Change gears

[SLK001]

If you look at the picture of your QCGB, you will see a column "STUD GEAR", which will have the value of 20 or 40. The picture above has the 40T stud gear currently driving the gear box. The 20T stud gear is right beside it, resting in its normal storage position. To use the 20T gear, just swap the positions of the two gears.

 

[mickri]

And by changing the bottom two gears with the right gears you can cut metric threads on your new to you lathe. Halligan142 has a video on this for a south bend lathe.

Being able to cut metric threads is handy.

 

[DavidR8]

And by changing the bottom two gears with the right gears you can cut metric threads on your new to you lathe. Halligan142 has a video on this for a south bend lathe.

Being able to cut metric threads is handy.

That was great! Thanks @mickr!

 

[Downunder Bob]

No lathe can cut every thread there is. The QCGB will cut most of the common threads but not all. If you must cut a thread that the installed gearing cannot cut then the only way to cut it is to change the gearing to enable you to cut it. These older American lathes came with gear sets to cut almost all common Imperial threads and if you do not have that set then you should go find it. They usually will not cut Metric threads.

More modern lathes can cut both Imperial and Metric threads plus modular and diametral pitches. All require change gears despite having a QCGB.
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It is my understanding that any lathe can be converted from imperial to metric threads, you just need the correct gears to change the ratio between the spindle and the leadscrew. Most larger machines use the 127 x 120 T wheels. Many smaller machine use the 63 x 60 T wheel set. other combinations also exist, but they are all approximations, close but not 100% only the 127 x 120 T set will give you perfect conversion It only matters if you are making a long threaded shaft like a lead screw, for normal nuts and bolts the difference is so small as to not matter.

 

[ErichKeane]

It is my understanding that any lathe can be converted from imperial to metric threads, you just need the correct gears to change the ratio between the spindle and the leadscrew. Most larger machines use the 127 x 120 T wheels. Many smaller machine use the 63 x 60 T wheel set. other combinations also exist, but they are all approximations, close but not 100% only the 127 x 120 T set will give you perfect conversion It only matters if you are making a long threaded shaft like a lead screw, for normal nuts and bolts the difference is so small as to not matter.

Close, the perfect set of change gears for metric is 127/100, however those tend to be too large for smaller lathes(like the 10" lathes). They don't tend to fit! However, you can use a 47/37 set that actually gets you REALLY close, apparently it is within 0.02%of perfect.​

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HOWEVER it DOES mean you cannot use the threading dial and have to leave the lathe on the leadscrew at all times. You have to stop the whole lathe at the end of the thread, and reverse the lathe (from the motor!) in order to keep from diengaging the leadscrew.​

 

[SLK001]

Close, the perfect set of change gears for metric is 127/100...​

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Actually both are correct. The perfect set will always have a 127T gear - it doesn't matter if the secondary gear is 120T or 100T (or even other values). The gear train down the line will determine the final metric thread. I have the 127/100 set that fits just fine in my later version 10L. The earlier versions (up to ~1950) had to have a different banjo and gear cover. This is the metric set for the early 10Ls:



For the later 10Ls, you just need the 127/100 combo gear and the set of loose spur gears.