Turning Square Threads

[TommyD]

Anybody do it?

My boss is a mentor on a high skool robotics team, I like this guy. Anyhow, he asked me if it is possible to machine square threads. I said 'sure it is'. He's been telling me about having to but square thread drive rods for student projects, this has come up more than once.

A student in my 'Lathe 101' class asked me if I was going to show them how to turn threads in class. I told her (yes, a HER) that I wasn't sure, I'd have to ask my boss, the instructor. See where I am going here?

I'm going to be hitting him up for tooling to cut threads. We need holders and inserts for our Dorian toolpost but what is used for square threads, a parting blade? I'm sure there has to be renewable carbide holders.

Gawd, it's been so long since I machined threads, I'm used to standard sizes that we'd machine with the lathe and a diestock. I just missed out on some p/t time work for a hydraulic company and another is advertising.

 

[TommyD]

Oh, it's a Jet lathe. The chucks have proven to not have the most concentric closing jaws. This is a great teaching moment for me. We ALWAYS bored soft jaws where I apprenticed for making bearing seals, the ones at skool are hardened, we ALWAYS put a magic marker line between the 2 jaws between the pinion over the manufacturers badge on the face of the chuck. I have shown them how the chucks run out by chucking a 3/4" dia. dowel pin. I then take a chip along the dia AFTER I place my mark. I'll take the piece out and rechuck it like 180° and show them the run out. I'll rechuck it between the lines and show them how the TIR stays with the mark.

I haven't gotten any feedback on my part of the class but students stay during their dinner break (this is a Monday night class) and after they are able to be dismissed for the night. I guess I'm doing OK?

 

[tertiaryjim]

Had to cut some square threads for pump shafts. Management wasn't able to understand the value of a machine shop and wouldn't pay for tooling.
So, I found some brazed carbide cutoff tools in a drawer and ground them to width and proper lead or pitch clearance .
Threaded at least a dozen shafts with it and had nice clean cuts.

 

[planeflyer21]

I'd imagine the pitch is fairly small for robotics? How big are the robots?

We cut some square thread for an exercise in school, just for the exposure (I believe their reasoning was the large aerospace manufacturing footprint here).

I'm looking forward to seeing your progress!

 

[seasicksteve]

I cut a 1.00" x 10 TPI square thread a few weeks back. I ground a tool on a HS steel blank, I left the tool tip just slightly under 1/2 of the thread pitch. I set the compound parallel to the work piece and touched off the tip of the tool on the work and set 0. I used the crosslide to feed the tool to the proper depth and then used the compound to get the thread fit to the mating part. This worked perfectly for my situation YMMV. There is info in the machinery's handbook on thread forms including square threads

 

[John Hasler]

My boss is a mentor on a high skool robotics team, I like this guy. Anyhow, he asked me if it is possible to machine square threads. I said 'sure it is'. He's been telling me about having to but square thread drive rods for student projects, this has come up more than once.

Just out of curiousity, why do they need square threads?

 

[TOOLMASTER]

 

[Rick Leslie]

I've cut square threads on rifle barrels a good bit. 12 to 16 pitch I believe. I just used HSS and ground it for size and relief as said above.

Please encourage the young lady in your class to continue. A young lady whom I consider to be a good friend says that she wishes more women would get into the mechanics/machinist field.

Just out of curiousity, why do they need square threads?

I believe the square threads bear loads much better than "V" threads.

 

[John Hasler]

I believe the square threads bear loads much better than "V" threads.

Square threads are more efficient and can be stronger than trapezoidal threads. I was wondering why they are needed in this particular case.

 

[4GSR]

.....snip......
I believe the square threads bear loads much better than "V" threads.

When you compare a square thread to an Acme thread, there is very little difference between which one can carry the heavier load. Designs I work on, most of the time I use the same design formulas for square threads and apply to Acme and Stub Acme threads. Most of the time, there's more thread strength by 3, than there is in cross section under the thread! In testing, I have sheared the threads out of things without pulling the part itself into.

One of the problems of an square thread carrying a load, it doesn't stay "centralized" like a
acme or vee thread will do when loaded.