Metric screw cutting

It is quite a long time ago that Richard asked "

This seems a cheap and easy solution. My concerns are that if it is so good why I haven't found any reference to it elsewhere".

I believe that John Stevenson provides the two gears in question at a reasonable price. The pitch error using the 34 tooth gear is very small at approx.1 in 2222 whereas the error using the 33 tooth gear is rather more at 1 in 464. If a 26 tooth gear was produced this would give better result for 1.25 mm and 2.5mm pitch at 1 in 666. For short threads these errors are probably acceptable.

Any conversion of imperial lathe to cut metric threads that does not include a 127 tooth gear will produce some pitch errors. There are lots of ways of reducing these errors using a change wheel set up (such as the Myford conversion kit) but the options are limited when trying to easily adapt the QC gearbox.

So I reiterate Richard's question and would be very interested in the experience of my fellows who have used these two gears in conjunction with the QC gearbox.

Eric

So I reiterate Richard's question and would be very interested in the experience of my fellows who have used these two gears in conjunction with the QC gearbox.

I used a 34T gear with the 'box set to 18tpi to cut the 2mm pitch threads for all the backplates for my Myford big-bore lathe (7 in total). Quick and easy to set up and theoretically accurate to 0.00024 over the half inch of thread. Good enough for me.

Andrew