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Thread: Determining splines

  1. #1
    Associate Engineer
    Join Date
    Jul 2012

    Determining splines


    A broken spline shaft came in to my shop today, and the costumer wants a new part made.
    I havent dealt with splines in the past, and i'm struggling with how to go about to determine what kind of splines it is. The diameter is 35mm, and the number of splines is 26.

    A picture of it:

  2. #2
    Technical Fellow Kelly_Bramble's Avatar
    Join Date
    Feb 2011
    Bold Springs, GA
    First, check out the following web page:

    Involute Spline Engineering Drawing Data

    This web page should give you an idea as to the spline data you need to reproduce the part. Also, I believe there are standard mill cutters that create involute spline geometry though hobbing is the best process..

    To reverse engineer the component, I would first try to figure out what the part goes on. The OEM may in fact have engineering drawings or specifications available for download or other.

    If you have a CMM then you already know what you need to do to determine the geometry. I would also know what the application is and try to estimate the loading as this will drive your engineering materials selection and any case hardening (like QPQ, Nitriding, etc.) you may need to do.

    Of course you simply have a metallurgical done ($$) to determine the material

  3. #3
    Lead Engineer RWOLFEJR's Avatar
    Join Date
    Mar 2011
    Rochester Pennsylvania
    This isn't going to be what any machine shop is going to want to hear but... You might want to sub this job out to a shop that is already equipped to do this sort of thing? If OEM are still available that would certainly be something to consider... given that they are possibly making them by the jillions already it could be that they'd sell this part for less than a person could bang out one piece? And then there's the question... Why or how did it break? A good look at the assembly might inspire a different way to manufacture that may hold up better? Might be able to find room for more generous fillets etc. to help prevent future breakage? Possibly different material or treatment?

    I'd hop on the Thomas Register and start shopping around for a shop already tooled up. Unless you have a desire to expand your knowledge and your tool crib you're gonna need to charge the customer an arm and a leg for one part given that it sounds like you aren't really familiar with the geometry and all. But the requested part does give cause to learn more about it and you could chalk up some of the time and tooling to learning and becoming better equipped for future work...! Cost of opportunity.

    Good Luck...!

  4. #4
    Technical Fellow
    Join Date
    Feb 2011
    Kelly +1
    Bob +1

    Splines, if they are to carry any decent load with little to no backlash or over-run play, need to be hobbed. Looking at that jigger, my first suggestion would be to go with Bob's suggestion and try and get an OEM replacment part. Way too many unknowns. You may be taking on a can of worms.

    If no OEM spare parts then suggest another machine shop to the client.

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