In November 2024, I used the parts of my Q-bot 3D-printer to build a 4-axis hot wire cutter. The main challenge of this project was to fit the machine into a compact box when it was not in use.

This also meant that the stepper motors had to be mounted in a compact belt assembly. The stepper motor pulleys are hidden inside the 2040 beams that form the X and A axis of the hot wire cutter.

To reduce the cost of the hot wire cutter, I reused as many parts from the Q-bot 3D printer as possible. The linear rails, stepper motors, end switches, and pulleys where all recovered from my old 3D printer

The design of this hot wire cutter is made in Onshape. The project can be found here. First, the mechanical assembly was tested. Some 3D printed parts had to be redesigned to allow for smooth operation

The motion system is a hybrid between conventional cartesian kinematics and an H-bot. The entire belt drive with pulleys and stepper motors is placed inside the 2040 extruded aluminium beams. Motor A directly drives the X-axis, but motor B is coupled through the X-axis to the Y-axis. The kinematic equations are as follows:

• X = A

• Y = A - B

Or:

• A = X

• B = X - Y

The hot wire foam cutter is running a custom compiled version of FluidNC. This was necessary because of the unique kinematics of the machine. The XY-axis pair functions as a kinematics group, and the AZ-axis pair is a second group. Using the coreXY kinematics file as an example, I defined my own makerbot_XYAZ.cpp kinematics definition to allow FluidNC to control this unique setup.

Unfortunately, the mechanics are not very reliable due to the complexity of the pulley system. This results in a couple of millimeters of play in the mechanism and possible step skipping (loss of position) of the motion system.