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Mounting linear rails on plywood/acrylic/whatever?

Posted by ruyvieira 
Mounting linear rails on plywood/acrylic/whatever?
November 11, 2018 08:52PM
I've done it before on aluminum extrusions and rolled aluminum plates which is a less than ideal solution, and it works. In the beginning there's a bit of resistance, but over time this resistance goes away as the balls wear down the rails. Now, how about other materials, like plywood and acrylic? Would I need something in between the linear rails and the sheet (e.g: a sheet of EPDM rubber) to account for the imperfections or can it be done with nothing in between?
Re: Mounting linear rails on plywood/acrylic/whatever?
November 11, 2018 09:11PM
linear rails need to be on something solid and flat as it will confirm to what they are attached to.

I wouldn't want to even consider putting it directly on plywood or acrylic.
Re: Mounting linear rails on plywood/acrylic/whatever?
November 11, 2018 11:30PM
Some people use linear_rail_only on their CoreXY gantry and it works with a light load like a remote- or Bowden extruder.
Placing rails in the corners of a solid woodframe might work too. But it can deform over time.
Re: Mounting linear rails on plywood/acrylic/whatever?
November 12, 2018 01:32AM
Quote
ruyvieira
I've done it before on aluminum extrusions and rolled aluminum plates which is a less than ideal solution, and it works. In the beginning there's a bit of resistance, but over time this resistance goes away as the balls wear down the rails. Now, how about other materials, like plywood and acrylic? Would I need something in between the linear rails and the sheet (e.g: a sheet of EPDM rubber) to account for the imperfections or can it be done with nothing in between?

That is the great advantage of these cheap chinese rails made out of high strength heat treated chinesium (a mix of recycled lychees cans and crushed chicken bones).
To mount them on plywood, acrylic, I would suggest bubble gum. Cheap, readily available, elastic, has all the qualities required in this case.


"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)
Re: Mounting linear rails on plywood/acrylic/whatever?
November 12, 2018 05:15AM
Quote
MKSA
Quote
ruyvieira
I've done it before on aluminum extrusions and rolled aluminum plates which is a less than ideal solution, and it works. In the beginning there's a bit of resistance, but over time this resistance goes away as the balls wear down the rails. Now, how about other materials, like plywood and acrylic? Would I need something in between the linear rails and the sheet (e.g: a sheet of EPDM rubber) to account for the imperfections or can it be done with nothing in between?

That is the great advantage of these cheap chinese rails made out of high strength heat treated chinesium (a mix of recycled lychees cans and crushed chicken bones).
To mount them on plywood, acrylic, I would suggest bubble gum. Cheap, readily available, elastic, has all the qualities required in this case.

Actually taiwanesium, but it's OK
Re: Mounting linear rails on plywood/acrylic/whatever?
November 12, 2018 09:00AM
Duct tape all the way. Or zip-ties.

Why on earth would anyone make something out of wood or acrylic and then try to put linear guides on it?


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
VDX
Re: Mounting linear rails on plywood/acrylic/whatever?
November 12, 2018 10:56AM
... I've made some of my micro-assembly stages from POM/Delrin and used mini linear guides with PZT motors ... was precise/accurate enough for accuracies below 1 micron (couldn't measure finer than 100 Nanometers winking smiley )


Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org]
Call for the project "garbage-free seas" - [reprap.org]
Re: Mounting linear rails on plywood/acrylic/whatever?
November 12, 2018 12:13PM
Quote
the_digital_dentist
Duct tape all the way. Or zip-ties.

Why on earth would anyone make something out of wood or acrylic and then try to put linear guides on it?
Cheaper than flat milled metal plates and not as bad as MDF

Quote
VDX
... I've made some of my micro-assembly stages from POM/Delrin and used mini linear guides with PZT motors ... was precise/accurate enough for accuracies below 1 micron (couldn't measure finer than 100 Nanometers winking smiley )
Good call, it costs almost the same as acrylic and I can mill it in my router
Re: Mounting linear rails on plywood/acrylic/whatever?
November 12, 2018 12:54PM
Eager to see a Delrin frame plus linear guides 3D printer. Will be a first. How comes nobody thought about it ?


"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)
VDX
Re: Mounting linear rails on plywood/acrylic/whatever?
November 12, 2018 01:07PM
... I've milled the frame of my first delta 2007 from Nylon, the colums from extruded aluminium and the gliders from PTFE -- but seems, it was something against the "RepRap-philosophy" then eye rolling smiley


Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org]
Call for the project "garbage-free seas" - [reprap.org]
Re: Mounting linear rails on plywood/acrylic/whatever?
November 12, 2018 03:38PM
Quote
VDX
... I've milled the frame of my first delta 2007 from Nylon, the colums from extruded aluminium and the gliders from PTFE -- but seems, it was something against the "RepRap-philosophy" then eye rolling smiley

I have no doubt you did it because you are a professional who knows what to use, how and where, design real parts etc...


"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)
Re: Mounting linear rails on plywood/acrylic/whatever?
November 12, 2018 04:46PM
Quote
MKSA
Eager to see a Delrin frame plus linear guides 3D printer. Will be a first. How comes nobody thought about it ?

I've seen some printers with linear rails mounted on MDF, which is quite possibly the worst material someone could use. As long as it doesn't change shape over time, it's good enough I guess, and that's why I asked about plywood. If it's marine grade it won't suffer with humidity or temperature changes. Maybe adding a facing operation to make it flatter would make it flat enough to mount linear guides without binding.
Re: Mounting linear rails on plywood/acrylic/whatever?
November 13, 2018 02:18AM
Quote
ruyvieira

I've seen some printers with linear rails mounted on MDF, which is quite possibly the worst material someone could use. As long as it doesn't change shape over time, it's good enough I guess, and that's why I asked about plywood. If it's marine grade it won't suffer with humidity or temperature changes. Maybe adding a facing operation to make it flatter would make it flat enough to mount linear guides without binding.

How about learning about linear guides ? How they are used, installed etc ???? No excuse with Internet !
OK, at least with plywood, the linear guides will probably not have to "adapt" like you stated in your original post ! "over time this resistance goes away as the balls wear down the rails" !!!!


"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)
Re: Mounting linear rails on plywood/acrylic/whatever?
November 13, 2018 07:03AM
All the surfaces mentioned are more likely to conform to the much stiffer linear guide more than the guide flexing to conform to the surface. If you really want to make something using one of those materials, why not use round rails instead of linear guides? Then all you have to worry about is supporting the ends of the rails. That and cheapness is why round rails were/are used in all the cheesy printers made of acrylic, laser cut plywood, and mdf.

If what you're after is the "look" of linear guides without the performance, buy the crappiest hiwin knockoffs you can find. They're all over ebay and they're cheap as dirt (I think they use pebbles instead of steel balls).


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: Mounting linear rails on plywood/acrylic/whatever?
November 13, 2018 07:22AM
Quote
MKSA
Quote
ruyvieira

I've seen some printers with linear rails mounted on MDF, which is quite possibly the worst material someone could use. As long as it doesn't change shape over time, it's good enough I guess, and that's why I asked about plywood. If it's marine grade it won't suffer with humidity or temperature changes. Maybe adding a facing operation to make it flatter would make it flat enough to mount linear guides without binding.

How about learning about linear guides ? How they are used, installed etc ???? No excuse with Internet !
OK, at least with plywood, the linear guides will probably not have to "adapt" like you stated in your original post ! "over time this resistance goes away as the balls wear down the rails" !!!!

Well yeah I can read the specs sheet, I know there's a maximum amount of misalignment they'll take and the proper mounting surface is something like flat milled steel. What I want to know is how does it work in practice when you mount them to alternative materials.

Quote
the_digital_dentist
All the surfaces mentioned are more likely to conform to the much stiffer linear guide more than the guide flexing to conform to the surface. If you really want to make something using one of those materials, why not use round rails instead of linear guides? Then all you have to worry about is supporting the ends of the rails. That and cheapness is why round rails were/are used in all the cheesy printers made of acrylic, laser cut plywood, and mdf.

If what you're after is the "look" of linear guides without the performance, buy the crappiest hiwin knockoffs you can find. They're all over ebay and they're cheap as dirt (I think they use pebbles instead of steel balls).

That's pretty much the idea behind mounting them over cork or rubber. They'll be a bit misaligned and they'll jiggle a bit as the carriage travels, but the stress should be well within their specs, which means they wouldn't wear down too much. I have tried several hiwin knock offs and the real hiwin things , I know they're not absolutely straight, but they're straigh enough for domestic 3d printing



Edited 1 time(s). Last edit at 11/13/2018 07:22AM by ruyvieira.
Re: Mounting linear rails on plywood/acrylic/whatever?
November 13, 2018 03:03PM
To prevent facepalm injuries, I give up !


"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)
Re: Mounting linear rails on plywood/acrylic/whatever?
November 14, 2018 02:43AM
Please don't give up MKSA, just learn to recognise that not everyone can afford to or wants to spend a large sum of money to get "perfect". Most people can only afford or are more than happy with "good enough".

Anyways, I'd recommend MDF over acrylic and plywood. It's usually cheaper than both, and more isotropic than plywood, plus I think it's actually more temperature and humitity stable. Downsides? Makes a ton of dust. Give it a clear coat and it'll have no problems with Moisture. If you're worries about stiffness, just make the part thicker. Geometry has a much greater role in overal stiffness than the specific stiffness of the material. The dimensions (radius, width, thickness, etc.) are raised to various powers but the young's modulus is not. For a rectangular cross section (which most of your MDF/Plywood/Acrylic parts will have), the bending moment of interia is determined by (bh^3)/12. So double the thickness in the direction you expect it to bend, and the stiffness effectively goes up by a factor of 8, very easily outweighing a difference in young modulus considering most of the aluminium and steel parts people use are relatively thin.
Re: Mounting linear rails on plywood/acrylic/whatever?
November 14, 2018 04:10PM
I've experienced MDF in a 3D printer kit, and I advise strongly against using it for anything structural because it warps. The first mechanical upgrade I did to that printer was to replace the MDF by aluminium. The kit manufacturer replaced it with plywood in the later model of the same printer.

Edited 1 time(s). Last edit at 11/14/2018 04:11PM by dc42.



Large delta printer [miscsolutions.wordpress.com], Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: Mounting linear rails on plywood/acrylic/whatever?
November 15, 2018 02:02PM
I agree with DC42 : MDF is not stable enough for any mechanichal application.

A new product of Portuguese origin, the VALCHROMAT, could be of interest to the 3D printing community. This product is moisture resistant, harder, denser, more stable, and more resistant to bending than MDF. As the product is coloured in the mass, architects and decorators are increasingly using it as a replacement for MDF, to make worktops and doors, even in wet environments.

It is in a way an intermediary between MDF and HPL. It's somewhat expensive, but not as expensive than HPL.

It is available in 8, 12, 16, 19 and 30mm thickness.
Re: Mounting linear rails on plywood/acrylic/whatever?
November 15, 2018 04:27PM
you could always cast some resin on top of the material. i've seen people use this method with cncs to produce a flat mounting surface on steel tube frames.
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