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My Onyx is visibly warped when compared to a straight edge. Despite hours of measuring, rotating, shimming, varying screw tension & clip placement, it still causes my boro to warp.

I'd like to try a MIC-6 plate. Are they stiff enough to not be affected by the warped Onyx, or should I ditch it & buy a silicone heater pad?

Thanks!

The thinest MIC-6 you can get is .25". It is MORE THAN rigid enough to constrain your misbehaved Onyx. You would put it on top of the Onyx, and I'd recommend thermal paste since you have a warping problem, screwed around the periphery. Unfortunately, the screw holes on the Onyx are just about at the limits of a 12" diameter disk but if you are careful you can get it to fit. Otherwise, you would need to find a larger (13" square) piece of MIC-6.

Keep in mind that it will take forever to heat up with the stock power supply and 12V. My recommendation is to get a dedicated 24V high amp supply and power it via an SSR to drive the Onyx. It can handle the current, mine's been in service for over 2 years that way.

Good to see they are still around. I bought a few of the 5/16" disks a few years ago. The small holes have no effect on their utility. But a 5/16" disk requires even more energy to heat up!

Thanks, gentlemen. This is what I had thought, but figured I would ask to be sure. I had already been shopping at S & S, as well as ebay (where they also sell). The catch is that they don't sell 1/4", and there's very little to choose from on ebay that thickness, and what there is costs more than what S & S sells.

If I go with 5/16", just how much more power would be required to get reasonable heating times?

I had been considering basalt, but aluminum seems the better route.

not sure what version onyx you have, be sure before you slap some metal on top to insulate any exposed traces!

I too have been dealing with a warped bed, I had not realised, and have been struggling for months to get it calibrated.
As a stop gap measure (which will likely be Permiant)
I did the fill owing, and now have it calibrated to about .05mm everywhere out to 255mm dia.

I removed the backing snowflake( which was warped too) and fixed the onyx on spacers at the 3 tower locations only.
I then put 3 big dobs of silicone sealant on the onyx directly above the fixing points, and gently pressed try glass down on it.
The sealant has taken up the gap and the glass still sits perfectly flat.

Might be worth a try for you too

Interesting idea, Jason, and thank you for joining in. I've tried aluminum foil shims but removed them, and am currently (as time allows) experimenting with washers at the fixing points. It's very aggravating, as the Onyx will warp dynamically - you shim one part up, another area drops down.

My concern with the silicon is it's insulating effects - I would think you'd have cold spots above the silicon. I do use a TrickLaser heat spreader, but it would take a lot of silicon for my Onyx. I can't help but think I would get very uneven heating despite the spreader. Also, I would now have either the heat spreader or glass bonded to the Onyx.

I'm pretty sure the market is ripe for a drop-in replacement for the snowflake & Onyx, with separate power supply & SSR.

That is a good solution Jason. The only thing to watch out for is that you get some reasonable contact with the glass so the heat can transfer. A thin coating of thermal paste over the Onyx with the glass pressed onto the silicone blobs should do the trick and not be too messy.

I've done something very similar with my latest FSR mounting system. Rather than mount the 3 plungers directly to the snowflake or bed, I dab silicone on them as you did, and sit the bed surface (or snowflake/bed) right on top of them and let the silicone cure. It works perfectly for the same reason your solution did.

The cold spots over the silicone would be so negligible as to not be an issue. The bond can be easily severed. These blobs don't have to be huge, 1/4" diameter in 3 places is ore than enough if you are patient enough to let it cure fully.

It's working for me, but yes there is a about a 1 mm air gap between the bed and glass around the perimeter.
I have held a thermocouple over the silicon blobs, and there is little temperature difference.
I did try coating the bed with thermal paste before squishing it down, but I found that the bed changed shape too much when hot up, and warped the glass.
I haven't tried abs since changing it, but pla sticks perfectly everywhere.