It's 1/2"-12 Ya Dummy, Not 1/2"-13!

[bill70j]

On my mill drill, one of the handles that drives the spindle drill press-style is badly bent. I read somewhere that they would be threaded 11.5 threads per inch but mine seem to measure 12 tpi. I haven't actually got the replacement piece threaded yet as life got in the way of my hobbies!

Craig

Craig:

FWIW, I bought an 80's drill press off Craig's List that was manufactured by King-Kong Industries which is a Taiwanese company. Its handles were also bent -- and badly rusted. I replaced all the handles with 1/2" stainless rod and cut 12TPI threads on both ends - and the fit is fine on both the ball and socket end. So you should be good to go at 12TPI.

Bill

 

[Janderso]

So what's the deal?
Is this 12 TPI produced on machines/dies that are specifically designed to produce this exact getto thread or is it due to incompetence?
I mean, we do live in an International business climate with standards worldwide.
The standards I am referring to are Imperial and metric fine and course.

 

[mcostello]

1/2 x 12tpi used to be common too many moons ago for Me to have been here. I have heard old timers say it was used.

 

[RJSakowski]

I suspect that there is a lot of legacy tooling around that probably sells for peanuts because it is no longer an accepted standard. I don't believe there is any specific requirement that parts be made to current standards. From a practical standpoint, it makes sense to do so as fasteners would be far more costly if they were made to an archaic specification. However, if you have a supply of parts and tooling, qwhy not? I have heard of manufacturers using crazy off the wall threads on parts specifically to discourage people from using other than OEM replacement parts.

 

[benmychree]

Ugh, yeah ... been there, lol. In 2014 my company purchased 7 new Summit machines and we had to go through that learning experience. Glad I learned at work because modding the coolant nozzle on my PM1236 ran me into a BSP thread. That could have gone sideways if I wasn't prepared.

The Brits use 1/4 BSP, 19 TPI I have a big cabinet of British taps and dies, if anyone is looking for them ---

 

[T Bredehoft]

Early in my apprenticeship, my foreman brought me a 5" 4 jaw chuck, missing one adjustment screw. He pointed out that it was English and I should determine the thread on the existing screws before I began. It turned out to be a Whitworth thread, 1/2 12. (55º). I made a threading tool (55º) and chased the thread, cut a square on the end to match the other screws. It turned out to be something a friend wanted fixed. I learned to use an optical comparitor and threading on that job and to watch what the threads really were, not to accept a guess.

 

[Winegrower]

I have a bunch of holddown rods for the Bridgeport that gave me fits until I figured out they were 1/2-12 instead of 1/2-13.

 

[benmychree]

One reason for the change from 12TPI to 13TPI was that 12 reduced the root diameter too much resulting in a weak tensile strength, it was changed at the period of WW-1, I was told.

 

[projectnut]

Craig:

FWIW, I bought an 80's drill press off Craig's List that was manufactured by King-Kong Industries which is a Taiwanese company. Its handles were also bent -- and badly rusted. I replaced all the handles with 1/2" stainless rod and cut 12TPI threads on both ends - and the fit is fine on both the ball and socket end. So you should be good to go at 12TPI.

Bill



View attachment 299921

I have 2 drill presses purchased new in the 1980's that identical to the one you have. Both were produced in Taiwan by the same company under private labels. One is labeled "Rockford" while the other is labeled "Farm & Fleet". They were both purchased at our local Farm & Fleet farm store. The first one was purchased in 1982 and the second in 1984. The company that made them would put any name on them you wanted with a minimum order of 500 units. I suspect the same drill presses were made under hundreds if not thousands of private name brands.

 

[Larry42]

British Standard Pipe threads are the standard on current European machines. They come as either tapered or straight.