Passive tilt

Discussed here are the various tilt/ slide and Z-Axis mechanisms
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258cj7
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Passive tilt

Postby 258cj7 » Tue Jan 28, 2014 11:37 pm

I have built what I am calling a passive tilt. It's really very simple. The tray is hinged on one side and free on the other. The vat floor is glass with PDMS (Sylgard) coating. As the z axis is lifted the free end is lifted causing the tray to tilt. when the suction is broken it falls back to level. With this setup I only need 1 axis (Z) of movement. The first few layers the tray lifts about 3/16" due to the surface area of the build platform. later layers with small cross sections barely lift it at all. For now I'm lifting about 1/4 inch for the 1st 5 layers and about 1/8th for the remaining ones. Sometimes even that is more than necessary. If I could determine the area of a layer I could modulate the z lift accordingly and shave some time off the print run.
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tray tilt.jpg

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PacManFan
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Re: Passive tilt

Postby PacManFan » Wed Jan 29, 2014 12:54 am

I really love this idea! Have you tried this out printing yet? How does it work?

sitzme
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Re: Passive tilt

Postby sitzme » Wed Jan 29, 2014 10:18 am

Do you think that there is any need for a shock absorber or anything to control the rate that the vat returns? Is there a stop that limits the vat travel? I too am glad to see someone try this as I am a fan of simplicity. Have you made any attempts without the Sylgard? Keep us posted. This could also provide an opportunity to shorten the cycle if there was a limit switch that indicated that the vat was down. It might be a pain from the software side but could take hours off of print times.

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258cj7
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Re: Passive tilt

Postby 258cj7 » Wed Jan 29, 2014 12:57 pm

@ sitzme, I don't have anything to slow the vat return. On most layers it is only droping maybe 1/16th of an inch. The viscosity of the resin has a big effect on how fast it falls. I guess I could put a felt pad or some other cusion so it doesnt "thud" each time. As for limiting the upward movement, Since it is anchored on one side it realy cant pull up to far without separating. I left it free so I could tilt it up to make it easier to drain and clean the vat between prints. I like the idea of sensing when the tray has dropped to speed up the cycle. The only problem is that when the exposure area is really small, the tray doesn't seem to lift at all. I think a better plan would be to calculate the z lift distance based on the exposure area then you could lift the z only enough to break the suction and return for the next exposure.

For vat coatings I experimented a bit with aquarium silicon (inexpensive but dificult to apply and didn't last) and Teflon sheet. The teflon worked well but the sheet I got was very thin and fragile. I also had trouble getting it to adhere to the glass. I may try the adhesive backed fep from McMaster. For now the Sylgard is working for me. I wish it was more durrable but I coated several pieces of glass last time so I'm set for a while. The Sylgard is expensive but I should be able to coat many 4x6 pieces with the small tub I got.

If you think about it:
Pulling one edge down like the traditional motorized tilt is mechanicaly no different then holding one edge and lifting the platform up. The forces exerted on the cured layer are the same.
The difference is fewer moving parts. Just some home hinges vs hinges, a mechanical linkage, stepper and driver.

I'm still tweaking the resin/exposure to get the best detail but you can see the passive tray tilting is working fine
Attachments
head-close-up-(1).gif
Last edited by 258cj7 on Wed Jan 29, 2014 9:57 pm, edited 1 time in total.

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258cj7
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Re: Passive tilt

Postby 258cj7 » Wed Jan 29, 2014 1:06 pm

I have a video of it printing on my blog.
http://johns3dp.blogspot.com/
Sorry about the bad cell phone video, but you get the idea.

John

watsonstudios
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Re: Passive tilt

Postby watsonstudios » Wed Jan 29, 2014 7:24 pm

This is the best price I've gotten for Sylgard. It's on Amazon.
It's not actual Sylgard but the same thing (Generic re-brand). I've been using it and it works great!

http://www.amazon.com/gp/product/B0061G208M/ref=oh_details_o06_s00_i00?ie=UTF8&psc=1

Only 37.00 for the kit!

Jon

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258cj7
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Re: Passive tilt

Postby 258cj7 » Wed Jan 29, 2014 9:54 pm

Good find! Even at $50, Sylgard really isn't that expensive when you consider how many coatings you get out of a container. Of course $37 is even better!

hp_
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Re: Passive tilt

Postby hp_ » Fri Jan 31, 2014 7:07 am

actually i bought this awhile ago.. but i never got arround to test it..

FEP film for me is the best vat bottom.. no chance of any burnin..

hp_