Hob Knobbing an Arbor for Involute Cutters.

cathead

CATWERKS LTD
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This morning I fabricated an arbor to mount in the rotary table for hobbing some gears. The previous tapered arbor I was using
was lacking to some degree in concentricity so this will work better I think. The the gear blanks are 1.000 inch inside diameter
to made the arbor with a snug sliding fit. Gear blanks are reamed to 1.000 inch so that works out great. The hobbing is done
toward the rotary table so there is little chance there will be any slippage in the Morse 4 taper. The arbor sticks out far enough
to there is plenty of clearance between the mill head and face of the rotary table.







P1020193.JPG



This is the MT4 arbor with 1.000 inch mount for the gear blank. I made
a nut with two flats so I can tighten it up with a big Crescent wrench.






P1020195.JPG
Here is the arbor mounted in the rotary table. This will be much
better than my previous set up that required a tail stock.





Even the shop foreman was impressed:grin:
 
Looks good, although I would suggest that you remake the nut with a center on it. That way you can add outboard support for a bulletproof set-up.

I use one of the common "stop set-up" you can make or buy and I made a long center for it (in place of the stop rod) for just this type of set-up.

https://www.mscdirect.com/product/details/56450539
 
Looks good, although I would suggest that you remake the nut with a center on it. That way you can add outboard support for a bulletproof set-up.

I use one of the common "stop set-up" you can make or buy and I made a long center for it (in place of the stop rod) for just this type of set-up.

https://www.mscdirect.com/product/details/56450539

The nut is open and there is a center on the arbor. I didn't want to thread a blind hole. I understand your thinking though. It seems really
rigid as it is.
It's a 1.5 inch shaft sticking out about 4 inches or so.
 
Cutting a gear with a single tooth type of cutter such as you show is not called hobbing, To be called hobbing, it would be cut with a hob, a cutter with a thread cut in it equivalent to a form of a rack tooth, and the spindle and dividing mechanism are geared together at a ratio to generate the required number of teeth to a form that is theoretically correct instead of approximate as in the range type cutter that you are using, which only approximates correct tooth form; in the eight cutters in the normal range set there is only one number of teeth that is correct for each cutter, about in the middle of the range. Gears cut with range cutters are good enough for ordinary work, but not good for sophisticated work.
Also, with the hob, the hob tool is rotated at an angle to the blank, equal to the spiral angle of the hob teeth.
 
John,

Thanks for the clarification. Maybe I need to change the name of my post to hob knobbing with an involute cutter or similar.:grin:
 
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