Atlas/craftsman 16/32 Combo Gear ?

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azscooby

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Hi all,
Long time lurker, first time poster...

I picked up a Craftsman 12x48 (54" bed- 07403) lathe a few weeks ago for $400, which is a very good deal in AZ where there is hardly any machinery. Junk goes for a premium.

I didn't have time to research much before having to make the purchase. I called and was at the owner's home within 2 hours and he had two other individuals waiting to come after me. I believe the guy, as I've been shopping for something for almost a year with very few "hobby lathes" showing up...mostly the big stuff at $3k+.

At the price I decided to grab it as the collet set itself is about $200. However I discovered after being told it had a "complete set of gears" that I was missing about 7-8 gears and a few other tidbits. But the gears could add up quickly.

I made the mistake initially to buy used on that auction site only to find out later a brand new steel gear could be purchased cheaper from Boston, via Amazon Prime even.. (Tip for anyone else - check out Boston Gears FIRST!!!! The price on the 48T and smaller are about the same price as used Zamak on Ebay, hope that helps.)

That's the background, now the issue....

The combo gear, 16/32, on the tumbler, a unique gear, not a catalog gear......cheapest I can find is about $70 used Zamak on the auction site. However, I've figured out that I can buy Boston Gear NB32 and NB16B, cut off the extra hub (about 1/2") and that should get me what I need while still being cheaper than buying a used Zamak part in unknown condition.

Here's my question.
Being that this is a "combo" gear I wanted to know if they need to be "fixed" together, or can they both freely rotate on the same axis, independently? I don't' have all my gears yet so I'm having a hard time visualizing this.
The threading chart is a bit confusing but it looks like the 32/16 is just "flipped" for the different scenarios, not used for one gear, the 16 for example, to drive the 32 and vice versa being that they're locked together, if that makes sense. If this is the case, they shouldn't need to be fixed together, which would save me some effort.

If in fact they need to be fixed together, is there any other suggestions other than tapping both gears and using a type of set screw to hold them together?

And BTW, I've already bought the NB32 and NB16B gears, so I'd like to use those. I realize I could have bought the GB32 and used the bushing, but this seemed easier, and one less part. (There is no GB16, as that would solve my problem altogether = GB32+GB16 with the keyway bushing.)

Thanks in advance for any help!
 
First, if your 101.07403 has a 54" long bed, it is a 12x36. Not a 12x48. Put a dead center in the spindle and in the tailstock ram. Slide the tailstock to the right end of the bed and retract the ram as far as it will go in with ejecting the center. The distance between the pointy ends is the center-to-center distance or rated length.

As Pierre indicated, the 16/32T gear on the tumbler is a compound gear. That means that driving one also drives the other. You cannot turn the gear around when the threading chart indicates that the 16T gear is driving for two reasons. First, because the 16T gear won't touch the Reverse gear. Second, as the original is a compound gear, you would lose a 2:1 reduction ratio. If you otherwise set up the lathe for 16 TPI and somehow could only use the 16T gear, you would cut an 8 TPI thread. Fortunately, the tumbler compound gear doesn't need the double keyway. (nor do the other two gears, although the originals may have them). You will, as Pierre indicated, need to turn down the hub of the 16T gear, prepare the bore of the 32T gear and press them together, making a compound gear.

All of the other original change gears are double keyed. They don't actually have to be all of the time but to use unkeyed stock gears, you would have to make unkeyed steel bushings for them to fit on. If the threading chart calls for a compound gear, those two gears MUST be keyed. Somewhere in DOWNLOADS under Atlas Lathes is a copy of an article on modifying a lathe to do keyway broaching. The method is slow but it does work (it's called single-tooth broaching). And using the index pin built into the headstock, you can ensure that the second keyway is exactly 180 deg. around from the first, which is critical. Fortunately, the keyway depth is not critical so long as it is deep enough.

So the Boston plain hub gears are cheaper IF you attach no dollar value to your time.
 
Pierre,
Fantastic! I'd read that post before, which in part got me going in the right direction. Your method seems like a great idea, and one I had just though about as I was looking at the two gears. I have a press as well, so this shouldn't be too difficult.
Thanks for the great post.

Robert -
Thanks for clearing up the names and sizes - I wondered why I always saw 12x36 - even though it has a 54" bed. I had been calling it 12x48 since that is how the owner had listed it. That helps.

And thanks for clarifying the compound gear and how it works, it makes sense that the one drives the other, it's what I sort of expected, since the other way would be way too easy, of course.

I've actually already cut a single key way, though I used a different method with my milling attachment. It was a single keyway, so it I didn't need indexing. I'll have to compare prices of the gears. But for now I think I've got all of the gears I need and will only need to buy replacements as they wear.

You guys answered my questions perfectly and with great detail, I really appreciate it! Thanks!
Brian
 
Pierre,
I've got the 32 tooth cut down to .500" on the face and was wondering how much you overlapped them? I've never attempted any type of press and was wondering what the two diameters might be at room temp. Doesn't need to be exact, but did you bore the larger gear .005" less than the OD of the smaller one (for example?)
thanks again.
 
It was about .001 - .002" if I remember correctly. I used the table in Machinery's Handbook. I did put a small chamfer to aid the starting and a little polishing of the two surfaces as well. As for the amount of overlap, I simply made it to fit the shaft that I had made, with the approximate length that allowed the correct engagement of the next gear in the gear train. I have a drawing somewhere but it was eyeball measuring.
Pierre
 
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The nominal face dimension (thickness at the gear teeth) of the 16/32T compound tumbler or stud gear (only on the later machines) is 1/2" for each gear and 1" total. All other gears are 3/8" face. Up through the 10D/E and the 101.07361, 101.07381 and 101.07401, the hubs are also 3.8" long. From the 10F and the 101.07262, 101.07382 and 101.07402. the hubs are 1/2" long.

Not particularly related but the other significant change in the drive train, the change from 5/8" diameter lead screw and without power cross feed to 3/4" diameter lead screw and with power cross feed, also changed with the advent of the 10F. But on the 12" machines, it didn't change until 101.07363, 101.07383 and 101.07403.
 
Pierre,
Thanks again, this helps a lot.

I'll probably put the 16t in the freezer tonight and give it a go tomorrow.

I'm surprised someone doesn't sell a complete set of steel gears for these machines like they do for the Chinese mini lathes (which I have 2.). I'm guessing the cost would be prohibitive...?

Once I get all the missing gears and other missing parts (steady rest, misc parts) I'll have more into these tidbits than I put into the machine at purchase. But I don't see myself selling this anytime soon as it's it really good shape otherwise with little wear on the ways.
 
You might also give Clausing a call on the gears you need. Something you will find out is it is sometimes cheaper to buy new from them than used on EBay. As I recall new gears are just a little more than used ones on EBay. Half Nuts are a lot cheaper new from Clausing than you can get on EBay. It is great the way they still support these old lathes.
 
Agreed. Clausing's continued support of these old machines, put the other more modern suppliers to shame.
Pierre
 
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