Metric Transposing Gears

DoogieB

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When I was lathe shopping last year, I had a list of features I wanted in a lathe: cross feed, tumbler reverse, QCGB and the option of cutting metric threads with change gears. The SB 10K I ended-up purchasing met all those needs well (and I really like it) but I was left scrounging around for the metric gears. South Bend manufactured a set specifically for these lathes (the 9A & 10K) back in the day but they are hard to find. Tools4Cheap sells a set made overseas, but they have been out-of-stock for most of the year. About a month ago I got the email saying they were back in stock, so I bit the bullet and made the purchase. Here's what $200 gets you:

metric_1.jpg

It's a box-O-gears! The transposing gear is 2 large cast gears (127T/120T) pinned together. The rest of the gears are steel and everything is nicely cut and fits well. The only clean-up needed was to grind the pin down in the transposing gear a bit with a Dremel as it was a bit proud. From the pictures I've seen, these look identical to the original SB set, except here you get another 40T gear.

metric_2.jpg

You'll need a spacer between the 56T gear and the gearbox to clear the 127T gear in the transposing set. You could use one of the small gears and some washers, but I made a simple aluminium spacer with clearance for the key cut with a file.

The next pic is what the gear cover on my lathe looks like and there's enough room inside to close it with the metric gears installed. The cover was hitting the thin shield at the gear box which is usually about a 1/2" inside the gear cover. The shield is adjustable, but the gear cover was closed enough so you didn't have to worry about getting your fingers caught in that buzzsaw of gears so I left it as is. After all, the metric gears are only installed temporary until the threads are cut and then it's back to the factory setup.

Next is what the stock gear setup looks like. Judging from the goop and filth on the gears, I don't think mine was ever touched in 40 years, the awesome advantage of the QCGB.

The last pic is what the lathe looks like with the transposing gear and a 48T stud gear. I was cutting a 1.50 pitch thread for a M10 bolt, but you could also cut a few other pitches with changes to the QCGB with this same stud gear. With this gear set, you can cut all the standard metric thread pitches and then some.

I couldn't find a really nice metric chart to print for in the shop, so I made one. You can download it here:

http://doug.freeshell.org/files/machinery/metric_chart.pdf

If you want to get your freak-on about cutting metric threads and have a few extra change gears laying around, you can grab this large chart for almost every conceivable combination of gears for various threads:

http://bnordgren.org/files/metchart2.pdf

If you are cutting metric threads with a inch lead screw, you often here "Don't move the half-nut lever until you are done". This isn't exactly true, you can pull the lever, you just have to catch the same thread on the lead screw when you are winding-backwards in reverse to the beginning of the thread you are cutting. I've read about this technique, but it didn't really make sense until I saw this video were Tom demonstrates how it works:


It's a really handy technique when you are cutting threads to a shoulder, which seems to be about 99% of the time. Worked great for me the first time.

While I try to stick to using SAE threads, I still have to dabble in the metric world occasionally and this will only become more common in the future. Yes, these gears are expensive to have in a box and only break them out a few times a year, but they are there if needed. Besides, if I wanted to not spend money, I would have taken-up knitting instead!
 
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very nice quality for 200. i just picked up a 1937 9 and for the life of me can't figure out why i have so many gears.
 
This is an old thread, but Tools4Cheap doesn't appear to exist any longer. Does anyone happen to know what a "full set" of metric transposing gears includes? I happened across a set and am wonder if I have a full set or not. Thanks!
 
The chart that was posted lists all the stud gears you need.
 
Ah, I missed that. So a complete set then would be:

127/100 combo
56T (Probably already on the lathe in most situations)
48T
44T
40T
36T
32T
28T
26T
Included spacer if you're really lucky.

___
Looks like I scored a nearly complete set- just missing the 40T! That's exciting!
IMG_7649_zpsdf5oof68.jpg
 
Looks like I scored a nearly complete set- just missing the 40T! That's exciting!

The 40T gear should already be with the lathe, parked on top of the 56T gear at the QC gearbox. It's included with the lathe because you swap the 20T spur gear with the 40T when you want to cut 4-7 TPI threads (rare). If it's missing, it's easy enough to find because originally every lathe had one, usually unused.

And yes, it is exciting to find a set since tools4cheap is gone and no one else has stepped up to the plate to import more sets. These transposing gears sets can get a little pricey now if you find one and I'm glad I bought mine when I did. That $200 doesn't seem so bad now. :)

Just to reiterate, the set that I have is for my lathe, a 10K which for this is the same as a 9A. The Heavy 10 gears are different.
 
The 40T gear should already be with the lathe, parked on top of the 56T gear at the QC gearbox. It's included with the lathe because you swap the 20T spur gear with the 40T when you want to cut 4-7 TPI threads (rare). If it's missing, it's easy enough to find because originally every lathe had one, usually unused.

Ah! So it is... I missed it on there. So sure enough- I have a complete set. Sweet! Thanks for the info on all this!
 
Sounds like you got the ideal gear set. For any others out there reading this- I built the gear/bushing described in this link:

http://ixian.ca/gallery/metric/metric.htm

It works great and was pretty easy to make. Probably all you need unless you are threading something really long.

Rick
 
FWIW, I remember seeing a metric gear set on Ebay ....I think it was new and they wanted $300 IIRC. Jeff @ Tools4cheap's a good guy and you got a great deal. I'm saddened to have found out only a month or two ago that he's no longer in biz. I wish him the best..
 
Hi,
Recently I had need to cut metric threads on my SB 10K. I fabricated a 37/47 transpose gear. I then looked at published setting guides an learned that my 20T stud gear needed to be changed to 32T for a 1mm screw pitch. Unfortunately I do not have the 32T gear. Darnit. I also realized that there may still be a way to cut the 1mm thread. I wrote a spread sheet in OpenOffice which I have attached in MSExcel format, (I have not run this in Excel Yet). Using this tool I found a setting for use with my 20T stud gear. So beware that some of the public resources are not complete. If you use the Excel sheet attached please let me know if it is understandable, and useful or not. thx dan
P.S. The formatting may not have transferred to the xls file from OpenOffice,....
 

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