Ideas for insulating underside of print bed

So I've got a 12" diameter disc of 1/4" thick Mic6 Cast Tooling plate that I'll be using for a print bed. It has a silicone heater attached to the bottom which has a 25mm hole at the center so I can Kapton tape the thermistor directly on the underside of the aluminum plate. I'll also be installing a thermal cutoff and securing it near the thermistor somewhere on the silcone heater. I plan to use Kapton tape to hold it there too.

I'm thinking of solutions that could solve a couple of problems with that idea plus a couple more and add the benefit of insulating from underneath.

I'm thinking of taking the above assembly and adding 1 or more of these beneath it:

https://www.amazon.com/dp/B00OLFDIO0/ref=psdc_13397451_t2_B07JZZ3RXM

And then adding one of these to create a sandwich:

https://www.amazon.com/American-Metalcraft-18912-Separators-Length/dp/B003DAP4HS/ref=sr_1_5?s=home-garden&ie=UTF8&qid=1544804684&sr=1-5&keywords=12%22+aluminum+pizza+pan+separator

The entire sandwich will then be clamped using my bed mounts at 120 degree interval (3 of them) which will also are slotted to mount to my frame and allow expansion.

I feel this design would:
1. Allow replacement of the thermistor and tco if they were to fail as opposed to bonding them permanently with silicone
2. Adequately keep the thermistor and tco in place
3. Prevent the heater from detaching from the aluminum plate
4. Insulate what's below from the heat.

Any opinions?
Think a couple of those silicone mats would give enough to conform around the thermistor some without crushing it?

Edited 2 time(s). Last edit at 12/14/2018 11:41AM by FA-MAS.

I like your solution; but if you're looking for alternatives, I like using ceramic sheets for the insulating layer. Look for 9353K31 at McMaster-Carr (12x12 inches for ~ $13). These are rigid sheets that are easily machined or carved and provide excellent insulation.

I found a place that sells aluminum discs in varying thicknesses. I'd probably go for something a little thicker than the pizza pan separator.

http://metalremnants.com/product/aluminum-discs/

Doesn't look like those silicone mats are gonna work. I got 3 of them and they don't have any give whatsoever. I did however find some Closed Cell Silicone Rubber Sponge that looks like it'll work.

I use cork sheet.

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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].

I thought about cork. I don't think I'm looking for the insulating property so much. I'm looking for something that can be used to put a little pressure on the silicone heater so that it doesn't fall away even if the adhesive were to fail. Also looking to hold the thermistor and tco in place without permanently affixing.

Edited 1 time(s). Last edit at 12/24/2018 11:18AM by FA-MAS.

Perhaps cork with an aluminium or MDF sheet underneath?

Edited 1 time(s). Last edit at 12/24/2018 12:13PM by dc42.

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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].

Think the cork will compress enough around the thermistor and tco without crushing them if I were to sandwich cork between my cast tooling plate and a thinner aluminum sheet?

If you are looking for something more compressible, how about glass fibre insulation?

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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].

Ever considered a silica aerogel blanket ? The thermal properties are remarkable.

I did run across this product actually. the only thing I dislike is that fiberglass is involved. I'd rather not deal with handling or cutting it. Plus I dunno how clean the cuts can be and if they'll stay that way or if they'll begin to fray. I'm still thinking silicone foam will be the option.

Quote
Gecko23
Ever considered a silica aerogel blanket ? The thermal properties are remarkable.

Try to add glue on the location where you will cut. Some glue which solidifies into something rubbery.

I have used aluminized bubble film on two of my printers - the kind that is sold to put behind radiators. Although I didn't expect it to work for longer than a short time it is still pristine some two years after I put it in.

Mike

In an attempt to improve the warm-up time, I tried various insulation configurations: fixed, under the bed, and removable, above.

These efforts have been very disappointing.

I understood when the bed is cold, most of the energy you supply it is used to heat the thermal mass it represents. Convection losses to ambient air are completely negligible in front of this mass heat to be supplied. In addition, convection only occurs when the temperature difference is significant, for example when the bed is above 100°C. And the energy dissipation, in this case, is relatively low (<100W for a Ø200mm bed). In any case, it is largely unavoidable, since we must leave the surface accessible.

In other words, if your concern is to improve the warm-up time, or to limit energy losses, insulating the bed is of little use.

If the bed is supported by three points, direct conduction losses between materials will be very limited, and a thin air gap will probably be created below the bed. If thin (<10mm), this air gap is as insulating as any insulation you could install instead.

On the other hand, it is true that if the electronics is just below the heated bed, after several hours, it will be in an uncomfortable situation because of the continuous radiation received. In this case, well-designed ventilation will be more effective than thin insulation. Glueing a thin sheet of household aluminum to reflect this radiation is the best you can do.

That's just my opinion....

Edited 1 time(s). Last edit at 01/01/2019 06:52AM by M_Xeno.

I probably should have titled the thread differently, something along the lines of "Securing the bed heater, thermistor and thermal cut-off in a way that will prevent the heater from separating if the adhesive were to fail and allowing the thermistor and thermal cut-off to be replaced if need be."

I'm not too worried heat up time or loss. I did the calculation for the mass of the bed and overpowered it slightly so I should be able to counteract those issues. I'm not too worried about the electronics. They are below the bed, but there will be whatever insulation material, a 1/8" aluminum disc, an air gap as well as a 6mm thick piece of cast tooling plate in between the bed heater and the electronics.

I received a sheet of 1/4" closed cell silicone foam pad. It looks like it will do the job. It is compressible enough so I can sandwich it between the bed and 1/" disc and put the thermistor and thermal cut-off in contact with the underside of the bed and they won't be crushed and everything will be held together so if the bed adhesive were to fail, it wouldn't come away from the bed.

I am writing this in hurry. sorry for my english.

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made a great effort to acheive what you are seeking.

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