Here you go, Lapidary Diamond a couple of large and small grit sizes to help fill in the space. I have lost the link to the research document but lapidary diamond is synthetic and because of the structure of its crystal being a tad bit different from real diamond, it conducts heat better than real diamond. (At least the synthetic diamond used for the engineering paper) I was going to try but did not have a good recipe for the epoxy, until now…
Have you gotten a chance to try it yet? I was looking at some materials’ thermal conductivity properties here and it seems to me that maybe a high concentration of diamond in epoxy might be a better heat conductor overall than pure copper! Do you think that’s possible? Especially, if it’s true that the lapidary diamond is an even better conductor than real diamond, it should do quite well if you can get enough diamond mixed into the epoxy. What do you think?
Edit: For example, if diamond has a thermal conductivity of 1000, and epoxy is negligible (0.35 though, if ya want to know) then a 40% mix would have a thermal conductivity of 400, right? Or am I doing the math wrong?
How much more light comes out the front, comparing a hot driver (one that truly needs cooling) potted with plain JB Weld vs. same driver potted with JB Weld + diamond/silicon carbide?
Who's got the time and resources to answer another innocent comfy Q? 
Sure is a simple question... 
I'm assuming this JB Weld and fine grit silicone carbide harden as much as JB Weld itself?
If it hasn't been tested there's no way to know if it helps or not. I'm not a fan of doing extra stuff that has no benefit, sorry but that's getting too close to superstition for my taste. :shrug:
I'd like to know a whole bunch of things of aluminum vs. copper, AS5 vs. toothepaste, but the comparative tests at the detailed and controlled level for our very specific applications would be a huge under taking, so, we have to fallback to theoretical premises.
I'd love to see some tests done on the Convoy S2 modded with triples and actually see what, if any, the RMM aluminum vs. copper spacer, but the tests would be insane - can't just do a simple output test, you'd have to test over time with typical batteries/
The critical point being overlooked is the amount of surface area vs. the amount of heat that has to be shifted. Why is the joint at the LED's thermal pad so critical? Because it's so small. But if you look at those wonderfully misleading 'thermal conductivity' charts, you see that solder in general has really awful thermal properties, and some is even worse than awful (lead free vs. the worse 63/37). But then... if these thermal conductivity numbers are so important, why then is there zero difference in light output between the thinnest possible layer of the best lead free solder, and an extra thick layer of the very worst 63/37 solder (like the extreme example of a non-direct thermal copper board with the dielectric layer gouged out)?
Because once you pass a certain level there are no gains to be found no matter what material you use. It's not that solder is good, it's that the dielectric layer inside the MCPCB is so bad. Even bad solder is enough to carry the heat, but even the best dielectric layer isn't (even the fancy boards with the DLC dielectric aren't as good as a layer of bad solder). Same goes for thermal pastes, and aluminum vs. copper vs. brass. In potting drivers that are trying to set themselves on fire, any decent material (so, a real epoxy and not Fujik Bathroom Caulk) has enough surface contact to carry that heat load.
This belief in adding exotic stuff where it's not needed because finding out if it does anything is too much work is like saying "I always cross my fingers and look both ways before crossing the street and I've never been hit by a car, therefore crossing your fingers makes you immune to being run over."
I had a light that the lumen output would drop to zero when the negative lead would desolder itself. Added some very common, non-exotic silicon carbide in the mix because what the hey. Why not put in the best cheap stuff I know of while I'm going through the trouble of potting. Sure expoxy or silicone may have been good enough. That's the great thing about a hobby. No one to answer to but myself.
+1 on the hobby sentiment.
Also, never discount the immeasurable value of cool 8) I think multiple grit sizes of lapidary diamond and JB Weld would work better than just JB Weld for thermal potting. I don’t think it would be equal to copper but it would fill in the negative space well. And it would be cool.
I have not played with it yet as I have too many unfinished projects in the works. I am entertaining the idea of making a lantern for camping out of Portland cement and lapidary diamond. Useful and quirky at the same time.
Is there a way to mold JB Weld?
> mold JB Weld?
Yep, multiple hits in google on ways to do that
> Jefferson
Many have tried to cite that quote. Must’ve been someone else.