Cutting threads on a micro-lathe?

[pgmrdan]

Is there any great advantage to using the lathe to cut threads instead of using taps and dies? On the scale of a Sherline or a Taig it seems to me that using taps and dies would be the way to go but I'm not certain about that. Come to think of it, I don't know that I've seen taps and dies in extremely small sizes in the catalogs I usually look at.

What are the pro's and con's of each method?

Thanks!

 

[markba633csi]

Certain types of threads must be lathe-cut such as large diameter, fine thread (think camera lens mounts)
I know that taps/dies are available down to at least 2-56 thread and maybe smaller, taps and dies larger than about 3/4" are difficult to use and expensive
Mark

 

[4ssss]

Lathe cut threads are more precise as you can measure the threads as you're cutting with 3 wires or a thread pitch mic.

 

[Latinrascalrg1]

IMHO the only thing a tap and die have over single point threading is the Convenience of portability and remote use.

 

[ThinWoodsman]

On that scale, it might be faster and easier to use taps and dies, then clean up the thread in the lathe only if you need to.

 

[4ssss]

On that scale, it might be faster and easier to use taps and dies, then clean up the thread in the lathe only if you need to.

Then you would have the added trouble of picking up the threads

 

[john.oliver35]

You can turn nice threads on a Sherline, although I wouldn't want to turn a big batch of them! You work under hand power when threading on a Sherline so you can go nice and slow and see what you are doing. With a nice sharp HSS single-point tool you can see the thread develop, and can feel if you are taking too much depth and stressing the part.

Threads cut on the lathe can be more concentric with the the rod or hold you are threading if you cut to size and then thread without removing the part from the chuck. Also you can sneak up on the fit if you are making a 'special' part where you are matching mating parts for a special fit. I have turned several 3/4-16 threads to make special fixture's/faceplates for the Sherline and they hold very securely to the spindle.

It's also just kinda fun and satisfying to do. Now if you have a buck of 50 parts to thread, the novelty will wear off quickly ;>

 

[ThinWoodsman]

Then you would have the added trouble of picking up the threads

It's not so bad, though yeah at small scale a bit of a pain. The third, expensive option of course is thread chasers. Haven't tried them as I haven't come across a cheap set.
I currently do most of my interior threading with taps and my exterior threading with the lathe. Been considering a tailstock die holder for the latter, as the screwcutting process requires a lot of time and care that doesn't always feel worth it. Saves on having to turn the spindle by hand, though.

 

[David S]

Most of my thread cutting is for sizes below 10-32. It is way quicker for me to cut external threads with a die rather than go through all the trouble to set up the change gears on my Atlas 618. On the other hand I have used the Lathe to cut special threads like 12mm x 1.

David

 

[Bi11Hudson]

An Old Fartz input here.

I use dies (and taps) as small as 3/0-120, which is 0.034 in. A fuzz smaller than 1 mm. Most times I use the die direct on wire. But, there are occasions where threading on the lathe is preferable. Where and when to do one or the other is mostly dependent on you and what you are working on.

My lathe(s), both of them, will cut threads to 120 TPI. I, on the other hand, am not near that good. 64 TPI is as about as small as I will tackle. When I do cut threads with the lathe, I don't cut to full depth. Then finish with the die. The lathe cut threads are coarse but provide true concentricity to the wire. Once they are started, the die provides a smoother full depth cut.

Anything below 1/4 inch is cut manually. I rigged a hand wheel on the spindle, on the far outside of the head stock. 1/4-40 and smaller. Conceded, much(most) of my work below Nr 2-56 is in brass. But it works well enough for what I do, model building and instrumentation.

I don't recall the last time I had to cut fine threads in the larger sizes. It has been a while though, many years . For that kind of work, it's vital to use the lathe. There are no taps and dies for the more specialty threads. But for small, more proportional threads it is well within the capabilities of a small machine.

My big lathe is a 12 inch machine, a Craftsman. Huge, but light weight. I use chucks adapted from a UniMat DB-200 for small work, below 3/16" / 5mm. Spindle thread M12X1. Even when I use a die with no guide cuts from the lathe, I still use the lathe to spin the work. And the die against a tail stock adapter. I don't have a tapping jig. Threading with a tap is done from the drill press, a tiny milling machine. With power off, obviously.

Sources: Taps and dies should be available from industrial suppliers down to 0-80 TPI. Smaller sizes from jeweler suppliers. I'm not too sure where, I haven't bought any for a long time. Fee Bay has metric taps and a "screw plate", a single plate with several threaded holes for making the male version. Sizes down to less than 1 mm. But I've only seen metric. USS sizes aren't listed. There was a supplier last year that had as small as 4/0. But I lost the address in a hard disk failure. But within 6 months.

Not a full discourse, but I hope I've added enough insight to be useful.

Bill Hudson​