Gallery, Projects and General > How do I??
Cutting internal gear teeth
tinkerer:
Are you saying you are trying to cut all of the internal teeth full profile in one whack? Wouldn't that take a drophammer? It might be able to be done. he support of the gear would be tough. maybe sandwiched in a holder of some type with only the effected area exposed. I hope you take a video of the process.
bogstandard:
John,
I am just wondering where you got the information that the cutter rotates.
The cutter is only round because that is the easiest way to make it with the cutting hobs I have, e'g make a spur gear out of high carbon steel (silver steel, drill rod) instead of say brass, then harden the cutter, and grind the cutting edges to shape afterwards. It is then locked onto the end of the ram with one cutting tooth perfectly horizontal.
The rest of the teeth except say two below and two above the main tooth could be ground away as they play no part in the cutting action.
The first tooth is cut by the slotting action of the cutter, then the blank is rotated to the next position and another tooth is cut, and so on until the inside gear is cut. Like cutting multiple keyway slots in a bore.
If you only used a single tooth cutter, then you wouldn't get the involute shape to the tooth form, it is the secondary cutting action of the above and below teeth, being 20 degs out from the major cutting tooth position that forms the involute 'shape'. It won't be a perfect involute because the two shaving cuts are in fact flat rather than curved, but close enough for the gear teeth to operate as though they were true to form.
John
John Hill:
Thanks John, I guess even Bandit would have understood it but not me! :doh:
tinkerer:
The dog is smarter than I am too. :( (now I know why my dog looks at me the way she does) On the referenced site, the cutter is spinning and he is cutting most of one tooth and parts of a tooth on either side. The full profiles are completed as he works around the gear. I see now that you will be doing the same interior cutting, but with the action a shaper makes. I am probably still shagging balls, but it exercises however many cells left between my ears.
andyf:
Bogs, your idea of making a hardened gearwheel to use as the cutter looks brilliant to me :clap:. The great advantage over a single point one is that if the tooth which is doing most of the work loses its edge, you can rotate the cutter, remesh it with the part-done job, and start off again with a fresh tooth.
BTW, you mentioned at one point that gearwheels at popular prices were hard to find. The cheapest I could find for my dedicated fine feed banjo were here:
http://www.technobots.co.uk/acatalog/Online_Catalogue_Gears_365.html (usual disclaimer), and they are thick enough (15mm) to cut up and get two approaching 7mm thick for the price of one, as in the first pic here: http://andysmachines.weebly.com/fine-feed-banjo.html
Andy
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