Homebuilt CNC Foam Cutter

Andrew Sarangan

The foam cutter consists of a heated Nichrome wire suspended between two posts. Both posts move in the X and Y axes independently, making it a four-axis system. A controller board for driving the stepper motors as well as a computer with parallel port and a CNC software are required.

The system was constructed using 1" x 2" aluminum tubes, nylon blocks, linear shafts, bearings and leadscrews. The nylon blocks were machined from stock materials on a mill and lathe. Important considerations were: low rolling friction, accurate alignment of the various parts to avoid binding, and ridgidity to prevent the Y-axis from rocking during mvoements. The Y axes were designed such that they can be detached from the X axis for easy storage.

The controller was built from the HobbyCNC driver kit, which also includes a heat control for the cutting wire. The power supplies were built from a single 24V 5A transformer with a center tap, which can be used as two separate 12V power supplies. One supply is for driving the CNC circuit and the other is for driving the heater circuit. After rectification, the 12V AC output will be about 17V DC. With a 5A max output, it was sufficient for this application.

9-pin D-sub plugs were used for the motor connections. This is convenient because it allows for easy removal for storage.

All the pieces were assembled on a 3’ x 3’ plywood and installed on a stand with wheels. A cheap laptop was used for the control software through the parallel port.

GMFC foam cutting software was used. Although this software is designed for cutting airfoils, virtually any shapes can also be cut if we can come up with the appropriate XY coordinates.

Here is one method to create the XY coordinates of arbitrary shapes. Draw the shapes on Powerpoint using the WordArt tool or line drawing tools. Then save this as a bitmap (BMP) file. Open this file with WinTopo software (freeware), which will vectorize the bitmap. This software has many parameters to specify how to do the translation. Then save the vector data as XYZ text file. Then import this file into Excel and delete everything except the two columns that contain the XY data. Normalize the numbers such that the maximum is 1.0 and   save the data as a tab separated text file. Then open this file on GMFC under “root profile”. The entire structure can be scaled by changing the “chord width”, and moved in the Y axis by changing the “Basic Height”.