Securing bed heater to bed plate
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I am building a new printer and am wondering what if anything people do to secure their bed heaters on the underside of the bed.
In the past, I have just glued the heater on but this is a known point of failure. People have used high temp silicone glue to either glue the whole thing on or just to seal the edges. I am thinking of using something to put pressure onto the heater and am wondering if anybody has gone that way.
What I am thinking of is to have a stack as follows: Bed plate, heater, insulation, some sort of device to put pressure on the sandwich.Thoughts ?
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https://www.canadiantire.ca/en/pdp/imperial-high-temperature-silicone-red-304-ml-0642712p.html
User's-Manual-Keenovo-Flexible-Heaters.pdf
The sealant should be more than enough to hold, but if you want a physical backstop just try to keep it from making much physical contact to the heater itself.
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@phaedrux, thanks.
I am still inclined to want to provide positive pressure somehow but the issue is that if you provide too much clamping force then you could in theory distort the build bed a bit. Seems silly to buy a cast tooling plate for the bed and then proceed to distort things.
Interesting that you are not supposed to use acetone to clean the plate .... -
@jens55 I think a combo of silicone adhesive backed up with some mechanical clamping is probably the ultimate in safety and long operating life. It doesn't take much clamping force, so I think it can be done without distorting the bed plate. If you include some mechanical clamping, you can mount the TCO on the plate instead of the heater.
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This is the recomanded Voron way. He uses JB Weld RED Hi-Temp RTV.
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@zapta, thanks for posting that. I am starting to feel like I am doing too much worrying about the sandwich arrangement.
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@jens55 said in Securing bed heater to bed plate:
@zapta, thanks for posting that. I am starting to feel like I am doing too much worrying about the sandwich arrangement.
That's understandable. I am sourcing parts for a new printer and plan to have two thermal fuses, one on the aluminum and one on the silicon, also reduced the Keenovo header standard 500w spec to 300w.
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@zapta, what do two thermal fuses get you other than if one falls off you still have another ....
I also happen to think that 700W is just right for a 300x300 bed. I am too impatient to wait for a 300W heater to bring the temp up before printing. -
@jens55 this is exactly the way I built my bed. From top to bottom, this is my assembly.
Pei or garolite LE
3M 468mp adhesive sheet
Steel spring sheet
Staymag magnetic sheet
3M 468mp adhesive sheet
325mm x 325mm Mic6 aluminum bed300mm x 300mm Keenovo 120v/750w silicone heater with adhesive sheet - edges sealed to mic6 plate with RTV sealant
3mm silicone insulating sheet.
3mm aluminum compression bottom plate secured to mic6 bed with spacer sleeves threaded into bed at three points to ensure compressive positive contact and prevent delamination failure.Thermal manual reset fuse attached to mic6 bed that trips at 150c.
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@nuramori, that is exactly what I was contemplating with the compression plate screwed to the MIC6 plate.
I would be using thermal insulating material (rock wool maybe) rather than the silicone insulating sheet you are using.
I was thinking that rather than fixed spacers, I would use springs to limit the amount of pull on the bed plate. Maybe have some slop in the mounting so as to allow differential expansion. -
@jens55 That's why I used spacers, so there's just enough contact to keep it in contact in the event of a delamination, which would not really happen with contact eliminating any gap. The spacers allow for preventing warping from over tightening, and the "pull" you state via a consistent distance. Since I mount my bed assembly to a support frame, it allows for decoupling mounting strain from the bed itself. By mounting the bed assembly by the bottom plate, it also thermally isolates the bed from the frame or any support, with the only thermal bridging occuring through three small M3 screws, yet a repeatable and consistent distance from the extruder that rarely needs calibrating.
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@nuramori said in Securing bed heater to bed plate:
Since I mount my bed assembly to a support frame, it allows for decoupling mounting strain from the bed itself. By mounting the bed assembly by the bottom plate, it also thermally isolates the bed from the frame or any support
You lost me there.
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You can get a pretty accurate estimate of bed heat-up time here: https://jscalc.io/calc/uS8JYjYISgIvzJ1x
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@jens55 said in Securing bed heater to bed plate:
@phaedrux, thanks.
I am still inclined to want to provide positive pressure somehow but the issue is that if you provide too much clamping force then you could in theory distort the build bed a bit. Seems silly to buy a cast tooling plate for the bed and then proceed to distort things.
Interesting that you are not supposed to use acetone to clean the plate ....Reason for not using Acetone (this I assume is to clean a plate that has already had Glue or 3m adhesive attached) is that £m 468 and acetone is a very bad mix the 3M just turn to mush and becomes very difficult to remove I guess that it may also leave a residue that effects the 3M as well. IMHO If I was to order another one it would be without the 3M Adhesive. I also like to get them with a small 10mm diameter hole in the middle so that I can fit my own temp sensor to the bed.
Doug
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@jens55 said in Securing bed heater to bed plate:
@zapta, what do two thermal fuses get you other than if one falls off you still have another ....
I also happen to think that 700W is just right for a 300x300 bed. I am too impatient to wait for a 300W heater to bring the temp up before printing.I plan to connected the two thermal fuses in series that that if one of them burns the heating will stop. Using a 200x200mm 300W 110VAC Keenovo on a 250x250x8mm bed.
Not sure about adding insulation at the bottom since it's a Voron 2 which has a closed chamber and thus needs to be heated.
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I think @Nuramori means, don't use the tool plate printing surface as the mechanical attachment to the machine.
What works really well for me is:
Print surface (MIC6 plate, which has magnets and gets a flex-plate type surface on top)
Silicone Encapsulated heater (mine has a thermal fuse built in, its a 200C one). Attached with PSA.
4x squares of VHB or any decent adhesive (in the corners, huge areas of glue can cause compounding issues), might even be epoxy... can't recall.
Sheet of 6mm Nylon foam (from McMaster in the US, but its made in the UK).
4x corner bits of glue.
1/8" aluminium sheet (not fancy MIC6 or anything).
The printer,That 1/8" sheet carries all the weight and is what is attached to the printer. The MIC6 plate is held in place by the adhesive, there's no need to add mechanical fasteners. You just need to allow enough adjustment in the mounting between the final sheet and the printer to get the MIC6 surface reasonably square and true to the gantry.
Because I'm not using mechanical fasteners I don't have to worry about thermal expansion, conduction or durability.
I have multiple machines built in this way that have been working without issues for several years. -
@theruttmeister, interesting arrangement !
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@jens55
It probably wouldn't work with anything other than that nylon foam. If you can find it...Its cheaper than silicone, excellent insulation value, actually sticks to glue and its rigid!
If I couldn't get that foam I'd probably go with something involving shoulder bolts in slots to let the MIC6 expand, with the heater sitting in a cutout in the mounting frame, and a retaining plate below that (to support the insulation), attached to the frame not the plate. And just use PEEK washers or thin spacers to insulate between the frame and plate.
