Gear cutting question.

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mcostello

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I bought the Wife a battery powered chainsaw for Christmas. She loves it. ;)
The drive pinion broke the teeth off. I tried to buy a new gear and no spare parts are made for this model. About 4 months old. I would like to cut a gear and have never done one yet. The dimensions are .748 OD X 17 teeth. Can Some one help with the math that I need. I am assuming it would be Module instead of Imperial as seems everything is not made in the West anymore.
 
1 Module is correct
Gear.jpg
 
What is the material the original gear is made from? Do you have similar or better material available? What tools do you have that would let you make the gear?
 
The original material is pressed power metal. I have all the normal machine shop tools. Full size mill and lathe. Dro's, rotary table, and indexing table. And enough ideas to get something to work.Spline bushing 2.jpg I made this on a metal shaper.
 
Any chance one of the gears available on amazon with search terms "17 tooth module 1 gear" would work or could be modified to work?

Make or buy a gear cutter. Only cutters I found in module one were all PA20 or horological cutters (wrong tooth and space forms). Making a cutter is a fair bit of work as you are cutting steel, so a fly cutter isn't likely to work, although if you approximate the teeth with a slitting saw a fly cutter MAY work to refine the tooth flanks. I did this sort of silliness when restoring clocks as very old clock gearing rarely matches up to current cutter tooth forms.

You might double check the PA of 14.5 is correct, it's pretty rare in any modern application. PA20 is all over the place, 14.5 is just about unobtanium on the tooling and prefab gear side. Even AliExpress doesn't list M1 PA14.5 cutters. They do however have a LOT of m1 17t gears listed, perhaps your part is a standard industrial item in China and you can make the problem go away for just a few dollars. Aliexpress gear cutters seem to run around $20 or less for a single piece. If you do buy a cutter you'll need an arbor and to do some fiddling to get all set up, but you likely have been though all that in your head already.

Sort of like screw cutting for some folks, the whole gear cutting thing has gotten this mystique. If I said please cut 17 through slots on the periphery of this cylinder with a width of X and a depth of Y, you wouldn't consider that a hard job, just one that might be a pain if you need a slitting saw of a different thickness than is on hand. It would probably take longer deciding what to charge than it would to figure out how to do the work. Replace the slitting saw with a gear cutter and repeat the exercise. Congratulations, you're in the gear business. A gear form can be approximated with an end mill and then refined, even on a manual mill although it's a darn sight easier on a CNC machine as you can use ball end mills and do many passes without going bonkers keeping track of it all.

Why the gear failed seems worth asking. Some cordless tools do not leave much room for overstress. A dull chain, continuing to use the tool as the battery gets weak, a pinched and stuck bar, or just trying to tackle too large a branch or limb could cause lighter examples of cordless saws to fail. I love cordless tools for outdoor work, love the no gas and oil or dragging cord behind me, low noise, no stink, but when it's time to dice up something big out come the larger gas powered tools. My neighbor works his Rigid brand cordless tools from Home Depot pretty hard and they hold up, my Ryobi and Milwaukee cordless stuff has been really solid too. Doing it again in todays world sourced market I wouldn't spend the premium for Milwaukee, I'd be doing the Ryobi One series for most stuff and their 40 or higher volt stuff for outdoor equipment that expects hard use. Just takes a while to get used to having Zombie Green tools laying around :) My neighbor uses a cordless demolition style saw with long blades for almost all of his heavier pruning needs rather than one of his chainsaws.

Cheers,
Stan
 
If...If the gear you are looking for really has a pressure angle of 14.5 and no cutters are readily available, why not get a 20 degree pressure angle and cut both gears so they match. It won't take a lot longer to cut 2 gears, less time than ordering a 14.5 pressure angle cutter.
 
Did not say what PA it was,as it slipped My mind when I posted it. As an interesting note, I looked all over to source a gear with no success. Sunday night I just happened upon a model racing track part company. They stock the gears with a shoulder that easily be removed for $8 apeice. I am busy and cannot take time right now to do some up. I don't know the PA of the mating gear. I really wanted to make a gear but not right now. Thanks all for the information, it is saved for the future.
 
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