Sunday, September 16, 2012

Print Head Dissection

My "successful-print-happiness" didn't last long as by the next print the print head went back to it's old behavior. Particularly not feeding enough plastic and as a result screwing up the print by ripping up what's already there.

Not exactly 100% fill anymore...
Figuring something must have gone wrong with the print head/nozzle I did a bit of reading on the SUMPOD forum and although I couldn't find anyone having issues with my exact configuration of the print head I found a couple of possible culprits. Time to take it apart and see if I were right.

Right away I discovered that the aluminum nozzle was loose and not tightly fastened to the peek anymore. My guess it's caused by the repeated heating and cooling of the print head. I think it's the MakerBot manual that states you need to heat the print head before tightening the screw so that's something to keep in mind.

The PTFE tube (below) has expanded quite a bit.
As you can see from the picture above the PTFE tube is no longer straight and has a bump where the gap between the nozzle and peek had a gap. Because of the expanded tube I had to cut it off before I could completely disassemble the print head. The brown stuff at the bottom of the nozzle is plastic from the print process (before I got everything tuned it was quite messy).

The inside of the tube has expanded as well and makes a reservoir where the plastic can bunch up. This is probably the main reason the flow of plastic isn't as good as it should be.

Underside of the print head holder showing the MDF fitting around the PEEK.
I also believe the filament get's too hot further away from the nozzle - which will possibly make it expand while still in the PTFE tube. The previously measured temperature on the fastener seems to indicate this. One of the reasons might be that the MDF has been routed in such a way that the PEEK is incapsulated and therefore not able to cool down as efficiently.

There's also quite a lot of surface connection between the PEEK and the aluminum increasing the heat transfer even more. One way to lessen this would be to let the nozzle screw into the PEEK instead of the other way around. As I don't have access to a lathe I won't be able to test that theory, but someone else hopefully might.

I've had to cut my bowden tube twice now the remaining part is to short to work leaving my print head out of business. Since I'm expecting a replacement head from QU-BD soon I figure I might just as well start preparing my printer. The "old" setup don't have room for the new print head so I'll have to remove the MDF and fabricate a new y-axis. I'm thinking using more aluminum (same as in the print bed), but we'll see. I'll also move the y-motor off the carriage to reduce the weight as much as possible.