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PTFE starts to degrade about 250C, and it deforms before that. Prior to Peek being used there were hot ends that used PTFE for the structural part of the Hotend, but it "creeps" at significantly less that 250C and the hotends failed relatively quickly. Peek then started to be used for the structural portion with a PTFE lining.

I strongly recommend reading through the Reprap.org site, both the wiki and the forums, most things have been tried at various points, you can save yourself some time by looking at other peoples results.
Pretty much the only liner material in common use is PTFE because of the very low coefficient of friction.

The all metal hotends are interesting because there were early attempts to use stainless steel as the thermal break but they basically failed, the concensus seems to be, that the failure was because the transition zone of the Hotend in the past were considerably longer than the new attempts.

I should also warm you it's easy to "test" a Hotend idea by hand, have it appear to work, then discover you can't actually print with it. The simplest Hotend is just a machined bolt with some sort of heater, and if you put one on a bench even without a heatsink, you will be able to hand feed PLA through it, however if you try and use it like that in a printer, it will likely be blocked before the first layer finishes.

If you don't care about printing PLA, things are a lot simpler. PLA behave differently to pretty much all the other plastics printed as it transitions to a molten state! and that makes it harder to deal with.

And there you are, Instead of having to replace the whole hotend, you would only have to replace the liner, teflon for PLA, and ABS. Want to try some nylon? unscrew the nozzle, pull out the teflon liner, and insert a stainless steel, or pyrex tube. An all in one solution may not be possible, but minimizing the operations to print another plastic is a plus in my book.

If you can get a working E3D they are pretty close to ideal run nylon through it at 250, drop the temp to 230, push a bit of PLA though it, drop the temp to 185 and print PLA. The ones that work are really very good with PLA.
Unscrewing the nozzle is a pain in the ass on most hotends, it's easier just to swap out the entire Hotend, making that easy to do is probably a better goal.
Before I had a working E3DV5 I would commonly swap to a jhead for PLA, I could do that in less than 2 minutes, and my setup is far from ideal. I'd do the same thing if I commonly used different diameter nozzles (though I rarely do).

If you can get a working E3D,,,, I've unscrewed the new nozzles hot and cold. I have not had a problem yet, although I did have a couple of "I prolly shouldn't have done that " moments. Changing out just the liner to print PLA or Nylon is way simpler then changing out the whole hotend.

...or just use a threaded thermistor and quit worrying about it.

g.

Macor cuts way easier then I thought it would.

My first attempt at cutting threads on a lathe that has no operators manual was successful,,,, If lefthanded threads were required.

And here is the second attempt. I'll have to see what happens this weekend.

[img]https://www.flickr.com/photos/87910005@N08/14721656122/[/img]

And the reason Macor (machinable ceramic) does not work, is that it doesn't care for the temperature differential between the hot end, and the mount.

Mac,

What happened, did the thermal stress crack the Macor?

I believe so, It was only a few minutes into a print, still on the first layer when I heard it snap. It snapped at the first cooling groove. I may try it again, only next time I wouldn't cut the grooves.

Bummer, my finger is poised over the "Place Order" button based on your experience/results.

Version 2 is still printing, after 20 minutes of ABS @ 255... I'm expecting it to break after this post.

255 my @ss. I thought the temp was only 10 degrees off, so I had set the temp for 265. That was only 230 degrees actual. If i have the temp set at 280, my thermal probe reads 255. I'll still need a substitute for the liner,,,, metal or glass.

What real temperature measuring device do you guys recommend?

Are the cheapo laser ones any good?

teoman wrote:What real temperature measuring device do you guys recommend?

Are the cheapo laser ones any good?

Laser temperature detectors do not work to measure the temperature of the hotend. Something to do with reflectivity of the aluminum.
What is recommended is a thermocouple attached to a meter and the thermocouple is inserted into the hotend, down to the nozzle. This
will give you the most accurate temperature.

A spot of black nailpolish?

teoman wrote:A spot of black nailpolish?

I have been on this forum a long time and have read hundreds of threads about using laser thermometers to measure the temperatures of hotends and so far
no one has done it accurately. Who knows you could be the first to figure it out but I doubt if nail polish would work, it would have to be a high temperature
paint. Nail polish was not designed to handle that kind of heat because ladies don't put their fingers into places that hot. (I think I may have opened a can of worms).

The problem with the non contact thermometers is that the measuring area is too big for the hot end. To get a decent measurement of the hot end temperature you need a thermocouple probe.

Here is a cheap on that I bought off Ebay, I unscrew the nozzle just enough to put the probe between the hex of the nozzle, and the hotend. Then I snug it a little bit to hold it in place. I've found that the temperature reported by the Rambo to be 8% higher then what the thermometer reports.

http://www.ebay.com/itm/Dual-Two-Channe ... 5d42376f14