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Z bed cantilever

Posted by MatthewHall 
Z bed cantilever
June 30, 2016 06:15PM
So I made a cantilevered bed out of wood for an upcoming build. How should I attach the bearings (12mm rods)? Also, will wood be strong enough for a 300mm square bed?

I've been building a printer and am on this step now.
Re: Z bed cantilever
July 01, 2016 06:37AM
Wood "works" and changes with themp and humidity. Wood is also pretty heavy if you are talking about hard woods like oak. It is also more expensive than ALU most of the times.
In my view you could get away with a wooden bed if you have a bed leveling probe and do the calibration routine before every print.

I would suggest to take some inspiration from wooden ultimakers and makerbots for a bed support construction.


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Re: Z bed cantilever
July 01, 2016 08:35AM
Hey,

Try to make a sketch on a piece of paper of how you imagine it, there are many designs out there.

Generally I think the consensus is that if you do NOT make it very solid then cantilevered is not recommended. If the 300 is print area, then I would say cantilevered wont do.

See the G&C printer that use cantileverd in a solid construction: [forums.reprap.org]



Have you read [forums.reprap.org] ? It was a very constructive debate we had some time back.
Re: Z bed cantilever
July 01, 2016 10:05PM
Here's a picture of my bed design (just the frame or seat for the bed, I'll use glass or plastic for the print surface)

cantilevered bed

Any comments?

PS: those are MGN 12 linear rails in the foreground. Got them from Aliexpress for $22 a pop! Great quality, surprisingly.

Edited 1 time(s). Last edit at 07/01/2016 10:06PM by MatthewHall.
Re: Z bed cantilever
July 02, 2016 04:42AM
Quote
MatthewHall


Any comments?

Just that wood is hygroscopic and, depending on species, will expand and contract by up to 2% with moisture content. When you heat it, the moisture will be driven out and the fibres will shrink and the whole thing will be thinner. When it cools, it will absorb moisture from the air, and the fibres will expand and it will get thicker. Hygroscopic expansion is far greater than thermal expansion which can largely be ignored in this application. The amount of hygroscopic expansion and contraction will depend on many factors, such as wood species (which we have no way of knowing as it is plywood), moisture content of the surrounding air (which will vary enormously), the grain direction of the various laminations etc. It may not be a great amount but as you need stability within 0.1mm throughout the duration of the print then it wouldn't be my personal choice of material. Sorry if that's not what you wanted to hear but you did invite comments.
Re: Z bed cantilever
July 02, 2016 12:17PM
The old reprap core with wood have made some really nice prints and so have many other printers with a lot of wood in them.

If you feel comfortable working in wood then that should be fine.

However, I think it will be too heavy for cantilevered. It is hard to estimate the exact dimensions from that photo but for me it seems too much.

Have a look at the [www.thingiverse.com] (AndreasL bed) I have finished moving to that setup and all though I am not blown away I think it is an improvement. In a week or two I will make a post of my experiences.


You still havent talked about if you will be using belts or leadscrew or how, to drive the bed?
Re: Z bed cantilever
July 02, 2016 02:41PM
I think for the bed size by the time you make a cantilevered bed fairly stable you will have built a very heavy duty axis, and yet it still won't be as stable as a two sided axis or better a 3 point supported axis. Which really aren't that much more complicated and might be lighter/cheaper etc....

I say this coming from a smartrapcore alu with a supplied cantilevered axis and moving over to a dual z axis, the difference in bed stability is massive. If I'm honest it only made a marginal improvement to print quality, the cantilevered axis wobbled a lot, but not when printing only when I put my finger on it and wobbled it (and when levelling the bed).

Have you considered something like this [www.thingiverse.com] belts really can run the z axis, and are every bit as accurate as leadscrews, plus are much easier to setup/align.


Simon.

[www.precisionpiezo.co.uk] Accurate, repeatable, versatile z-probe plus piezo discs, endstop cables, pt100, 50w heaters. PT1000 cartridge sensors plug straight into duet boards and others.
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