Posted by Bill S. on August 16, 2000 at 23:45:01:
In Reply to: hobbing a single thread posted by Michael Kelly on August 15, 2000 at 07:28:32:
Since you're using the hob like a thread milling machine, you need to use a feed gear ratio of .375/.075 or 5:1. 60/24 x 60/30 should work. If you used this (or a similar ratio) when "scratching" the surface, did you get the desired .375 spacing?
The index change gear ratio is controlling the chip load, or cutting rate. You need to control the workpiece rotation rate to control chip load.
Since you're using a milling cutter, syncronizing cutter and workpiece rotation is unnecessary.
I believe chip load per tooth will be:
Chip Thick. = ( PI x Workpiece OD x R )/( 12 x t )
where R is the index gear ratio and t is number of teeth in the cutter. For instance, if you used 30/90 x 30/90 as index change gears, and the cutter has 6 teeth, and the Workpiece OD is 2", then by the formula above the chip load would be 0.009 per tooth. 40/90 x 40/90 would give you 0.017 per tooth.
This is the first time I've looked at using a hob this way, so let me know how it turns out.
Hope This Helps,
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