Hello. Today I wanted to trace a 1.25mm pitch thread on my lathe, which is my first time threading. The biggest issue I have is that my lathe has no metric threading chart, even tough the leadscrew is a 3mm pitch one. There is some sort of chart on the side of the apron, I think it's for the threading dial, but it's confusing me... 
Firstly, why would there only be an imperial threading chart and only a metric threading dial chart? Secondly, there are no worm gears anywhere that I know of, tough the threading dial has 3 spur gears that you can swap between. Also, what are the numbers in the chart supposed to mean anyways, that I can only stay on x number on the dial? But since for cutting metric threads with a metric leadscrew, any number works if the pitch is a multiple of the leadscrew pitch, right? At least several of those threads would allow more than one number, correct?
I guess it's possible there were a metric chart and it's missing, but there really isn't any flat areas left where it could have sat. Also I can't find any rivet holes. Anyways, here's the Imperial chart that's on the machine:
The gear configuration seems like the standard metric to inch conversion to me, but how are the gears supposed to be configured normally? I have no manual unfortunately and finding one for a generic Taiwanise 13xsomething with a metric leadscrew has proven a lot more difficult than one with an imperial leadscrew.
I currently have the gears set up such that one turn of the spindle turns the input shaft to the qcgb one turn also. Here is a picture of the ratios that I calculated quickly:
The numbers tells how many revolutions the leadscrew/feed shaft turn per 1 turn of the input shaft to the gearbox, for each combination of the 2 selectors. Numbers that were long in decimal form are written as fractions to save space. Since the leadscrew is 3mm pitch, the pitch of the cut thread should be these numbers times 3 with the current 1:1 gearing before the gearbox, unless I messed up (very possible). Say I want that 1.25mm pitch thread, I would need the leadscrew to turn 5/12 of a turn per revolution of the spindle, which is not an option here.
Is there any difference between a typical inch and a typical metric quick change gear box? These numbers don't seem to give me a whole lot of standard metric pitches... I feel like I'm missing something and any help is appreciated.
Firstly, why would there only be an imperial threading chart and only a metric threading dial chart? Secondly, there are no worm gears anywhere that I know of, tough the threading dial has 3 spur gears that you can swap between. Also, what are the numbers in the chart supposed to mean anyways, that I can only stay on x number on the dial? But since for cutting metric threads with a metric leadscrew, any number works if the pitch is a multiple of the leadscrew pitch, right? At least several of those threads would allow more than one number, correct?
I guess it's possible there were a metric chart and it's missing, but there really isn't any flat areas left where it could have sat. Also I can't find any rivet holes. Anyways, here's the Imperial chart that's on the machine:
The gear configuration seems like the standard metric to inch conversion to me, but how are the gears supposed to be configured normally? I have no manual unfortunately and finding one for a generic Taiwanise 13xsomething with a metric leadscrew has proven a lot more difficult than one with an imperial leadscrew.
I currently have the gears set up such that one turn of the spindle turns the input shaft to the qcgb one turn also. Here is a picture of the ratios that I calculated quickly:
The numbers tells how many revolutions the leadscrew/feed shaft turn per 1 turn of the input shaft to the gearbox, for each combination of the 2 selectors. Numbers that were long in decimal form are written as fractions to save space. Since the leadscrew is 3mm pitch, the pitch of the cut thread should be these numbers times 3 with the current 1:1 gearing before the gearbox, unless I messed up (very possible). Say I want that 1.25mm pitch thread, I would need the leadscrew to turn 5/12 of a turn per revolution of the spindle, which is not an option here.
Is there any difference between a typical inch and a typical metric quick change gear box? These numbers don't seem to give me a whole lot of standard metric pitches... I feel like I'm missing something and any help is appreciated.
