Ok, I heard rumors that there is a good thread on here somewhere about building a 4th axis for a milling machine. I'm thinking I would LOVE a spindle on my table... and then the thought occurred to somehow run the main tool with a servo motor so that I could tap holes... anyway, any input on the matter would be appreciated... especially if you can direct me to some good information. I did a bunch of searches but couldn't find anything.
Usually, it's a fixture to hold your work that's set up sort of like a lathe on top of the mill bed, with a rotary table on one end and a tailstock on the other, the long axis between them parallel to X. The rotary table, equipped with planetary gears and a fairly low gear ratio, typically goes pretty slowly; it's not often fast enough to use as a lathe, with a fixed tool, but is typically used with rotary tools in the regular spindle, revolving the workpiece as it's carved on.
It is possible to set up your mill's spindle with a servo and encoder to do rigid tapping, but that's another issue entirely. Most of us don't bother with it, and use spiral taps and a tapping head, like a Procunier or Tapmatic, which don't require synchrony between the spindle and the Z axis.
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