Machining An Existing Gear

steve45 · Dec 31, 2018

I found some change gears for my lathe so I can cut metric threads. Correct pressure angle, teeth, etc. but they are a little too thick and the bores need to be enlarged to fit, and keyways need to be cut in them.

The gears are hardened, so my question is how to proceed? Should I try to anneal them with the O-A torch, then try to re-heat treat them? (Never done it before). Is this something I should take to a professional machine shop?

Your thoughts would be appreciated!

Totallyrc · Dec 31, 2018

It all depends on how "hard" they are. If your lathe is fairly rigid, and they are not "too" hard, you can just machine them as is.

Mike.

steve45 · Dec 31, 2018

I don't have a hardness tester, but I gently tried drilling a dimple into the face of one of the gears and the drill wouldn't bite.

My lathe is an older Taiwan Enco 12x40. I don't think it would be up to cutting stuff very hard. Another concern would be cutting a keyway with a broach. Can a typical broach cut hardened steel?

gbent · Dec 31, 2018

If I were to do it, I'd anneal the center with an O/A torch. Lay wet rags around the outside so you don't retemper the teeth. Heat the center until it becomes nonmagnetic. Back off with the torch so it takes at least 10 seconds to cool about 200 degrees. Then keep cool with water around the teeth to avoid increasing the temper.

Don't trust the center hole to remachine. Use pitch pins in the teeth to pick up the center of the pitch circle. Hold the pitch pins on with a rubber band. I usually use appropriately sized drill blanks or dowel pins, and don't worry to much about the exact pitch circle.

As for thickness, I'd grind the thickness down with an angle grinder before I'd anneal the teeth.

L Vanice · Dec 31, 2018

A file is a better tool for evaluating hardness than a drill.

There is no need for change gears on a 12" lathe to be hard. The simple way to soften hardened steel gears is to temper them at around 1100 degrees F. That should assure they are soft enough to machine and tempering is easier and less likely to affect dimensional accuracy and surface finish than annealing. Professional heat treaters usually do simple stuff for cheap, and they know how to do it right. Uniform heating to the correct temperature and quick cooling are the main tricks, which would be unlikely with a torch.

Larry

RJT · Dec 31, 2018

Take it to a shop with a wire EDM, for about an hours EDM time, it will be done without changing the hardness.

HuFlungDung · Dec 31, 2018

steve45 said:
I found some change gears for my lathe so I can cut metric threads. Correct pressure angle, teeth, etc. but they are a little too thick and the bores need to be enlarged to fit, and keyways need to be cut in them.

The gears are hardened, so my question is how to proceed? Should I try to anneal them with the O-A torch, then try to re-heat treat them? (Never done it before). Is this something I should take to a professional machine shop?

Your thoughts would be appreciated!

You are extremely fortunate to have found exact replacements that fit. Does the extra width even matter? Probably easier to make shims or whatever to boost the separation or spacing of the gears that need to clear one another.

Heating the gears to 'spoil the temper' as it were, is the way to go, especially if they are case hardened. You don't have to go a full anneal to make something machinable, although some alloys are very tough to soften up because of the long transition time. I've welded shit that went hard, and no tricks with a torch would help soften it up because the parent material was always robbing too much heat off the desired area.

steve45 · Dec 31, 2018

HuFlungDung said:
You are extremely fortunate to have found exact replacements that fit. Does the extra width even matter? Probably easier to make shims or whatever to boost the separation or spacing of the gears that need to clear one another.

Yes, the round portion of the gear is too thick to allow it to mesh with the other gear. (see photo)

I like the EDM idea, I'll have to find someone that can do it. I know we have a local waterjet shop, would they be able to hold the dimensions needed with a waterjet?

EmGo · Dec 31, 2018

steve45 said:
Yes, the round portion of the gear is too thick to allow it to mesh with the other gear. (see photo)

You can cut through that with carbide even in a belt-drive South Bend, but the bore and keyseat ...

I'd just have them annealed. Won't matter to their lifespan and it will solve all your problems at one go.

mTeryk · Dec 31, 2018

steve45 said:
Yes, the round portion of the gear is too thick to allow it to mesh with the other gear. (see photo)

I like the EDM idea, I'll have to find someone that can do it. I know we have a local waterjet shop, would they be able to hold the dimensions needed with a waterjet?
View attachment 245718

steve45 said:
Yes, the round portion of the gear is too thick to allow it to mesh with the other gear. (see photo)

The idea would be to shim the gear it mate's to.

I like the EDM idea, I'll have to find someone that can do it. I know we have a local waterjet shop, would they be able to hold the dimensions needed with a waterjet?
View attachment 245718

No, you cannot waterjet a bore and keyseat.

I bet that gear isn't hardened, just black oxided. Carbide boring bar would probably get through it.

Teryk

Sent from my XT1710-02 using Tapatalk

iwananew10K · Dec 31, 2018

Not what you asked but if you give the specs( pitch,pressure angle,bore,face width,and key way I bet I can find direct fits.

Got nothing else to do and sourcing is my thing.

metalmagpie · Dec 31, 2018

steve45 said:
I know we have a local waterjet shop, would they be able to hold the dimensions needed with a waterjet?

Waterjet is only good for +/- .010 or .015". That's why the other poster said no, an opinion I agree with.

metalmagpie

dalmatiangirl61 · Dec 31, 2018

If that is an off the shelf gear with a blank bore it would only have hardened gear teeth, should be able to bore face and broach without annealing.

steve45 · Jan 1, 2019

I didn't think the waterjet would work, but I've never had any experience with one.

dalmatiangirl61 said:
If that is an off the shelf gear with a blank bore it would only have hardened gear teeth, should be able to bore face and broach without annealing.

Yes, they're off-the-shelf gears from Martin. I'll give it a shot with a carbide cutting tip.

fciron · Jan 1, 2019

I had no trouble boring and broaching a Martin gear on my south bend using cheap brazed carbide boring bar and a Dumont broach.

TedinNorfolk · Jan 1, 2019

As Larry advises,the file test is better. I've to admit,I've never come across hardened changewheels. If the file will bite,then with care they should be machinable. If you anneal and reharden(especially when they aren't actually hard)I'd expect them to not be the same shape at the finish!

steve45 · Jan 2, 2019

fciron said:
I had no trouble boring and broaching a Martin gear on my south bend using cheap brazed carbide boring bar and a Dumont broach.

Thanks, fciron! I'll give it a try.

EPAIII · Jan 2, 2019

I totally agree with annealing the center only. But as for the thickness, you may be able to get away with only reducing the area near the bore so it will fit on the existing studs. Just let the extra width of the teeth hang out there.

gbent said:
If I were to do it, I'd anneal the center with an O/A torch. Lay wet rags around the outside so you don't retemper the teeth. Heat the center until it becomes nonmagnetic. Back off with the torch so it takes at least 10 seconds to cool about 200 degrees. Then keep cool with water around the teeth to avoid increasing the temper.

Don't trust the center hole to remachine. Use pitch pins in the teeth to pick up the center of the pitch circle. Hold the pitch pins on with a rubber band. I usually use appropriately sized drill blanks or dowel pins, and don't worry to much about the exact pitch circle.

As for thickness, I'd grind the thickness down with an angle grinder before I'd anneal the teeth.

AD Design · Jan 3, 2019

As others have posted an off the shelf Martin gear with a blank bore should be soft enough to cut with HSS or carbide and broach with no trouble. If it does seem to have a hard surface it's still possible to broach if it's only a surface hardened skin by grinding the required broach area down about .03-.06 with a die grinder on both sides of the gear to get under the skin. Test for depth hardness with a file as you grind off material. When the file easily "bites" it's ready to broach. We often had to do this when a ready replacement gear/sprocket was not available and the closest relative had to be machined. As another suggested, use appropriate sized pins set in the teeth to center the pitch circle, blank bores are off sometimes. A water jet will not likely produce results you'd be happy with from my limited experience.

richard newman · Jan 3, 2019

Why not contact Martin to find out exactly what you have there?

Machining An Existing Gear

Stainless

Aluminum

Stainless

Diamond

Diamond

Titanium

Diamond

Stainless

Diamond

Hot Rolled

Diamond

Titanium

Diamond

Stainless

Stainless

Stainless

Stainless

Diamond

Stainless

Titanium

Similar threads