Milling Machine Spindle Lock

This is an essential modification to the milling machine. The standard way to lock the spindle is to use a rather daft little pin spanner (similar to those used on a lot of angle grinders) to engage with two holes on the underside of the spindle.

This works, but has two issues:

  • It's fiddly and quite difficult to align the pin spanner with the holes.
  • As soon as you put tooling with a large head (e.g. a boring head) into the spindle, the holes are covered by the tooling and it's impossible to use.
  • It's not a good design! Replacing it is actually quite simple (although slightly scary as it involves milling the top cover of your brand-new milling machine!). My spindle lock is very closely based on one designed by Paula Stephens; she describes it in this post.

    I made a few very minor modifications to the drawings, but nothing substantial. I changed a few dimensions to metric (for example using metric threads and using a 12 mm reamed hole instead of a 1/2" one). My design for the pivot shaft is also different, but then Paula didn't provide a drawing for that anyway.


    Unlike Paula, I actually quite like the drawbar arrangement that comes with the SX3 (Paula replaced hers with a hex-topped bar and a hammer for release). The intention of the standard drawbar is that it is loosened with the provided 8 mm Allen key and undoing it pushes the top of the drawbar against the inside of the cylindrical housing: this forces the taper out of the spindle. This generally works well, but I found that with quite a few tools I had, the drawbar thread wasn't long enough to actually release the taper. I resolved this by adding a simple washer to the top of the drawbar (shown in the right-hand picture above) to make it engage with the cylindrical housing a little earlier. Since making this modification, I've never had to hit my spindle with a hammer and that makes me much happier!

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