Hot wire cutter version 2!
Now with a thru going bolt with threaded end, some spacers and shims. The most important upgrade is that it's a lot easier to make truly flat cuts with this, as the guitar string can't move around in any way. Almost as important: no fiddling around tying up the guitar string! Insert into right height slot and tighten the wing nut. That's it! Much better.

With the spacers inserted, cuts can be varied in 1mm steps between 4.5 and 5mm. Also went up to 014 guitar string, got tired of the .010 breaking. Made some test cuts with it today and it is a lot more stable than the nail binding post cutter. Though, for those on the cheap, making a notch in the nail is probably good enough to avoid having the string slipping around..
Still waiting for spray paint.. TBC..