Monday, December 5, 2011

Machining Pictures

On occasion,  I am asked as to how some of the parts are made.  Here is a picture of a Mk IV nozzle holder, still in the mill, after the vents have been milled.  Prior to the milling of the vents, the nozzle holder is first machined from bar stock, on a turret lathe, and the flats are cut on a manual 4-axis Sherline 2000 milling machine.  The nozzle holder still needs de-burred.

Here is a picture of a batch of freshly band-sawed brass pieces that are ready to be machined into J-Head nozzles.  They first need to be prepared by machining them into blanks that can be finished in the Harding DSM-59 turret lathe.  However, I don't always make all of the blanks in-house anymore.  Sitting on top is a blank that I had CNC machined at a CNC machine shop.  Once the blanks have been machined, to the stage of the CNC'd blank, it is ready for the turret lathe.

After I am finished with the initial 2 operations that are required to turn them into blanks, the brass pieces will look like the blank on top and will be ready for the turret lathe.

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.

Wednesday, October 19, 2011

J Head Mk IV-B Is Now Available

The J-Head Mk IV-B is now available at hotends.com.  As with the Mk III-B, a cooling fan will be highly recommended for printing with PLA.  Printing, with ABS, will not be a problem.

Until more information is available, the shorter version, with the 36.5mm nozzle holder will still be experimental.

A Mk IV, with an aluminum nozzle, will be made; but, will probably not be sold regularly as the available sizes of raw aluminum bar stock require additional machining in order to manufacture the J-Head nozzle.  This, of course, would increase the price.  In addition, for best results, the aluminum nozzles should be insulated.

Sunday, October 16, 2011

The Short MK IV Prototype Probably Needs Active Cooling

The short Mk IV prototype has been reported to jam when printing long prints with PLA.  A cooling fan is going to be tried in the near future.  However, due to the number of vents (3) and their locations, this may be difficult.

Tuesday, October 11, 2011

The Short MK IV Prototype Has Successfully Printed

Today, I have received word that the Mk IV prototype, with the 3 grooved 36.5mm nozzle holder, has successfully printed with PLA.  This hot-end was equipped with the standard brass nozzle/heater unit.

Sunday, October 9, 2011

The Original Mk IV Prototype Prints!

The original Mk IV prototype has printed PLA successfully.  (The Mk IV prototype is shown on the right, next to a Mk III-B) 

The original Mk IV prototype was built with a new, vented, nozzle holder in order to help cool the liner.  The goal of the new nozzle holder was to eliminate the heat-sink used in the Mk III-B. 

The nozzle/heater unit was made with a 1/2" x 1/2" (13mm x 13mm) piece of 2024 aluminum bar stock as opposed to the 5/8" x 1/2" (16mm x 13mm) brass bar stock that is normally used.  Since a 6.8 ohm resistor has a smaller diameter than the 5.6 ohm resistor, the 6.8 ohm resistor was used.  The biggest change, however, is that the PTFE sleeve doesn't go all the way to the tip as with the earlier design.  Due to the smaller size, there wasn't enough room so a compromise had to be made.  The PTFE sleeve now stops slightly above the heater resistor and the filament is in direct contact with the aluminum from there to the tip.

Even though the test results, of the smaller nozzle/heater unit are positive, I am not going to use move to the smaller design at this time.  Instead, the Mk IV will use the tried and proven earlier nozzle/heater unit with a vented nozzle holder.  I will, however, continue testing and improving the smaller nozzle/heater unit and plan on making it part of the Mk V. 


Monday, October 3, 2011

Custom Cooling System For The J-Head Mk III-B


I received some pictures, this morning, from a customer who designed and printed this great cooling system for the J-Head Mk III-B Hot End.  The Mk III-B was used to print the fan mount and it was added it to his carriage afterwards.  He also uploaded the instructions and .stl file to Thingiverse.

Nice Work!

Sunday, October 2, 2011

Initial Testing of the Short Mk IV Prototype Hot End

Initial testing of the short Mk IV prototype, with a 36.5mm nozzle holder, has concluded that PLA only expands 6mm from the tip.

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.