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Thread: Newbie gear question

  1. #1
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    Default Newbie gear question

    Had a buddy bring a gear to me he would like copied. I understand the hows and whys of gear cutting. Have all proper tooling except for the cutter. My question is how do I measure an existing gear to get the correct cutter. Is there a formula or way to measure an existing gear to find the pressure angle and the pitch, etc, so I can order the correct cutter.

    Thanks in advance
    Rich

  2. #2
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    Default

    I don't know of any way to determine the pressure angle easily. Maybe somebody else does.

    You can calculate the diametral pitch (assuming it is not metric module) by counting the number of teeth, adding 2, and dividing by the o.d. in inches. Things being what they are, it won't come out exactly even, but if you get something like 16.06 or 15.92, you can probably assume it's 16 diametral pitch.
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  3. #3
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    Don't suppose you could beg,buy, borrow, or... (sorry, I on't want to encouragfe theft ;o) ) a gear tooth profile gage? I snagged a plastic Martin gear tooth profile gage from a gear supplier in Vancouver when I bought a small pinion and a length of rack for a project several years ago (like 20+ ).

  4. #4
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    I would think many gear suppliers would sell tooth gages or tell where to get them. I too have a thin plastic gage. Don't you have to use several cutters to do a gear? The few gears I cut at work was done by selecting a cutter off the wall of hundreds of them that matched the tooth profile and was cut with that one cutter. It always seemed to work but I always thought it was really done with more than one cutter.
    It's only ink and paper

  5. #5
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    a gear tooth gage set which measures only 14 1/2* is available from MSC for about $50. Boston gear makes a dual pitch set, and runs in the $100.00 range, think Mc Master may have this.
    gvasale

  6. #6
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    Quote Originally Posted by rjazz
    Had a buddy bring a gear to me he would like copied. I understand the hows and whys of gear cutting. Have all proper tooling except for the cutter. My question is how do I measure an existing gear to get the correct cutter. Is there a formula or way to measure an existing gear to find the pressure angle and the pitch, etc, so I can order the correct cutter.

    Thanks in advance
    Rich
    put engineers blue on it ..press it on a piece of card ..and send it to one of the guys here who have the devices for measuring.

    or scan the card ..put the diameter on the card and post pic here .

    all the best.markj

  7. #7
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    Quote Originally Posted by Carld
    I would think many gear suppliers would sell tooth gages or tell where to get them. I too have a thin plastic gage. Don't you have to use several cutters to do a gear? The few gears I cut at work was done by selecting a cutter off the wall of hundreds of them that matched the tooth profile and was cut with that one cutter. It always seemed to work but I always thought it was really done with more than one cutter.
    Several cutters for the same gear? umm, no... At most two, one to remove the bulk of material and one to the exact profile... If you don't want to cut the whole profile in a single setup and if you're not profile milling.

    Cutters for milling come in sets each one suitable for approximating the profile of a certain range for gears. Hob's will cut any # of teeth with a single cutter, but require sophisicated setups or dedicated machinery.

  8. #8
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    Aug 2002
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    Of course I guess you are talking about a spur gear. Depending on the pressure angle, size and whether or not it is a metric gear you might want to check on just buying the gear from Boston Gear as opposed to buying a gear cutter. It is difficult to rationalize the cost of buying a gear cutter to make one gear The purchased gear would also be more accurately made. I say all this because I had to have debate with myself about whether it made sense to go to the expense of buying two gear cutters at $30 a piece plus an arbor for the gear cutter in order to make two small gears (which I could have purchased for $50) for a model engine I was building. I did actually buy the gear cutters, but I am not so sure I would do that again.

  9. #9
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    Default Devil's advocate or an alternate method....

    Quote Originally Posted by rjazz
    Had a buddy bring a gear to me he would like copied. I understand the hows and whys of gear cutting. Have all proper tooling except for the cutter. My question is how do I measure an existing gear to get the correct cutter. Is there a formula or way to measure an existing gear to find the pressure angle and the pitch, etc, so I can order the correct cutter.

    Thanks in advance
    Rich
    Ummm, unless this is for a critical application, a hand ground profile cutter can be made to fit a flycutter that will make serviceable gears for some applications. And you have the old gear in hand right? Gashing with a slitting saw will make the whole process more manageable.... I made some steel change gears for a lathe that way. After all, as has been thrashed to death around this site before, all gear cutters including hobs are approximations. How close an approximation is necessary is determined by application, the tools available, and the machinist's choices.
    Last edited by camdigger; 08-12-2009 at 02:53 PM.

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