Hobbing a rack?

I've discovered a tacho with 72 slots per rev, and with a 72:1 worm/wheel combination, I will continue by using the milling head.

This leaves me with one question, and that is, how slow, in terms of RPM can one run a hob?

I seem to recall cutting a short rack on bridgeport mill years ago. Clamped metal to an angle plate, took one pass with a single tooth cutter, dropped quill down, took another cut and so on. The last one was done on a CNC bridgeport with the same process, just the quill went down via the controller No problem ? bob

A bit late in the thread.

You can run a hob as slow as you want to, HSS doesn't have a minimum cutting speed.

However... I can see no reason whatsoever to hob a rack. Hobbing is used because it's a generating process and can make involute gear teeth for a wide range of tooth counts. The involute shape of rack teeth is that for an infinite diameter, which happens to be a trapezoid. If you really want to use a hob to cut the rack, use one with a zero lead angle as a simple multiple row cutter and cork across a number of teeth per batch. Trying to use a continuous traverse will lead to a horribly scalloped end result.

Regards Mark Rand RTFM

Having just converted my X2 to CNC (I can still run manually) I needed a longer rack for the Z. I only needed an extension to allow the up/down manual handle to stay engaged whilst driving with the Z axis ball screw.I therefore just used aluminium and ground a single point cutter from an engraving bit. I programmed the routine and happily cut the rack with a few manual Z increments (ball screw not yet fitted.) It is now fitted and works well. I would either use Marks or this method.

Not possible for those of us still using a cold chisel and anvil along with our lathes :-)