it might work (if that is what you are describing)
>> then won't there be a lot of slop in the actual movements of the whole axis
>> and won't that effect other movements such as adjustments in response to
>> the THC during cutting?  Or perhaps I totally misunderstand what you are
>> saying
>>> Tom
>>>
>>> On Nov 9, 2012, at 5:42 PM, Viesturs La-cis wrote:
>>>
 Hello!

 Little too late but still - I suddenly realized that I need some
 provisions for something similar to floating head for plasma torch.
 I would like to ask plasma table owners to share their experience, how
 they have solved the following issue:
 Hypertherm (and most probably other manufacturers' as well) plasma
 sources have a signal for cnc controller, when torch has touched the
 material, which is used to probe the material surface and then retract
 to pierce height. Since decelerating the plasma torch from the moment,
 when touch is sensed, takes some time and distance of travel, some
 provisions for that extra travel are needed.

 I have seen lots of videos on Youtube with floating torches, but there
 are 2 things that keep me reserved about them:
 1) vast majority of them are not used with LinuxCNC
 2) they require additional construction - bearings etc that I would
>> like to skip
 So the question is - how do other plasma table owners feel about my
 superior invention of non-fixed fixture of Z axis ballscrew nut:
 The basic concept is something like this - motor and ballscrew is
 attached to Z axis, ballscrew nut is attached to Y axis. And I thought
 that I could leave the screws, holding the ballscrew nut in place,
 turned (sorry, I do not know the correct word for that) so that they
 allow for something like 10 mm free travel of nut to accommodate the
 deceleration distance. What I mean here is to have the Z axis balscrew
 nut to lay on its support plate, have screws in place that do not
 allow it to rotate, but that allow it to move extra 10-15 mm for the
 situations, when torch has touched material and is not supposed to
 move further in -Z direction.

 The question is - has anyone ever attempted something similar and are
 there any potential issues that I am running into? I am not sure that
 the nut will be so eager to slide along those screws and that the
 whole concept would generally fail...

 --
 Viesturs

 If you can't fix it, you don't own it.
 http://www.ifixit.com/Manifesto


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Re: [Emc-users] Floating plasma torch - asking to share experience

[jeremy youngs]

capacitve pidkup?
http://rick.sparber.org/sceef.pdf

like this?


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Re: [Emc-users] Floating plasma torch - asking to share experience

[Tom Easterday]

On Nov 10, 2012, at 10:06 AM, Viesturs Lācis wrote:
> Ok, thanks, I will once again think over my approach!
> The thing is that the floating head has to be designed and
> manufactured, but I already am over the project deadline, while giving
> a nut freedom to move some 10 mm in axial
> direction can be set up very quickly. But risk of wearing out the
> ballscrew nut from outside is not something nice to have...
> 
> Can anyone share some nice and simple floating head design?

We were given a torch holder off a Plasmacam machine 
(http://www.plasmacam.com/indexfla.php).  These machines look kind of crappy, 
almost as crappy as their website! :-), but the holder is simple and fairly 
well done and seems to be holding up well on our machine.  It just uses slit 
steel in order to provide the spring action.  I suspect they make one to hold a 
machine torch as well as handheld (like ours).  If you are under a deadline 
perhaps you could just buy the holder from them...?  Not sure since their 
website is pretty much useless you have to call them.

There are a couple pictures of it here: 
http://wiki.linuxcnc.org/cgi-bin/wiki.pl?GantryPlasmaMachine

> It is just for probing move to find material surface, then retract and
> start piercing. I intend to use plasma tip voltage feedback for
> maintaining the torch height during cutting process.
> I guess that some kind of capacitance sensor might be used for this
> probing purpose, but I have dealt with them only once and actually do
> not know, where to get one for a reasonable price.

The probing happens before every single cut so there can be hundreds or probes 
when you are cutting lots of parts and/or large sheets.

-Tom


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Re: [Emc-users] Floating plasma torch - asking to share experience

[Viesturs Lācis]

2012/11/10 Marius Liebenberg :
> I dont think your idea is a good practical idee for a production
> machine. The torch does touch off thousands of times and the loose nuts
> will wear out in no time. There is nothing wrong with a well designed
> floating head and in my opinion it is the best possible pactise to date.

Ok, thanks, I will once again think over my approach!
The thing is that the floating head has to be designed and
manufactured, but I already am over the project deadline, while giving
a nut freedom to move some 10 mm in axial
direction can be set up very quickly. But risk of wearing out the
ballscrew nut from outside is not something nice to have...

Can anyone share some nice and simple floating head design?

2012/11/10 Jim Coleman :
> I know that the big commercial machine I interacted with at my previous job
> would run over diamond plate and run it's head up and down to maintain the
> distance from the surface without actually touching the surface.  I'm
> guessing it had to do with it's current/voltage sensing feedback.  I did
> not follow the THC module that the guys here were working on years ago, I'd
> bet those threads have alot of info regarding the subject, how it works and
> how to implement it. I would think that just riding the surface on a
> floating head would be rather stressful to the mechanisms involved.  Then
> again I doubt you'll want your machine to be running every possible second
> it can, 10 hours a day 5 days a week.

It is just for probing move to find material surface, then retract and
start piercing. I intend to use plasma tip voltage feedback for
maintaining the torch height during cutting process.
I guess that some kind of capacitance sensor might be used for this
probing purpose, but I have dealt with them only once and actually do
not know, where to get one for a reasonable price.

-- 
Viesturs

If you can't fix it, you don't own it.
http://www.ifixit.com/Manifesto

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Re: [Emc-users] Floating plasma torch - asking to share experience

[Jim Coleman]

I know that the big commercial machine I interacted with at my previous job
would run over diamond plate and run it's head up and down to maintain the
distance from the surface without actually touching the surface.  I'm
guessing it had to do with it's current/voltage sensing feedback.  I did
not follow the THC module that the guys here were working on years ago, I'd
bet those threads have alot of info regarding the subject, how it works and
how to implement it. I would think that just riding the surface on a
floating head would be rather stressful to the mechanisms involved.  Then
again I doubt you'll want your machine to be running every possible second
it can, 10 hours a day 5 days a week.

Jim

On Sat, Nov 10, 2012 at 1:20 AM, Marius Liebenberg
wrote:

> I dont think your idea is a good practical idee for a production
> machine. The torch does touch off thousands of times and the loose nuts
> will wear out in no time. There is nothing wrong with a well designed
> floating head and in my opinion it is the best possible pactise to date.
> I do call out service to cnc machines as part of my income and most of
> the problems that I attend to re badly designed or built mechanics on
> machines. Sometimes the electronics are not good but mostly mechanics.
> I will leave you with his idee - Because a thing works once does not
> mean it will work well forever.
>
>
> On 2012/11/10 02:51 AM, Tom Easterday wrote:
> > Perhaps a drawing or something?  I am not following what you are
> proposing.  Sounds like you are talking about having a set up where the
> z-axis ball nut (and hence the whole z-axis) is "sloppy" and can move
> 10-15mm up/down?  While it might work (if that is what you are describing)
> then won't there be a lot of slop in the actual movements of the whole axis
> and won't that effect other movements such as adjustments in response to
> the THC during cutting?  Or perhaps I totally misunderstand what you are
> saying
> > Tom
> >
> > On Nov 9, 2012, at 5:42 PM, Viesturs La-cis wrote:
> >
> >> Hello!
> >>
> >> Little too late but still - I suddenly realized that I need some
> >> provisions for something similar to floating head for plasma torch.
> >> I would like to ask plasma table owners to share their experience, how
> >> they have solved the following issue:
> >> Hypertherm (and most probably other manufacturers' as well) plasma
> >> sources have a signal for cnc controller, when torch has touched the
> >> material, which is used to probe the material surface and then retract
> >> to pierce height. Since decelerating the plasma torch from the moment,
> >> when touch is sensed, takes some time and distance of travel, some
> >> provisions for that extra travel are needed.
> >>
> >> I have seen lots of videos on Youtube with floating torches, but there
> >> are 2 things that keep me reserved about them:
> >> 1) vast majority of them are not used with LinuxCNC
> >> 2) they require additional construction - bearings etc that I would
> like to skip
> >>
> >> So the question is - how do other plasma table owners feel about my
> >> superior invention of non-fixed fixture of Z axis ballscrew nut:
> >> The basic concept is something like this - motor and ballscrew is
> >> attached to Z axis, ballscrew nut is attached to Y axis. And I thought
> >> that I could leave the screws, holding the ballscrew nut in place,
> >> turned (sorry, I do not know the correct word for that) so that they
> >> allow for something like 10 mm free travel of nut to accommodate the
> >> deceleration distance. What I mean here is to have the Z axis balscrew
> >> nut to lay on its support plate, have screws in place that do not
> >> allow it to rotate, but that allow it to move extra 10-15 mm for the
> >> situations, when torch has touched material and is not supposed to
> >> move further in -Z direction.
> >>
> >> The question is - has anyone ever attempted something similar and are
> >> there any potential issues that I am running into? I am not sure that
> >> the nut will be so eager to slide along those screws and that the
> >> whole concept would generally fail...
> >>
> >> --
> >> Viesturs
> >>
> >> If you can't fix it, you don't own it.
> >> http://www.ifixit.com/Manifesto
> >>
> >>
> --
> >> Everyone hates slow websites. So do we.
> >> Make your web apps faster with AppDynamics
> >> Download AppDynamics Lite for free today:
> >> http://p.sf.net/sfu/appdyn_d2d_nov
> >> ___
> >> Emc-users mailing list
> >> Emc-users@lists.sourceforge.net
> >> https://lists.sourceforge.net/lists/listinfo/emc-users
> >
> >
>
> --
> Regards / Groete
>
> Marius D. Liebenberg
> MasterCut cc
> Cel: +27 82 698 3251
> Tel: +27 12 743 6064
> Fax: +27 86 551 8029
> Skype: marius_d.liebenberg
> Skype Me^(TM)! 
> Get Skype  and call me for free.
>
>
>
>
> ---
> avast! Antivirus: Outbound message clean

Re: [Emc-users] Floating plasma torch - asking to share experience

[Marius Liebenberg]

I dont think your idea is a good practical idee for a production 
machine. The torch does touch off thousands of times and the loose nuts 
will wear out in no time. There is nothing wrong with a well designed 
floating head and in my opinion it is the best possible pactise to date.
I do call out service to cnc machines as part of my income and most of 
the problems that I attend to re badly designed or built mechanics on 
machines. Sometimes the electronics are not good but mostly mechanics.
I will leave you with his idee - Because a thing works once does not 
mean it will work well forever.


On 2012/11/10 02:51 AM, Tom Easterday wrote:
> Perhaps a drawing or something?  I am not following what you are proposing.  
> Sounds like you are talking about having a set up where the z-axis ball nut 
> (and hence the whole z-axis) is "sloppy" and can move 10-15mm up/down?  While 
> it might work (if that is what you are describing) then won't there be a lot 
> of slop in the actual movements of the whole axis and won't that effect other 
> movements such as adjustments in response to the THC during cutting?  Or 
> perhaps I totally misunderstand what you are saying
> Tom
>
> On Nov 9, 2012, at 5:42 PM, Viesturs La-cis wrote:
>
>> Hello!
>>
>> Little too late but still - I suddenly realized that I need some
>> provisions for something similar to floating head for plasma torch.
>> I would like to ask plasma table owners to share their experience, how
>> they have solved the following issue:
>> Hypertherm (and most probably other manufacturers' as well) plasma
>> sources have a signal for cnc controller, when torch has touched the
>> material, which is used to probe the material surface and then retract
>> to pierce height. Since decelerating the plasma torch from the moment,
>> when touch is sensed, takes some time and distance of travel, some
>> provisions for that extra travel are needed.
>>
>> I have seen lots of videos on Youtube with floating torches, but there
>> are 2 things that keep me reserved about them:
>> 1) vast majority of them are not used with LinuxCNC
>> 2) they require additional construction - bearings etc that I would like to 
>> skip
>>
>> So the question is - how do other plasma table owners feel about my
>> superior invention of non-fixed fixture of Z axis ballscrew nut:
>> The basic concept is something like this - motor and ballscrew is
>> attached to Z axis, ballscrew nut is attached to Y axis. And I thought
>> that I could leave the screws, holding the ballscrew nut in place,
>> turned (sorry, I do not know the correct word for that) so that they
>> allow for something like 10 mm free travel of nut to accommodate the
>> deceleration distance. What I mean here is to have the Z axis balscrew
>> nut to lay on its support plate, have screws in place that do not
>> allow it to rotate, but that allow it to move extra 10-15 mm for the
>> situations, when torch has touched material and is not supposed to
>> move further in -Z direction.
>>
>> The question is - has anyone ever attempted something similar and are
>> there any potential issues that I am running into? I am not sure that
>> the nut will be so eager to slide along those screws and that the
>> whole concept would generally fail...
>>
>> -- 
>> Viesturs
>>
>> If you can't fix it, you don't own it.
>> http://www.ifixit.com/Manifesto
>>
>> --
>> Everyone hates slow websites. So do we.
>> Make your web apps faster with AppDynamics
>> Download AppDynamics Lite for free today:
>> http://p.sf.net/sfu/appdyn_d2d_nov
>> ___
>> Emc-users mailing list
>> Emc-users@lists.sourceforge.net
>> https://lists.sourceforge.net/lists/listinfo/emc-users
>
>

-- 
Regards / Groete

Marius D. Liebenberg
MasterCut cc
Cel: +27 82 698 3251
Tel: +27 12 743 6064
Fax: +27 86 551 8029
Skype: marius_d.liebenberg
Skype Me^(TM)! 
Get Skype  and call me for free.




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Re: [Emc-users] Floating plasma torch - asking to share experience

[Tom Easterday]

Perhaps a drawing or something?  I am not following what you are proposing.  
Sounds like you are talking about having a set up where the z-axis ball nut 
(and hence the whole z-axis) is "sloppy" and can move 10-15mm up/down?  While 
it might work (if that is what you are describing) then won't there be a lot of 
slop in the actual movements of the whole axis and won't that effect other 
movements such as adjustments in response to the THC during cutting?  Or 
perhaps I totally misunderstand what you are saying
Tom

On Nov 9, 2012, at 5:42 PM, Viesturs Lācis wrote:

> Hello!
> 
> Little too late but still - I suddenly realized that I need some
> provisions for something similar to floating head for plasma torch.
> I would like to ask plasma table owners to share their experience, how
> they have solved the following issue:
> Hypertherm (and most probably other manufacturers' as well) plasma
> sources have a signal for cnc controller, when torch has touched the
> material, which is used to probe the material surface and then retract
> to pierce height. Since decelerating the plasma torch from the moment,
> when touch is sensed, takes some time and distance of travel, some
> provisions for that extra travel are needed.
> 
> I have seen lots of videos on Youtube with floating torches, but there
> are 2 things that keep me reserved about them:
> 1) vast majority of them are not used with LinuxCNC
> 2) they require additional construction - bearings etc that I would like to 
> skip
> 
> So the question is - how do other plasma table owners feel about my
> superior invention of non-fixed fixture of Z axis ballscrew nut:
> The basic concept is something like this - motor and ballscrew is
> attached to Z axis, ballscrew nut is attached to Y axis. And I thought
> that I could leave the screws, holding the ballscrew nut in place,
> turned (sorry, I do not know the correct word for that) so that they
> allow for something like 10 mm free travel of nut to accommodate the
> deceleration distance. What I mean here is to have the Z axis balscrew
> nut to lay on its support plate, have screws in place that do not
> allow it to rotate, but that allow it to move extra 10-15 mm for the
> situations, when torch has touched material and is not supposed to
> move further in -Z direction.
> 
> The question is - has anyone ever attempted something similar and are
> there any potential issues that I am running into? I am not sure that
> the nut will be so eager to slide along those screws and that the
> whole concept would generally fail...
> 
> -- 
> Viesturs
> 
> If you can't fix it, you don't own it.
> http://www.ifixit.com/Manifesto
> 
> --
> Everyone hates slow websites. So do we.
> Make your web apps faster with AppDynamics
> Download AppDynamics Lite for free today:
> http://p.sf.net/sfu/appdyn_d2d_nov
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