@Shai_Schechter Always trust the physical test more than internet theorists 
@Ryan_Carlyle Of course! But I have a good feeling about this design. It should work very well 
Two ideas.
Take a strip of foil and run it between loosely meshed gears to get a compliant shim to go between. (crimped copper wire or mesh works too)
Or, seal the bottom edge to the nozzle with hi-temp silicone and pack the gap with metal powder. Mebbe mix in some thermal paste.
It would be better if you had a split in one side so that it wasnāt a full circle. Ceramicās not the most flexible material, but a little spring pressure will allow you to use a much tighter tolerance between the heater and the tube going through it while still being possible to assemble. There might also be a way to manufacture the heater so that it will permanently shrink or bend a little bit the first time it heats up to constrict more tightly around the tube. Some soft aluminum between might even deform a little to create a better bond.
Sensor placement is also critical for something like this. You probably want a thermocouple either embedded in the interior face or pressed between the heater and the tube to measure the temperature of that interface with as little latency as possible. With a lower-power heater, measuring the temperature of the tube just above the heater might be better, but a high-power heater will need low latency measurements of the heater to give the PID algorithm any hope of keeping up.
You bring up good points @Whosa_whatsis ! Creating a split might work, have to check how prone these heaters are to cracking/breaking.
We are going to use the regular Semitec (104G-2 ?) and attach it in the middle on the side with PTFE tape. It would sit on the outside of course. I think maybe adding some high temp silicone for better heat transfer between the thermistor/heater might help with obtaining better temperature reading.
@Shai_Schechter I think youāre going to be much better off sensing at the barrel near the heater rather than the outside. The heater will always run much hotter than the nozzle, by a variable amount depending on heat flux due to melt power, airflow, etc.
Have you seen the Atomās hotend ceramic disk heater Shai? I think the Makibox had one too. https://www.youtube.com/watch?v=OPo0glnRIy8 That style of heater seems a lot easier to work with.
@Billy Yes Iāve seen it, but it requires a few additional components. Trying to make this whole setup as simple as possible.
@Ryan_Carlyle Iām going to try using copper leaf. I originally was going to use aluminum leaf; but, my local Hobby Lobby only had copper. I will most likely have dissimilar metal issues; but, this should be OK just to assess the performance. The reasoning behind metal leaf is that it is incredibly thin and I can use multiple layers to build up thickness as needed.
@Alan_Thomason Cool, let us know how it goes Annealed copper seems like pretty much the perfect material (aside from gold/silver), as long as you donāt run into galvanic corrosion issues of course. But we already use brass, aluminum, and steel in intimate contact, I just canāt see copper being a big issue.
@Ryan_Carlyle I think the potential problems will be application and abrasion resistance during assembly - this material is crazy fragile. Iāll let you know how it turns out.
@Billy The Makibox had a similar clamping system, but it was just a kapton heater inside, not a ceramic one. Unsurprisingly, I did hear about some failures because, while the entire unit should be staying within the polyimideās thermal rating, the heating element itself must have gotten significantly hotter.
I lack of imagination of āhow to mountā this heater 
@Rene_Jurack you just slide it on a 6mm screw and hold it between two thin nuts
Dissimilar rates of thermal expansion will potentially cause problems with developing a mounting method for this heater. If the heater expands more than the metal tube, the heater will get loose and transfer less heat. If the heater expands less than the metal tube, the heater my crackā¦
hereās what M3D looks like
@Step_Cia Where is the thermistor on the M3D? Maybe I canāt see it because Iām on phone.
I scratch myself over that as wellā¦ It ia there but not sure where. When it is heating up i see the softwate diaplay the temperature going up
From reading some of the M3D troubleshooting articles, it looks like they calibrate heater power to nozzle temp at the factory, and do not actually sense nozzle temp in realtime. (If so, wow.) Although the software can detect heater failures, so perhaps they use board-end current monitoring or something.
Well, the software allows you to set the temperature and when I enter in the different filament codes it has different temperature so it has to be able to sense somehow.