Wednesday, December 24, 2014

J-Head Mk 8 Prototype

A J-Head Mk 8 hot-end prototype has been machined using concepts borrowed from the Mk IV, Mk VI, and Mk VII J-Head hot-ends as well as the mini J-Head Mk II.





In order to accommodate 3mm filament, and use the axial thermistor, I would have to re-visit the larger heater blocks as used with the Mk IV-B and earlier hot-ends.  Since the market is moving towards 1.75mm filament, I decided to design the new Mk 8 for 1.75mm filament only.  I'll continue to make Mk V through Mk VII variants for users of 3mm filament.

The goals of the Mk 8 hot-end were to fix two main problems.  The first problem is that sealing the threads with ptfe tape still results in a minimal number of failures due to leakage.  So, I re-added the tapered internal sealing surface between the brass and PEEK as was used in Mk IV and earlier hot-ends.  In theory, no ptfe tape should be required.  However, I will still use it so as to provide for a second seal.

The second issue to resolve was related to the thermistor.  While dual thermistors will allow for a safe shut-down in the event that one thermistor falls out, it would be better to make for an easier thermistor installation.  Therefore, I decided that the Mk 8 would use an axial thermistor like the 1.75mm MK VI hot-ends.  Unfortunately, there is not enough space to properly install an axial thermistor in 3mm hot-ends. 

Since this hot-end is for 1.75mm only, and 2mm/4mm tubing had been tested with the mini J-Head, I decided to switch over to using the smaller tubing as a liner.

The cooling vent design has been borrowed from the Mk VII design, which was derived from a modified Mk II.  Originally, the fluted design was used to simply lighten an old Mk II hot-end.  However, it also helped considerably to cool the core of the hot-end.  So, the fluted design was adapted for use on the Mk VII design as well.  For the Mk 8, the flutes were modified so as to be closer to the core of the PEEK nozzle holder.


A set-screw stack of a solid set-screw and hollow set-screw has also been borrowed from the Mk VI and Mk VII designs so as to secure the heater cartridge.  By using a hollow set-screw, as the top set-screw, it is possible to loosen or tighten both set-screws without having to remove them.  The top, hollow, set-screw is used to jam against the bottom set-screw and lock it in place.


In the near future, I am going to run off a limited production run of these hot-ends for both field testing and to explore additional minor design improvements.



Monday, October 6, 2014

Experimental J-Head with a Vespel Polyimide body and Rulon liner shipping out for field testing

For months, I have had a piece of Vespel Polyimide sitting on a shelf.  Last week, a customer asked if I had anything that would print at a higher temperature than the standard J-Head.  After I mentioned that Vespel Polyimide is rated for 288 degrees he expressed interest in testing it.  This weekend, I finished machining it and it is shipping out today.

As PTFE is only rated for 260 degrees, a Rulon liner had to be used as Rulon is rated for 288 degrees.  Since this hot-end is quite special, I decided to assemble it with a 2024 aluminum nozzle.  Set screws have also been added to retain the heater cartridge.


Saturday, November 30, 2013

Hot-end Collection

From time to time, the subject of my hot-end collection is mentioned on the #reprap IRC.  I took a picture of what I have and here it is:
 


A.  Arcol V3
B.  Budaschnozzle 1.1
C.  E3d
D.  Darwin/Thermoplast Extruder Nozzle v1.1
E.  Darwin/Thermoplast Extruder Nozzle v2
F.  Darwin/Thermoplast Extruder Nozzle hybrid variant
G.  "Big-Head Style" hybrid nozzle
H.  "Big-Head Style" hybrid nozzle with brass thermal barrier
I.  MakerGear
J.  Wildseyed
K.  MakerBot Mk 5
L.  J-Head Clone 2012 Mk IV from China
M.  J-Head Clone 2013 Mk V fromChina
N.  J-Head Mk V from Reprap-UK (~2012)
O.  Experimental thermally fused J-Head  (Reifsnyder Precision Works)
P.  ParCan V2
Q.  Ultimaker
R.  Mini J-Head Mk I  (Reifsnyder Precision Works)
S.  J-Head Chess from 2engineers
T.  JGR all-metal hot-end
U.  Trinity Labs Magma
V.  Trinity Labs All-Metal J-Head

Available or formally available at http://www.hotends.com

1.  J-Head MK I
2.  J-Head MK II
3.  J-Head MK III-B
4.  J-Head MK IV
5.  J-Head MK IV-B
6.  J-Head MK V
7.  J-Head MK V-B
8.  J-Head MK V-BV


Not Shown:

J-Head MK VI-B
J-Head MK VII-B (experimental)
Hammerhead MK I
Geared Extruder Nozzle

Mini J-Head MK II


Note:  Any company names, trademarks, logos, etc., mentioned belong to their respective companies.  So there.


Enabling Dual Thermistor Support in Marlin

The J-Head Mk VI-B has two thermistor holes and can have redundant thermistors in in order to ensure that the failure of one thermistor does not result in the failure of the PEEK nozzle holder.

In order to enabling dual thermistor support, for one hot-end, the latest version of Marlin needs to be installed. In Marlin, the thermistors are referenced as "TEMP_SENSOR_x", where x is the number of the thermistor.

Starting on line 123, of Configuration.h, is the following code:

#define TEMP_SENSOR_0 -1
#define TEMP_SENSOR_1 -1
#define TEMP_SENSOR_2 0
#define TEMP_SENSOR_BED 0
// This makes temp sensor 1 a redundant sensor for sensor 0. If the temperatures difference between these sensors is to high the print will be aborted.
//#define TEMP_SENSOR_1_AS_REDUNDANT
#define MAX_REDUNDANT_TEMP_SENSOR_DIFF 10

This code will have to be changed so that it is similar to the following:

#define TEMP_SENSOR_0 5
#define TEMP_SENSOR_1 5
#define TEMP_SENSOR_2 0
#define TEMP_SENSOR_BED 0
// This makes temp sensor 1 a redundant sensor for sensor 0. If the temperatures difference between these sensors is to high the print will be aborted.
#define TEMP_SENSOR_1_AS_REDUNDANT
#define MAX_REDUNDANT_TEMP_SENSOR_DIFF 10

The above changes define two type 5 thermistors for the hot-end. (The thermistor type table is just before this code snippet.) In addition, thermistor number 1 is set to be redundant to thermistor number 0. (#define TEMP_SENSOR_1_AS_REDUNDANT turns on this feature.) The last line sets the maximum allowed temperature difference between the two thermistors before the firmware aborts the print.

Sunday, November 3, 2013

Comparing real J-Heads and clones.



Pictured, above, are 5 "J-Head" hot-ends.  The top two hot-ends are listed as being "RPW".  These were made by myself and I have them labeled as per my company's name, Reifsnyder Precision Works or RPW.  (Reifsnyder Precision Works sells hot-ends via http://www.hotends.com.)  The middle hot-end was purchased from MakerFarm, Inc.  The bottom two hot-ends were purchased off of E-Bay and originated in China.  I have colored bars, on the right, indicating which hot-ends are made to the proper specifications and which were not.  I do need to purchase a Mk V hot-end, from a company in the UK, that appears to be made to the proper specifications and review it at some point in the future.

Externally, you'll notice that the top 3 hot-ends all have 5 rows of cooling vents and the Mk IV-B hot-ends are the same length.  The Mk V clone has 4 cooling vents, a push-to-fit connector that could be nice for a bowden extruder, an over-sized nozzle, and the vents are not milled to the rounded contour of the core.  (This will negatively affect cooling.) The Mk IV clone is shorter than a true Mk IV and has 4 cooling vents.



After I made the first picture, I took each hot-end apart so as to display the internal differences.

The first hot-end, a Mk V-BV, is made to the proper specifications.  It has a hollow set-screw, bearing washer (to protect the liner from being distorted by the hollow set-screw), a PTFE liner, PEEK nozzle holder, and brass nozzle.

The second hot-end, a Mk IV-B, is also made to the proper specifications.  This hot-end has the hollow set-screw, PTFE liner, PEEK nozzle holder, and brass nozzle.  Note that the PTFE liner is longer than that of the 3rd hot-end.  This is because this Mk IV-B was made to the original Mk IV-B specifications.

Note that the first two hot-ends have red PTFE liners.  Since the Mk II hot-ends, I have made all hot-ends with red PTFE liners.  This is not-so-obvious way to tell that you may have a hot-end that came from my shop.

The third hot-end, also a Mk IV-B, is also made to the proper specifications.  This hot-end has all of the same components as the previous hot-end.  However, the PTFE liner is made out of white PTFE and is shorter.  The later Mk IV-B hot-ends had a shorter liner so as to have a proper melt chamber.  This hot-end is made to the newer Mk IV-B specifications.

The fourth hot-end is completely missing the PTFE liner.  It also is not bored out so as to install a PTFE liner.  As a result, it will not work with PLA.  I have also noted that any internal nozzle clearances cannot be compensated for that it is quite possible to have an internal gap between the nozzle and PEEK.  I have serious doubts that this hot-end would work, for long, with ABS either.

The final hot-end is supposed to be a Mk IV clone.  There is no hollow set-scew and no way to retain the liner.  This will result in a rapid failure of the hot-end.  To compound problems, the nozzle is threaded all the way to the end.  This will result in the nozzle not seating properly and has been proven to result in early failure of the hot-end.  In addition, it is a little shorter than the Mk IV specifications. 

The top 3 hot-ends are made to the proper specifications that have been proven to work successfully.  The bottom 2 hot-ends differ so much from the J-Head specification that I really can't think of them as J-Heads hot-ends.

It appears that the fastest way to tell the difference between a quality J-Head and a cheap clone is to count the rows of nozzle vents.  If there are 4 rows, short-cuts were taken and it will be of questionable value.  If there are 5 rows, the proper care may have been taken to machine the rest of the hot-end.  Of course, if you buy it from me, or one of my re-sellers, I will guarantee that it is free from defects and readily replace the rare hot-end that fails due to a manufacturing defect.


Tuesday, October 15, 2013

$22 J-Head Mk V Clone

I saw this $22 J-Head Mk V clone, on E-bay, and decided to order one to see what it looked like.  I figured that since the J-Head Mk V series of hot-ends are well over a year old, and the specifications out for the same amount of time, that the clones should be getting better.



Today, I received it in my mailbox and immediately opened it up to take a look.  This is what I received:



Once I took it apart, I noticed that the PTFE liner is missing.  There isn't even space to install one.


Including the lack of a PTFE liner, I noted the following issues:

  • There is no thread sealant between the nozzle and PEEK.  Most likely, the hot-end will leak.
  • There is no way to adjust out any internal gap between the nozzle and PEEK.  This can result in the nozzle jamming.
  • The PEEK vents are 0.115 inches deep and the specification is that they need to be 0.150 inches deep.  In addition, the PEEK vents do not follow the rounded contour of the filament path.  They are milled flat so that the PEEK gets thicker towards the milled struts.  This will not provide for optimal cooling.
  • The heater block section is considerably larger than the normal specification at 0.725" x 0.625" x 0.378" as opposed to 0.500" x 0.500" x 0.325".  This shouldn't cause much of a problem, however.
  • There was no PTFE liner.  This hot-end will not work with PLA.
On a more positive note, the orifice length was 0.027" or slightly over 1/2mm.

I guess this just re-enforces the adage that you get what you pay for.





Tuesday, June 4, 2013

J-Head Dual Thermistor Testing

Hot-end melt-downs are a problem.  Last year, I was experimenting with a thermally fused hot-end.  While it worked great and I really liked the simplicity, the proper thermal fuses are not available for this application.  Recently, on the #reprap IRC, there was a discussion about using two thermistors and having the firmware compare them and shutdown the hot-end if they didn't match.

Afterwards, I contacted a couple firmware developers and one of the Marlin developers, "EvdZ", was kind enough to work with me to test out this concept.  As I only had Sanguinololu boards available, I picked up a RAMPS board, from Ultimachine, and tested the concept with just a couple thermistors.  The thermistors were at room temperature and, as a test, I put one of the thermistors between my thumb and forefinger to see if the firmware would shutdown the heater when the thermistors no longer agreed on the temperature.  After a little debugging, I sent my findings back to EvdZ and he made the proper adjustments to the code.  Next up was a static test of a proper hot-end.

Tonight, I setup a test for a dual thermistor J-Head hot-end.  The thermistors were not properly secured as I wanted to be able to pull either one out for testing.  In addition, this hot-end has a heater cartridge and a set-screw/jam screw in order to hold the heater cartridge in place.  The thermistor holes are drilled at 90 degrees to each-other in an attempt to ensure that if one thermistor were to fall out, the other thermistor would not be pulled out with it.  (Creating a situation where both thermistors would still agree on the temperature.)






The test worked flawlessly.  I heated the hot-end up to 230 degrees.  Upon removing either thermistor, the heater cartridge was shut off in under 2 seconds.  I repeated the test a couple times to ensure that the result was always the same.





Once the dual thermistor changes are part of Marlin, I'll post the complete instructions for the dual thermistor configuration.

Of course, in the near future, the hot-end needs to be tested printing.  As the only differences, from a J-Head Mk V-BV, are the thermistor and heater cartridge hole configurations, I don't foresee any issues.