Anyone Tried a Removable PEI Bed?

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jballard86
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Re: Anyone Tried a Removable PEI Bed?

Post by jballard86 » Wed Mar 23, 2016 7:35 pm

20160323_212959.jpg
The one that I annealed is perfectly flat though, but it is cracked in a few places

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piercet
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Re: Anyone Tried a Removable PEI Bed?

Post by piercet » Wed Mar 23, 2016 7:42 pm

Pei is actually available in a castable resin form as well. I want to someday get an aluminum tool plate milled with thin slots in it, then cast a Pei top on it.

jballard86
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Re: Anyone Tried a Removable PEI Bed?

Post by jballard86 » Wed Mar 23, 2016 8:07 pm

piercet wrote:Pei is actually available in a castable resin form as well. I want to someday get an aluminum tool plate milled with thin slots in it, then cast a Pei top on it.
If I can find the resin affordable, ill mill a plate and test it. I love having a bridgeport.

kcchen_00
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Re: Anyone Tried a Removable PEI Bed?

Post by kcchen_00 » Wed Mar 23, 2016 11:50 pm

moejt wrote: Anyone know what lulzbot uses to glue their sheets to the plate? I feel like it's pretty lack luster, although I hear the issue is possibly more due to moisture during assembly?
This video is a bit dated, but they could be using the same DryTac machine to apply adhesive to the glass for PEI. See 3:30 mark:
https://www.youtube.com/watch?v=f4RGU2jXQiE

From the DryTac mounting adhesives lineup, MultiTac seems to be the most versatile and has a heat range of 110C-120C. Unfortunately, that's where a lot of us are at printing with ABS. We should probably drop to 100C to be safe with the OEM film... otherwise contraction of the ABS during cooling could be causing bubbling inadvertently.

Hopefully they are using some a flavor 3M 200MP adhesive that holds to 200C. Which, BTW, is the same adhesive used in the recommended 468MP for DIY application of the PEI. Just depends on if its 2.3mil (467MP) or 5.3mil (468MP) based on this spec sheet.


Just a note on the Zebra plate... It seems to work okay, but the material seems to "bubble" from heat. I've tried a 240C extrusion temp with the bed at 70C, and if the nozzle is too close to the bed the combined heat causes the plate to bubble. So I'd gladly switch back to PEI if a removable solution is found or the bubbling stopped.

kmanley57
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Re: Anyone Tried a Removable PEI Bed?

Post by kmanley57 » Thu Mar 24, 2016 7:16 am

The B.O.M. shows they get the Rolls of 3M 468MP 5.2 Mil.
I will express my CRAZY ideas at any time! So you have been warned. None of my opinions are Lulzbots and can be wrong at any second.

moejt
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Re: Anyone Tried a Removable PEI Bed?

Post by moejt » Mon Apr 04, 2016 9:39 am

Haven't had a chance to get back to this topic in a while.

So the PEI sheets seem to be uniformed thickness, they are just bowed. I might have to order some and experiment.

How would casting PEI in aluminum work? Would the PEI be removable from the aluminum or would they be one piece?

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piercet
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Re: Anyone Tried a Removable PEI Bed?

Post by piercet » Mon Apr 04, 2016 10:27 am

I've throught of two approaches. cast in place non removable, where the aluminum base plate has really shallow "T slot" profiles milled into its surface, maybe 2mm deep, which would be really difficult to mill with any strength (maybe a trapazoidal profile instead) surrounded on 4 sides by a thin aluminum edge wall, or the same thing surrounded on 3 sides, but able to slide out on the 4th side, with some sort of retention mechanism to prevent that under normal operation (possibly a [ shaped hinge bracket that would swing down to allow PEI removal. Getting such a profile made is going to be extremely complicated though.

An edge retention method would work, but then you have the issue of PEI flex in the middle.

ANother thought would be a permanent vaccumme plate. Start with a 2 part aluminum plate with vaccume ports in the bottom, add a small vaccuume charge port lever on the side, push the lever down once or a couple of times, PEI is sucked down onto the aluminum. Turn the handle and the plate releases. That would work really well, but I'm not sure it could be made small enough to be effective. You could run a very small flexible vaccume line to the plate, and put the charging pump on the main frame which would make it more feasable, but you are still looking at a fairly complex milling profile, call it 7.5mm worth of space to work with, 1.5mm of that would normally be PEI and adhesive, the other 6mm would be the baseplate, so you need at least a 1mm rim around the edge, 1-2mm thick upper vaccume plate with holes in it, at least 1mm thick channels for air to travel from the holes to the pump, and at least 2mm worth of bottom plate and .5mm worth of gasket. Then you still have to put the vaccume charge port somewhere accessable with enough mass to even thread the port in (probably on the top or bottom of the plate since that would allow for a larger port without making the plate thicker.

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piercet
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Re: Anyone Tried a Removable PEI Bed?

Post by piercet » Mon Apr 04, 2016 10:55 am

You know, now that I look at the vaccum pei plate option a bit more, its actually not that bad an idea. You can get very small threaded vaccum ports. The plate itself could be basically just 2 parts. a top plate with 3-4mm holes spaced every 2cm or so and a 1-2mm wide groove channel connecting each port. A small 24v vaccum pump could be tied off the main PSU with an on off switch and a vent valve, use RTV or similar higher temperature gasket material to hold the bottom plate with the heater attached on, a couple of low profile screws to hold the whole assembly together, maybe some artic silver thermal grease to promote better heat transfer, use the stock bed corners to hold the main plate in place and keep the PEI from moving around when vaccume is off. That way you still get good thermal transfer, a removable PEI sheet, the benifits of an Aluminum core and no worries about replacing adhesive.

That might be a good first project for my mill now that it's almost functional.

ttabbal
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Re: Anyone Tried a Removable PEI Bed?

Post by ttabbal » Mon Apr 04, 2016 1:17 pm

Rather than vacuum, how about magnetic? Embed magnets in the PEI base plate and the build table. Combined with an edge clip to prevent the whole thing from shifting, it seems like it would be strong enough. I use ABS clips and Binder clips on my Zebra plate, and it doesn't go anywhere. It does, however, bow in the middle some. I had thought about cutting some holes in one side, adding magnets with epoxy or similar, then using matching magnets on the build table to attach it.

PEI is too thin to do that directly, at least, reasonably priced PEI is anyway. However, if you were to cast PEI onto an aluminum plate or similar, it might be doable.

Not as easy to remove as venting vacuum, but fewer failure points with no hoses/connections to leak etc... Either way, I like the idea.

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piercet
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Re: Anyone Tried a Removable PEI Bed?

Post by piercet » Mon Apr 04, 2016 2:22 pm

Magnets could work, the tricky bit would be how they would hold up to temperature cycles over time. The ones at the edge would be fine, the ones in the middle might not be.

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