Gear Project

I want to undertake a gear making project for practice if not nothing else. I figure I'll try something I'll likely need in the future.
I have a Star Wars game that uses a yoke controller that has gears inside the housing:
http://i290.photobucket.com/albums/ll257/Statenislander/Joystick%20Projects/StarWars.jpg
http://i290.photobucket.com/albums/ll257/Statenislander/Joystick%20Projects/StarWarsYoke.jpg
http://i290.photobucket.com/albums/ll257/Statenislander/Joystick%20Projects/StarWarsYoke2.jpg
http://i290.photobucket.com/albums/ll257/Statenislander/Joystick%20Projects/StarWarsYokeKit.jpg
I'd like to reproduce the spur gears inside the yoke, but make them better if that is possible.
They are about 11/16", 1-1/4" and 2-9/16" respectively.
So I'm curious as to what would be the absolute best material to make these gears out of if the goal was that they last as long as possible, as well as any tips in making them. (The original ones were some sort of plastic and someone did make reproductions out of Delrin).
Thanks.
Darren Harris Staten Island, New York.
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get a cheap book, "Gears and gear cutting" by Ivan Law.
Delrin sounds like a good choice here. or maybe move up to brass which is veryeasy to machine for this project.
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On 11/16/2012 4:23 AM, Karl Townsend wrote:

the headlights of my corvette have a plastic (delrin?) gear that is known for turning to dust in about 10 years or so. the replacement ones available are brass. i'd agree with karl about this.
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Ok, so making the gears out of brass is a *step-up* from Delrin. (I'm assuming that that's the best I can do on a mini-lathe).
I do already have the book "Gears and gear cutting" by Ivan Law.
Thanks a lot.
Darren Harris Staten Island, New York.
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    [ ... ]

    Do you have a milling machine as well? And an index head? Otherwise, how do you plan to cut the teeth? I feel it unlikely for you to have a hobbing machine -- those are typically large, heavy, and rare.

    A good start.
    Good Luck,         DoN.
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Oops! Yes I have an HF Mini-Mill. :-) (Along with a rotary table).

But all I have is an over sized spin index fixture. (www.ebay.com/itm/
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On Fri, 16 Nov 2012 22:41:39 -0800 (PST), Searcher7

Can you machine a 28 tooth gear with that thing. 360/28.857 degrees?
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John B.
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On 11/17/2012 1:41 AM, Searcher7 wrote:

I had to cut a one-off steering gear for my tractor when the original was no longer available.
I made a really simple fixture, it was basically an angle plate that the gear blank mounted to and a dowel pin. I cut a tooth, repositioned the blank so the dowel pin was locating the tooth, and repeated.
MikeB
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That's a very good idea for a sector gear but not for a full one, as the spacing error accumulates and the tooth width between the first and last cuts is unlikely to be acceptable.
Long ago master index plates were generated a similar way, by stepping around the circle with dividers and attempting to adjust out the closure error.
Cutting a steering sector: https://picasaweb.google.com/KB1DAL/HomeMadeMachines#5285710360947850418 https://picasaweb.google.com/KB1DAL/HomeMadeMachines#5285710370886636434 https://picasaweb.google.com/KB1DAL/HomeMadeMachines#5286421964003279458
jsw
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On Fri, 16 Nov 2012 22:41:39 -0800 (PST), Searcher7

Brass or bronze running against Delrin or aluminum will work fine. Common bearing bronze is not much harder to machine than brass so use what you want. Since you have Ivan Law's book you know how to grind a fly cutter to the proper shape. Does your rotary table have index plates? If not then maybe you should make at least one for cutting the gears. Eric
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    [ ... ]

    [ ... ]

    O.K. Does the rotary table have a hole plate and arm with sector arms? If not, it will be tricky for some of the gears. 60 tooh is no problem. 16 tooth (if I am right about that gear), also no problem. But the 26 tooth (or was it 28?) will be tricky. For each cut you need to advance it:
26    13.8462 degrees (13 degrees 50 minutes 46 seconds) 28    12.8571 degrees (12 degrees 51 minutes 26 seconds)
    With the right hole plate, and the arm and sector arms, it is easy to set it up to avoid problems. And that is what an index head has.

    The rotary table is a far better choice than this. The finest rotation you can accomplish with the spin indexer is 1 degree. And even for the 16 tooth gear, you need 22.500 degrees -- that half a degree you can't get on the spin indexer. (Yes, it would work with the 60 tooth gear, which only requires 6 degrees advance for each tooth. Still a little tricky to calculate the position of the pin for each one.
    Good Luck,         DoN.
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g
Oops! I forgot not to give approximate numbers. :-) 60 tooth = 2.575" 28 tooth = 1.245" 14 tooth = 0.655

These reproduction gears I measured are made of Delrin. But I can't attest to the degree of quality control. So I'd just as well start from scratch as long as the number of teeth are correct for each gear.

Thanks. Here are some pics of the 60 tooth gear:
http://i290.photobucket.com/albums/ll257/Statenislander/Joystick%20Projects /60Tb.jpg http://i290.photobucket.com/albums/ll257/Statenislander/Joystick%20Projects /60Ta.jpg http://i290.photobucket.com/albums/ll257/Statenislander/Joystick%20Projects /60Tc.jpg

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As far as "hole plate and arm with sector arms". I have a rotary table with dividing plates that I haven't used yet. In fact, this one: www.ebay.com/itm/321022783132.
Thanks a lot.
Darren Harris Staten Island, New York.
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That little table will be perfect with the dividing plates to make your little gears. Please post photos of your finished work. Eric
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    [ ... ]

    Not 16-tooth, O.K.
    O.K. A little different from my calculations. It sounds as though the crest of the teeth has been shaved a little, No problem as long as the pitch diameter is correct.

    [ ... ]

http://i290.photobucket.com/albums/ll257/Statenislander/Joystick%20Projects/60Tb.jpg

http://i290.photobucket.com/albums/ll257/Statenislander/Joystick%20Projects/60Ta.jpg

http://i290.photobucket.com/albums/ll257/Statenislander/Joystick%20Projects/60Tc.jpg
    O.K. But we knew the count of teeth there. It was the smaller ones which I was wondering about -- and you have now told met hat the smallest one was 14 teeth, not 16, so my calculation for size was wrong.

    O.K. That should do it. Did it come with a table of settings for different divisions? If not, you will need to know how many turns of the crank for a full turn of the table. Common ratios are 90:1 (larger rotary tables, at least), 40:1 (my dividing head), and I believe 10:1 on some heads.
    Good luck,         DoN.
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I haven't dug out my manual but an internet search says 90:1 http://www.t4i.com.au/R006
The most difficult part will be the gear cutter. (So I'm off to do my reading).
Thanks a lot.
Darren Harris Staten Island, New York.
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On Tue, 20 Nov 2012 16:50:00 -0800 (PST), Searcher7

The gear cutter will be easy. You can make the button cutter as outlined in Law's book and then use that cutter to make a fly cutter to cut the teeth. You can use water hardening or oil hardening tool steel. Both are easily available and pretty easy to machine. And heat treating with a propane torch will work. For that matter, since the cutters are so small, you could use a gas stove or even an electric burner. Eric
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    [ ... ]

    O.K. That will be 1-1/2 turns per tooth for the 60-tooth one, Easy to set up with any circle of holes with an even number of holes.
    The 20 tooth one is 0.2222 turns per tooth, or 1/4.5, so any circle with a multiple of 9 holes (likely 18 holes) will do. (The chart I found later does it a different way.)
    As for the 14 tooth one -- that is 0.1556 turns per tooth, I can't come up with an easy one for that -- check the dividing tables which should have come with our table. If not -- go into _Machinery's Handbook_ and see if they have the tables for the 90:1 ratio.
    O.K. Here is a site where you can download the table (and instructions for a similar rotary table).
    http://www.minitech.com.au/images/PDFs/Rotary%20Table%20Guide.PDF
    And looking at that -- it is doing 6 full turns plus 9 holes on a 21-hole circle. Interesting approach. That is over 24 degrees per tooth, so you eventually come around to complete the set with some number of trips around the gear.

    Once you find the pressure angle, you have the choice of making your own cutter for each gear, or buying cutters for each gear. (yes, a separate one for each of those three gears. A set of cutters consists of eight total -- each covering a range of teeth. The last of them covers something like 100 to infinity (I would have to look it up), The first of them has a range of only three different adjacent tooth counts IIRC. The shape of the cutter has to be a little different for each number of teeth. You can sometimes find 1/2 numbered cutters to fill in the gaps and make a better fitting gear. There is a remote possibility that your 14 and 20 tooth gears will use the same cutter, but I don't think so. The tooth count is fairly small, so they probably don't span the same cutter.
    Good Luck,         DoN.
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That is a good, simple explanation of the math. If you have trouble with mixed fractions and know how to set up a spreadsheet you can use one to create a table of all the full and fractional turns from say 2 to 100 divisions. The low numbers are useful for cutting wrench flats etc. In OpenOfficeCalc the format code is # ??/??. jsw
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Thanks a lot.

Darren Harris
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I would not look for the absolute best material for wear resistance. Anything that is real wear resistant will be a pain to machine. Better to make ten sets of gears out of something that is easy to machine than one set out of a material that has to be ground because it is very hard.
Dan
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