cutting small involute spur gears


i'm trying to figure out how to make some very small (think small servo-sized) involute spur gears. i have a taig CNC with rotary table and a sherline lathe. ...and i'm not averse to purchasing some equipment.

the smallest / most complex spur gears i'd like to make are 90 diametral pitch (120 DP would be great), and perhaps 90 or more teeth. (pressure angle is not critical to me: 20 or 14 1/2 degree PA seem pretty standard.)

i've tried to find involute gear cutters, but i can't find anything greater than 60 DP.

i'd try to find a service provider to help...but since i'll probably want to go through several iterations to find the right DP and tooth count, it would probably get expensive quickly. (plus, it'd be fun to be able to make these on my equipment at home.) ...or am i crazy to try to do this type of thing at home?

any help would be greatly appreciated...

thanks, tom

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Get yourself a copy of "Gears and Gear Cutting" by Ivan Law. (Amazon is one source.) Among other things, it will show you how to fabricate your own gear cutters for any DP and number of teeth.

Reply to
Marvin W. Klotz

I'll second Marvin's comment. The above mentioned book is very good and has all the info you need to make the desired gears. Not only that, it has theory in it explained in such a way that your average hobbiest can understand it. ERS

Reply to
Eric R Snow

I agree. I have this book and it's great.

You can also make single tooth cutters like fly cutters for cheap prototyping until you know what you want.

The CNC Taig w/4th axis will do this nicely. I hope your rotary table is cnc!

Ron Thompson On the Beautiful Florida Space Coast, right beside the Kennedy Space Center, USA

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Reply to
Ron Thompson

First, Marvin and Eric have it right. Get Ivan Law's book as your first step. After digesting the theory and the actual cutting operations, you will have to decide whether to invest in commercially available cutters, or make your own. The commercial cutters are expensive, but nice to use and may be worth the cost if you are going to make a lot of gears. If you are only going to cut a few gears, and enjoy the challenge of a real "do it yourself" approach, study Law's Chapter 12, which tells you how to make a single point form tool to use in a fly-cutter for cutting specific gears. (See his Figures 95 and


Law's method involves two heat treating operations -- one for making the "button" tool, and another for the actual form tool. I have used an alternate method, which produces the form tool directly by grinding the form tool from HSS stock in full hard condition.

If there is interest, I will write this up and post it in the drop box.

Reply to

The one coming to my mind for small gears is Hugh Sparks (haven't read him here for a long time).

Check his site for other interesting stuff.


Reply to
Nick Mueller

Before making your own, check what may be availible in the hobby world.

NorthWest Short Line makes mod 3 gears.

Howard Garner

Reply to
Howard R Garner

thanks for your (and everyone else's!) feedback - it's been very helpful. i've ordered ivan law's book and anticipate it will arrive in a week or so.

if you have time to write up your alternate method, i would greatly appreciate it. i'm sure it will help...

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