Posted by Bill S. on August 07, 2000 at 17:23:28:
In Reply to: Hobbing posted by Kevin on August 01, 2000 at 08:02:08:
I'm not experienced with carbide hobs or skiving, but my understanding is that you need a very "solid" or stiff machine with very stiff work piece fixturing.
The No. 12 BC is probably not stiff enough. If it's like the one I had, the bearings are sleeve type and there has to be some endplay and slack in all bearings to keep them from heating up and "freezing". Also, there is backlash in the index gearing and in the hob drive gearing. Index backlash will make accuracy difficult to control when skiving hard material.
Backlash in the hob drive gearing is not good for the kind of interrupted cutting that a hob experiences. Also, the table drive is not ideally stiff, driven by a single lead screw.
I think these small endplays and backlash amounts, plus the springiness in the table feed lead screw, keep the No. 12 from being suitably stiff enough for carbide.
Having said all that, though, the carbide in a hob is probably more forgiving than that used for insert tooling used in machining.
I would try taking out as much play, backlash, etc. as practical and make the workholding fixtures very stiff before attempting it. Accuracy on a No. 12 will be improved by the same effort.
If you try it out, I would be very interested in your results.
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