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Helical splines for linear motion (Bendix Drive)

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  • Helical splines for linear motion (Bendix Drive)

    For a given diameter of shaft: when
    planning a helical spline in an application
    with the objective of providing linear motion,
    what considerations influence the number of
    splines?

    For instance, to enable the pinon gear of a
    Bendix Drive on a starter motor to advance
    along the armature shaft, engage with a ring
    gear and then retract back to its initial
    position.

    In general terms, will a greater spline count
    produce more bearing surface for smoother
    travel at the expense of reduced torsional
    strength and increased mfg cost?

    The back story here is that a change-up p/n
    for a replacement pinion for an old ('70s)
    Bendix for a Tecumseh (Toro) starter turns
    out to have 7 helical splines, instead of 6.

    Looks right with the correct gear tooth count
    and slips right onto the armature like it
    should, just doesn't engage w/ the helical
    portion of the shaft.

    Sourced from a local Tecumseh rep, though
    with the company long departed, I suppose
    all parts now are aftermarket. Looking online,
    I have not come across a single instance
    where spline count is given in the description
    of parts purported to fit.

    For a fixed shaft size, by the 70's and beyond
    one would think there would have been some
    standard settled on, obviating the need to
    mess with spline counts.

    .
    Last edited by EddyCurr; 11-29-2014, 12:12 PM.
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