Help with gear

[skeptonomicon]

i had a gear break on my antique lathe. It is the main gear, a 10.6" 104 tooth DP 10 gear. It was cast iron. I have DXF or STL files for the gear. This is an antique lathe, so all the gears are fairly rough. I don't have the equipment to cut a replacement. I am thinking about replacing with aluminum or steel. I have talked to a few professional shops that want an arm and a leg (more than my entire lathe cost) to make a precision gear that is way more than I need. Are there any less expensive options?

 

[Brento]

Perhaps someone on here can make it for you.

 

[matthewsx]

i had a gear break on my antique lathe. It is the main gear, a 10.6" 104 tooth DP 10 gear. It was cast iron. I have DXF or STL files for the gear. This is an antique lathe, so all the gears are fairly rough. I don't have the equipment to cut a replacement. I am thinking about replacing with aluminum or steel. I have talked to a few professional shops that want an arm and a leg (more than my entire lathe cost) to make a precision gear that is way more than I need. Are there any less expensive options?

Have you looked for one on eBay?

Alternatively McMaster-Carr has a pretty good selection. Boston Gear has almost anything else.

John

 

[benmychree]

If it were mine, I would make a pattern for a new cast iron gear, have it cast and machine it to match the original, or perhaps braze it up where broken and re machine to suit.

 

[Bi11Hudson]

gear break on my antique lathe.

So the first point to consider is if the machine is a "working machine" that can be kept running by any means necessary or an antique that is to be kept original as possible. To answer in reverse order, a real "antique" would require casting a blank or finding an exact replacement. For that, more information is required. Further, the nature of the break is a salient point. Can it be repaired? Some repairs are timeless in that they are as old, or older, than the machine itself.

Then there is the matter of the former question. Making a gear is not really a big deal. Though the nature of the break is still a matter of import. There are many methods to repair/replace a gear, some will be "rougher" than others. If a few teeth are stripped off, they can be be brazed up and fitted by hand. If it is shattered, a replacement would need to be built from scratch.

Then there is the matter of material. There are cases where cast iron is better than steel. And others where the opposite is true. The "main" gear could be assumed to be the back gears on the spindle. Aluminium would not be a good replacement here, and plastic is out of the question. Many repairs can be accomplished with the lathe alone, again knowing "which" gear and how badly it is damaged. We literally need more information. . .

.

 

[skeptonomicon]

Thanks for the comments. This is a working lathe, and will remain so while in my possession so I am looking for a functional gear. The gear is part of the screw cutting gears. It is I think used in all the ratios, and also involved in the feed screw, so it effects the cradle and cross slide feed. It is shattered, 4 prices total. I already tried brazing it but could not get the brazing to flow without over heating the cast iron. It could be tig welded perhaps, but being cast iron, it would take a real expert.

 

[ericc]

... I already tried brazing it but could not get the brazing to flow without over heating the cast iron. It could be tig welded perhaps, but being cast iron, it would take a real expert.

Interesting. Exactly what are you doing to braze the gear? I have found that it is much easier to torch braze tricky cast iron than it is to tig weld or braze it. There is something funny about the oxy-fuel flame that just makes it seem stickier. I have had success on challenging cast iron by grinding a shallow vee with some barely touched areas for tacks. This allows the cast iron to be fit together precisely along the fracture. Then tack with tig and inconel or super missile rod or something similar with nickel in it. These tacks will be small, so it is no big deal if they are not machinable. They can be ground off anyway. Then, hit it with an oxidizing flame which burns the graphite out. Use good brazing flux, the kind with the fluoride in it, not borax. Most of the time borax works fine, but not on the tricky stuff. Dip the heated low fuming bronze (actually brass) in the flux and it should wet in. I guess you could try on a small area to see if it works first.

 

[skeptonomicon]

I cut a vee one half way through from the top so the backside would mate perfectly, then made a special clamping arrangement that held it all in place. I preheated with oxy acetylene, then got it cherry red, used a rod made for cast iron, dipped it into flux and the rod either pooled or ran off. I could not find a happy medium where it would stick and puddle. I got some to stick but it did not fill the vee. I am clearly just not experienced enough to pull the brazing off. Also I suspect I could use better rod/flux. I also do not have a tig setup, only mig, so I didn't even try tacking it with the welder.

 

[matthewsx]

Pictures?

 

[Bi11Hudson]

is a working lathe, and will remain so while in my possession so I am looking for a functional gear. The gear is part of the screw cutting gears. It is I think used in all the ratios, and also involved in the feed screw, so it effects the cradle and cross slide feed.

Both responses simplify matters a great deal. As a functional gear, appearance doesn't matter, and being in the carriage drive train can be brass, aluminium, or even plastic. As for the original, busted like that it likely won't be recoverable. A real old time machinist might be able to repair the gear, when he was so drunk he couldn't walk. Maybe. . . But an amateur wouldn't be able to restore a usable gear. Stick the pieces together, sure. Even I could do that. But to line up everything where the teeth would be usable, not very likely.

You will want to reassemble the gear enough to determine the details. Nothing accurately, just enough to get bore diameter, overall diameter, tooth count and pitch, thickness at the bore and at the rim. Being a change gear, likely is consistant thickness. But be sure. Once the details are noted, keep the pieces to chunk at a 'possum or a 'coon. Bore diameter and pitch can be determined from another intact gear in the train. The bottom line here is that once these are known, there are innumerable ways to deal with a replacement.

Simplist is to go to a vendor, such as Boston Gear, to get another gear. They might not have the thickness you need, change gears are usually thin and "flat". Running gears will have a wider rim (teeth) and hub and need to be faced down. If you have access to a 3D printer, make one. Or get a friend to. A gear can be cut on a lathe. It takes a little tinkering to get all the misc pieces together, but doesn't require the lead screw to run. A gear cutter is the most optimal but can be done with a lathe tool ground to the proper profile. You have the broken gear as a pattern, just grind a tool to match.

Change gears can be thought of as "timing gears", there is little torque involved. Just enough to turn the lead screw. Aluminium makes a good choice here, my Atlas built machine uses ZAMAK, a zinc and aluminium alloy, for change gears. I also have an Asian machine that has cast iron(?) gears. There are many users here that have 3D printed change gears. The plastic holds up quite well in such a low torque use.

Gear pitch will be dependent on the lathe. My Craftsman/Atlas has 16DP gears. The Asian machine uses Modulus 1 (25.4 DP). When and where your machine was built will determine the pitch. American machines use both systems, DP being the most common. Asian and European also use both with Modulus being the most common. A lathe is often refered to as the "queen" of machine tools. With the appropriate knowledge, it can build itself. Repairing itself is a derivitive of that. Everything (literally all) you would need to know is in "Machinery's Handbook". A recent copy is a little overbearing with all the leading edge technology they have. The ones from around WW2 to about 1960 are the most useful to the amateur. Less sorting out of hi-tech stuff to go through. The end result is that you are looking at time and knowledge being the only limiting factors. The actual gear is a piece of cake.

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