The metal sheet I used as a flat, machinable build plate was not the proper surface, so I attached a PMMA sheet, covered with polyimide, using bulldog clips (from the writing materials department).
Not ideal for printing PLA (crepe tape would have been the appropriate choice), but enough to continue calibration.
As I expected the circle was egg-shaped, but bootstrapping is meant to be the first step. If the egg is repeatable, it is good enough to print the next version of itself…
…but throughput of the hot end was pathetic. And PLA jams were still haapening regularly.
I had to fix this first.
- The filament was 1.75mm for real – so it was not too thick.
- Extrusion was not starting too early either. The jams happenend after printing for a while.
- Retraction was not activated. It caused problems later, but not here.
- Different temperatures were tested, so I was sure it was not too low (http://forums.reprap.org/read.php?252,217620).
Finally I went after this issue: http://forums.reprap.org/read.php?4,175501,175501
Hot ends vary in how much force they require to extrude filament, it’s a combination of how large the melt zone is and most importantly how long the nozzle orifice is.
If the nozzle orifice is too long it can require a tremendous amount of force to extrude even with a 0.5mm nozzle. Look for the thread on JHead copies where people were having issues because of the longer orifice.
Buddaschnozles IME require very little force to extrude, JHeads seem to be pretty good, my SeeMeCNC hotend requires a lot more force to extrude, you can trivially feel the difference if you push the plastic through the extruder by hand.
If you are shredding plastic, the extruder is clearly overpowering the grip the hobbed bolt has on it, assuming the hobbed bolt is a reasonable design, then you need to reduce the amount of force that has to be applied, changing the extruder won’t change that.
…after all my J-Head was not made by Reifsnyder Precision Works.
The Budaschnozzle was good – look at that: Budaschnozzle 1.1, Printing infill at 200mm/s (youtube)
Here is the critical dimension…
…and I measured more than a millimeter. So i ordered a set of small drills (to clear the cuttings afterwards) and started to drill. Unfortunately a bit too far. -.-
Can the blowtorch braze the aluminium nozzle? Guess not, but it’s wasted anyay…
Time for Plan B. http://jheadnozzle.blogspot.com/ is not online anymore, but I think Reifsnyder used maggot screws and/or acorn nuts for the first prototypes. As I had to drill out the aluminium block it had to be one of those grub screws.
First the larger bore. The nuts were countered tightly enough to allow drilling into the hexagon socket.
13.06 – 12.47 = 0.59 mm orifice – close enough for the tools I had at my disposal. (And the melt zone was large – so I had the hot end dripping permanently afterwards.)
The difficult part (after spanning it generally) was to get the 0.5 mm drill to bite into the ground tip. And then came “not breaking it”.
Success! Now I used the drill press to get the thread-cutting tap aligned (but drilled by hand afterwards).
After not using PTFE tape on the grub screw I later had to use high temperature silicon to seal it up (without disassembly – I was lazy). The aluminium block was tightened properly against the PEEK, but PLA was leaking at the side of the setscrew.
Testing before installation:
First try on printing:
=> Half way thorugh my original thread in metalforum-owl.de now. 🙂