Cutting multiple threads

[tornitore45]

The lead on that thread is 2 threads per inch.

You mean 2 inch per thread = 0.5 TPI. Even worst!

[JimGlass]

Lets think about this. 2 tpi, single thread the lead is .500. 2 tpi, double thread, the lead is 1.000.
2 tpi, triple thread, the lead is 1.500. 2 tpi, 5 threads, the lead will be 2.5,,,,,,right?

The nut will advance 2.5" per revolution right?

I think I would call a shaft like that a "spiral spline"

Jim

[stevec]

The lead on that thread is 2 threads per inch. Not many lathes capable of that lead. Most limited to 4 threads or more per inch.

Jim, 50% of my lathes are capable of 2 threads per inch (I have 2 lathes) But if I remember correctly the OP has an older model SB or Logan that doesn't have a 2 tpi capability, so the question seems purely academic.

Mr. Ron, is there NO possibility of gearing (or cog belt driving) the stepper 5 to 1?

To respond to your original question "How difficult is it to machine a nut for acme 1/2"-2, 5-start for 1/2", 5-start acme threaded rod?"
I'd say, in your case, "too difficult" because of the above (and other) constraints.

[tornitore45]

Note to self: Engage brain before unlocking keyboard. The number after the diameter is usually the TPI, not the lead as I took it for.
Jim you are right.

[f350ca]

Just for interest sake , and what would you use it for, my 16 inch Summit cuts 1/4 tpi , I've never tried closing the half nuts with that setting engaged. Even at 20 rpm the carriage would be traveling 1 1/3 inches per second.

Greg

[Mr Ron]

I may not be stating this correctly. What I need is a nut that will advance quickly along an acme screw, 1/2-10 with 5-starts.

[Conrad_R_Hoffman]

Possibly this sort of thing-
http://www.jagsonsindustries.com/screw.html

[JimGlass]

Note to self: Engage brain before unlocking keyboard. The number after the diameter is usually the TPI, not the lead as I took it for.
Jim you are right.

I'm not sure this 1/2-2, 5 start thread can be considered a thread. I would call it a helical spiral.

With a lead of 2.5" per revolution, I doubt this shape can be cut on a conventional lathe.

A while back I needed to cut a thread with three starts on my 13" JET lathe. It was a prototype job and was not real fussy. What I did was set the compound rest 90* to the cross slide. Set the gear box for the correct lead. Must have been 4 TPI. I calculated the thread depth. I cut the first thread
to full thread deep. For the next thread I advanced the compound rest 1 thread pitch and cut the second thread to full depth. Advanced the compound rest again and cut the third thread to full depth.

Very time consuming because the tool bit in feed was straight in so the chip load was rather heavy, but I got it done. Several weeks later the customer contacted me wondering how I made the thread.

http://smg.photobucket.com/user/jglass/ ... t=3&page=1



Took time just explaining to the engineers exactly what the thread was.


Jim

[Hopefuldave]

My personal preference when cutting multi-start threads is "walking" the spindle gear - it does depend on the teeth on the spindle gear being divisible by the number of starts!

Start by cutting one start to full depth, then mark mating geartrain teeth with a spot of correcting fluid and ease the banjo to disengage, then count around the required fraction of the spindle gear (by turning the spindle) and reengage with the spindle gear rotated relative to the idler - then cut another to full depth, rinse and repeat.

The most likely problem will be putting excess stress on the leadscrew geartrain, as there'll be a big speed-up of the leadscrew relative to the spindle - some take very light cuts, some drive the spindle via the leadscrew (not using the spindle motor), some use a milling spindle at right angles to the thread's helix angle to cut the thread with the spindle at very low RPM - many ways to skin this particular cat!