I still have not come to terms with what gear you are refering to. What gets my attention is that you state that you can cut both metric and imperial threads without changing the gear. The leadscrew may be metric, it may be imperial, it doesn't matter. But either way, one or the other will require a change to cut the other thread. As in, if you have a metric lead screw, imperial threads must be cut without releasing the half nuts. If you have an imperial leadscrew, metric threads must be cut without releasing the half nuts. That is a given, as the two(metric or imperial) are not directly related. That 25.4 relationship is as close as it gets.
Assuming you are trying to find the gears listed in the original post, where 11, 13, 14, and 15 are listed, you can measure the existing gear(s) to determine what size is needed. They most likely will be metric (modulus) gears with 20 degree pressure angle. I would bet on them being modulus 1.5, but in reality that is just a wild guess. The best advice would be to take a mating gear to someone knowledable of gears and get their opinion. Someone that speaks your language. There are many nuances to English that do not translate well. There are many variables on gears and you need to know what they are to fit to them.
Then there are a pair that run together to do metric/imperial conversion. For smaller machines, these will be 127 and 120(or 100) teeth. For larger machines such as yours, they probably are internal to the gear box and may be a different number that gets close enough but not exact to 5 decimals. 127 is a prime number necessary for exact conversion. One of my machines uses 16DP gears, which is close to Modulus 1.5, almost. A 127 tooth gear in that pitch is quite large, being 150mm plus in diameter.
Then lastly, you speak of "waiting for the gear to come around" to the mark to start the next pass. This gear
must not be changed. It is related to the pitch of the lead screw and varies depending on that. It is the one on the front apron that drives the rotating button for alignment to engage the half nuts.
Waiting for that button to come around is a pain in the wazoo. It may only be used for cutting threads native to the lead screw. A metric leadscrew cutting metric threads for example. For the opposing thread, the half nuts must never be opened until complete. The machine is run in reverse with the half nuts closed to start another pass. That is noted in the first paragraph.
My (large) machine is very old, ca. 1950-52. A Craftsman (Atlas) 12x36 that is as old as I am. It is loose and creaky at best. When I am threading, I never release the half nuts, for Imperial or Metric. It allows me to maintain registration for the entire gear train from the spindle out. I took the indicator off the machine so it would not distract me, running the machine in reverse to start the next pass. I highly recommend doing this for anyone until they are conversant with a particular machine. It reduces mistakes. . . I have a smaller machine that is of Chinese origon. It has modulus 1.0 gears. The same details apply to both machines, varying only in specifics.
I apologize for being so verbose. You are having trouble expressing yourself in English and I truely do not understand what you are trying to describe. So I hit the major points and hope for the best.
Bi11 Hudson
