By the time you buy the timing belts, pulleys, shafts, machine the
brackets, to do a double belt reduction to get to 10:1, you are money
ahead to just buy a servo grade 10:1 gearbox. If you mount a pinion
directly to the gearbox shaft and drive the rack with this pinion, you
will have a very rigid drive system.
There are things like this out there.
https://www.ebay.com/itm/planetary-reducer-gearbox-3-1-to-10-1-for-1kw-2kw-130-AC-servo-motor-input-22mm/263810208961?hash=item3d6c5054c1:g:dFAAAOSwBd1bRsP1
If you buying Chinese servo motors and drives, ask them about a 10:1
gearbox.
Dave
On 10/4/2018 11:13 AM, Leonardo Marsaglia wrote:
Hello Dave,
Well, to avoid the backlash is that or may be using timing belts and
pulleys to drive the shaft too. The gearbox is a good idea but I think that
can raise the cost too much. Anyway I'll give it a look because I don't
want to discard any option.
In any case I'm still not sure about wheter use two motors or one motor
with a shaft. The latter option makes me feel more secure because it can't
go out of squaress easily, unless you have loose belt or something breaks.
By the way I just re send another message that was rejected by the list
because of the size of the pictures, I don't know if now you can see it.
El jue., 4 oct. 2018 a las 12:04, Leonardo Marsaglia (<ldmarsag...@gmail.com>)
escribió:
Hello Les,
No, I plan to support 50 mm bars every 600 mm more or less. I'm attaching
some pictures of the design I'm working on. (The adjustable stands for
levelling are not in the assembly because I'm saving resources on this
laptop)
I like the idea of using the rectangular ways but unfortunately they are
quite expensive for this project and also there's the aligning problem.
With the setup I'm trying to do I can adjust the parallelism on every
corner of the machine and also individually adjust every suport to level
the guides perfectly. I'm sending pictures of everything to clarify what
I'm intending to do. Please note this is under development and some things
are going to change a little bit.
The idea of welding the frame is out of discussion because I plan to move
and set up this thing in place. Also, I don't have the means to guarantee a
clean and squared welding for the frame. Instead I decided to do what you
can see in the pictures, having an enormous amount of bolts to keep the
parts rigid and firm.
No problem about using tubing to lower the inertia. I also thought about
reducing the 3000 max RPM with the worm and gear to 100 RPM on the shaft
and then increase the size of the pinions to have the linear speed I want.
This way the long shaft doesn't have to withstand the high RPMs.
(Second attempt to attach the pictures)
El jue., 4 oct. 2018 a las 12:00, Dave Cole (<linuxcncro...@gmail.com>)
escribió:
I'd avoid a worm gear drive. They are prone to wear and backlash.
I'd look for a good deal on a servo grade planetary 10:1 gearbox that
fits your Chinese motor.
Probably the easiest and most rigid drive solution is to use two motors
each with a planetary gear box and direct drive a pinion on a rack.
If you want to mill aluminum and need rigidity, that's the way I would go.
You might want to weld the frame in sections and then bolt it together.
If you don't have a platen to weld it on, you might want to contract out
part of the frame welding.
Dave
On 10/4/2018 10:41 AM, Leonardo Marsaglia wrote:
By the way, on the pictures there are missing details I didn't draw yet,
like setscrews for parallel regulation and things like that. Also, I
have
yet to modify the design for the one motor and shaft approach and see
wich
is better.
El jue., 4 oct. 2018 a las 11:37, Leonardo Marsaglia (<
ldmarsag...@gmail.com>)
escribió:
Hello Les,
No, I plan to support 50 mm bars every 600 mm more or less. I'm
attaching
some pictures of the design I'm working on. (The adjustable stands for
levelling are not in the assembly because I'm saving resources on this
laptop)
I like the idea of using the rectangular ways but unfortunately they
are
quite expensive for this project and also there's the aligning problem.
With the setup I'm trying to do I can adjust the parallelism on every
corner of the machine and also individually adjust every suport to
level
the guides perfectly. I'm sending pictures of everything to clarify
what
I'm intending to do. Please note this is under development and some
things
are going to change a little bit.
The idea of welding the frame is out of discussion because I plan to
move
and set up this thing in place. Also, I don't have the means to
guarantee a
clean and squared welding for the frame. Instead I decided to do what
you
can see in the pictures, having an enormous amount of bolts to keep the
parts rigid and firm.
No problem about using tubing to lower the inertia. I also thought
about
reducing the 3000 max RPM with the worm and gear to 100 RPM on the
shaft
and then increase the size of the pinions to have the linear speed I
want.
This way the long shaft doesn't have to withstand the high RPMs.
Let me know if you can see the pictures.
El jue., 4 oct. 2018 a las 10:52, Les Newell (<
les.new...@fastmail.co.uk>)
escribió:
Using two motors is mechanically simpler and has lower rotational
inertia but I am not a fan of this setup. If you use a tube rather
than
a solid shaft, you won't add a lot of inertia. I'm thinking of
building
another plasma cutter and it will probably use a shaft rather than 2
motors.
But the thing is, I'm planning to use round guides
with bronze adjustable bearings.
Do you mean guides that are only supported at the ends? This is a very
bad idea. They'll flex and bounce all over the place. You are also
likely to get a lot of wear unless you pressure feed lubricant. If you
do that oil will go everywhere. My router uses box ways on the Y and Z
axes with oil feed. It gets pretty messy at times.
Most modern commercial routers and many machining centres use
rectangular linear ways, such as this
<
https://www.qualitybearingsonline.com/lwl25r240bhs2-iko-maintenance-free-linear-guide-rail/
.
They are very rigid and lasts a long time with very little wear. The
only disadvantage is that you need to be careful to make sure
everything
is perfectly aligned. These have very little give in them. Another
option is supported round rail such as this
<
https://www.amazon.co.uk/TEN-HIGH-Supported-SBR40UU-BlockBearing-Bearing/dp/B01N10JF5N
.
For the sort of size machine you are talking about you'll need at
least
40mm round rail. Round rails wear faster than rectangular but are a
lot
less fussy about alignment.
So, to sum up, with these kind of bearings I expect more resistance
on
the
joints, and also the router is 2 meters x 3,8 meters long so to have
enough
rigidity I'm planning to use steel and cast iron, so that's why I'm
oversizing the motors.
To give you an idea about motor sizing the motors on my router (1 per
axis) are about 1.8kw and it's scary. My tool changer is mounted on a
bracket made from 50mmx50mm box section. I messed up the tool change
sequencing a while back and it pushed the tool changer out of the way
without breaking a sweat. It tool a lot of effort with big levers to
twist it straight again. Here is a link to a similar machine to mine
but
without a tool changer
<
https://www.bidspotter.co.uk/en-gb/auction-catalogues/cjm-asset/catalogue-id-cjm10389/lot-47df49af-bf1a-4676-ab88-a75a00f5f92b
.
Lots of heavy steel and cast iron. Mine originally had 4 drill heads
and
2 spindles. If it was easy to dial back the power I would. If
something
goes wrong the machine will keep pushing until something breaks.
I do maintenance work on a router with 750W motors. A while back the
spindle stalled while it was cutting. It bent the 1/2" cutter nearly
90
degrees and carried on.
Les
On 04/10/2018 13:47, Leonardo Marsaglia wrote:
First of all, thank you guys for your advices as always!
I'm gonna try an asnwer this on one message because sadly gmail
doesn't
have the quote selected text feature anymore.
About the oversized motors. Yes, I also think that for a normal
router
1 kw
per side is too much. But the thing is, I'm planning to use round
guides
with bronze adjustable bearings. I decided this because I want more
rigidity for an eventual need of machining aluminum, and also
because I
think this kind of guides with whipers are much more reliable than
the
recirculating ball ones. Also, I don't think I can have the
adjustable
feature with the slotted ball bearings. I'm attaching a picture of
the
bearing I plan to make, there are no lube channels on the model but
they
will be on the final part.
So, to sum up, with these kind of bearings I expect more resistance
on
the
joints, and also the router is 2 meters x 3,8 meters long so to have
enough
rigidity I'm planning to use steel and cast iron, so that's why I'm
oversizing the motors. Besides, there's no much difference between a
400W
and a 1Kw chinese servo motor and drive on ebay.
About how to drive and home the gantry. From what we've been talking
and
thinking it through a little more, I'm thinking that the best
solution
is
the one Gregg suggested. To have a transversal shaft on the gantry
driven
by the servo motor by a worm and gear reduction with the timing
pulleys
on
each end of the shaft driving the pinions. This way I can adjust and
square
the two columns and it should stay squared at any time. This is
really
important because this is going to be used by a regular operator, so
this
has to be as reliable and fail proof as possible.
About the last question. Is there any disadvantage other than may be
a
little more mechanical complexity with the one motor and shaft
approach?
Because I've seen lots of routers driven with two motors that I
almost
think it's mandatory for some reason.
Thanks again!
Leonardo
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