Attaching silicone heater to borosilicate glass

I'm nearing completion of my Vulcanus V1.1 build. (http://www.thingiverse.com/thing:1130016) Everything is coming along nicely. I am working through ideas for attaching the heated bed. I have a 400mm x 400mm piece of borosilicate glass, a 400mm x 400mm silicone heat element that has an adhesive backing. I also have a piece of 440mm x 440mm .1" thick 6061 aluminum plate that I was going to stick the silicone heater to, and then have the glass sit on top of the aluminum. While this should work, it is very heavy. Has anyone tried attaching the silicone heater directly to the borosilicate glass and eliminating the aluminum plate entirely? The glass seems very rigid and I'm thinking it would stay flat enough. Thoughts?

The trouble is if you break the glass, I doubt the silicone heater will come off so you'll need to replace that as well. Personally I have 2 or 3 pieces of glass which clip on top of the aluminium heat spreader. So at the end of the print, I can unclip the glass, fit a new one and start printing again without having to wait for the bed to cool to remove the "just printed" object.

How large/thick is your aluminum plate? Is it heavy?

We have a Taz 3 printer at the Milwaukee Makerspace that had a silicone heater glued directly to a glass bed plate. Here's what it looked like to a thermal camera:



Notice the 30+ C variation in temperature across the surface. The bed was set to 105C to print some ABS. Imagine how well the ABS would have stuck in the areas that are 20-30C cooler. Glass is a thermal insulator. This is what you can expect if you glue a heater directly to the glass.

Recently, the glass bed did what glass does- it broke. Fortunately, no one was cut when the bed was removed from the printer and the glass shards were peeled off the heater. I glued the silicone heater to a piece of cast aluminum tooling plate, 1/4" thick, and changed the leveling system from 4 points, which bends the undercarriage and the bed plate, to 3 points, which actually levels the bed.

Here's the thermal performance of the cast aluminum bed plate:



Notice the order-of-magnitude improvement in temperature distribution.

Here's the undercarriage modified for 3 point leveling. The white pieces are teflon blocks, selected for heat resistance. The leveling screws thread into the teflon which grips them tightly and holds them upright without wobble.



One of the nice things about an aluminum bed is you can drill holes in it, making the 3 point leveling easy to implement. This is a detail of one of the leveling screws- just a countersunk hole in the plate and a screw and a spring. There is nothing standing above the bed surface for the extruder nozzle to crash into. I would have preferred to add thumbwheels to adjust the level from under the bed but the construction of the machine wouldn't allow it.



I cut the original undercarriage down to about 50% of its original mass, which helps compensate for the approximately 2X greater mass of the cast aluminum compared to the glass. I have not had to reduce acceleration due to the higher mass, but that might be necessary on a printer with a weaker motor/driver. Leveling with 3 points is trivially easy and the machine is stable enough that it only requires infrequent releveling.

Each teflon block is held on the undercarriage plate using two screws. The silicone heater was glued using high temperature silicone from an auto parts store (about $6 for a tube).



Here's what it looks like with the aluminum bed, before application of PET tape:



Edited 1 time(s). Last edit at 05/22/2016 02:25PM by the_digital_dentist.

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Thanks @the_digital_dentist.

Ok, I will go with my original plan then. The heat dissipation photos alone were enough to convince me. Although I think the weight is not as much as an issue for yours since the Z doesn't go up and down like mine. I have two Nema 17s and ball bearing lead screws. Maybe I can upgrade those to Nema 23s if the weight is too much.

I suggest you use a thinner piece of aluminium, say 1.5mm, and clip the glass on top of that. With a heat spreader you don't need expensive borosilicate glass, ordinary float glass will do. You can have several build plates, which is useful if you want to start a new print while the previous one is cooling, or if you want to try different surfaces on top of the glass.

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Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Nice thermal profile NO GLASS

440mm x 440mm 0.1" thick 6061 aluminum plate
1.31 kg 2.9 lb

Oh my those tiny NEMA 17 motors may go on strike or melt down

May need:
Allison Transmissions
and
Cummins Diesels

440mm x 440mm 1.0" thick 6061 aluminum plate
13.06 kg 28.8 lb

Definitely go to hydraulic motors
and
with hydraulic pump driven by Cummins Diesels

Quote
svenyonson
... I think the weight is not as much as an issue for yours since the Z doesn't go up and down like mine. I have two Nema 17s and ball bearing lead screws. Maybe I can upgrade those to Nema 23s if the weight is too much.

Actually, I think the weight is much less important with the bed moving in the Z axis. You're not throwing the bed around at high speeds like machines moving it in the Y axis. The lead screws provide some leverage for lifting the bed in the Z axis. Bigger motors and high current drivers are always an option if needed. Oriental Motor has some on line calculators that help design this sort of thing by calculating required motor torque.

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If the plan is to use glass on top of the aluminum you might end up in the same situation with the uneven heat spread in the picture. That nicer alu picture is without glass ontop, just aluminum.

Is it the properties of the molten glass which solidifies with random crystals that make it behave so poorly with distributing heat? I think I understand that it's an insulator but why those random areas that don't transfer the heat as well as the others? Are there better glasses and poorer glasses depending on the manufacturing process/ raw material quality etc? Would a mirror glass be better (because more care is exercised to have it flatter as to not distort the reflected image)...

Edited 1 time(s). Last edit at 05/25/2016 11:04AM by realthor.

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Glass doesn't have a crystalline structure, it's a supercooled liquid. It conducts heat uniformly in all directions (tempered glass may be slightly different). It's not a thermal insulator - if it were then we wouldn't need double glazed windows - but it's not a good thermal conductor either.

Glass backed by an aluminium heat speeder works just fine in my experience. Using 4mm glass, there is a temperature drop from bottom to top of about 5C at 65C bed temperature, and about 10C at 110C. So you need to turn up the bed temperature a litre compared to printing on aluminium.

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Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

So why would glass backed by a silicone heater behave in such a way that we get the thermal images like d_d posted?

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Quote
realthor
So why would glass backed by a silicone heater behave in such a way that we get the thermal images like d_d posted?

Because silicone heaters don't heat very evenly, and a thin sheet of glass won't conduct heat well enough to spread the heat well enough from the hot spots to the cooler spots.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Quote
dc42
Because silicone heaters don't heat very evenly

Indeed that is a deal-breaker

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Quote
realthor

Quote
dc42
Because silicone heaters don't heat very evenly

Indeed that is a deal-breaker

It's not a problem if you use an aluminium heat spreader between the heater and the glass. I'm not sure that PCB bed heaters are any better in general.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Quote
dc42

Quote
realthor

Quote
dc42
Because silicone heaters don't heat very evenly

Indeed that is a deal-breaker

It's not a problem if you use an aluminum heat spreader between the heater and the glass. I'm not sure that PCB bed heaters are any better in general.

I meant deal-breaker for the silicone-to-glass sandwich I was thinking about. Now if that aluminum heat spreader has to be Mic6 6mm that's a show-stopper for many altogether.

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i uses boro glass and 1.5 mm head spreader with silicon heater. it works very well.
But be care full aluminum will expand 2 times of the boro glass.
I used 10x10cm squares and used dubble side tape to stick these squares to the glass with 1mm spacing
This is to avoid deformation of the glass when the alluminium is expanding more then the boro glass

No fir image but measured heat map



and on aly express you can get the dubble side tape sheets for a good price

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No, a heat spreader does not need to be cast tooling plate or even all that thick (1.5 to 2mm).

Edited 1 time(s). Last edit at 05/25/2016 05:56PM by WZ9V.

Quote
amigob
i uses boro glass and 1.5 mm head spreader with silicon heater. it works very well.
But be care full aluminum will expand 2 times of the boro glass.
I used 10x10cm squares and used dubble side tape to stick these squares to the glass with 1mm spacing
This is to avoid deformation of the glass when the alluminium is expanding more then the boro glass

I'd be interested to see a few pictures with that. Do you have any thread opened or blog that you describe/show it? This is an intriguing technique and I like it BUT don't the double sided tape pads inhibit heat to be transferred to the glass by the aluminum squares? Are they some sort of special heat conducting double sided tape that is also heat resistant?

Edited 2 time(s). Last edit at 05/25/2016 06:01PM by realthor.

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Haven't made pictures when I made this

I ordered a Boro glass on aliexpress with the size of 220x220mm
Sprayed it with exhaust black, and backed it in the oven
Printed mounting blocks from PLA.
Without sticking the heater on it I put every thing together leveled a little bit.
and then uses epoxy glue to glue the mounting blocks to paint on the boro glass
after that I used carpet dubble sided tap ( not the best choice, but thin enough )
I would now uses the head resisting tap of 3M big sheets are available on aliexpress
I cut my 1.5mm sheet aluminum with a 0.8 mm grinder disk ( 100x100mm), don't aluminum will deform.
Just use a metal saw.

The heater had already dubble side tape from 3M,
until now it works perfect.

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P3steel DXL, with Due/RADDS/Raps128 dual Wade's extruder

Fantastic, thanks for the trouble of taking the picture.

Couple questions
- is the "exhaust black" a heat resisting paint used to paint exhaust pipes? Just to make sure i got it right
- why bake in the oven? is that how that specific paint works or there's something else evading me?
- doesn't the heat from the silicone pad creep to the PLA mounting blocks to deform them?

You seem to have a beast there, it's a pity no link to it ("P3steel DXL, with Due/RADDS/Raps128 dual Wade's extruder")

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reading the other thread , glueing is not that smart. Use the double sided tap because it also creates a flexible connection,
I have no insulator underneath the heater, yet, and it takes 7min to 90c

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Quote
amigob
reading the other thread , glueing is not that smart. Use the double sided tap because it also creates a flexible connection,
I have no insulator underneath the heater, yet, and it takes 7min to 90c

Yeah, I was referring "glue" as a generic term as in "attaching", I don't actually know of a glue to bond glass to alu and take high heat and also conduct heat to the glass.
I am still trying to get my head around it because there is no direct contact between your alu 1.5mm pads and the glass.

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PLA in contact with the heated bed? Hmmmmm....

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but there is also no direct contact between the heater and the aluminum.
Yes you loose energy, but it seems to be no problem, without the insulator it already heads up pretty quick, ( I uses 200w , 220Vfor 200x200mm )
I have by the way a infrared sensor on the printer head and that sensor I use for pre heating so that the glass
really reaches the designated temperature.
You can read about that here

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Quote
amigob
but there is also no direct contact between the heater and the aluminum.

Isn't the silicone heater glued to the aluminum (it should have had some sort of adhesive that you would expose by peeling a foil off of it). Do you refer to that glue (or maybe tape) as preventing the heater to contact the aluminum?

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The PLA, I thought that I need to replace them when starting to print ABS,
But it is now test to 130c , and no problem at all

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