Any ideas on cutting worm threads?

[markb2346]

I need to make some worms to run helical cut gears for adjusting parts on a machine.

Length is 6.500"
Major dia. is 3.75"
Pitch is 1.165"
Depth of thread is 0.885"
Flat on top of thread is 0.420"

I have an Okuma LB35-ll and a Fadal 5020 mill with a 4th axis. I have a few ideas but just wondering if anyone would have any suggestions on the easiest way to do this. Thanks.

[fizzissist]

Boston Gear.

[RICHARD ZASTROW]

You might want to consider the advice from fizzissist. I'm not saying it can't be done but it is a challenge.

Thre is also Martin Sprocket & Gear.

Dick Z

[markb2346]

I need the worm, not the worm gear. The worm gear is a 2 pitch and Boston and Martin go up to a 3 pitch. Martins worm for a 3 pitch has a pitch dia. of 4" and what I need has an outside dia. of 3.75". THIS IS NOT A STOCK ITEM.

[dickda1]

Probably way too primitive for you, but take a look at Making Gears the Easy Way video by Jose Rodriguez. You can rent cheap from Smartflix. I have used his methods to generate a worm and hob pair and then cut a worm gear.

[fizzissist]

My 1959 edition of the Tool Engineers Handbook published by ASTME (now SME) has an excellent treatise gears in chapters #42 and #44.

#44 especially because it shows the machinery, fixtures, cutters, and theory. Other editions may have the chapters renumbered.

There's one available right this moment on Ebay for $7.99, with zero bids.

Machinery's Handbook doesn't have the same depth of information, but you can derive the numbers you'll need from their Gears section.

[Geof]

Originally Posted by markb2346 .....I have a few ideas but just wondering if anyone would have any suggestions on the easiest way to do this. Thanks.

If I was faced with this project I would use the 4th axis and generate the thread in several passes using the X axis and the A axis. You don't mention whether the gear you have is actually a worm gear or whether it is just a helical gear. The thread angle would need to match the pressure angle of the gear which, I think, for regular simple worm gears is the same as acme.

You are never going to cut this thread in one pass, it will need several passes with regular mills to rough out the bulk of the material. Then the flanks can be done with a tapered mill of the appropriate angle.

[markb2346]

That is one of the ways I was thinking about. The angle on the side of the worm tooth figures out to 21.6 degrees so I am probably going to need to find someone to grind a special cutter. The gear is a helical and not just a worm gear because the gear has threads on the inside and as it turns the gear moves in and outon the machine, so as it moves the point of contact moves across the face of the gear.

[Geof]

Okay cut it on the lathe. Programming it would be more of a challenge than using the 4th on a mill but you would be able to simply set a pair of tools slightly askew to get your 21.6 degrees.