Tuesday, May 22, 2012

Initial Field Test Results

At this point in time, one beta tester has tested the J-head Mk V.  For a total of at least 6 hours, PLA was printed successfully.  He is going to try to print ABS in the near future. 

There were two minor issues encountered early on, however.  The first issue was that the hot-end jammed.  This was theorized to be due to dirt and the hot-end was cleaned out.  Afterwards, it printed fine.  The second issue was that some PLA was leaking out of the hot-end.  After the set-screw was tightened down, the leaking stopped. 

As both issues were relatively minor, and were easily fixed, the initial results are fairly positive. 


The Mini J-head has also been successfully tested printing PLA and no issues were reported.

Tuesday, May 15, 2012

New Aluminum Mounting Plates Have Arrived!

I had new aluminum mounting plates made up.  These plates are milled down, to the proper thickness for a standard mounting groove, and fit perfectly.

Friday, May 11, 2012

J-Head Hot-Ends Shipped Out For Field Testing

The first 3 Mk V-B hot-ends were shipped out, today, for field testing.  I added the extra vent and the mounting groove, to them, and I am considering CNC'ing the mounting grooves in the future.  The mounting groove, shown here, was made on a 4 axis milling machine as opposed to a form tool on the turret lathe.  I will have to compare both the time required to make such a groove and clean it up, using the CNC mill, or the time required for setup and other issues, on the turret lathe.  Another factor is that the Mk VI J-Head will required a CNC'd mounting system as I am planning on improving that at some point in the future.

In addition, I shipped out two "Mini" J-head hot-ends, for testing.  The Mk II Mini J-Head looks identical to the MK V.  However, internally, it is designed specifically for 1.75mm filament and I will be updating the Wiki Page and adding more information about it in the near future.

Unlike the Mk IV-B 1.75mm hot-end, the Mk II Mini J-Head is not a conversion.  It has quietly been in development for several months at this time.  The Mk II Mini J-Head was already very similar to the Mk V and I decided to make it identical, externally, in order to reduce the inventory required to produce either hot-end.  In many respects, the Mk V (3mm) hot-end is basically a Mini J-Head adapted for 3mm filament.

Internally, the Mini J-Head uses a PTFE liner that has an OD of 4mm and an ID of 2mm.  The means that there will no longer be a custom machined liner used to convert a standard hot-end to 1.75mm filament.  The brass nozzle is also different, internally, in order to accomodate the smaller filament size.  Some of the testing, and lessons learned, from the Mini J-Head were used in the development of the Mk V version of the standard J-Head hot-end.

Wednesday, May 9, 2012

First Prototype of the J-Head Mk V


While I have built two or three J-Head Mk V concept models, shown above is the first prototype.  For the sake of comparision, above the prototype is a J-Head Mk IV-B.  While it needs to be tested, I believe that there is a pretty good chance it will meet the 3 most important primary goals.

The Mk V goals were:

  • Shorter overall length  (Met.)
  • Lower extrusion pressure and faster speed  (May be met, needs testing.)
    • The melt chamber is more than double the size of the melt chamber in the Mk IV-B.
    • The orifice length will be kept to around 0.030".
    • A special drill bit has been ground that creates a steeper taper at the nozzle orifice.  This change is similar to other hot-ends that are available as a 118 degree drill bit is not ideal for a hot-end.
  • Designed for the 6.8 ohm resistor  (Was not met.)
    • I was able to fit the 5.6 ohm resistor in the Mk V prototype.  However, if the 5.6 ohm resistor becomes unavailable, I will re-visit this decision.
  • Nozzle may use 1/2" x 1/2" brass stock  (Met.)
  • Different thermistor mounting location  (Was not met.)
    • I decided to keep the thermistor mounting location the same, for now.
Overall, I met 3 out of five goals.  I changed my mind about 2 of them as the 5.6 ohm resistor is now plentiful and the thermistor mounting location is working fine.  Of course, if testing fails, it's back to the drawing board.  For the prototype, I only have 4 vents cut as I was concerned that the fifth vent location would be too close to the chuck in the CNC mill.  This is not the case and I am planning to add the fifth vent back in.  The original Mk IV prototype had 6 vents.  However, the 6th vent was too close to the chuck and created a serious machining issue as the chips would wrap around the chuck and damage the nozzle holder.  The mounting groove hasn't been added as that is usually done on the turret lathe and, as long as the space is available, it wasn't necessary to machine at this time.  In some cases, the mounting groove isn't added to the hot-end anyhow.


On the left is the new nozzle.  It uses a square piece of brass that is 13mm x 13mm.  (Disregard the scratches as it was screwed into the nozzle holder on many occassions in order to test the proper fit.)  On the right is the old version, used in the Mk IV-B and prevous hot-ends, that uses a 13mm x 16mm piece of brass stock.  In the new nozzle, the threads are 5/16-24.  The old nozzle used 3/8-24 threads.  Since the thread size is smaller, the internal dimensions had to be changed considerably.  However, the melt zone is the entire length of the nozzle.  I decided not to use a smaller thread size, such as M6x1, so that there would be a greater mass of metal around the entire melt chamber.  As the threaded section is now completely screwed into the PEEK, the bottom of the nozzle holder should double as insulation for the melt chamber.  The first cooling vent starts almost precisely at the very top end of the nozzle.


Here are the internal parts of the Mk V hot-end.  Between the hollow set-screw is now a washer.  This washer keeps the hollow set-screw from deforming the PTFE liner.  I was considering adding the washer to the Mk IV-B.  However, in the Mk IV-B, if you tighten the set-screw too tight, the taper at the hot-end will force the liner into the nozzle and cause a jam.  The liner is now faced off flat and seats tight against the flat face of the brass nozzle.  The result is that the set-screw can be tightened considerably.

Since the nozzle has been machined out of 13mm x 13mm square brass stock, an aluminum nozzle is now feasible.  I will probably keep the same naming convention.  Therefore, the J-Head Mk V will be aluminum and the J-Head Mk V-B will be brass.



Friday, May 4, 2012

Nozzle Orifice Measurements

After my previous blog, I've had some requests to measure the length of the nozzle orifice.  Tonight, I made up a little stand (shown under the height gauge) that is designed to mount a nozzle in order to properly measure it's orifice length.  The tip (obscured by the height gauge) has a steep taper that is designed to allow the nozzle to seat on inside edge of the orifice itself.  Due to the shape, of the tip of the nozzle orifice measurement stand, it is entirely possible that the nozzle orifice length is slightly longer than the measurement that was observed as the very tip will most likely slightly enter the nozzle orifice itself.  The length of this engagement is, unfortunately, very difficult to measure.  The entire nozzle orifice measurement stand measures 1.6215 inches and all measurements took place on a granite surface plate with the same height gauge.  (Please note that height gauges, of this variety, are generally not considered to have a precision greater than a couple of thousandths of an inch.)

I took each nozzle, listed below, and perched them on the stand.  Then, I took the height gauge and took a measurement at the tip of the nozzle.  The following measurements were observed:

  • Budaschnozzle:     1.631
  • MakerBot Mk V:     1.673
  • MakerGear:     1.655
  • J-Head:     1.671
Note:  All measurements are in inches.

This will leave the following  nozzle orifice lengths:

  • Budaschnozzle:     0.0095     (0.24mm)
  • MakerBot Mk V:     0.0515     (1.32mm)
  • MakerGear:     0.0335     (0.85mm)
  • J-Head:     0.0495     (1.26mm)

Note:  These nozzles come from different manufactures, companies, etc., and these measurements may not have been requested, endorsed, etc., by them.  So there.


Wednesday, May 2, 2012

Nozzle Orifice Diameters

On the RepRap IRC, tonight, the subject of nozzle orifice diameters came up.  For the J-Head hot-end, I have always used a slightly smaller drill bit in order to drill the nozzle orifice.  This is because a drill bit usually drills a slightly larger hole than it's rated size.

Since this subject came up, and I have a small collection of other hot-ends, I decided to use a set of pin gauges and measure the nozzle orifice to see what the size really is.  Since my pin gauges are in SAE, the closest I can get is to one thousandth of an inch.  In order to measure them, I started with a pin gauge that was a little smaller than the hole and incrementally worked my way up through the pin gauges until I found one that didn't fit.  So, the size that I have listed is the last size that actually fit the hole.  It is entirely possible that the orifice is slightly bigger than that which is listed; but, it is certainly smaller than the next size pin gauge.  So, these measurements are giving the hot-end orifice the "benefit of the doubt", so to speak.

All hot-ends listed were purchased with a 0.50mm orifice specified.

  • Budaschnozzle (Lulzbot)....0.021
  • J-Head Mk IV-B (Reifsnyder Precision Works)....0.019
  • MakerBot Mk V (MakerBot)....0.019
  • MakerGear (MakerGear)....0.019
  • ParCan 2 (ParCan)....0.019

The metric to SAE conversion is as follows:

  • 0.01969    0.50mm
  • 0.02008    0.51mm
  • 0.02047    0.52mm
  • 0.02087    0.53mm
  • 0.02126    0.54mm
  • 0.02165    0.55mm
  • 0.02205    0.56mm

Please note that the listed hot-ends may be from other companies and/or individuals and they are in no way related to and/or endorsed these measurements.