Fiber Cutting Blade Replacement

The below procedure is intended for those who feel comfortable removing the fiber extruder and removing/replacing the cutter blade. If you do not feel comfortable performing this procedure, please contact MarkForged and arrange for a refurbished fiber extruder to be sent to you.


See “Fiber Extruder Removal & Reinstallation” in the Printer Maintenance section in our Support Portal to learn how to remove the Fiber Assembly from your printer:

Remove the Fiber Extruder from the Printer



  1. Once removed, remove the four screws that hold the fiber extruder cover on. There is a light press fit holding the cover on but you should be able to remove it by hand. Below shows the fiber extruder with the cover removed.

  2. With the cover off, locate the four brick like blocks that are each held in by a single M3 socket head cap screw (circled in red below). These blocks hold in the four stainless steel guide tubes that the fiber travels through.

    When looking at the extruder from the front, the fiber travels from right to left (as indicated by yellow arrows above). From the above photo, the far left block is not holding a guide tube because the guide tube it holds is the one attached to the fiber Bowden tube that goes to the print head.
  3. The cutter blade is housed in a diamond shaped aluminum plate that is linked to the black servo by a steel link rod with hooks bent into each end (as shown below). This plate with the blade installed is called the cutter assembly or sometimes just, “the cutter”.

    Important: When the cutter blade is replaced, the two fiber feed tubes on each side of the blade need to be adjusted. Incorrectly adjusting these tubes can cause the cutter blade to collide with them during cutting, and damage the blade.


  4. Before removing the cutter, ensure that it is in the non-cutting state (shown below) where the blade is not blocking the fiber path in the tubes.

  5. If it is not in the non-cutting state, use two hands where one is rotating the drive wheel of the servo and the other is pulling the cutter away from the servo. The servo has significant drag from the large amount of gear reduction in the servo. Even though this instruction set started with removing the extruder from the printer, it is an important reminder that the servo will not turn by hand when it is plugged into the wire harness of the printer.

  6. To remove the old cutter, loosen the M4 shoulder screw at the pivot point of the cutter. Do not remove the screw.

  7. Carefully disengage the cutter from the screw without losing the flanged bearing at the cutter end of the screw.

  8. With the cutter disengaged from the screw, carefully maneuver the cutter to remove it from the link rod.

  9. Carefully maneuver the new cutter onto the link rod and position the pivot end to allow screwing the shoulder screw back into place. Torque to 8.5 in-oz. Do not let the link rod carry the load when torquing the screw.

  10. Loosen the tube retaining blocks on each side of the cutter. Just loosen them a little. You want to be able to slide the guide tubes with a pair of tweezers, but not have them so loose that they are out of linear orientation.

  11. With tweezers, move the guide tubes out of the way so that the blade can be moved between them. Below shows the left guide tube being moved out of the way using the tweezers. Repeat this for the right guide tube.

  12. With one hand, spin the servo drive wheel to move the blade into the cutting location and use the other hand to push the cutter until it is clearly between the two tubes. Be careful not to bend the link rod. You want the sharp edge of the cutter blade to be a good two millimeters past the tubes. We call this the ‘cut’ location of the cutter.

Adjusting the Guide Tubes to their Correct Positions

The guide tube to the right of the cutter takes the fiber from the roller and presents it to the cutter. This tube does not have much adjustment. If it is too far to the right, it rubs on the rollers. If it is too far to the left, it could obstruct the cutter. The goal is to have it not touching the rollers and still give some clearance for the cutter blade. The best way to set it is to use the tweezers to move the tube so that it is touching the side of the cutter blade. Then, the act of tightening the screw on the retaining block moves the tube away from the blade a small but sufficient amount.

  1. The guide tube on the left side is more difficult to adjust correctly. With the cutter still in the ‘cut’ location and the screw on the left tube block slightly loosened, move the tube with tweezers toward the cutter. Use the tan shim from the accessory kit and put it between the tube and the cutter blade, as shown below.

  2. Use the point from one end of the tweezers to gently push on the tube to ‘clamp’ the shim between the tube and the blade (using very little force). Then tighten the screw on the retaining block. Pull the shim out – it should come out easily.

  3. Manually cycle the cutter back and forth to ensure smooth motion and no contact with the tubes.

  4. With magnification, look at the end of the tube that is close to the rollers to ensure there is some clearance. It can be very small but there should be some, as shown below.

  5. With the extruder cover still off, place the extruder in its normal location on the printer and plug in the harnesses. Do not hook up the Bowden tube or thread the plastic inlet tube.

  6. With the wire harnesses connected and the printer on, cycle the cutter using the touch screen utility menu. Be careful not to have fingers or anything else, obstructing the cutter and/or servo motion.

  7. If the cutter cycles correctly, turn off the power, reassemble the cover and re-install the fiber extruder per the above mentioned instructions.