# Help with gear



## skeptonomicon (Jan 3, 2022)

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 (Jan 3, 2022)

Perhaps someone on here can make it for you.


----------



## matthewsx (Jan 3, 2022)

skeptonomicon said:


> 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 (Jan 3, 2022)

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 (Jan 4, 2022)

skeptonomicon said:


> 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 (Jan 5, 2022)

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 (Jan 5, 2022)

skeptonomicon said:


> ... 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 (Jan 5, 2022)

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 (Jan 5, 2022)

Pictures?


----------



## Bi11Hudson (Jan 6, 2022)

skeptonomicon said:


> 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.

.


----------



## ericc (Jan 6, 2022)

skeptonomicon said:


> 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.


That's not brazing!  Using a rod made for cast iron is welding.  This works completely differently from brazing.  It also requires some degree of skill.  The base metal has to be melted pretty completely.  It gets pasty under the flux, so it doesn't really drop through.  The weld region is pretty large, and I would never attempt this on a gear.  It requires a lot of heat.

Brazing is getting the metal bright red, but nowhere near melting, and melting brass over it.  At the right temperature, the brass is quite fluid and moves around pretty well compared to the cast iron welding rods.  The cast iron rods are kind of sluggish, and they end up leaving a pretty blobby deposit, which can be left or machined off.


----------



## skeptonomicon (Jan 6, 2022)

It wasn't a cast iron brazing rod, but a brass brazing rod made for brazing cast iron.


----------



## skeptonomicon (Jan 6, 2022)

Bi11Hudson said:


> 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.
> 
> ...


Thanks for the book reference, I will get a copy, and thanks for the other advice as well, I really appreciate your time in responding. The gear is a 10DP, 14.5 degree, 104 tooth gear with a .719" bore hole, .6" thick, but in its use, the thickness is not critical. I created a cad model, rewrote the involute gear code in the cad tool because it was all wrong, and laser cut a MDF gear to test fit. The MDF gear meshed well and worked when I spun everything by hand, so I have the gear parameters down pat, and I have a cad model if that is useful.

I can't figure out how to cut the gear on my lathe since the size is so large, 10.6" diameter. I can't hang a rotary table off the side far enough, and cant figure out how to raise/lower the rotary table so the the tooth cut is not deeper in the center than the outer surfaces. I would be fine cutting one of the smaller gears, but this one large gear is more of a problem. I think I just don't know enough about how to do this, and also don't have the right equipment. 

I did ask Boston for a quote on the gear, it would require a second mortgage in order to get them to look at it, and would be 4 magnitudes more accuracy than the original.


----------



## skeptonomicon (Jan 6, 2022)

Ya'll asked for pictures, The last 2 are cad models of aluminum (no spokes) or steel (with spokes).


----------



## lordbeezer (Jan 6, 2022)

I have a 10” gear but not sure of number of teeth. Might could find a manual flywheel starter ring gear of correct size


----------



## skeptonomicon (Jan 6, 2022)

I have looked, but getting the combination of pressure angle, teeth, and DP has turned up no options. There is a 104 tooth gear about the right size used on a 70s Jaguar flywheel, but I can't verify the pressure angle or DP. That is as close as I have found.


----------



## matthewsx (Jan 6, 2022)

Sounds like you need another machine tool

John


----------



## ericc (Jan 7, 2022)

Oh wow, those are informative pictures.  That must be pretty tough cast iron.  I would have expected to see a lot more flux.  The brazing flux is really tenacious when it flows in and requires a lot of chipping or grinding to get it off.  It won't fall off by itself or get removed with a wire brush.  It almost looks like not enough heat and flux.  Experts use just enough flux.  I use an excess and it gets all over the place.  Usually, I'll just play the torch over the metal and warm it up.  Then, touch a rod dipped in flux occasionally to the heated spot.  Don't melt the rod.  Eventually, the flux will start flowing and more can be added.  It helps conduct heat around too, so the joint stays at a more even temperature.  Good flux should wet in at a decent red heat.  Brass won't melt until bright orange.  The cast iron is not in danger until yellow.


----------



## skeptonomicon (Jan 8, 2022)

I had the gear cherry red. It would not melt the rod unless it was real hot. I might try this again with new flux/rod. Any recommendations for specific products??


----------



## skeptonomicon (Jan 8, 2022)

Everyone on this thread has been so helpful. I had an idea, and wanted to get an opinion if it sounds good. All the change gear ratios either use this gear paired and locked to a 52 tooth gear, or use just the 104 tooth gear. The ratios in the gear chart below that have a black for the "stud" gear use the 104 tooth gear only, and it engages both the spindle and screw gear. Thus the 104 tooth gear is used to either have a gear ratio of 1 when alone or 1/2 when paired with the 52 tooth gear. I am thinking that replacing both gears with a 100/50 tooth pair would preserve the ratios. 100 and 50 tooth gears are catalog items, whereas the 104 tooth is not. Does this sound reasonable???

The pictures below show the gear ratio chart and a typical usage with my mock up wooden gear. The spindle on top, the stud gear as shown is in divide by 2 configuration with the 104(wooden) gear and the 52 behind it. woodruff keys on the bushing lock the 104 to the 52.  On the bottom right, I think is a 48 tooth on the screw, for a 24 TPI ratio.

View attachment 391373


----------



## brino (Jan 8, 2022)

@skeptonomicon

Oooops, no photo of the change gear chart; but we may not need it.....

Yeah, good thinking!
That sounds like the best path forward.

The diameters of the 100/50 should be so close to the 104/52 that you should have enough banjo/quadrant/bracket movement to accommodate them. It might be worth cutting out some simple cardboard discs (no teeth required) of the same size and verify with a test fit. Just so there are no surprises; like interference somewhere else.

Brian


----------



## ericc (Jan 8, 2022)

skeptonomicon said:


> I had the gear cherry red. It would not melt the rod unless it was real hot. I might try this again with new flux/rod. Any recommendations for specific products??


What I use probably doesn't mean much to you.  My favorite flux for this application is Marvel No. 162 welding and brazing flux made by the Air Reduction company.  There probably isn't a store that carries it, since it is a very old product.  It is probably similar to Harris 600.  These are high temperature fluxes suitable for brazing and welding cast iron, and they contain fluorides.

Depending on what you call "cherry red", it may not be hot enough.  A lot of curmudgeon blacksmiths say that old time cherries were more orange like carrots.  Have you practiced on junk cast iron?  Recently, a lot of cast iron drain covers have been shattering, and the little pieces get strewn all over the road.  This is very good for practice, and I've made welding rods and replacement gear teeth out of the chunks.


----------

