I am learning to cut threads on my SB Heavy 10 Lathe. I put a piece of plastic rod in the chuck and a pen in the tool holder to simulate thread cutting. However I am having trouble matching up the actual TPI vs what the lathe is set for. At first I tried to replicate 10 tpi. I set the gear to the correct slot, put the sliding gear "in" and put my3 position gear selecter in the "center". The result was much more than 10 tpi and more that I could count. So I set it for 5 tpi and tried again. This time I got about 15 tpi. I have my Bull gear pin "out" and my back gear "in" and my flat belt on the middle pully.
What am I doing wrong? Could I have metric gears? I bought the lathe used and dont know its history.
Any ideas on what to try? Thanks Steve