Re: Spiral bevel gears

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Posted by BillS on September 22, 2008 at 12:19:07:

In Reply to: Re: Spiral bevel gears posted by Tim on September 20, 2008 at 18:32:45:

Things can get more complicated than pitch and PA. First, it may have been generated by a Gleason machine or by a non-Gleason machine. These types are not, I believe, interchangeable.

Of course, if you plan to make both members, you can set your own pitch/PA/spiral angle, etc.

An approx pitch can be determined from measuring the gear OD.

Approx Normal Diametral Pitch = (Teeth+2)/(OD x COS(Outer spiral angle))

Imagine a cone of pitch lines whose apex is on the bore centerline. Imagine a line (radix) in the cone surface intersecting with the outer tooth pitch circle halfway between outer teeth. Imagine a second line passing through the same pitch circle point halfway between tooth flanks. The second line is tangent to an imaginary average of tooth flank surfaces at the same pitch circle point. The approx. outer spiral angle is measured between these two lines.

Naturally, the tangent doesn't intersect bore centerline. Also it touches the pitch cone only at the single point of intersection with the radix on the outer tooth pitch circle. This is not a true definition of spiral angle, but for a physical (e.g. protractor) measurement, it's probably good enough.

Approx Module = 25.4/NDP

Design of bevel gearing (esp. Spiral gearing) doesn't necessarily rely on standard pitch or module sizes so don't be surprised at a decimal value for these.

Do you plan to cut these yourself, or send them out?

I think the cheapest way to go is to buy a spiral set off-the-shelf. There may be a few vendors who have them (anyone listening?). I'm pretty sure that QTC does. They post here some times, but you can easily Google them on the web.

Years ago, I bought a spiral set from a vendor's catalog for a gear hobber. It worked out very well. With bluing and some trial and error, I was able to get the mesh right.

If you find an off-the-shelf spiral bevel set you will have to bore, key, and harden them. You will also need to face or shim the hub to get proper mesh. You might luck into the pitch and ratio you need, or you may be able to "live" with a variation available from a catalog.

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