Fellowes Stub tooth helical gears

[vintagengineerParticipant @vintagengineer]

I need to make a Fellowes stub tooth helical gear. Do I a special cutter or do you use to different cutters?

[John HaineParticipant @johnhaine32865]

I don’t know if this might help answer your question:

http://vintagemachinery.org/pubs/2186/5660.pdf

It probably isn’t related but back in the 19th century a clockmaker invented a form of helical gear that could achieve very high ratios in a single pair and could be made with a straight cutter – I had a go at making a couple.

[vintagengineer]

On 3 December 2025 at 12:20 vintagengineer Said:

I need to make a Fellowes stub tooth helical gear. Do I a special cutter or do you use to different cutters?

What tooth pattern are you looking for and what helix angle? I’ve not had to produce a stub tooth gear yet but I believe that if you were producing say a 22/29DP you an use a 22DP cutter and cut to reduced depth. i’d have to check up on that though. There’s also a formula for adjusting the DP according to the helix angle presumably it will apply in a similar way to stub teeth.

[vintagengineerParticipant @vintagengineer]

20dp 20 teeth 45degrees

[Pete RimmerParticipant @peterimmer30576]

After doing some reading-up it seems a lot mine complicated that you might expect especially with that high helix angle.

Whats the application is it automotive or heavy-loaded mechanical or light load/static display?

[Pete Rimmer]

On Pete Rimmer Said:

After doing some reading-up…

It is always useful to list the texts to which you have referred.

Fellows were in the business of selling gear shaper machines. They would not make a tooth form unable to be cut by their own machine. Hence, someone with that brand of machine* and the correct cutter would be a commercial solution.

FWIW, this is what the correct cutter would look like:

https://dathan.co.uk/gear-shape-cutters/ (choose helical in the LH menu).

Be aware that there are two systems of stub gear in use: the Fellows system and the US (AGMA) system. How does the OP know for sure the gear is made to the Fellows system?

In any case, a stub tooth gear is specified by two numbers, expressed as a fraction. The post above only gives one number. It is difficult to find any information on stub tooth gears of that fineness – most references stop at 12/14. This shows 16/21:

http://ashgear.com/pdfs/kcb20.pdf

There is lots of information from Fellows available at vintagemachinery.org

This is of particular interest. The cover picture is similar to your actual gear:

http://vintagemachinery.org/pubs/detail.aspx?id=3732

* I think Drummond and Sykes made similar machines, presumably under license from Fellows.

[BazyleParticipant @bazyle]

I have often seen gear cutters on ebay with this 2 number format an never before understood it so thanks for bringing it up.
To save the strain on google the first number is the DP used so presumably the cutter and the second is the depth of cut ie being equivalent to the DP of a smaller gear.

[DC31kParticipant @dc31k]

It is not intuitive, but the best description of the Fellows system is in the operating and setup instructions for their machines. See:

https://archive.org/details/instructionsfors00fell/page/n9/mode/2up (page 143 of pdf)

Note comment in helical gear section about helix angles used.

Also of interest is this:

https://archive.org/details/sim_american-machinist_june-6-27-1907_30_23-26 (page 14 of pdf)

See also final paragraph here:

Cycloidal teeth must not only be accurately spaced and shaped; their wheel centers must be fixed with equal care

 

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