I had gotten about 20-30 hours out of the last modification and I than I had a extrusion failure.
Initially, I thought I thought, the failure was the pla seizing on the nut holding the hollowed out M6 threaded rod and the PTFE tube.
Later it became apparent the my nozzle was partially clogged. In the process of removing the nozzle I snapped the threaded rod. Initially, I made a quick fixture when I drilled out the threaded rod. Basically a piece of 7/8 ? bar with a tapped hole in it. I believe the drill walked when I but the hole in and It looks like that didn’t help the cause. I broke the other one when I was drilling out the hole.
Anyway…. I’m not going to spend 8 bucks on a piece of machined threaded rod that I need to mod anyway… Soooooo… I guess I’m going to take the time to make a nicer fixture by boring out rod so it’s concentric, and doing a small production run of these and to have the PTFE liner.
At some point, I think I’m going to wind up making my own extruder… While my modded qu-bd is performing better now, I think it would be easier to have the features I want by starting from scratch.
if you consider starting from scratch, and have a lathe at hand, you could take a look at some ‘historical data’ in regard printing nozzles: http://reprap.org/wiki/Extruder_Nozzle_Variations
Most of the current printers use heater elements instead of NiCr DIY stuff, but it gives you some ideas on the PEEK / PTFE / PTFE lined designs.
Thank you for those links to some very interesting reading.
I actually purchased a J-head but at the time I didn’t realize it was for 3mm filament, I purchased a ex-struder also but wasn’t sure if the direct drive was going to work with 3mm PLA…(plus 1.75 was what I had on hand…) I ran across the PTFE fix for the qu-bd after I purchased this, and it was an easy enough mod to try.
After thinking my recent failure and looking at the evidence, I’m pretty sure things went wrong because of the clogged nozzle plus I was printing basically a thick walled hollow vertical cylinder.
The cooling fan on the carriage was off and x-axis wasn’t moving that much whose motion helps with cooling… (pretty much a perfect storm)
Anyway… the heat basically travelled up the tube and the pla siezed on my stainless hollow end nut that was holding the ptfe tubing. What bothered me about this is that I saw some evidence of discoloration on on tip PTFE tubing adjacent to the hot end.(It looked bit white..) I’ve read that overheating PTFE is not a good thing at all. http://en.wikipedia.org/wiki/Polymer_fume_fever
[edit looking closer this whiteness that I’m seeing, might be from trying to pull the PTFE liner out of the tube. Don’t know forsure.
At some point, I think I’ll write up something, about the shortcomings of the modifications… I do have a lathe and a mill so machining something is not an issue. For now, I’m still in a learning mode and working with lower temperature PLA is just the right speed for me. Eventually, I want to add venting to my printing area, and I’ll give some higher temperature stuff a try.
One thing I’ve been thinking about is to have a tube to insulate the hot end from the cold end. It seems to me that PTFE in the cold end is the way to go and protecting it from excessive heat as much as possible is probably a good thing. I think that feature should be optimized.
I’m thinking that there needs to be some type of intermediate material between the hot and cold end. The material should be a good insulator, have a low coefficient of friction and should be machinable. Original thought is a rare thing, but these are the conclusions I’m reaching based on what I’ve been thinking about. I’m sure a little googling will bring that to me. (Or.. hey I’ll take a comment on the blog 😉
Another wacky thought I’m having is integrating some type of stirling cycle into the system… It seems you need a hot and cold end which is something that the stirling cycle provides… That would be totally cool, but I don’t have the bandwidth in my life to try that at this moment. (I’m thinking this will be my Mk9…
For now, I’m just to fix up the qu-bd to get it going and start working on my own Mk0 extruder. I think I’m going to move the fan down to directly blow on the tube with the ptfe liner which will give me better access to the hobbed gear.