A cnc milling machine could be very easily converted to a pen plotter by just replacing the spindle with a pen.
pen holder for pen plotter attached to the z-axis
I wanted an attachment which was simple and could be used for both the movable gantry cnc machine and the movable bed cnc machine, so the measurements was cut to the optimum size accordingly. Also I wanted it to be versatile enough to be able to fit in a variety of pen or pencil sizes.
So I came out with a single piece of wood strip, cut lengthwise with a v-groove and fitted with a clamping strip to hold a pen in place. The v-groove was cut long enough to accommodate the whole length of the pen. This pen assembly was secured in position in place of the spindle holder of the cnc machine.
Faced Wasteboard contain no lines for reference. It was difficult to position any work pieces for machining.
The whole assembly worked well. One of my first jobs that I did with the pen plotter was to mark out the waste board of the movable gantry cnc machine with evenly spaced lines. These lines helped me align and clamp my work pieces easily so that I was able to position them accurately when I wanted to mill them.
The waste board that I install at the movable gantry cnc machine bed was faced flat previously so that all work pieces when placed on it would be placed exactly flat. Unfortunately, after I had done the facing, what I was left with was a blank waste board with no reference marking. Drawing the lines over it was a good move.