CNC – Update 2: Cutting text in plastic

Well, this was an interesting experiment.

I’ve been playing with the CNC USB Controller software and found a function to “Import Text”. The function opens a window that allows you to type in any text, in just about any TrueType font, and have it convert to G-code (and also DFX code). There are also some rudimentary font control and alignment options. The “Advanced” button allows you to control aspects of the cutting including the number and depth of successive passes taken by the machine.  With the text set at 72 point (?), the resulting image (and g-code limits) is just under 40mm square.

CNC Text input

CNC text input

CNC Text Input

CNC text cutting path

I tried some test cuts in plastic but soon found that no matter what feed rate I used, the end mill bit would gum up with melted plastic. I tried various size mill bits and at different feed rates but the results were much the same. A blob of melted plastic would gradually accrete on the end of the mill. The mill would then ‘smear’ the plastic, blurring the cutting contour. In addition, I had to pause the program regularly to remove this hard plastic build-up.

I then tried a curious bit that was in the box of tools included with the milling machine. The bit is shaped like a flat spade with no flutes, a long tapered edge and a sharp tip. I figured that this bit may be good for plastic as the cutting angle was acute and it had just one cutting (shearing) edge. These bits, available on eBay, are called engraving bits and are available in carbide or titanium carbide and a wide variety of cutting angles – from 10 – 60°.


CNC engraving bit

Using the speed override, I dialed back the default cutting rate of 250 to 100mm per minute and scaled the G-code to take 2 passes, each of 0.05mm depth. I cut the text into 1/8″ clear plastic with the protective backing paper removed as previous attempts had the plastic paper gumming up the bit. The results were quire impressive (and Lise, my partner, was quite taken with it). The finished text is crisp, clean and precise and very easy to read.

CNC: Text cut into 1/8" plastic

CNC: Text cut into 1/8″ plastic

So, from now on, when I cut into plastic I will use this spade bit, fast spindle speed, slow feed rate, and multiple fine passes.

Nice results (and sentiment), huh?

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