asking for advice on making gears

gbent · Jan 28, 2007

I am going to make a set of metric change gears for my 15" Leblond. I am looking for advice about cutting gears using an involute cutter and a dividing head. The machine work is no big deal, but I am looking for tips, hints, or cautions about gears that don't show up in books.

The gears are 14DP, 14 1/2 pressure angle. I have a photo of the threading chart LeBlond used on an inch/metric the same as mine. My lathe uses a 120 tooth idler now, so my metric change will be a 127/120 compound. I have the #3 cutter, I still have to find the #2.

matt_isserstedt · Jan 28, 2007

Gbent, be very particular about the ID and OD of the gear blank being concentric and to diameter within .001".

The Whole Depth of the tooth is usually referenced from the OD of the blank.

CHIPMASTER BILL · Jan 28, 2007

Travers Tool has the singel tooth gear cutters i usually bought 2 at a time one to rough with then finish with the other. If you are cutting steel go slow in rpm and feed plenty of coolant, if you are doing nylon or something like that go faster but not so fast that the nylon melts. Make sure the math is correct with the OD of the blank center the cutter over the blank and go to town on it. I have done many gears this way never a problem.
Chipmaster Bill

Hammer n Chisel · Jan 28, 2007

How are you going to heat treat them?

Unless you have a gear hobbing machine - they are't going to be right.

You are better off to PAY some company to make you a set or BUY a set off a reputable dealer.

Here is a link that will confirm what I just said.

http://en.wikipedia.org/wiki/Involute_gear

Hammer n Chisel · Jan 28, 2007

Here is what a real gear hobbing machine looks like and a buisness that can do the job.

http://www.femcomachine.com/gears.html

Peter from Holland · Jan 28, 2007

Hammer n Chisel
Heat treat for change gears????

Make the big ones out of cast iron and the smaller ones out of c45 In general the smaller gear is of a better material as the bigger one. 2 different materials wear less

matt_isserstedt · Jan 28, 2007

Hammer, I disagree with the statement about "if it ain't hobbed it's crap". [Also wiki didn't present a very compelling technical argument either]

As long as the user is particular about indexing, uses the correct cutter, the gear will come out perfectly serviceable. Yes it takes considerably longer than hobbing but that's part of the tradeoff.

We could also say that if they aren't shaved and then ground they aren't worth a hoot either. Few of us here have the cubic dollars required for high-end prototype gears, and the end-gearing on a lathe sure isn't a critical application in my book.

[Atlas used die-cast non-ferrous Zamak end-gears on their lathe that still work perfectly well 50 years later if lube has been maintained]

Cast iron is one of the most perfect "wearing" materials there is, and gears are an excellent place for it if uber-strength is not required.

mobile_bob · Jan 28, 2007

just curious

has anyone had a gear laser cut?

our local steel supplier has two lasers, and cuts gears for those that are no longer available
and can hold .001 tolerance with very good finish.

just wondered
bob g

matt_isserstedt · Jan 28, 2007

Mobile Bob, I saw some change gears for metric (same subject as this) which were wire EDM'd over on the Monarch forum and they looked impressive.

Limy Sami · Jan 28, 2007

Mobile Bob, a few thoughts on your question, based on my experince.

1 Cast iron and steel would be fine, in fact CI on CI, is good too.

2 Acuracy acuracy acuracy etc, you get the message.

3 127 can be a right SOB to get on some dividing heads, been there, done that.

4 Think about making a batch up, I know you're well behind us on the metric thing (no dig intended) but I don't think you'll have the extras long, as even if they were available from the manufacturers, they'll be really pricey.

5 Check out your gearbox and train data very carefully, there may be extra oddball no's to get some pitches,.......... then there's the DP and Module sets as well? yeah I can here the groans now, take care Sami.

deere_x475guy · Jan 28, 2007

gbent I have been cutting some gears lately just like you are planning on. As Matt stated be sure to have the correct ID and OD that you need. Also the be very particular when setting up the dividing head on your mill. Everything needs to be square to the mill. Also your cutter needs to be centered to the dividing head. Here is how I set centered it.

Here is the blank ready to cut.

Here are three gears pin to a test bar to check mesh. The came out great.

You should be able to cut those gear with no problem. I would first cut them with a slitting saw to cut the major part of the tooth out. Then go back with the cutter. They aren't cheap.

johnoder · Jan 28, 2007

Hammer n Chisel

The end gears on my 1920 24" Lodge & Shipley were abused most every day for over eighty years. They are soft steel. They'll be just fine.

John

stroker · Jan 29, 2007

gbent
I'd be approaching a wire cut man. If he's running Mastercam there's a link to create the program - sorry I can't remember the keystrokes get there though - can any Mastercam users help?

JST · Jan 29, 2007

Don't even bother listening to the nay-sayers on this one.

These are freakin spur gears.... no big deal, they ain't in your tranny.

Key issues are:

Right diameter of blank

right cutter

right depth of cut

Making sure the blank is dead square to the cutter and bore is parallel to the table movement.

Correct count of divider holes!

I prefer to gash the teeth first, to reduce wear on teh cutter.

I can cut gears that work well, and I'm no machinist.... I'd probl'y be fired in 3 hours at most shops, and laughed out of the rest.

But I can cut good gears. Spur gears, even bevel gears. I've cut them on the mill and with a shaper. They all worked.

If you wanted to buy them, I wouldn't think less of you. But if you want to cut them, go for it.

Chris Figgatt · Jan 29, 2007

Spur gears can be made very accurately on a horizontal mill with a dividing head, or on a shaper with a dividing head. Really, you only need a hob when making helical gears; however, if you have a universal horizontal mill with a geared dividing head, helical gears can be made as well. While heat treating your gears would be ideal, you can get away without it if your gears will see limited use. Where I work, we have hobbed helical gears and EDM'ed spur gears from 4140 for gearboxes on production milling and turning machines all without any additional heat treatment. Although not the ideal way to produce these gears, it's what we had to do to get them up and running.

stroker · Jan 29, 2007

gbent
Hit Alt+c when in Mastercam and choose Gear.dll
Mike

toastydeath · Jan 29, 2007

I've seen setups that use a single cutter for helical gears on horizontal milling machines. They use a universal dividing head, tilt the table to the correct pitch angle, and link the dividing head to the table's leadscrew with a geartrain (also set to produce the correct pitch). Same process - rough out with a slitting saw, and then finish up with the cutter.

My understanding regarding the advantage to hobbing is that hobbing generates an involute gear profile with whatever pressure angle that has been cut into the hobber. The hobbing cutter itself is not involute, it just generates that profile. If you've got a talented toolmaker on hand, this allows you to come up with whatever profile fits your needs. It's far easier to generate a straight angle tooth on the hobber, which creates a very accurate involute, versus using a pre-formed cutter with whatever error in the involute profile the cutter has.

rjibosh · Jan 29, 2007

gbent,

As someone said above you will have a difficult time finding a dividing plate to cut the 127 spaces. 127 is a prime number and there is no way to get to it from a wheel with less divisions and the smallest number of dividions over 127 would be 254. Your best bet is to rig up another 127 to your setup and use it to index.

Also, a 14DP 127 will have an OD of about 9.25 and most likely an id of under 1". This could be a very springy set up if you use a mandrel with out a healthy shoulder and accurately made (flat and substantial) back up plates on both sides.

Rick

JST · Jan 29, 2007

Oh... making a 127 tooth.... that could be different. I missed that the first time thru.

I think I did once see a scheme for doing gears of larger numbers than you can directly divide where you indexed a number of teeth ahead, a number that you COULD evenly divide to. Each time around you filled in more teeth, until it was done. A lot more cranking than normal, for sure.

It sounds reasonable, but it may not work on a prime number. I've never tried to figure that method out for any gear, let alone a 127 tooth.

That 127 tooth gear might be a candidate for checkbook machining, unless you can wait for it, or are just plain determined to make it.

But as far as the mechanics of makuing gears, it's actually surprisingly easy to do it.

usmachine · Jan 29, 2007

Wire edm is a good choice. I had a 48DP pinion gear cut for a Brown & Sharpe OD grinder fine feed out of a piece of 2" thick D2 in about 45 minutes using the mastercam that stroker mentioned.

Then we had it checked for error by a guy who grinds gears for cruise missle engines and even he was impressed at how accurate it was.

Good luck, Doug

asking for advice on making gears

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