@projectnut - Most Excellent, Sir. Thank you very much!
Okay, new question. No threading dial and (at the moment) no reverse capability. Is threading even possible? I know there are techniques for threading without the dial, but as far as I know, they require the ability to reverse the lathe.
EDIT: Checked the plate on the motor and it is reversable. Ordered a drum switch.
Glad to hear your motor is reversible. Your solution for threading is the same as mine. I installed a 1 hp 110/220 single phase 1725 rpm reversible motor and drum switch on my machine to accommodate threading. Like most machines of this vintage a threading dial was not an option. If you look through the catalogs on the Vintage Machine website I don't think you'll find a single Seneca Falls machine that lists it as a standard or optional feature.
When starting a thread (either internal or external) I select and install the necessary gears, and chuck up the stock. I then back the carriage off about an inch or so from the stock before I engage the lead screw. Engaging the gearset and leadscrew for several revolutions before engaging the cutter in the stock eliminates the play. Set the cutter depth to about .002" and make a pass. You can scribe a pattern on the stock that can be measured with a thread gauge. Each pass will require backing the cutter past the end of the stock to a similar start position to keep proper registration.
Without a thread gauge threading to a shoulder can be tricky. You have to either A. shut off the machine and let the cutter coast to the end point, then back off the cutter and reverse the machine, or B. leave the machine running and have the coordination to back off the cutter and reverse the lead screw before crashing. Since the chuck on these machines is threaded to the spindle there is the possibility that it can come unscrewed should you try an instant reverse. My machine will go as slow as 40 rpm when in using the back gear and the largest cone on the spindle pulley. To date I have not unscrewed the chuck, but most threading to a shoulder has been done using method A.
Often times on an external thread I cheat and make the stock longer than necessary. Then I can turn down a section to a diameter smaller than the root of the thread and put that end in the chuck. Now you don't have to be so precise as when to stop or back off the cutter. You can let it run until the full diameter section of the shaft is threaded then shut it off as the cutter passes onto the smaller diameter portion of the shaft. Then back off, reverse, and repeat until the proper thread depth is achieved.
Another method is to use a longer piece of stock and just cut a groove at the end of the length needed to be threaded and follow the same procedure as mentioned above. When finished threading just part off the unneeded section.
Essentially you shouldn't disengage the leadscrew if you want to keep proper registration.
I have used these methods to cut hundreds if not thousands of threads using my Seneca Falls machine without a thread dial. I must admit it is far easier to do the same procedures on my Sheldon machine with a quick change gear box and thread dial. As benmychree mentioned any thread dial from a machine with the same pitch on the leadscrew should work. Maybe I'm old school, but these methods have worked for me so I see no need for a thread dial on this machine. If I'm in a hurry or lazy I'll use the other machine.
Here are a couple [pictures of my machine. Note I mounted the drum switch on the left front leg of the stand. It's in a convenient place so I don't have to move or reach over anything to use it. I also have a gravity tension on the motor belt. Should I do something stupid the belt will slip rather than crashing tooling or stripping gear teeth.
