# Metric Transposing Gears



## DoogieB

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:




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.




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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## pete1972

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.


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## wildo

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!


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## DoogieB

The chart that was posted lists all the stud gears you need.


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## wildo

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!


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## DoogieB

wildo said:


> 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.


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## wildo

DoogieB said:


> 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!


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## Surprman

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


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## Splat

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..


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## Sparky

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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## jocat54

I have a full set of shop made gears for metric threading on SB9A using the 37/47 transposing gear, they are made from aluminum but work well. I no longer have the SB9A, when I sold it the buyer was in a rush and I  just plumb forgot about the gears and have no way of contacting him now.
If anyone has any interest in them let me know.


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## rmd5555

jocat54 said:


> I have a full set of shop made gears for metric threading on SB9A using the 37/47 transposing gear, they are made from aluminum but work well. I no longer have the SB9A, when I sold it the buyer was in a rush and I  just plumb forgot about the gears and have no way of contacting him now.
> If anyone has any interest in them let me know.



Are the gears still available?


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## Mark_f

I don't believe this works on a QCGB lathe, but for the SB 9 "B" you can cut metric threads without buying expensive gears. 
Transposing gear is made from two existing change gears. A 44 tooth and a 56 tooth gear. I bought two spare gears off eBay so l dont have to take them apart.





You can see the transposing gear made by bolting the two gears together. I have used this several times and it works great. There is a very small error but you would have to thread two or three feet of threads before the error would cause a problem. There is a chart on what gears to use for the various threads. All this is on the internet somewhere but I can't remember the site. It can be found by searching "cut metric threads on a SB 9 lathe".


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## Ulma Doctor

mark_f said:


> I don't believe this works on a QCGB lathe, but for the SB 9 "B" you can cut metric threads without buying expensive gears.
> Transposing gear is made from two existing change gears. A 44 tooth and a 56 tooth gear. I bought two spare gears off eBay so l dont have to take them apart.
> You can see the transposing gear made by bolting the two gears together. I have used this several times and it works great. There is a very small error but you would have to thread two or three feet of threads before the error would cause a problem. There is a chart on what gears to use for the various threads. All this is on the internet somewhere but I can't remember the site. It can be found by searching "cut metric threads on a SB 9 lathe".


Great stuff Mark, thanks for posting!


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## Mark_f

If anyone wants to make this gear, i will post the chart.


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## jocat54

rmd5555 said:


> Are the gears still available?




Yes, I still have them.


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## wileyone123

mark_f said:


> If anyone wants to make this gear, i will post the chart.



I wouldnt mind seeing the chart....thank U


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## Mark_f

Here are the files for metric threading on a South Bend 9 "B" or "C" lathe.


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## wileyone123

Much appreciated!

Thank U


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## Terrywerm

Thanks Mark!  I assume that the SB 9 B&C lathes use a lead screw with 8 TPI?  If that is correct, your instructions would also work on a Logan 200 and a few other machines.


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## wileyone123

mark_f said:


> If anyone wants to make this gear, i will post the chart.



Just wondering, other than using the most Helpful chart U provided, is there a Formula/equation to figure out Metric thread pitches turned with an 8TPI leadscrew?

Obviously, there are few common Stud and Screw gears to use....but the Compound gear ratios are confusing me....specially when the Transposing gears come into play.
In addition to that, others have posted % of error (in Thousands/ft) with the Transposing gear sets.....im wondering how to figure that?
So far im aware of 4 different Metric gear sets.....100/127 (being perfect), and others with marginal error....but how much error?
Those other Marginal gear sets: 63/80, 37/47, and 44/56.

Any help with calculating formulas would be appreciated


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## Asm109

Perfect ratio is 1.27:1  Take the other ratios and divide to get decimals  47/37= 1.27027027...
Error = 1.270707/1.27*100= 100.0213%


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## Mark_f

wileyone123 said:


> Just wondering, other than using the most Helpful chart U provided, is there a Formula/equation to figure out Metric thread pitches turned with an 8TPI leadscrew?
> 
> Obviously, there are few common Stud and Screw gears to use....but the Compound gear ratios are confusing me....specially when the Transposing gears come into play.
> In addition to that, others have posted % of error (in Thousands/ft) with the Transposing gear sets.....im wondering how to figure that?
> So far im aware of 4 different Metric gear sets.....100/127 (being perfect), and others with marginal error....but how much error?
> Those other Marginal gear sets: 63/80, 37/47, and 44/56.
> 
> Any help with calculating formulas would be appreciated


Yes,  there are formulas to figure this stuff .... But ...... They hurt my brain and besides, even though there is a slight error, you will be hard pressed to measure it. You would have to thread about 3 feet before the error was noticable. THAT'S CLOSE ENOUGH for anything I do. Also, it can be done buy picking up the gears for around $10 on eBay instead of hundreds of dollars. But if you want to figure it out, it is just a matter of dividing the number of teeth on one gear into the number of teeth on the other gear to get the ratio and do this with all gears in the train to get the total ratio and then divide using the lead screw pitch to get the thread pitch ....... My brain already hurts. I would only calculate if I was making a special proprietary thread ..... Which I will never do ..... I think.


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## Mark_f

terrywerm said:


> Thanks Mark!  I assume that the SB 9 B&C lathes use a lead screw with 8 TPI?  If that is correct, your instructions would also work on a Logan 200 and a few other machines.


You are correct.


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## wileyone123

Asm109 said:


> Perfect ratio is 1.27:1  Take the other ratios and divide to get decimals  47/37= 1.27027027...
> Error = 1.270707/1.27*100= 100.0213%



That said, .0213% error equates to What exactly in Thousands/Foot?

I have no plans on threading extensive lengths either....but just wanted to see in perspective just how much difference(.0000/ft) there was between the different transposing gear sets.

Reason being for the Equation/formula question and how to figure it out, is that i also have a 10" Rockwell that doesnt have the Impossible to fine Metric 
25-875 kit....nor can i find ANYone with specifics/pics of it.
Its metric gears are change gears are totally different from most.
I was contemplating fabrication of a banjo/quadrant to allow metric threading....while not having the typical Change gears of a SB, Logan etc...


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## Mark_f

wileyone123 said:


> That said, .0213% error equates to What exactly in Thousands/Foot?
> 
> I have no plans on threading extensive lengths either....but just wanted to see in perspective just how much difference(.0000/ft) there was between the different transposing gear sets.
> 
> Reason being for the Equation/formula question and how to figure it out, is that i also have a 10" Rockwell that doesnt have the Impossible to fine Metric
> 25-875 kit....nor can i find ANYone with specifics/pics of it.
> Its metric gears are change gears are totally different from most.
> I was contemplating fabrication of a banjo/quadrant to allow metric threading....while not having the typical Change gears of a SB, Logan etc...


The transposing gears I am speaking of here are only for change gear lathes. You can make or get a set for QCGB lathes but they use other gears in conjunction with the QCGB to get the metric threads. There is a lot of calculations for this. For example, the SB lathe with a QCGB uses the 127/100 combo but comes with several other gears that must be used by following a chart supplied for the gears required and the settings on the QCGB to cut the desired thread.


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## wileyone123

Thought id help others out by posting my latest find for Metric threading on a Logan 10" (and 11"?).  

Found a guy on Ebay that was willing to work with me and make up, via 3D printing,  some Transposing gears(37/47t) for my Wards/Logan 10".

He has other gears to accommodate the gearset as well: 20T - 32T - 40T - 80T - 100T (for metric threading)

Gear Face Width = .4375" (7/16")
Keyed center bore = .625" (5/8)
Teeth are 16DP

I suppose U can search on Ebay for them or contact Dennis at FDMprints@Gmail.com

Other items he offers: gearsets for Southbend, threading dials; misc gears and a lathe bed clamp/indicator.


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## Canuck75

The errors with alternate gear sets are small. For instance, the 37/47 set will give an error of .0032"/ft; the 44/56 set will give an error of .0327"/ft; and, the 63/80 set will give an error of .0002"/ft. If any set was to be problematic it would be the 44/56, however, you should not notice anything over the length of any normal nut, or any nut, even a long one, running on any length of shaft that you thread using these alternate gear sets.

For what it is worth.


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## ericc

mark_f said:


> Yes,  there are formulas to figure this stuff .... But ...... They hurt my brain and besides, even though there is a slight error, you will be hard pressed to measure it. You would have to thread about 3 feet before the error was noticable. THAT'S CLOSE ENOUGH for anything I do. Also, it can be done buy picking up the gears for around $10 on eBay instead of hundreds of dollars. But if you want to figure it out, it is just a matter of dividing the number of teeth on one gear into the number of teeth on the other gear to get the ratio and do this with all gears in the train to get the total ratio and then divide using the lead screw pitch to get the thread pitch ....... My brain already hurts. I would only calculate if I was making a special proprietary thread ..... Which I will never do ..... I think.



Hi.  Are these South Bend 9B gears that you can pick up for $10 on eBay?  How would one search for them?  Thanks!


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## Mark_f

They are S B 9 change gears. They are usually available on eBay. I got mine there for $10 each. Some sellers charge more. ( I see the prices on S B parts going up and up. If there is a demand, the prices go up. )


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## wileyone123

Canuck75 said:


> The errors with alternate gear sets are small. For instance, the 37/47 set will give an error of .0032"/ft; the 44/56 set will give an error of .0327"/ft; and, the 63/80 set will give an error of .0002"/ft. If any set was to be problematic it would be the 44/56, however, you should not notice anything over the length of any normal nut, or any nut, even a long one, running on any length of shaft that you thread using these alternate gear sets.
> 
> For what it is worth.



This was posted earlier: 
"Perfect ratio is 1.27:1 Take the other ratios and divide to get decimals 47/37= 1.27027027...
Error = 1.270707/1.27*100= 100.0213%"

If that is Correct, im still wondering what Math equation is used to obtain "the 37/47 set will give an error of .0032"/ft" ?

In the past, i believe i had read that the error for this (37/47)gearset was .0026"/ft.

In no way am i arguing the fact that the % of error is minimal for any of the gearsets, i only want to know exactly  how it is calculated.....ie, how the % error equates to 0.000"/ft


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## andre8998

wileyone123 said:


> This was posted earlier:
> "Perfect ratio is 1.27:1 Take the other ratios and divide to get decimals 47/37= 1.27027027...
> Error = 1.270707/1.27*100= 100.0213%"
> 
> If that is Correct, im still wondering what Math equation is used to obtain "the 37/47 set will give an error of .0032"/ft" ?
> 
> In the past, i believe i had read that the error for this (37/47)gearset was .0026"/ft.
> 
> In no way am i arguing the fact that the % of error is minimal for any of the gearsets, i only want to know exactly  how it is calculated.....ie, how the % error equates to 0.000"/ft


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## andre8998

Last week, I cut the 37 and 47 gears in a 0,400" nylon plate for my SB 9" changing gears using a milling attachment and a protractor to index each toot.  The gears are not perfect but they wook perfectly.  And today, I just read all this interesting forum.

The way to calcculate the error is :  (1,27027 - 1,27) / 1,27  =  0,00027   or  0,027 %.

This error applies to any measure coming from the gear combo so, in one foot or 12 inches the error is  0,00027 x 12  = 0,00324 inches.

If any is interested with the way I cut my gears just ask, I will post some photos and explanations.

Good wook to all,   Andre


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## magicniner

Surprman said:


> 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



Evan took his site down to reduce his "Internet Visibility" and quit lots of forum sites so the Government couldn't follow him but the linked page (and most of the rest of his site) is still available here  -

https://web.archive.org/web/20150812072032/http://ixian.ca/gallery/metric/metric.htm


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