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    Default Hardening gears

    Is hardening of gears/shafts common practice ?
    I ordered an input shaft/gear for my old Startrite Sabre gearbox and this turned out to be NOT hardened. The company who manufactured this shaft according to original specs/drawings claims that hardening is not called for.
    Is this correct ?

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    It all depends on load and operating conditions.

    If a gear can be reasonably sized for the load and decently lubricated there is little benefit in hardening. Stock gears from distributors such as HPC, Boston gear at all are not hardened.

    Hardening adds considerable extra manufacturing work resulting in a significantly more expensive gear. Not only does it have to be hardened, an extra step which may also need a more expensive steel to start with it has to be finished by grinding. If you are going to grind a gear might as well do the job properly to higher levels of precision. Having done that for a pair of gears you might as well make the housing really accurately so the shafts are precisely positioned. Having done all that you have something capable of taking much, much higher loads. Its the sort of thing you do for automotive gearboxes et al. If done on a one off or few off basis theres is also a risk of hardening failure under load with the hard case spalling off.

    Your Startite bandsaw has modest power and there is plenty of room to fit an unhardened gear large enough to easily cope with the load. So Startrite kept things simple. Indeed hardened gears appropriately sized for the load might well have been too small and hard to design in. Far as I can see, if properly lubricated, those gears should last pretty much for any reasonable machine life. But seals do leak and who changes the oil on their bandsaw!.

    Clive
    Last edited by Clive603; 02-25-2020 at 02:46 AM.

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    Clive, thank you very much for this explanation !

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    An addition to that, at least for HPC, is that they offer gears in EN24T/4340PH, which can be heat hardened/tempered, but can also be nitrided later if you need to do any machining on them before using them. Nitriding cost about the same as hardening/tempering, but results in even less change in dimensions.

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    Thanks for explaining such amazing information.

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    When I worked for a company that used to buy in certain mould tools from China the unscrewing geared tools always had hardened gears, they nearly always shattered in a year.

    When I see hardened gears now, it makes me giggle.

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    Quote Originally Posted by Luke.kerbey View Post
    When I see hardened gears now, it makes me giggle.
    Like in the transmission of your car ?

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    No, in mould tools.


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