Monday, November 14, 2011

1.75mm Test J-Head Nozzle Prototype Developed

I took the best elements of the Mk III and Mk IV designs, combined them, and scaled the design down to create the 1.75mm prototype nozzle seen here.  The nozzle itself is machined out of a piece of 13mm x 13mm brass bar stock and is very similar to it's larger sibling.  I machined the nozzle holder out of black PEEK and milled out the grooves in similar fashion to the grooves on the Mk IV.  However, I also drilled out the center and installed an aluminum heat-sink tube to provide support and heat dissipation for the PTFE core.  A small PEEK spacer is used to insulate the aluminum tube from the brass nozzle.

This hot-end ships out tomorrow for testing.  If it is successful, I am planning to use the same concept for the Mk V as this design will allow for a shorter hot-end.

Nozzles With Heat Chambers Improve Print Speed

The special nozzles, with heat chambers, have been shown to be an improvement.  100mm/min print speeds have been obtained with PLA by having a heat chamber that is approximately 12mm long.  Without the heat chamber, the print speed was much less than 70mm/min.

In the near future, all J-Head nozzles will be shipped with heat chambers.

Tuesday, November 8, 2011

J-Head Nozzle Feedback

I received an e-mail, from "Dazed" this evening, providing feedback on his experience with the J-Head hot-end.  I appreciate any feedback anybody would like to supply as it really helps me to make improvements to the hot-end. 

After receiving permission to post his e-mail, here it is:


I've been using your J-head hot end for a few days now. For what its worth, here
is my input:
 
Huge kudos for having it pre-assembled. Probably the only issue I had with hybrid
insulators is getting the PTFE to brass junction tight but not too tight. It
either allowed a plug to form or I was clamping down on the filament via
over-compressed PTFE. All I had to do here was install a resistor and thermistor.
That was pretty cool.
 
My past experience with resistor based heaters has not been too great. They
always burned out after a couple of weeks. Yours is a bit different from what I
had been using, so maybe it holds up better. It fits much more snugly too, so it
should dissipate the heat better. I'm really interested in seeing what kind of
lifespan it gets. If it only lasts as long as my other resistors, I'll probably
be hunting for a heater cartridge to replace it or at the very least finding a
way to wrap nichrome around the heater block.
 
The PTFE insert has been a really awesome improvement so far. Again, I'm not sure
what to expect as far as life span but yesterday I wanted to use a new groove
mount holder. Normally I would have had to heat up the filament before it would
back out. Without even really meaning to, the cold plug actually popped out while
I was changing the holder piece. I thought that was a pretty impressive display
of the difference in friction. I'm not sure if the camera really captured it
well, but I thought it was impressive enough that I took a picture of it. I
assume this has to do with the fact that the PTFE feeds further into the hot end
than normal?
 
The tip on this hot end is much more blunt than what I have seen before. I'm not
sure yet if this is a good or a bad thing. In theory, as the extrusion is pressed
flat, the wider tip would keep it more evenly pressed flat against the previous
layer. This presumably would lead to better layer adhesion. However, I had a lot
of difficulty yesterday printing a 110mm fan cover. There was just a hair too
much plastic being extruded, I think my Z endstop slipped a little and let the
extruder drop lower than normal which caused the extrusion to widen out too much.
After a while, little balls of excess plastic started forming. My other extruder
tip would have plowed right through them no problem, but the wider tip on this
one seemed to snag more and eventually caused skipped steps. Extruder tips with a
sharp cone point seem to handle plowing through excess plastic better which makes
it less difficult to reach "usable" printer settings.
 

Wednesday, November 2, 2011

J-Head Nozzle Review and Testing Update

The J-Head Mk III-B has been reviewed here:  http://captain-slow.dk/2011/10/30/j-head-nozzle/

While this review is very positive, there is clearly room for improvement.

Over the past weekend, others have also indicated that PLA takes an exceptional amount of force to extrude.  After some experimentation, it appeared that the melt zone should be increased.  Therefore, I have machined a small batch of test nozzles that have a small 3.5mm diameter "heat-chamber" machined into them.  These nozzles are shipping out for testing today.  If this change proves to be an improvement, it will be implemented shortly after the results are known.