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Athena Dual Extrusion Single Hotend

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Revision as of 00:27, 13 January 2017 by Lmbrueck (Talk | Contributions) (Construction)

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MOST Delta filament as guide.JPG This page was part of an MTU course MSE4777 OA and MSE4777 OB/MSE5777/EE4777/EE5777: Open-source 3-D printing

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Athena Dual Extrusion Mod

Dual extrusion opens up many possibilities for 3D printing. The most obvious use for dual extrusion is to have 2 color models printed. However there are even more useful ways to take advantage of dual extrusion such as being able to print a dissolvable support material which will allow you to print much more complicated geometries than would otherwise be possible as you no longer have to worry about overhangs and bridging.

The traditional method for dual extrusion has been to use two hotends and two extruders. This method however requires extra hardware and reduces the size of your build space. Also this method requires careful calibration of nozzle heights to insure that the nozzle not in use is not hitting the printed part. Often times the results with these dual extrusion setups have ooze from the nozzle not in use ending up on the printed part and other artifacts.

The dual extrusion solution that I have chosen is one which uses a single hotend and only requires the addition of another extruder and a printed part to merge the outputs of the two filament extruders. This solution has the advantage of requiring no additional calibration, not needing added hardware for the second hotend and inputs and outputs to drive that hotend, and maintaining full build volume.

Project Created by: User:Lmbrueck

Example Prints

Dual extrusion print with the prime tower Dual extrusion cat model Dual extrusion cat model with prime tower still on bed

Design

For this modification I have used the bowden tube merger by AxMod found here. It uses the same PC4-M6 bowden tube connectors used elsewhere on the printer.

The second extruder used is the same as the one already used on the Athena printers and the file for it can be found here and the required SCAD libraries here. The drive gear dimensions for the extruder should be changed to match those of the drive gear which you are using.

Construction and BOM

Bill of Materials

BOM
Item Quantity Price
Extruder Body 1 cost of filament
Bowden Tube Merger 1 cost of filament
PC4-M6 fittings 4 $6.99 (10)
Bowden Tubing 1.5m $6.49
A4988 Stepper Driver 1 $9.69 (5)
100µF 35V cpacitor 1 $0.35
Nema 17 Stepper Motor 1 $11.99
608ZZ Bearing 1 $7.32 (10)
MR105ZZ Bearing 1 $10.49
1/4" Fuel Line 25mm $7.95 (5 ft)
MK7 Drive Gear 1 $6.99 (2)
M3 washer 2
M3 Nut 2
M3 x 6 Cap Head Screw 1
M3 x 25 Cap Head Screw 1
M3 x 30 Cap Head Screw 2
M3 x 45 Cap Head Screw 2
#6 x 1/2" sheet metal screw 2
Misc Wiring
Total Cost $65.26

Construction

Tools Needed
Soldering Iron
Desoldering Braid
2.5mm Hex Wrench
2mm Hex Wrench
File
Wire Stripper
Knife
  1. Print extruder body and bowden tube merger. Note that you may need to change the dimensions of the drive gear in the OpenSCAD for the extruder body. Do this by measuring the diameter and diameter of the hobbed section with a calipers and inputting these values into the extruder_drive_renderer file.
  2. Wiring Wiring diagrams and stepper driver info. More stepper driver info for non-pololu driver boards.
    1. Remove the Bridge Board from the melzi and beaglebone and disconnect it's power.
    2. Desolder the DC-DC converter from the top of the bridge board to gain access to the pins below it.
    3. At this point you will want to solder three wires to the unused pins on the bridge board. These will be the pins to control the stepper driver. I have chosen to use pins A1, A2, and A3 as pictured. However only pins D10, D11, and A4 are already used on this header so other options would also work.
    4. You will then need to resolder the dc-dc converter. You can solder it in place as originally done with your control wires running underneath however I have chosen to have it connected with a short bit of wiring so that I still have access to the pin header.
    5. Finally you need to solder two sets of power wires to the dc-dc converter for your stepper driver. You will need both the 24v and the 5v lines for the stepper driver.
    6. You are now ready to wire up and connect the stepper driver. Connect the 24v supply to Vmot and GND with at lest a 47µF bypass capacitor soldered very close to or on the board.
    7. Then solder the 5v supply to Vdd and GND.
    8. Connect the Sleep and Reset pins together.
    9. Now wire your three control wires to Enable, Step, and Dir. The order in which you wire them is not important just take note of it as you will need to enter it in the firmware later.
    10. Finally connect Vdd to MS1, MS2, and MS3 to enable 1/16 microstepping.
    11. Now plug the bridge board back into the melzi and beaglebone and reconnect it's power to the dc-dc converter.
    12. Now simply plug in with pin headers or solder your stepper motor to the 1A, 1B, 2A, 2B pins making sure to wire it correctly (consult the pololu page).
    13. You will also need to power on the system and trim the current regulation voltage. Note that not all drivers use the same value sense resistor. The value of the sense resistor will change what Vref you will want to set for a given current limit. The formula for current limit on the A4988 driver is Vref = 8 * Imax * Rs where Vref is your reference voltage in volts, Imax is your current limit in amps, and Rs is your sense resistor value in ohms.

Bridge board wiring.jpg A4988 wiring bottom.jpg A4988 wiring top.jpg

  1. Now go ahead and mount the stepper motor to the extruder drive per the instructions in the build guide. Athena Extruder Drive and Spool Holder Assembly
  2. Cut a length of teflon tubing about equal to the one already connected to your first extruder and push it into the coupling on the new extruder.
  3. Put a coupling onto all 3 ports of the extruder merger.
  4. Cut a short piece of teflon tubing just a long enough that it sticks out of the hotend just a bit and there is only a small gap when you push the extruder merger coupling onto it.
  5. Now connect both extruders tubes to the extruder merger.

Franklin 2 extruders.JPG Franklin extruder offset.JPG Franklin extruder io.JPG

Common Problems

  • There does seem to be some sort of bug in the Franklin firmware that will cause the printer to pause when running the tool change script. This problem only happens with certain G-code setups though and I have been unable to determine what causes it. My current G-code does not have this issue.
  • Make sure your hotend temps are high enough to prevent jamming of the material. Standard filament temperatures seem to work fine but just don't go too cold.