How Accurate Does the Angle on a Gear Hob Have to Be?

SteveHGraham · Post by **SteveHGraham** » Mon Jan 21, 2013 12:20 pm

Does anyone know how accurate the angle on a gear hob has to be? I'm going to make a 40° cobalt cutter for creating hobs. I'm awaiting the arrival of my supposedly-amazing Chinese bezel protractor, but other than that, the only tools I have for setting angles are a cheesy General protractor and some rotary tables.

ctwo · Post by **ctwo** » Mon Jan 21, 2013 1:13 pm

Your Physics degree may come in handy here...?

It's only 3 pages and has a few images/graphs...

http://www.iaeng.org/publication/WCE201 ... 1-2363.pdf

SteveHGraham · Post by **SteveHGraham** » Mon Jan 21, 2013 1:55 pm

I was kind of hoping someone would say something like "half a degree."

atomarc · Post by **atomarc** » Mon Jan 21, 2013 2:00 pm

Probably about half a degree.

Stuart

SteveHGraham · Post by **SteveHGraham** » Mon Jan 21, 2013 2:17 pm

Now that's more like it.

ctwo · Post by **ctwo** » Mon Jan 21, 2013 2:22 pm

Now I can't think of what angle you're asking for, but I came up with 0.19 degrees.

SteveHGraham · Post by **SteveHGraham** » Mon Jan 21, 2013 2:26 pm

This is all so helpful. I don't know how to thank you.

ctwo · Post by **ctwo** » Mon Jan 21, 2013 2:48 pm

What kind of hob are you trying to make? I read a few of your posts, about the grinder table and some about a hob, but not quite clear exactly which kind.

SteveHGraham · Post by **SteveHGraham** » Mon Jan 21, 2013 2:54 pm

I got a video where a guy makes spiral hobs using a 40° cutter. He cuts flat-topped threads in a cylindrical piece of steel, mills relief and gaps into them, and puts the hob on his mill. He mounts the work in a tilted rotary table and goes to town.

It worked beautifully. He ended up with gears that meshed perfectly.

ctwo · Post by **ctwo** » Mon Jan 21, 2013 3:31 pm

That sounds interesting and maybe a better way than making a single tooth cutter or fly cutting the teeth, which is what I was thinking of doing.

Anyway, I remember it was hobbynut, so I'll look into his videos.

SteveHGraham · Post by **SteveHGraham** » Mon Jan 21, 2013 3:36 pm

Hobbynut is one source. The other is a long DVD by a guy named Jose Rodriguez.

To use the spiral hob, he cuts small slots in the blank with a straight hob. These are there to engage the spiral hob's teeth. Once he has the small cuts made, he backs the work up to the spiral hob, turns it on, and slowly moves the work into the hob as it cuts. It carves the gear automatically, in one operation. You can make worm gears or ordinary spur gears with it.

SteveHGraham · Post by **SteveHGraham** » Mon Jan 21, 2013 3:53 pm

Forgot to say, the other cool thing is that one 50-cent hob replaces 8 involute cutters.

The Home Machinist!

How Accurate Does the Angle on a Gear Hob Have to Be?

How Accurate Does the Angle on a Gear Hob Have to Be?

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