Metric Change Gears for SB 9A

jocat54

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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.

gears.JPGmetric chart.jpg

gears.JPG metric chart.jpg
 
can that be done on one that has the change gears on it, I have a 1925 Model 25A (9A)
 
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.
 
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
 
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
 
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:))
 
Here are a couple of pictures with gears installed to cut 1.0mm threads and the gear box set to the chart.

gears 1.jpggears.jpg

gears 1.jpg gears.jpg
 
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
 
Great job :drink:
FYI all year use by jocat54 can be cut on 0 bs dividing head. No compound gearing

Dave


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.

View attachment 80386View attachment 80387
 
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