Tilt&slide

Discussed here are the various tilt/ slide and Z-Axis mechanisms
johnrpm
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Tilt&slide

Postby johnrpm » Wed Dec 04, 2013 6:30 am

I have made my vat with tilt and slide, a worm and wheel, salvaged from an old piece of kit
driven by a stepper motor salvaged from an ancient hard drive, rotates an eccentric pin
to slide the vat and then tilt it down, the other end slides on small bearings.
At the present time I do not know what forces are needed, and if the stepper is up to the job,
but it would not be hard to fit a bigger one if needed.



vatworm.jpg
underside of plate



I still need to cut the aperture for the glass plate, but will mount the projector in position
and mark on the vat the actual display area, then cut it out.

more info as I progress.
Last edited by johnrpm on Sat Dec 07, 2013 4:02 pm, edited 1 time in total.
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PacManFan
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Re: Tilt&slide

Postby PacManFan » Wed Dec 04, 2013 10:02 am

I'd like to see the worm gear you're using. I'm using a leadscrew drive mechanism on my machine. The stepper motor on mine is mounted on a tilting axis to arc back and forth while it pulls down on the bottom of the vat.

johnrpm
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Re: Tilt&slide

Postby johnrpm » Wed Dec 04, 2013 3:05 pm

Believe it or not, I do not have a camera, apart from the phone one, but
the images are rubbish, so I ask the wife to use her camera, then I will post images,
which will explain better than I.
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sitzme
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Re: Tilt&slide

Postby sitzme » Thu Dec 05, 2013 11:05 pm

The machine I built uses an X axis to slide. After looking at tilt, I thought that it would still take a lot of force to peal it off. The vat window probably has some flex which would work in favor of this method. I saw a slide setup that moved the width of the build platform into an area that was deeper to break the vacuum. It seemed to work but looked like a slosh waiting to happen. Since it is early in this process, I thought that using an X axis would allow the option to slide and lift at different rates and ramps to find the optimal. It is too early to say for sure if I am on to anything here. The results of last nights prints (failed) showed that too high of a feed resulted in an abrupt and noisy separation. When I cut the feed rate from 200 to 20 I could not tell when the release occurred. On the other hand, at some point I was losing the bond to the build plate but I believe it was several layers in and my observations are based on the first few layers.

Time will tell what the most effective method(s) is. Being either easy to build or reasonable to purchase will probably be a factor. A cam slot would be another variation with motion similar to johnrpm's. Another option would be an eccentric pin on the basic tilt mechanism to provide the initial force to shear and separate. I am a fan of simple and hope that a bullet proof method to adhere to the build plate and separate from the vat is found.

For tonight I only roughed up the build plate. It was originally ground and you couldn't feel and scratches with a finger nail. Approx a 32 finish with some dings from laying around. I started the roughing process by scoring the surface with a utility knife about every .38" and then hit it with a 24 grit wheel on an angle grinder briefly. Very little material was removed. The scoring left raised material that I thought would damage the Sylgard during the slide.

sitzme
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Re: Tilt&slide

Postby sitzme » Sat Dec 07, 2013 8:11 pm

Did some testing today with the roughened aluminum build plate and bare glass. This was done off the machine. I used two pieces of blue painters tape to set the layer thickness and put about 4-6 drops of SubG+ on the plate then place the glass on top. In every case the cured resin stuck to the aluminum plate. When using thick glass there was no detectable flex and I had to pry the glass off. It was hard enough that I expected breakage but none happened. Then I tried the standard window glass that I used on the vat. It was easier to get off so I did a quick check on how flexible it is. A 12" long piece with a .12" thick shim under one end is flexible enough to press the center down to the table surface without breaking. It appears that there is probably some pealing going on.

Bad news is that when I cleaned my vat the coating was damaged in the area of the last prints. I will try some prints on the other end and then may try a couple on bare glass.

The plan is to use a move of;
G1Z1
G1Z1X7

instead of a straight ramp to put some tension on the glass and then slide to help it release.

I also played with some clear plastic film between the glass and resin. It released really well but I can't see how to keep it flat. Even pulling a vacuum between the plastic and glass would probably fail due to air bubbles based on some vacuum bagging experience.

johnrpm
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Re: Tilt&slide

Postby johnrpm » Thu Dec 12, 2013 5:07 pm

Thanks for sharing your tests, I am following your progress, I wonder if OHP sheet would block uv, or be damaged by the resin, would be nice to have a cheap alternative to sylgard.
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maxman
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Re: Tilt&slide

Postby maxman » Wed Dec 18, 2013 2:59 pm

Sorry, maybe it's a very stupid question, but doesn't anybody use a high torque rc Servo?

You can get cheap ones with a torque up to 40kg/cm an more. It's very easy to control servos, they are very strong, their accuracy should be sufficient. Also there is no need for a second stepper driver.

sitzme
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Re: Tilt&slide

Postby sitzme » Thu Dec 19, 2013 10:58 am

I have a 12" sq piece of Gorilla glass coming from www.mcmaster.com. It is very flexible for glass so I plan to mount it such that the print can peal easier. There will be some tests off the machine first followed by some live testing. I am going to try to mount the Gorilla glass so that one or both ends are captured in Z and use silicone tubing to allow it to flex when pealing the print away. It will probably require a thicker glass pane under it to reduce sagging. It would be great if this could be used without any coating but that might be like winning the lottery.

johnrpm
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Re: Tilt&slide

Postby johnrpm » Thu Dec 19, 2013 3:30 pm

That gorilla glass looks interesting, pmma or plexiglas is supposed to be UV transmisive, so I intend
giving it a try, this whole vat thing is making me wonder if I should have gone for top down.
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sitzme
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Re: Tilt&slide

Postby sitzme » Thu Dec 19, 2013 3:54 pm

There is a lot of moaning about acrylic vats over on the B9 Creator forum. If the resin gets on the acrylic they are more or less shot. I like the flexibility though. Just need a durable coating.


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