Posted by Bill S on April 27, 2005 at 13:39:42:
In Reply to: Min & Max Dia of Hob? posted by lee on April 26, 2005 at 14:47:13:
In general, I believe the hob cutter diameter should be:
Worm Diameter + (2 x Clearance) + Delta
where the Clearance is the difference between Whole depth and Working depth, and the Delta is a small amount to assure that the contact pattern doesn't extend from face-to-face. Maybe someone has a formula or can offer some thoughts for accepted practice here.
The additional (Delta) diameter allows for some axial mounting misalignment of the gear, and improves lubrication between worm and gear.
If the hob cutter is significantly larger than the worm, or if the cutter is a different number of starts and/or hand, then the additional table angle displacement from 0 Deg effectively cuts even larger than the actual hob diameter. It seems that the gear's throat and root would follow an eliptical shape. I'm guessing here.
I hope others join in on this interesting subject.
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