Thanks everyone for your responses. Somehow notifications on this thread didn't get to me so I'm sorry for the delay.
@Flyinfool I understand that none of the conversions for an English lathe to cut metric threads are going to be perfect other than the 100/127. I don't often need metric pitches, but want to have something that works for many common pitches in my arsenal when needed. As you said with the short length of thread on a nut (probably all I'll ever need) the accumulated error is negligible.
@Canuck75 With your 63/80 setup, what settings do you use on the QCGB to set metric pitches? Do you have to install other gears to open up more options? Maybe I'm missing something because I don't see many common metric pitches in the converted chart using this ratio.
@KyleG I can cut English pitches just fine. There should be a 2:1 ratio from the spindle to the gearbox input. Mine came equipped with 24/48. You can see from Canuck75's picture that he has the same 2:1 ratio using 28/56. I'm working from a spreadsheet that I made to try and help myself to understand the challenge. I cannot guarantee it is free of mistakes, which is why I asked for some advice here. I may be totally wrong or missing something.
@mickri I'll look again for threads in the Craftsman/Atlas forum on this. I have one of these machines and many people use 56/44 to transpose for metric pitches. I've never used the Craftsman to cut metric threads either. I did look at Halligan's video on this and it seems that he was doing what I was thinking of by trying to effectively transform the 8 tpi leadscrew into a 6mm pitch
@Flyinfool I understand that none of the conversions for an English lathe to cut metric threads are going to be perfect other than the 100/127. I don't often need metric pitches, but want to have something that works for many common pitches in my arsenal when needed. As you said with the short length of thread on a nut (probably all I'll ever need) the accumulated error is negligible.
@Canuck75 With your 63/80 setup, what settings do you use on the QCGB to set metric pitches? Do you have to install other gears to open up more options? Maybe I'm missing something because I don't see many common metric pitches in the converted chart using this ratio.
@KyleG I can cut English pitches just fine. There should be a 2:1 ratio from the spindle to the gearbox input. Mine came equipped with 24/48. You can see from Canuck75's picture that he has the same 2:1 ratio using 28/56. I'm working from a spreadsheet that I made to try and help myself to understand the challenge. I cannot guarantee it is free of mistakes, which is why I asked for some advice here. I may be totally wrong or missing something.
@mickri I'll look again for threads in the Craftsman/Atlas forum on this. I have one of these machines and many people use 56/44 to transpose for metric pitches. I've never used the Craftsman to cut metric threads either. I did look at Halligan's video on this and it seems that he was doing what I was thinking of by trying to effectively transform the 8 tpi leadscrew into a 6mm pitch