Hirth Coupling

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Well-Known Member
HMEM Supporting Member
Jun 24, 2010
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I bought some plans from Modelltechnik, maybe the next project, not sure yet.
He uses a built-up crankshaft method with Hirth couplings to join mid span crankshaft journal segments, which are then concentrically retained within journal bearings. His CAD plans show the 60-deg vee cut, the vee inclination angle & number of teeth. This yields the theoretical profile, meaning crest to trough of sharp vee. It looks a bit intimidating, but basically I think you just set the dividing head at the specific angle & cut across the cylinder face with a vee cuter to prescribed depth.

Through these links I was able to replicate the cut profile. The teeth appear to mate properly in section views & I get agreement with the axial inter-mesh distance. The first link shows the underlying equations in spreadsheet form. Some of the output parameters I can correlate to my 3D model, others I'm not too sure about.
- Has anyone machined this profile before? (maybe specifically on a model engine crankshaft).

- Would a double angle cutter like attached pic do the job?

- Where things get interesting is the cutter will have some defined flat or nose radius which will define the trough profile. And the tooth crown should probably have some defined flat for intermesh clearance. I worked this into my CAD model to derive a physical cut depth, but I'm not exactly sure how to measure this in-situ while machining.

- Does anyone have links to Hirth geometry/equations (ideally for simple minds LOL).


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