J Head Nozzle

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J-Head Nozzle

Release status: experimental

Jhn j head nozzle.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.

Jhn assembled.jpg

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 GilesBathgate's Extruder_Nozzle_Variations#Inline_Heater_-_Variation. 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.

Required Parts

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 Thermistor 100K (B57560G104F)
1 Support Washer Optional 1/2" Fender Washer

Machined Parts

More information coming soon

J-Head Nozzle

A mechanical drawing will be posted soon. (I either need to get a CAD program or just draw it up by hand. I'll probably draw it up by hand.)

Jhn machining.jpg

Material: Brass Bar Stock, 5/8" Square Or 5/8" x 1/2" Rectangular, 1.125" Long

Note: These instructions differ from the machining example displayed in the above picture and are only one example of how the nozzle can be machined. The machining process can vary depending upon available machinery and tooling. The minimum machining requirements are a metal lathe with a 4-jaw independent chuck.

  1. Cut a piece of brass bar stock 1.125" long plus enough to adequately hold the stock in the lathe.
  2. On the 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.
  3. Mount the brass bar stock in a 4-jaw chuck on a lathe. Adjust the chuck so that the nozzle axis is on center.
  4. Turn the threaded end of the nozzle down to 0.375 +0.000 -0.004.
  5. Thread the nozzle to 3/8-24 up to the shoulder of the heater section.
  6. Drill out the center of the nozzle using a 6.5mm drill bit.
  7. Turn off the last 3 threads, at the end of the nozzle, and cleanup the threads.
  8. 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.
  9. Remove the work piece and mount it by the threaded end so that the threaded end is centered in the lathe.
  10. Cut-off any excess material.
  11. Machine the nozzle tip to the desired profile.
  12. Drill the nozzle orifice.
  13. Mill or turn off the excess material in the heater section. This can be accomplished by mounting the nozzle in the 4-jaw chuck sideways so that the excess material is presented for machining. If available, a milling machine can also be used. (If a 5/8" x 1/2" piece of bar stock is used, this step will be skipped.)
  14. Drill out the holes for heater resistor and thermistor.

Thermal Barrier

A mechanical drawing will be posted soon.

Jhn thermal barrier.jpg

Material: PEEK, 5/8" Round, 35mm Long

  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

Material: PTFE tubing, 0.250" OD, 0.125" ID, 50mm Long

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

Support Washer

Jhn support washer.jpg

The support washer is optional. It can be drilled out with 3mm 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

Jhn assembly.jpg

Jhn assembled w washer.jpg

  1. Secure the brass nozzle in a vise 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. (Note: The above pictures do not have holes drilled as it is possible that the hole locations could vary.)
  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 gap 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 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

General

  1. 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.

Testing

  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. 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.
  3. 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.
  4. Testing of units with the internal gap, at the joint of the PEEK and the brass, have resulted in early failure. Replacing the PTFE liner would allow the nozzle to continue printing.
  5. Even with the internal gap, after two weeks the the initial prototype nozzle is still working.
  6. Initial testing of a nozzle, with the internal gap problem resolved, is very positive.

Future Modifications

  1. 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.
  2. If the extruder will not retain the PTFE liner, it may be possible to install a 5/16-24 hollow-lock socket set screw (McMaster-Carr part number 91318A550) in the cold-end of the PEEK thermal barrier.
  3. Using 5/8 x 1/2 inch rectangular brass bar stock, instead of 5/8 inch square bar stock, will eliminate 1 machining operation, slightly reduce the cost of the raw materials, and may reduce the machining time for other operations as there will be less material to remove.
  4. This design could be scaled down to create a mini version using a 4mm OD/2mm ID PTFE sleeve.

See also: Extruder Nozzle Variations

Test