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Electronics

CNC Foam Cutter

In December 2011, the need arose to cut foam wings for model airplane kits. Outsourcing looked attractive innitially, but in the end, building a CNC foam cutter seemed like the best solution - mainly because it would allow me to have control over the quality of the foam cores.

A friend very generously supplied information about a CNC cutter that he had built some time before. And fortunately, I already had some stepper motors that were salvaged from old 5.25" TEAC floppy drives. The DIY stepper driver electronics seemed quite easy to build, although I had to make the PC board myself - something I had never done before.

Construction

The foam cutter consists of two parts:
1. The mechanical part - the base, plus the left and right X-Y stages
2. The electronic part - the Stepper Driver

Mechanical

The foam cutter is constructed around a base, or more accurately, an upside-down box made of 12mm MDF (local trade name: SupaWood). The X-Y stages are two sets of drawer tracks. The Y-tracks are connected perpendicular to the X-tracks using 4mm bolts which fit into tapped holes. The X-tracks are mounted either side of the base, while the Y-tracks ride on the X-tracks. All tracks are used in a 'vertical orientation' to minimise play.

The stepper motors turn 6mm threaded brass rods. Short pieces of petrol tubing were glued (CA) between the motor shafts and brass rods to connect them together while providing some degree of flexibility.

Stepper Driver

The 4-Axis Stepper Driver is quite easy to build. There are only 5 components for each axis; a stepper motor controller IC and 4 power transistors. The PC Board artwork can be downloaded here in PDF format. Print it on a sheet of transparency film using a laser printer. Keep in mind that only unipolar stepper motors can be used with this circuit.

The stepper motors and stepper driver require 12 Volt and 5 Volt supplies. I've used a modified PC power supply for this.

Bill of Materials (Stepper Driver)

Quantity Designator Value
4 IC1 L297
16 T1..T4 TIP122
1 PC Board
14 Terminal Blocks

 

Software

Foamworks is used to drive the foam cutter, and CadWorks to generate the cut-files.

Interface

The Stepper Driver unit connects to the parallel port of a Windows 7 machine via a 25-core cable with DB-25 connector. I doubt that a Parallel-USB converter connected to a USB port will work.

Conclusion

The remaining pieces of equipment to complete the foam cutter are the bow with cutting wire and the power supply to heat the wire. These are not discussed here since both are pretty much standard and quite easy to make or acquire. I will just add that after cutting hundreds of wing cores, I've found that contrary to common opinion, the best cutting wire is steel fishing trace, not nichrome wire.