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| NormanV:
Am I missing something here? I read an article on making a hob to cut gears and it showed the teeth on the hob being cut straight. It was then used in steps to cut each tooth individually, but also cut a little of the following tooth and preceding tooth. In doing this it shaped the teeth correctly irrespective of the number of teeth on the gear. |
| eskoilola:
I think that helix thing does exactly the same and in fact is more precise. However it needs a special machine to do the hobbing as it does not work in steps but continuously ... i think :scratch: The tool is most certainly NOT placed on 90/180 degree angle to get straight tooth. Edit: Ärgh... In fact ... if I look the tool from side it actually looks like a lot of triangels. So it might actually BE placed on straight angle to get straight teeth.... |
| awemawson:
The hob rotates in synchronism with the blank at a ratio suitable to cut the right number of teeth. The hob is then transversed across the blank at a fixed cutting depth. Depending on materials it may take several passes at increasing depths before the full tooth form emerges |
| chipenter:
The hob is also at an angle to match the hobs pitch , you also can't start at the edge of the gear if trying to cut a gear being driven by the hob , I have tried this and bent the mandrill for my hob and totaled the gear . |
| NormanV:
I have been reading a copy of Model Engineer magazine from 1955 and I came across an article on gear cutting by Martin Cleeve. He said that in his early days he just bought a No 3 cutter and used it to cut gears from 25 to a rack with acceptable results. I might be able to get away with two cutters no3 and no 6. That's not so expensive! |
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