Old Myford lathe LA 232 circa 1935

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Old Myford lathe LA 232 circa 1935

This topic has 8 replies, 6 voices, and was last updated 12 December 2023 at 20:07 by Mike Hobden.

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8 December 2023 at 20:47 #698279
Mike Hobden
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@mikehobden70671
It’s an old m/c with all the faults, problems, wear and dings you would expect from nearly 90 years of use and abuse.

But it still works! Also I’ve managed to collect a full set of change wheels and quite a few odd ones besides. It’s versality despite all it’s faults is amazing.

My latest addition is a skewed worm wheel to engage on any change wheel from about 60T to 125T mounted on the rear end of the headstock. So far I’ve used it to engrave handwheels of 100 divisions with a 100T wheel (1/1,000 of a revolution per division, could easily be 1/10,000 via a vernier) and 150 divisions for another smallet old lathe I’m working on that I’ve upgraded to metric using M10 x1. 5mm stainless studding for feed screws. Numbers are typed in with punches held in jig. Slow but it works.

Problem: I’ve a 90T wheel I obtained cheaply as it has 4 broken teeth that have been badly repaired. Can file it all out dovetail, and silver solder a piece of mehanite in to replace the teeth.

Q: how accurate would it be to recut the teeth by copying the existing profile on the good teeth by filing a piece of gauge plate and using this to (effectively) progressively bludgeon the new teeth? Straight plunge or cobble up a flycutter. and either way use the slide and cross feed. (Have cut key ways like this but it’s a bit hairy plunge cutting)

I do have an old camera lens that I’ve previously used as a shadowgraph. A 50mm lens gives 10x mag at 0.5m so can get the shape reasonably close. It’s the lining up with the existing teeth that’s the real headache. Getting to the stage of over thinking things.

Anyway, thanks for reading!
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8 December 2023 at 23:18 #698298
Ady1
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@ady1
Sounds fine, a 1935 repair for a 1935 lathe

If the current “repair” is solid then it might be easier to tidy it up with solder, a picture would give the guys a better idea

well done you
9 December 2023 at 09:27 #698316
Brian Wood
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@brianwood45127
Hello Mike,

I think you could make a sufficiently accurate gauge for the missing teeth by casting lead into a dam around a section of good teeth, tidy it up and use that as your profile to shape the teeth in your insert. It would certainly be the kind of repair that would have carried out in 1935.

Regards

Brian
9 December 2023 at 13:07 #698331
Chris Crew
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@chriscrew66644
I recently had a ‘crash’ and broke a tooth out on a 55T change-wheel. I milled the broken tooth out and silver soldered in a fillet of mild steel. I then set the change-wheel up on the dividing head and, as far as I could judge by eye, aligned the correct involute gear-cutter up between existing teeth and then rotated the dividing head, obviously using the correct division plate holes, to position the fillet to be profiled. I then ran the cutter between the fillet and the adjacent existing tooth and then rotated the dividing head, again using the correct division, to profile the other side of the fillet. I have to say that, by eye, the repaired tooth looked pretty good but when it was meshed closely with another gear it jammed. Giving slightly more clearance between the meshing wheels allows the wheels to rotate without jamming, so I have to be happy.

I guess the point I am trying to make is that, because of the precise geometric shaping of gear teeth, you will have to be very accurate if you attempt to re-repair the teeth on your gear. Involute gears have a reputation for being a little ‘forgiving’ when the mesh is not quite so precise but I had not realised how very accurate they need to be in a repaired gear which looks OK. I had never made a repair like this before and it has taught me a lesson about the need for great accuracy in gear teeth.
9 December 2023 at 13:51 #698341
bernard towers
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@bernardtowers37738
definitely repair it, if its a cast iron gear put a cast-iron dovetail in you will find it easier to cut and as its a 90t gear it will not be moving very quickly when in train. even if you only get it close there is the choice of running it on a jig with grinding paste.
12 December 2023 at 09:14 #698749
Mike Hobden
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@mikehobden70671
12 December 2023 at 09:18 #698752
Mike Hobden
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@mikehobden70671
Above pics of existing cold repair and subsequent damage.

Thanks for all the replies and interest, some interesting approaches suggested.
12 December 2023 at 11:07 #698772
Pete Rimmer
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@peterimmer30576
Mike, I suppose that is a 20DP gear like more modern myfords? 4.6″ diameter if so.

If you want to braze, solder or glue in a piece and post it to me I can cut new teeth into it for you. The tooth form will be perfect and I can even cut a few thou over-depth to clean up all of the existing teeth since it’s a change gear and not constrained to existing centres.
12 December 2023 at 20:07 #698954
Mike Hobden
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@mikehobden70671
On 12 December 2023 at 11:07 Pete Rimmer Said:

Mike, I suppose that is a 20DP gear like more modern myfords? 4.6″ diameter if so.

If you want to braze, solder or glue in a piece and post it to me I can cut new teeth into it for you. The tooth form will be perfect and I can even cut a few thou over-depth to clean up all of the existing teeth since it’s a change gear and not constrained to existing centres.

That’s a very kind offer, many thanks! Will see how I get on with letting in a new insert.

Early Myford change wheels were 20DP with a 14.5 deg pressure angle. Originally they were coupled by 3/32″ shear pins. Later lathes kept the tooth profile but adopted a key and keyway coupling. Some of my gears obtained from various sources have both a hole for a shear pin and a keyway. I’ve even cut my own keyways on a couple!

Also, I belive some very late machines used wider(1/2″?) 20DP, 20 deg pressure angle for the backgear arrangement. They are not interchangeable with the normal change wheels.
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