Anycubic Kossel BMG Upgrade

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This Anycubic Kossel BMG Upgrade guide will help you to install BMG extruder.
This is a dual extruder that really helps with underextrusion problems.
It comes with a smaller motor (optional), because it is geared 3:1 instead of 1:1. 

Step 1: Order a BMG Dual Driver Extruder

If you want to save up a few bucks, order a BMG without motor, you can use the stock one.

BMG Dual Drive Extruder

This is a complete BMG Dual Driver Extruder set with everything you need to install it. I prefer TriangleLab, because it has been tested by thousands of people.

Mirror BMG Dual Drive Extruder

If you prefer a mirror BMG, you can order this one. I used a standard BMG, but I think that this Mirror type will be better for our Kossel.

Step 2: BMG package

This is a complete package with BMG, motor and accessory.

Step 3: Remove and disassemble stock extruder

Remove old extruder and disassemble it.
You will need a HEX 2.5 for the motor and a HEX 1.5 for the gear on the shaft.

Step 4: Comparison

You can see the difference between the motor sizes in this picture.
Shaft diameter is the same, just the stock motor’s shaft has a D cut .

Step 5: Install bowden coupler

Double check the gear installation.
Insert black plastic pastr into the bowden coupler.
Insert a new PTFE tube and insert the orange lock.

Step 6: BMG assembly

Put the extruder mount on the motor and assemble the extruder.

Step 7: Install tensioner

Install the tensioner:
Plastic washer – spring – screw.

Step 8: Install BMG on the frame

I have used differen holes to have the BMG at desired angle.
Do not forget to install PTFE tube to the bottom of the BMG.
I have taken photos of both options – stock and new BMG motor (pancake type)

Step 9: Marlin FW modification

BMG is a geared extruder with a ratio of 3:1.
Stock extruder has a 1:1 gear ratio.
This means that you will need 3x more steps to extrude the same amount of filament as with the stock extruder.

Read the actual step values:
You can send M501 command to restore and view settings.

Calculate the new value: steps * 3 = new steps
Use this M92 command to set the new step value: 

Anycubic Kossel Marlin flow calibration

After extruder calibration you should calibrate material flow.It is possible that without flow calibration you printer will be over extruding and your print quality will be bad.You can easily modify it in your slicer, such as Cura. 1. Download cube

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Anycubic Kossel Marlin extruder calibration

1. Preparation 1.1. Heat up the nozzle Start by heating up the nozzle to your printing temperature PLA 190°C, PETG 230°C, ABS/ASA 250°C 1.2. Retract filament Push the extruder calipers and retract filament from bowden with the other hand 1.3.

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Step 9: Klipper FW modification

Just change the step distance to 1/3 value you see and upload new configuration.

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  1. Hi Lukas, can you please share your parameter for the updated klipper’s rotation distance for the BMG extruder?

  2. I did this upgrade about a year ago but have just reverted back to more stock extruder (actually an Ender 3 all-metal extruder) as the ~25mm/s max retraction rate really doesn’t work well with printers with such a long bowden tube. Particularly if you want to take advantage of Linear/Pressure Advance, you will get reduced effectiveness and the extruder will be quite loud.

  3. if i use retraction speed over 30 mm/s with 5mm retraction its like it want to destroy the gears inside extruder
    below that speed all is ok.(i used you canfig with trigorilla board)

  4. uhhhhh uhhh, i needed this blog about 3 Years ago q.q…

    Verry nice and Clear instructions. I will consider upgrades when im starting to print again. I had allready under extrusion thanks to the nozzle extruder combo at 30mm/s at 0,2mm layer hight. And allready had tried multiple cold pulls or what it was called. so a new nozzle would be also appropriate.

    My printer was not Pluged in for Over a Year now. Any expirience with degeneration of the linear rails?

    1. 😀

      Hi, just lube them.
      It is possible that the problem is with the PTFE (bowden) tube – heat up the hot end as much as you can, remove it, cut off about 1-2 cm and you should be good to go.
      Just be sure that the cut is straight.

  5. hi lukas. can tyou tell me the voltage of bgm extruder (stock kossel motor) tmc 2209 driver
    i have very strange noises
    thank you

    1. Hi, I have used about 0.6A (UART mode).
      Stock TMC2209 drivers have a current 0.9 – 1A.

      Do you have a problem with motor overheating?
      How does the strange noise sound like?

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