J Head Nozzle

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J-Head Nozzle

Release status: experimental

Jhn assembled.jpg
Description
J-Head Nozzle and Thermal Barrier Based on a combination of ideas from the Makerbot Mk 5 hot end, The Inline Heater Variation, some ideas from Brian Briggs, as well as myself.
License
GPL
Author
Contributors
Based-on
Categories
CAD Models
External Link


Introduction

UNDER CONSTRUCTION

More information coming soon.

Note Regarding Picture: Picture is from a test production run of the J-Head Nozzle. After the initial prototype, 6 nozzles were produced in order to test production methods. This nozzle is part of the 6 and does not have the top two or three threads removed. I'll update the picture as newer versions come available.

This nozzle is a combination of ideas from other nozzle designs combined with a goal to reduce the number of custom machined parts to a bare minimum. By reducing the number of machined parts, it is hoped that the cost of this hot-end can be kept down while improving the reliability.

The use of a piece of PTFE tubing, as a liner, was requested by Brian Briggs. The idea of using the PTFE tubing as a liner, from the Cold End to the tip, was borrowed from the Makerbot Mk V extruder design. The PTFE tubing also acts to "bridge" the joint between the PEEK insulator and the brass nozzle/heater. By not having the filament in contact with this joint it is hoped that any possibility of leakage will be completely eliminated.

The use of a combination heater and nozzle was borrowed from the "Inline Heater - Variation" on the Extruder Nozzle Variations page. However, instead of the heater resistor being mounted parallel to the path of the filament it is mounted perpendicular to the path of the filament. This was done to both reduce the length of the nozzle and to make it a little easier to run the leads from the heater resistor. Combining the heater and nozzle also helped meet the goal to reduce the number of custom machined parts to a minimum.

Eliminating a separate heater block and any heater barrel altogether removes many machining operations, reduces the number of parts, and should reduce the overall cost.

Bill of materials

Quantity Part Description
1 Brass J-Head Nozzle Machined Brass Nozzle/Heater Combination
1 PEEK Insulator Machined PEEK Insulator
1 PTFE liner 1/8" ID, 1/4" OD PTFE tubing
1 Heater Resistor Axial, 5.6 ohm, 1%, 5W (UB5C-5.6-ND)
1 Support Washer Optional 1/2" Fender Washer

Machined parts

More information coming soon

J-Head Nozzle

Jhn machining.jpg


A mechanical drawing will be posted when available.

I have drawings made, in a notebook. I am working on making a nicer, computer generated, drawing for release.

Thermal Barrier

Jhn thermal barrier.jpg

A mechanical drawing will be posted when available.

Machining

More information coming soon

J-Head Nozzle

  1. On the 5/8" square brass bar stock, find the center of the axis of the nozzle. This can be done by various means ranging from using a milling machine to using marking fluid, a height gauge, and a surface plate.
  2. Mount the 5/8" brass bar stock in a 4-jaw chuck on a lathe. Adjust the chuck so that the nozzle axis is on center.
  3. Turn the threaded end of the nozzle down to 0.375 +0.000 -0.004.
  4. Thread the nozzle to 3/8-24 up to the shoulder of the heater section.
  5. Drill out the center of the nozzle using a 6.5mm drill bit.
  6. Turn off the last 3 threads, at the end of the nozzle, and cleanup the threads.
  7. Cut a 30 degree taper on the very end of the threaded end of the brass nozzle. This is to completely eliminate the internal gap between the brass nozzle and the PEEK thermal barrier. This gap would exist due to the internal taper created by the cutting edge of the drill bit.
  8. Remove the work piece and mount it by the threaded end so that the threaded end is centered in the lathe.
  9. Machine the nozzle tip to the desired profile.
  10. Drill the nozzle orifice.
  11. Mount the nozzle in a milling machine and mill off the excess material in the heater section.
  12. Drill out the holes for heater resistor and thermistor.

Thermal Barrier

  1. Cut a piece of 5/8" round PEEK to length.
  2. Drill out the PEEK using a 6.5mm drill bit.
  3. Using a letter size Q drill bit, enlarge one end to a depth of 0.450 +-0.005.
  4. Internally thread the end to 3/8-24 using a bottom tap.
  5. Finally, turn a 0.500 -0.000 +0.003 shoulder for a distance of approximately 0.050. This is an optional step to center the optional support washer.

PTFE Liner

Jhn ptfe liner.jpg

  1. Cut an approximately 30 degree taper on what will be the hot-end of the PTFE liner.

Support Washer

The support washer is optional. It can be drilled out with M3 holes and M3 threaded rod can be used in order to provide additional support for the hot-end. If the support washer is not used, the PEEK thermal barrier can be secured in the extruder by using other means.

Assembly

  1. Secure the brass nozzle in a vice by the heater section.
  2. Optionally, install the support washer. If the support washer is to be used, drill the appropriate holes for the support rods prior to installation.
  3. Screw the PEEK thermal barrier down onto the nozzle. If necessary, use a pair of pliers to tighten the nozzle. The PEEK can be protected from the pliers by first wrapping it with a rag or paper towel.
  4. Using a dental pick, straightened out paper clip, small screw driver, etc., ensure that the PEEK is screwed down all the way by feeling for an internal gap between the brass and the PEEK. If a gap can be felt, screw the PEEK thermal barrier even tighter. If there is a gap, the PTFE liner can flow into the cap and eventually cause the print head to fail.
  5. Slide the PTFE liner down into the nozzle. The liner must be inserted by the tapered end and it is important that the tapered end is in contact with the inside of the tip of the nozzle.
  6. Cut the top end of the PTFE liner with a razor knife. It should probably project out of the PEEK thermal barrier slightly to ensure that the extruder keeps the PTFE liner from backing out.
  7. If the support washer is used, install the support rods, nuts, etc.
  8. If an extruder such as Wade's_Geared_Extruder is used, the sides of the PEEK thermal barrier will need to be filed in order to accommodate the retaining screws.

Notes

  1. While this nozzle is experimental, initial tests have proven to be very positive. At this time, the prototype has printed for well over 20 hours.
  2. It may be possible to adapt this extruder to 1.75mm by replacing the PTFE tubing with a piece of 1/4" PTFE that has been drilled out to 1.75mm.
  3. Further testing indicates that it is critical that the internal gap, between the brass and the PEEK, is completely eliminated. If there is a gap, the PTFE will tend to "flow" into the gap and create a place for the filament to form a plug.
  4. Since this nozzle, internally, is similar to the Makerbot Mk V, testing indicates that it is probably a good idea to taper the PTFE at the hot-end of the nozzle.
  5. The cold-end, of the PTFE liner, will need to be retained in order to prevent it from backing out of the hot-end. With some extruders, such as Wade's_Geared_Extruder, the PTFE liner will easily be retained by the socket that retains the hot-end.

See also: Extruder Nozzle Variations