J Head Nozzle

From RepRap
Revision as of 20:21, 11 July 2011 by Reifsnyderb (talk | contribs)
Jump to: navigation, search
Crystal Clear action run.png
J-Head Nozzle

Release status: working

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, and some ideas from me.
License
GPL
Author
Contributors
Based-on
Categories
CAD Models
External Link


Introduction

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 machined piece of round PTFE, as a liner, was requested in one of two designs 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 Inline Heater Nozzle 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 to meet the goal to keep the number of custom machined parts to a minimum.

Advantages

  • Internally, the filament path is identical to that of an already proven design.
  • The design is simple as there are only two machined parts.
  • If necessary, the PTFE liner can be replaced by using an off-the-shelf piece of PTFE tubing.
  • A resistor is used as a heater. There is no need to wrap nichrome wire.
  • Heat transmission is improved as there is no thermal junction where a separate heater screws onto the nozzle.

Disadvantages

  • The brass nozzle requires considerable machining.

Parts List

Quantity Part Description Part Number
1 J-Head Nozzle Machined Brass Nozzle/Heater Combination
1 Thermal Barrier Machined PEEK Insulator
1 Heat Sink Optional Experimental Machined Aluminum Heat Sink
1 PTFE liner 1/8" ID, 1/4" OD PTFE tubing McMaster-Carr 5033K31
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 McMaster-Carr 91090A114

Machined Parts

J-Head Nozzle

Jhn machining.jpg

Jhn md brass heater nozzle.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. Using a letter size A drill bit, drill out the hole for the heater resistor.
  15. Drill out the hole for the thermistor.

Thermal Barrier

Jhn thermal barrier.jpg

Jhn md thermal barrier.jpg

Material: PEEK, 5/8" Round, 36.5mm 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 +0.005 shoulder for a distance of approximately 0.050. (This is an optional step to keep the optional support washer centered.)

Heat Sink

Material: Aluminum, 3/8" Round, 25.4mm Long

Note: This item is an optional experimental addition and may help when printing with PLA.

  1. Cut a piece of 3/8" round aluminum to length.
  2. Using a 1mm (0.040) cutoff tool, make 2 grooves in each end. The grooves will be 0.050 deep.
  3. Cross-drill the PTFE liner hole with a 6.5mm drill bit. This hole is to be centered in both directions.

PTFE Liner

Jhn ptfe liner.jpg

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

  1. Using a razor knife, cut the tubing to length.
  2. Cut an approximately 30 degree (or greater) taper on what will be the hot-end of the PTFE liner.

Note: The prototype nozzle has worked without this taper. However, the taper would not have to be too precise as PTFE is quite flexible. If a lathe is not available, it may be possible to cut a workable taper with a pencil sharpener.

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.

Securing To The Cold End

Using Wire

Example

  1. Cut 4 evenly-spaced slots in the fender washer.
  2. Run the wire into the channels.
  3. Tighten the wire vertically and diagonally. Then wrap wire around the middle tightly, tightening all of the vertical and diagonal runs.

Using the Mounting Holes in the Wade Extruder

Wade Extruder

  1. Insert the PEEK thermal barrier in the 5/8 inch (16mm) hot-end socket.
  2. Using a sharp instrument or other object, mark the 4 hole locations on the PEEK thermal barrier.
  3. Remove the PEEK thermal barrier.
  4. Using a round file, file the mounting grooves in the PEEK thermal barrier in order to create 2 grooves for the mounting screws or bolts to pass through.
  5. Install the hot end.

Using Support Rods

  1. Prior to installing the optional support washer, mark and drill the appropriate mounting holes on the support washer.
  2. Install the optional support washer in between the J-Head Nozzle and the Thermal Barrier
  3. Use the support rods, screws, and/or washers to hold the hot-end in place.

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 the Wade 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 the time this note was added, 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.
  7. After almost a month, the initial prototype nozzle is still working. Due to the gap problem, it needs to have the PTFE liner replaced around once a week.
  8. A nozzle has been successfully tested extruding PLA.
  9. Some reservations have been expressed regarding the mounting of the nozzle. (Maybe the fender washer should be the recommended method or another method should be devised?)
  10. Extruding PLA can result in an early failure of the PTFE liner. This failure has been prevented by both increasing the feed rate of the filament and using a cooling fan. This is to keep the filament from getting to hot too high up in the liner. A heat-sink may be required in order to provide a more adequate solution.
  11. Due to the success of printing both ABS and PLA, this entry has been updated to "working".

Future Modifications

  1. It may be possible to convert 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 and 2mm ID PTFE sleeve.
  5. A Mini J-Head nozzle design has been started.
  6. Either the total length should be increased or two versions should be made available. The longer version would have a 50mm thermal barrier and the liner should have an initial length of 3 1/2 inches.
  7. A heat-sink option could be added to the PEEK thermal barrier.

Pictures

Jhn prototype test a.jpg First prototype in action. (Photo provided by Brian Briggs.)