shop smithy 1239 questions

||I have a shop smithy 1239 that I traded for and I am being asked to ||thread a rifle bbl on it. I didnt get any paperwork with it so I am ||confused if its possible to cut threads with it. what little I can ||find on it looks like it can but I cant figure out how you decide ||where to start the thread. I have cut threads before on other ||machines and they all had that dial that had the 1-2-3-4 position on ||it to show where to start your thread. I always used the same number ||although I was told you could start on the opposit nuber also....any ||info would be appreciated. || ||Ben

Specs say it has change gears, but no mention of a threading dial

Just like any threading indicator dial, some threads can be done on any mark while others are limited. Starting on the same one all the time is indeed a good safe procedure to do as you never end up having to make the choices of what is acceptable.

-- Bob May Losing weight is easy! If you ever want to lose weight, eat and drink less. Works every time it is tried!

"Paperwork"? You mean operator's manuals? They typically all assume that you already know how to *use* a lathe, and focus on how this particular one is built so you can repair it later.

Hmm ... I don't know them by number, but there is the Smithy line, and the ShopTask line -- two competitors. Both are import machines from China, so they presumably have certain similarities.

I've never touched a Smithy, but a friend has an older ShopTask, and it has what I consider to be a somewhat strange setup for threading. (Aside from having to build a train of gears specific to the desired thread pitch, which is common on many older machines.) Anyway -- I tried to thread on it, to show him how to do it. I could do it, but it was a bit fast for the thread which he wanted.

But what it has is a dog clutch between the gear train and the threading leadscrew. There is an electronic "threading dial" which lights four LEDs in sequence, and you have to flip the lever at the right point as indicated by these LEDs -- or keep the dog clutch engaged the whole time and turn the spindle forwards and backwards by hand. The LEDs are currently supplied installed in the ShopTask machines, but were originally kits to be added on your own later.

Unless you also have the slow-speed option installed, the slowest spindle speed will be too fast at the thread pitches common with rifle barrels -- unless you have a *lot* of practice engaging the dog clutch at just the right time.

And since you will be threading to a shoulder, there is also the secondary problem of disengaging the clutch in time. Normal practice is to machine a runout groove to allow the threading tool to stop in, but I think that rifle threads tend to be made without a runout groove (to avoid generating stress risers where the barrel can fail), so you really will want to hand crank the spindle while cutting the thread.

Frankly -- I would rather use a more solid lathe with slower spindle speeds available for this task, but if you want to badly enough, you can probably do it. I would suggest that you make some mock-ups of the barrels from plain steel and practice cutting them first, before you risk a barrel which may be worth significant money.

I would suggest that you sign up for a machining class at a local high school or community college -- if any are still taught in your area. Once you have this, you are in a better position to understand how to thread you your own machine. But you *will* have to adapt to the idiosyncrasies of your machine.

Good Luck, DoN.