Posted by BillS on December 04, 2006 at 13:57:36:
In Reply to: Bevel Gear Problem posted by bijan on December 04, 2006 at 08:38:16:
What are the models of the machines you are using?
It sounds like you are using a Duplex method/machine and cutting each member in one pass, but you are using cutters designed for machine/methods performing two-step (single side) finishing. The #12-20 cutter you mention has a 120 minute difference between inboard and outboard pressure angle. A #0-20 cutter would be neutral or balanced in PA and this is the cutter I'm thinking you are trying to achieve by modifying your #12-20. I think if you look closely you will see that PA of inboard and outboard cutters is different.
The intention of this difference in PA is to take advantage of special machine settings to allow the same cutters to cut over a range of ratios. The calculations (AKA methods and summaries) can be elaborate, and require as many as 3 machine setups (roughing, IB and OB) per member, but ideal for contact control in small-lot job shop work. Machines and production processes designed for Duplex generation finish in one pass (or two with roughing) and require precise tool design to achieve correct contact. Duplex generators either don't have or don't use settings and adjustments like those found on machines designed for Single Side two-step finishing.
Gleason uses terms like "Single-Side" and "Versacut" to refer to the method, cutters and machines that are used in two-step finishing and contact control. The type of cutter you refer to is described in the following FAQ topic:
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