Sunday, December 2, 2012

J-Head Mk V-BV hot-ends shipping Monday!

On Monday, December 3rd, the first J-Head Mk V-BV hot-ends start shipping.  Above, on the left, is the J-Head Mk V-BV and, on the right, is the J-Head Mk V-B.  The only differences are all thermistor-related and they are as follows:  The thermistor itself, the mounting location, and the size of the thermistor hole.  Otherwise, both hot-ends are identical.

I decided to add the trailing "V" to the J-Head model number solely in an attempt to avoid confusion and bring attention to the fact that the thermistor changed.  Historically, the J-Head hot-end has always used the type 1 (EPCOS) thermistor and this is the first time the thermistor has had to change.  The "V" has been added to denote that thermistor 5 will have to be selected in most firmware configurations.

In addition, the thermistors are shown separately, above, in the center.  The new thermistor is on the left and the original thermistor is on the right.

The J-Head Mk V-BV was created due to the fact that EPCOS is no longer manufacturing the original type 1 thermistor.  While a substitute appears to be available, the lead time is excessive and I have noticed that it is only available in large quantity orders.  After some testing, I selected the type 5 thermistor as it is already used in other hot-ends and has been proven to be able to perform the job at hand.

The information, on the new thermistor, is as follows:

Part Number: 104GT-2
Manufacturer: Semitec
Description: NTC 100k ohm 3%
Tolerance: 3%
Data Sheet: High Heat-Resistance and High Sensitive Thermistor
Diameter of Glass Bead: 1.35mm +-0.15mm
Length of Glass Bead: 3mm +-1mm
Lead Length: 45mm +-1mm
Lead Diameter: 0.15mm to 0.18mm
If using Sprinter firmware, select temperature table #5.

Please note that I do have a limited supply  of brass nozzles that are already drilled out for the original thermistor.  During the transition, to the new thermistor, these nozzles may have the new thermistor hole added and, as a result, will be able to handle either thermistor.  If the thermistor fits the small hole, it will be the new thermistor.

Saturday, December 1, 2012

J-Head Clones!

It's been quite a while since I updated the blog, so I figured I'd post the results of my examination of two J-Head hot-ends that are for sale online.  So, within the last 2 weeks, I purchased a Mk IV clone off of e-bay and Mk IV-B from MakerFarm.  I'll talk about the e-bay clone, first.

The E-Bay J-Head Mk IV Clone

The e-bay clone arrived, straight from China, and came fully assembled with a heater cartridge.  (The heater cartridge is held in by a set-screw.)  The most obvious difference is that this clone has 4 cooling vents instead of the specified 5.  Looking at the cooling vents it was apparent that the machining is a little rough. 

On my way to my machine shop, I dropped the hot-end and the PTFE liner fell out.  This should not happen as it is supposed to be secured with a hollow set-screw.  No hollow set-screw was installed and there are not any threads in which to install one.  So, the PTFE liner will only be held in place by the extruder body.  This was tried, on the J-Head Mk I, and it would result in the failure of the hot-end if the liner moved.  As the PTFE liner is not projecting out of the hot-end, as per the J-Head Mk I specification, it is apparent that the liner will not stay in it's proper place.

Looking more closely, at the PTFE liner, it has a smaller OD, than the liner that is specified.  Also, the tapered end is roughly finished and the cold end, of the liner, looks like it was just cut off with a razor knife.  However, the cold end does have an internal taper.  I don't understand why this end wasn't cleaned up properly when the taper was cut.

The PEEK nozzle holder has 4 cooling vents instead of the usual 5.  They are bigger and deeper than the specified cooling vents.  I would say that using a larger end-mill, to create these vents, is possible due to the PTFE liner having a smaller OD.  (Using a larger end-mill also should reduce the machining time and cost of making this part.)  The mounting groove fits nicely into an aluminum mounting plate.  On the hot end, of the PEEK, there is a shoulder for the optional mounting washer.  The original specification, of the root of the shoulder, is 13mm and this is 12mm.  In addition, the flats to tighten the nozzle holder with a wrench are completely missing.  Since I was able to loosen the PEEK nozzle holder, by hand, it wasn't very tight.

The aluminum/PEEK junction is an improvement as there is no longer a taper between the two.  In addition, some sort of thread sealant was applied to the aluminum threads.

The aluminum nozzle/heater is made to different specifications and really has too many minor differences to mention.  There are 3 major problems with it, however.  The first is that the interior is based upon the original design and does not have a melt chamber section.  So, the liner goes all the way to the tip.  Another issue is that the nozzle orifice is supposed to be 0.50mm; however, it is closer to 0.53mm in diameter.  The final issue is that the nozzle orifice length is a whopping 3mm long.  I would bet that the extrusion pressure is pretty high.

Do to all of the noted differences, this hot-end is more of a hybrid between a J-Head Mk I and an early J-Head Mk IV.  In addition, some effort was taken to cheapen the design.

The MakerFarm J-Head Mk IV-B

The first thing I noticed about the J-Head Mk IV-B, from MakerFarm, is that the machining is very nice.  After taking some measurements, it is obvious that care was taken to ensure that it is made to the J-Head specification.

I only noticed two very slight differences.  The first is that there is a dimple in the brass next to the thermistor.  It could be for locating, work-holding, or something else.  I don't know why it is there; but, it will not affect the functioning of the hot-end.  The other, minor difference, is that the taper is missing on the ID on the cold end of the PTFE liner.  This may cause the filament to slightly catch when it is initially threaded and will not make any difference to the normal functioning of the hot-end afterwards.

The orifice measured 0.50mm and was 1.9mm long.  These measurements were expected and have been proven to work fine.

In summary, MakerFarm sells a very impressive J-Head Mk IV-B.

Friday, August 17, 2012

Initial testing of a thermally fused concept nozzle.

I finished machining a concept nozzle for the J-Head Mk VI-B this evening.  Since some people have had the PEEK nozzle holder melt after the hot-end exceeded 248 degrees Celsius, for one reason or another, I decided to try a hot-end with a thermal fuse wired in series with the heater resistor.

For this purpose, thermal fuses were purchased with a "Rated Functioning Temperature" of 240 degrees.  Unfortunately, I didn't realize that 240 degrees was the upper temperature limit and that the "Holding Temperature" was really 200 degrees and that is the temperature, above which, the circuit is broken.

In order to test the thermal fuse concept, the hot-end was suspended, from the ceiling, and hooked up to a Sanguinololu board.  At 185 degrees, the fuse holds fine.  When the temperature was set to 230 degrees, however, the hot-end didn't quite reach 210 degrees before it started to cool.  The thermal fuse opened up and shut the heater resistor down as it was supposed to do.

I am planning on mounting it in a printer and testing it with PLA in the near future.  However, until a higher temperature thermal fuse is available, it clearly would not be able to print ABS unless the heater resistor is wired without the thermal fuse.

As it appears that the thermal fuse manufacturer is testing thermal fuses, with "Holding Temperatures" up to 230 degrees, maybe this concept will be more useful at some point in the future.

Wednesday, July 25, 2012

Drill Bit Sizes Used For J-Head Nozzles

At one time, about 2 years ago, I used metric sized drill bits to drill the nozzle orifice.  It was discovered that these drill bits were drilling holes larger than the rated size.  For example, a 0.50mm drill bit would drill out a hole about 0.55mm in size.  I then made a decision to use slightly smaller drill bits in order to ensure that the orifice would be as close to the rated size as possible.  The drill bits used are as follows:

Orifice Size  SAE Drill Bit  Actual Metric Size
0.35mm   0.0135  0.343mm
0.40mm  0.0157  0.399mm
0.50mm  0.0189  0.480mm

Monday, July 23, 2012

Aluminum J-Head Mk V, 1.75mm conversion, and Mini J-Head Updates

The 13 gram aluminum J-Head Mk V has been tested and proven to work fine.  While the only advantage is it's light weight, I am planning on making it available in the near future.

Many people have asked me if and/or when I will have 1.75mm hot-ends available again.  While I was planning on producing the mini J-Heads, that was when the 3mm to 1.75mm conversions were a lot more involved than they are now.  With the Mk V design, a conversion is a lot simpler than with the Mk IV design.  As a result, I am planning on making Mk V-B 1.75mm conversions available in the very near future.

Tuesday, June 26, 2012

Pondering the Nozzle Orifice Drill Bits

From time to time I see people mention that the J-Head nozzle extrudes slightly under what is expected.  This may be because I have been drilling out the nozzle orifice with a similar concept to what is done with machine tools.  A quality lathe will be built with the tailstock that is about 0.001" high.  This way, as it wears, it will eventually line up perfectly before wearing to a point under the center line.  Taking this concept to the hot-end, the J-Head nozzle orifice is drilled out slightly smaller than the specification in order to provide room for wear. 

A 0.50mm nozzle is therefore drilled out with a 0.4572mm drill bit.

This concept has been creating issues.  For example, in Slic3r, the nozzle diameter needs to be set to a lower size in order to generate the proper gcode.

At this point, I am considering abandoning strategy of providing room for wear, and using exact size drill bits.  While there will be less room for wear, this should result in a hot-end that is easier to use.


Monday, June 11, 2012

Machining Mk V-B brass nozzles.

Today, I made a video of the first turning operation performed on the J-Head Mk V-B brass nozzle blanks.  This is the 4th step undertaken when machining these nozzles and is performed on a Hardinge DSM-59 turret lathe.

Sunday, June 10, 2012

Machining J-Head Nozzle Blanks

Sometimes I get requests for machining pictures.  Here is a series of pictures detailing the process of machining the J-Head nozzle blanks for the nozzles that fit the J-Head Mk I to Mk IV hot-ends.  Note that the fixture has 20 pockets.  The rear 10 pockets are for the J-Head Mk V hot-ends.

The brass stock has been cut and placed in the fixture.

Machine has been started and is performing the first CNC operation on the brass stock.

The first operation has been completed.

The brass stock is removed and flipped so that the opposite end can be machined.

The second CNC operation is in progress.

A view of Mach3 running the second operation.

The second CNC operation has been completed.

Finally, the completed nozzle blanks are removed from the fixture.  They are now ready for the turret lathe.

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.

Monday, April 9, 2012

Mean Time Between Failure?

For some time, I have been wondering what the meant-time-between-failure is for the J-head hot-end.  Today, I received an e-mail from a customer and he writes:

BTW: I've now done over 24 rolls of PLA through your head and NO ISSUES at all! (So thats like 2.5klms plus of plastic!)
An 6 month old early J-Head Mk III, that is regularly used to print ABS, is also reported to be still going strong.

Tonight, I was asked what the common reasons for failure were and I responded with 3.  Those are:

  1. Cheap filament with contaminants.
  2. Overheating to the point that the PEEK nozzle holder softens.
  3. If the PTFE liner gets "crimped" at the junction between the PTFE and the brass.
Does anybody have any experiences they would like to add?

Monday, March 12, 2012

Goals for the J-Head Mk V

While I am always looking for ways to improve the J-Head Hot End, I am finally listing the goals and design changes planned for the J-Head Mk V.

  • Shorter Overall Length
    • A shorter nozzle holder and nozzle have been designed.  The overall length will be about 13mm shorter than the J-Head Mk IV-B.
  • Lower Extrusion Pressure and Faster Extrusion Speed
    • These two go together as increasing the length of the melt chamber will do both.
  • Designed For the 6.8 ohm Resistor
    • While the 5.6 ohm resistor works great, it is hard to find and the 6.8 ohm resistor is more common. 
  • Nozzle May Use 1/2" x 1/2" Brass Stock.
    • This will make the nozzle footprint slightly smaller.  In addition, it will make the use of aluminum much more feasible as 2024 is readily available in this stock size.
  • Different Thermistor Mounting Location.
    • The thermistor mounting location will most likely change due to space considerations in the nozzle.
    • It may be a good idea to put the thermistor closer to the resistor and PEEK in order to reduce the possibility of reaching a temperature that results in the PEEK nozzle holder melting when the temperature is set near 248 degrees C.

Wednesday, February 15, 2012

Aluminum Mounting Plates Are Here

I just received a package of aluminum mounting plates today.  The hot-end mounting groove slides into the large groove and the slots are for the screws to hold the mounting plate in the extruder.  I decided to have slots as some extruders do not have the screw holes in the same location as the holes in other mounting plates.

I have noticed that the hot-end fits very snug and some filing is required in order to properly fit the hot-end to the mounting plate.  I believe this is because the mounting groove was originally designed around the use of laser-cut plywood.  As plywood is compressible, the fit wasn't a problem before.

Friday, February 3, 2012

Mk III and MK V Decisions

I have made some decisions regarding the Mk III and Mk V designs. 

  1. Due to the success, of the Mk IV, I am going to stop production of the Mk III hot-ends.  The Mk IV has been shown to successfully extrude PLA as well as the Mk III.
  2. The Mk V design is no longer going to include an internal aluminum heat-sink.  The Mk IV has proven that it isn't required and I would rather lean towards design simplification as per one of the original goals.  Adding the internal heat-sink and spacer only unnecessarily complicates the design.
  3. The Mk V will be improvements built upon the Mk IV.  Some possibilities include shortening the brass that projects into the nozzle holder, shortening the nozzle holder, and adding additional cooling to the nozzle holder.

Wednesday, February 1, 2012

Rulon Failed

The Rulon-lined hot-end printed ABS, for about 2 hours, then jammed up.  So, initial testing of Rulon was not positive.

Thursday, January 26, 2012


I just received feedback from Paul, in Australia.  He stated: 

BTW: Your Heads are amazing! I've been printing with it for 10hours plus per day for almost a month and a half. So its done many hours and its been running perfectly! Great job. I only now have a true appreciation for the size of the hole you put in these things! So very Very VERY small.

After I obtained permission to quote him, he added the following:

I can't wait to get my second machine up so that way the load can be shared between both machines. Your Hothead is the first and only one I've ever used and it was a no brainer to set up and get going and it just works! I have no idea why more people in Australia aren't using them.
Needless to say, I am absolutely pleased that the J-Head is performing so well and it has such a high mean time between failures.

Thanks Paul!

Friday, January 13, 2012


Today I shipped out a hot-end, for testing, that had a liner made out of Rulon instead of PTFE.  Rulon is supposed to be very similar to PTFE.  However, it is rated for a temperature up to 288 degrees Celsius.

I figured I would have it tested as some users have reported PTFE degradation, at the hot-end, after months of heavy use.  While the PTFE liners are fairly easy to replace, I figured that it wouldn't hurt to test other materials.

Even if this material is initially successful, many questions will still remain.

Blowout! (On an experimental hot-end.)

The 1.75mm J-Head Nozzle Prototype was being used for the last month and this happened.  Apparently, there isn't enough thread engagement, on the hollow set-screw, in order to withstand the pressure.  I'll have to think of another solution.

Note:  The standard J-Head hot-end uses larger relatively course threads, in the hollow set-screw, and does not have this problem.