Thursday, September 29, 2011

The Ultra-Light Hot-End Works!





A while back, I made up this hot-end to get an idea of how light I could machine one.  Completely assembled and configured with a PTFE sleeve for 3mm filament, this little guy weighed in at 14.7 grams.

Not long after, I sent it out to be tested.  Before sending it out, I had to convert it to 1.75mm by making up a PTFE liner with a 2mm ID.

Today, I received a confirmation that this nozzle does indeed print PLA with a 1.75mm filament!  While a cooling fan was required in order to keep the nozzle holder cool, this proves that a 15 gram hot-end is certainly feasible.

Some concerns were expressed, however.  Once concern was that the hot-end is too long.  This is easily rectified as, without an aluminum heat-sink, I can shorten a hot-end.  The other concern was that the nozzle tip would sometimes hang on the prints.  At the present time, the nozzle tip has a 2mm OD.  Reducing the OD, of the tip, may be a reasonable compromise to this problem while still ensuring that a nice, flat, layer is extruded.

Monday, September 19, 2011

J-Head Nozzle News!

 Read about building a Prusa Mendel, with a J-Head nozzle, in the following blog:  Building a RepRap Prusa Mendel

Mk IV Prototype Nozzle With a 36.5mm Nozzle Holder






I have had a request to test a 36.5mm Mk IV nozzle holder.  So, I machined this little guy out and it is going to be shipped out tomorrow.   In addition to machining out the vents, I have also added flats, for a 1/2" (13mm) wrench, so that it is easier to disassemble.  I have installed the standard (version 1) brass nozzle/heater as that has been proven to work.

Mark IV Decision Change

While the final specifications, of the J-Head Mk IV will not be finalized until all test results are in, I have decided to limit the number of changes.

Specifically, I will not be changing the design of the nozzle/heater piece at this time.  This is because the new design would not have a PTFE liner all the way to the tip and the current design is both compact, has been proven to work,  and has been working successfully for at least 3 months.  Therefore, I have decided that any changes should and will be more incremental in nature.  If the vented nozzle holder design is successful, I will be implementing that change and that change only for the Mk IV.

By changing the nozzle holder, only the method of cooling will change slightly and not the filament path.  In addition, if the new nozzle holder is successful, it will be possible to add cooling to the more compact 36.5mm long nozzle holders.  (I have one made and will be posting a picture within a day or two.)

The smaller 13x13mm 6.8 ohm nozzle/heater will, however, be tested extensively as I believe that if it works the weight savings and size reduction will be a positive improvement.  However, the number one priority above all else is reliability.

Wednesday, September 14, 2011

J-Head Mk IV Prototype Ready For Testing


On the right is the J-Head Mk IV prototype nozzle.  For the sake of comparison, I have a J-Head Mk III-B on the left.  The nozzle itself was machined out of a piece of 13mm x 13mm square 2024 aluminum rod stock and is much smaller and lighter than the brass nozzle on the left.  The entire unit, with the heater resistor and thermistor, only weighs 15.3 grams.


 
Replacing the aluminum heat-sink, used in the Mk III and Mk III-B, are milled grooves in the PEEK.  In addition, the PEEK has been drilled out to form what could be described as fins with supporting struts.  At the root of of each fin there is only 1mm of PEEK between the PTFE liner and the outside air.  The goal is for the fins to not only provide some cooling but to also act as a thermal break.  While PEEK is not a good conductor of heat, it is hoped that the fins will be adequate to eliminate the need for the aluminum heat sink.

I will be shipping this prototype out soon so that it can be tested.  If the Mk IV prototype is successful, I may be able to lighten the nozzle holder even more in order to approach a maximum weight of 14 grams.

Tuesday, September 13, 2011

Introduction and Design Goals

 I have started this blog in order to further document the current developments in the life cycle of the J-Head nozzle.

At this time, the design goals are as follows: 
  • Reliable
  • Accurate
  • Easy To Use
  • Minimum Number of Custom Machined Parts
  • Light Weight
In summary, I am aiming to create the absolute highest quality, state of the art, open-source hot-end that is available.  In addition, all of the blueprints will be made available online.

I have posted all of the technical information here and will continue to keep the Wiki page updated as new improvements become available.