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Thread: Spur gear computations

  1. #1
    mklotz mklotz's Avatar
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    Aug 2015
    LA, CA, USA
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    Spur gear computations

    More good stuff from the bookmarks file... This time the subject is spur gears. This source has the formula for virtually every dimension associated with spur gears that use the diametral/circular pitch description.

    This one covers the formulae for so-called metric gears that use the module description...

    This one duplicates a lot of the formulae mentioned above but has the advantage of supplying an online calculator that, given the gear descriptors, will automatically calculate a lot of the dimensions you'll want to know. It's down at the bottom of the page. Just above the calculator on the page is a short treatise on how to identify unknown gears; very useful when restoring old equipment.

    Notes on Spur Gears

    A note here...

    One of the tougher jobs for the amateur is determining the pressure angle of a gear. I wrote a program to implement my procedure for doing this; it's available on my site under the name, GEARPA. Several accomplished machinists have used it and commented on it favorably so, while perhaps not perfect, it should provide help for a difficult job.
    Regards, Marv

    Home Shop Freeware

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  3. #2
    thehomeengineer's Avatar
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    Berkshire UK
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    Gear hobing machine

    Hi Marv
    I was very lucky to have a very dear friend (Miles) who was mad for gear cutting. What he didn't know about the subject was incredible. Unfortunately, he is no longer with us. What was even more impressive about the man he was self-taught as he was a retired Medical Doctor.
    He made his own hobs and had built a hob backing off tool and a small hobbing machine along with tool and cutter machinery to support his passion for gear cutting.
    My Foden steam wagon needed a 111 tooth gear which is difficult to do with a manual 40:1 dividing head. (not impossible but a compound gear train has to be used)
    Miles offered me the access to one of his gear hobbing machines and this was used to cut all the gear blanks for the engine. I have included some photos of the machine below and the finished gears.

    Spur gear computations-dscf1185.jpg.opt652x489o0-0s652x489%5B1%5D.jpg Spur gear computations-dscf1184.jpg.opt652x489o0-0s652x489.jpg Spur gear computations-dscf1186.jpg.opt652x489o0-0s652x489.jpg Spur gear computations-dscf1213.jpg.opt652x489o0-0s652x489%5B1%5D.jpg

    The Home Engineer

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    Seedtick (02-17-2018)

  5. #3
    kquiggle's Avatar
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    Southwest Michigan
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    Thanks to mklotz for the links to gear information. I added those links to some other information links on gears which I have collected over time; see below for the list of links.

    Go to this link: and then scroll down to "Gears".

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