Mounting and attaching a heated bed

I just ordered a circular PCB heated bed for my Kossel. At the moment, I have a 3/8" basalt printbed shaped like a Reuleaux triangle, and I'm wondering how to attach the bed to the stone and how to mount the whole assembly. My whole printer is printed in PLA, so heat is a concern.

First of all, there's insulation. My steppers are just below my bed and they tend to get hot, so I have a fan blowing straight up at the bed. I need good insulation, therefore, both to keep the bed warm and to prevent the hot air from causing the steppers to overheat or melt their mounts. Would a sheet of Styrofoam or polyethylene foam work? How would you recommend attaching it to the bed? I was considering silicone caulk.

Secondly, there is the issue of attaching the heater to the bed. I'd like to be able to remove it, so I can wash the bed and such. Is it enough to just have the bed pressed against the basalt, or will the thin layer of air be a problem? Are there thermal pastes that can take ~130C?

Third, my bed is a weird shape, and it's bigger than the heater. How necessary is a spreader? Am I in danger of cracking my bed from thermal strain, or would it just mess with printing near the edges? I have some aluminum laying around, so adding a spreader wouldn't be too hard, but I would have to cut it to size and anchor it to either the heater or the bed.

Fourth, I need to mount the whole bed assembly to the printer in a way that won't heat the frame up. My bed has a small hole in each corner, so my current plan is to have three bolts on the printer and to use some springs to hold the bed away from the bars. This has the added benefit of mitigating head crashes, but it would require a hex wrench to take the bed off. Is there a way I could do this that would let me remove the bed quickly, without tools? Could I use this method with the heater and/or spreader, and just place the bed on top? Keep in mind I can't print in ABS yet, so everything has to be PLA-safe.

Lastly, I have a cheap Chinese 12v PSU rated for 360W. The bed takes 140W and my hotend takes 60W, so I should be fine, but is there anything I should keep in mind?

Thanks for the help, fellow RepRappers!

The usual way to insulate the bed from whatever it is below it is a sheet of thick corrugated cardboard.

Why don't you use an aluminium heat spreader, attached to the bars via 3 or 6 steel standoff pillars, and then use 3 clips or clamps on the corners of the basalt bed to secure it to the heat spreader? That would make it easy to remove, as well as reduce the risk of thermal stress cracking the basalt. I don't think you need to use thermal paste, I don't.

If your stepper motors get hot then you should consider reducing the current. Try about 20% less current.

That PSU should be more than adequate.

Edited 1 time(s). Last edit at 03/03/2015 12:52PM 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].

Thank you for your advice! How does one normally anchor cardboard to the bed?

Using steel standoffs sounds like a good plan, though I do want a way to keep the bed from sliding around.

I'll try reducing the current, but I need all the torque I can get for my 300 mm/s moves. I love deltas.

I use a thin (1.5mm) sheet of cork glued with normal white (wood) glue to the underside of the PCB heatbed, as suggested in the wiki: [reprap.org]

and it works just fine.

Thank you! Can all wood glue survive HBP temperatures?

You can use ...
Fibre Paper (3mm thick) .. to insulate the heat bed . its a ceramic material available from pottery kiln suppliers.
Also you can use picture frame clips called Swiss clips, I am using them to hold a piece of glass down onto some fibre paper which is on the heated bed which then sits on a aluminium plate.

Cheers

Quote
RepRot
You can use ...
Fibre Paper (3mm thick) .. to insulate the heat bed . its a ceramic material available from pottery kiln suppliers.
Also you can use picture frame clips called Swiss clips, I am using them to hold a piece of glass down onto some fibre paper which is on the heated bed which then sits on a aluminium plate.

Why are you using fibre paper on top of the aluminium? I use glass direct on the aluminium on both my printers, with Swiss clips on one of them.

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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 assume the fiber paper goes below the aluminum, to insulate it from the air.

I use it under my heat bed which means it on top of the aluminium plate. I have my glass (which I print on) on the heat bed, why waste heat to heat the aluminium plate.
It also means it takes longer to get up to temperature.

It may depend on your type of construction, I use it on a CoreXY machine. Just giving other possibly options.....

I use it under my heat bed which means it on top of the aluminium plate. I have my glass (which I print on) on the heat bed, why waste heat to heat the aluminium plate.
It also means it takes longer to get up to temperature.

It may depend on your type of construction, I use it on a CoreXY machine. Just giving other possibly options.....

I use it under my heat bed which means it on top of the aluminium plate. I have my glass (which I print on) on the heat bed, why waste heat to heat the aluminium plate.
It also means it takes longer to get up to temperature.

It may depend on your type of construction, I use it on a CoreXY machine. Just giving other possibly options.....

I see, the aluminium plate is being used as a support underneath the heater pcb, not as a heat spreader on top of it.

Edited 1 time(s). Last edit at 03/06/2015 02:51AM 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].

Is wood a plausible material for holding the heater and spreader? Would it insulate enough? Can it take the temperatures?