# Re: How do I cut helical gears on a Newark 3 hobbing machine?

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Posted by BillS on April 09, 2010 at 13:24:40:

In Reply to: How do I cut helical gears on a Newark 3 hobbing machine? posted by Chuck on April 08, 2010 at 20:43:35:

For that machine, you should use the differential.

The index is set same as for spur gear- 12/teeth is the index ratio.

The differential is used to create the helix angle. It also allows you to take multiple passes.

Feed change gears control only the table feed.

There is a formula for differential change gears that you need to find. There are a number of hobbing topics in the FAQ (click on Gear FAQ link above) that might help you understand how to find and apply the formula, etc.

The FAQ lists a Newark No. 3 with the following:

Differential gearing decimal ratio =
0.318309886 x SIN(helix angle) x NDP / hob starts

Once you solve the formula above, you want to find a gear set that closely matches the decimal ratio.

If this formula doesn't work for you (i.e. wrong helix angle) then the constant (0.318309886) must be different for your machine.

The other thing is that you will need to either use (or not use) an idler in the differential set to generate the hand (L or R) you want.

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