# Metric Change Gears for SB 9A



## jocat54 (Jul 17, 2014)

I finished my change gears for my SB 9A to cut metric threads using the QCGB. They are made from aluminum but work well.
I made the compound gear 47/37 instead of the 127/100 and they are so small that I could not get enough adjustment to get them to engage so I made another stud and bushing for the banjo to use another idler gear. When you add another idler it changes the feed direction of the lead screw (duh).

Anyhow I tried a couple of them out (1.5mm and 1mm) and they were right on. I just set the QCGB to the SB metric thread plate. I don't cut metric threads often but it was a good learning project.


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## cajun lathe (Jul 18, 2014)

can that be done on one that has the change gears on it, I have a 1925 Model 25A (9A)


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## jocat54 (Jul 18, 2014)

cajun lathe said:


> can that be done on one that has the change gears on it, I have a 1925 Model 25A (9A)




Yes, and if you already have the change gears you would probably only have to make (buy, ect.) the transposing compound gears.
Here is a nice article for doing it.     http://conradhoffman.com/metricthreading.htm.

He made his gears from Delrin and seem to hold up. I also made a set from Delrin to practice on, because I had the Delrin and it is so easy to machine and if (when)) to you mess one up it is easy and cheap to start over.


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## Ulma Doctor (Jul 20, 2014)

nice work on the gears
thanks for sharing!!


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## jlrice54 (Aug 8, 2014)

Jocat, this is something I've been researching.  Can you shoot a pic of the gear train the next time you have them mounted?  I've been looking at the OEM South Bend 100/127 sets on eBay but haven't pulled the trigger yet.  Since I've been thinking of trying gear cutting for a while, your project looks very interesting.  

James


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## cajun lathe (Aug 9, 2014)

Thanks, I am also going to look to see if I can find if that can be done with my Craftsman 12" with a quick change box, thanks again, Cajun Lathe


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## jocat54 (Aug 9, 2014)

jlrice54 said:


> Jocat, this is something I've been researching.  Can you shoot a pic of the gear train the next time you have them mounted?  I've been looking at the OEM South Bend 100/127 sets on eBay but haven't pulled the trigger yet.  Since I've been thinking of trying gear cutting for a while, your project looks very interesting.
> 
> James



James,
I will try to get them set up in a day or two and post a picture.
Sometimes life gets in the way of my shop time)


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## jocat54 (Aug 10, 2014)

Here are a couple of pictures with gears installed to cut 1.0mm threads and the gear box set to the chart.


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## bogster (Dec 16, 2014)

Hi Jocat,

I've been researching exactly the same thing myself for my 9A and hit this thread with a Google search. Can I ask you how many teeth were on the idler gear set you used and what sort of tool did you use to cut the gears? Was it a tool you ground yourself or did you buy and involute gear cutter?

I'm in the UK and am having a hard time sourcing the 18dp 14.5pa involute gear cutters. If I can't find what i need then I will have a go at grinding my own form tool and use a fly cutter.

Regards


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## Smithdoor (Dec 16, 2014)

Great job 
FYI all year use by jocat54 can be cut on 0 bs dividing head. No compound gearing

Dave




jocat54 said:


> I finished my change gears for my SB 9A to cut metric threads using the QCGB. They are made from aluminum but work well.
> I made the compound gear 47/37 instead of the 127/100 and they are so small that I could not get enough adjustment to get them to engage so I made another stud and bushing for the banjo to use another idler gear. When you add another idler it changes the feed direction of the lead screw (duh).
> 
> Anyhow I tried a couple of them out (1.5mm and 1mm) and they were right on. I just set the QCGB to the SB metric thread plate. I don't cut metric threads often but it was a good learning project.
> ...


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## jocat54 (Dec 16, 2014)

bogster said:


> Hi Jocat,
> 
> I've been researching exactly the same thing myself for my 9A and hit this thread with a Google search. Can I ask you how many teeth were on the idler gear set you used and what sort of tool did you use to cut the gears? Was it a tool you ground yourself or did you buy and involute gear cutter?
> 
> ...




I think that I used a 48t gear for the idler in that set up-----but it does not matter what the idler gear is as long as you can get engagement, it does not change the ratio. (any gear will work).

I bought some metric module cutters from http://www.ctctools.biz/servlet/the-628/hss-involute-gear-cutter/Detail
I did some research and don't remember which module was real close to the right DP (I think it was m1.25 or m1.5---way down the list on the link) Really believe it was the m1.25 module though. Just chose the number of teeth for each cutter. They are not exact but close enough for what I use them for.


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## Mark_f (Dec 17, 2014)

I been trying to figure out how to do it on an SB 9 B. I guess you need the transposing gears but is a different gear chart needed since it  doesn't have a QCGB?

Mark

EDIT: I seem to remember somewhere when I first saw the transposing gear setup that someone had said it did not work on the change gear lathe like the SB 9 B or C, but I have no idea if that is correct or not. That was why I stopped pursuing the idea.


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## bogster (Dec 17, 2014)

jocat54 said:


> I think that I used a 48t gear for the idler in that set up-----but it does not matter what the idler gear is as long as you can get engagement, it does not change the ratio. (any gear will work).
> 
> I bought some metric module cutters from http://www.ctctools.biz/servlet/the-628/hss-involute-gear-cutter/Detail
> I did some research and don't remember which module was real close to the right DP (I think it was m1.25 or m1.5---way down the list on the link) Really believe it was the m1.25 module though. Just chose the number of teeth for each cutter. They are not exact but close enough for what I use them for.



Thanks for that information Jocat and the link to the CTC Tools website. I've ordered the M1.25 involute cutters I need at a very reasonable price including shipping.


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## jocat54 (Dec 17, 2014)

mark_f said:


> I been trying to figure out how to do it on an SB 9 B. I guess you need the transposing gears but is a different gear chart needed since it  doesn't have a QCGB?
> 
> Mark
> 
> EDIT: I seem to remember somewhere when I first saw the transposing gear setup that someone had said it did not work on the change gear lathe like the SB 9 B or C, but I have no idea if that is correct or not. That was why I stopped pursuing the idea.




Mark I believe that it will work on a change gear lathe. A lot of my reading on this was from http://conradhoffman.com/metricthreading.htm and i think his is a change gear lathe (Logan). There is a lot of good reading there. Somewhere I did see a chart for a change gear lathe, I will see if I can find it again.

Having seen all your OUTSTANDING work on this forum---this would be a piece of cake for you.

John


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## Mark_f (Dec 17, 2014)

jocat54 said:


> Mark I believe that it will work on a change gear lathe. A lot of my reading on this was from http://conradhoffman.com/metricthreading.htm and i think his is a change gear lathe (Logan). There is a lot of good reading there. Somewhere I did see a chart for a change gear lathe, I will see if I can find it again.
> 
> Having seen all your OUTSTANDING work on this forum---this would be a piece of cake for you.
> 
> John



I'd like to try it and I would like to make the gear myself too, If I find the info and it will work.

Mark


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## bogster (Dec 19, 2014)

mark_f said:


> I'd like to try it and I would like to make the gear myself too, If I find the info and it will work.
> 
> Mark



Hi Mark,

There are quite a few threads on various forums with good information on how to go about this. If you Google "South Bend metric threading" you will hit quite a few. Basically your starting point is to buy or make a pair of transposing gears - 127/100 is the classic but 47/37 work as well as Jocat54 has shown. Depending on how accurate you want to be and what metric threads you want to cut you might find this reference useful as well:-

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


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## Mark_f (Dec 19, 2014)

bogster said:


> Hi Mark,
> 
> There are quite a few threads on various forums with good information on how to go about this. If you Google "South Bend metric threading" you will hit quite a few. Basically your starting point is to buy or make a pair of transposing gears - 127/100 is the classic but 47/37 work as well as Jocat54 has shown. Depending on how accurate you want to be and what metric threads you want to cut you might find this reference useful as well:-
> 
> http://ixian.ca/gallery/metric/metric.htm




Thank you,

I am going to check this out .

Mark Frazier


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## LEEQ (Dec 20, 2014)

tools for cheap is clearing out some south bend metric change gear stuff. Worth a look if only to see how someone else is doing it.


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