Model A gear box conversion

Has anyone put a model A gear. Box on a model C? I have a 1937. I ordered a gear box and now I was just told by someone on here that I have to mill down part of the underside of the bed and use a model A skirt? I though I just had to drill the 3rd hole through the bed and mod the lead screw., Why would I have to use a different skirt? That doesn't make much sense to me cause the skirt is indapendant of the gear box and head stock.. Any input would be great, There is a vid on YT of a guy putting a gear box on a model B. He did nothing with the bed or skirt.

Some beds have a ridge on the lower edge which prevents the power feed apron from fitting. The gearbox itself should be fine once you add the extra screw hole.

As for the apron, you don't have to swap it, but power long and cross feeds sure are nice. They are also far easier to use with a qcgb.

allan

Why would I have to use a different skirt?

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The point of the gear box is to not have to mess about with change gears as much. Without the A apron, your finest feed will be about .004 IPR (224 TPI) without messing with change gears.

WITH the A apron your finest feed will be .0015 IPR

Suit yourself

Greg (Halligan142) has three YouTube videos showing his B to A conversion. The first is at <https://www.youtube.com/watch?v=IXLs47swl8k>. I learned a lot from those videos and several others of his.

To add...the saddle on some earlier non power feed models is not drilled large enough for it to accept the geared cross feed screw needed for power cross feed and "may" even have clearance issues with the apron cross feed gear...that is what Joe referred to in the other thread.

you have 3 potential points of interference. Check what you have before diving in.

Also the skirt as you call it, is the same on the model A and B, the C is a totally different animal.

i have a model B that I converted to an A about 10 years ago, for a B model adding a screw hole to the bed, bolting on the box and changing the lead screw is really all you need to do. The C has a different apron from the B and A models. The C model does not have cross feed and technically doesn't have longitudinal feed, it uses the half nuts for this where the the A and B models use the apron selector lever and worm with a clutch to drive both feeds. The half nut lever on these is used only for threading. The bed issue is mainly due to the fact that yours is one of older ones as in the first of these produced.

You wouldn't happen to know what banjo gears I need for the quick change box? I know I need a 20tpi stud gear and I have that..

mcruff said:

Also the skirt as you call it, is the same on the model A and B, the C is a totally different animal.

i have a model B that I converted to an A about 10 years ago, for a B model adding a screw hole to the bed, bolting on the box and changing the lead screw is really all you need to do. The C has a different apron from the B and A models. The C model does not have cross feed and technically doesn't have longitudinal feed, it uses the half nuts for this where the the A and B models use the apron selector lever and worm with a clutch to drive both feeds. The half nut lever on these is used only for threading. The bed issue is mainly due to the fact that yours is one of older ones as in the first of these produced.

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that's another part you might have to change. The banjo on the early model C were slightly different than they were for the model A. Specifically the clamping bolt was in a different place and when used on the quickchange gearbox, it would hit the casting.

So in order to convert a early model C, to an model A, you would have to change,

1: the gearbox.

2: the lead screw.

3: the apron.

4: The saddle.

5: the banjo.

I believe this is true for the early models up to 1942 model C, and maybe 1943. at least that's what it would take to change my 1942 model C, to a model A.

stay safe and have fun.

Joe.

PS, the standard gears for the quickchange gearbox is, 20T, 40T, 56T, and an 80T idler. If you have other gears, don't get rid of them you may need them to cut special threads or metric threads.

Sell the model C complete on C-list or eBay to some other unsuspecting (ahem) "soul" that supposes it will be cheap and easy to convert it to an A model with a mere gearbox swap. Heck, throw the gearbox in with the deal. Or sell it separately for a few more $$

Take the money and buy an actual A model.

smt

^^^ sounds like the best advice I've heard. Seems like it would be money to convert vs replace the machine with one that has what you're after.

I did the conversion a few years ago on a 1934 SB Model 405-Y 36 inch lathe. It is not specifically a Model C but is somewhat close (it is a lathe). There are several major exception, which are: Left hand lead screw (requires Model A type); no lead screw reversing lever (requires a reversing gear which plugs into the headstock); apron and cross feed is different (requires Model A type apron and cross-feed). By the time that I finished, I had changed the lead-screw, head-stock, apron, crossfeed and lead-screw reversing lever. Oh yes, I also had to grind the lower flange of the lathe bed so that it didn't interfere with the apron (not difficult with an angle grinder) and drill an additional hole in the bed for the QC Gear Box. The only original parts of the 405-Y left was the bed (modified) and the tail stock. Yes I know it would have been cheaper to have found a Model A to start with, but it seemed like a good idea at the time.