Methods for producting straight threads?

[amillertobe]

When the conditions are such that a lathe is not available, or a lathe is too featureless or lightweight to produce sufficient threads, what are the options for producing straight threads?

Basically all hand wrenched threads are crooked. For some purposes even a very slight misalignment will cause problems, such as tubular structures that have long distance between the attaching point and the critical point. Imagine for example a suppressor, which has to be concentric or it will destroy itself from the first shot.

So, what are the options for making straight threads? Are thread dies true to their faces in general so they could be supported to align them with the part? All options can be considered, including 3D printing jigs and buying stuff that may be even a bit expensive, but obviously "just buy a lathe", although being a problem solver, would not suffice, because that would nullify the whole question. Also, many parts can not be mounted on a lathe that will have features to be threaded.

Using dies and taps WITH a lathe that is not good enough to produce threads will usually produce quite sufficient threads. Aligning parts with a mill is also an option.

[JoeLee]

How do you figure that all hand wrenched threads are crooked ?? and what do you call crooked ? What makes you think your die cut or tapped threads are cut crooked and that whats giving you the illusion of crooked threads aren't the nut or what ever your threading on your cut threads?

If you want to start and cut straight make a die holder like this.............. I have a few of them for different sizes.

If you try to start a die with the two handle die holder that comes with most sets then there's a good chance that you'll end up cutting "drunken threads" as some have referred to them as.



JL......................

[J Tiers]

Hand die cut threads are crooked. He's right.

And, they have the wrong pitch.

Why? Because nothing in the process stops that from happening, so it will.

What keeps the die so perfectly straight that it does not cut at an angle, or slightly vary the angle according to the forces put on the handle? How does the very short section of thread in the die keep the pitch perfectly correct?

Yes, of course the errors are small, but they will be considerably larger than decently single-pointed threads. How large or small the errors are depends upon the way the die is used. For a lot of uses, and for short distances, it is usually fine to use a die.

If you do not believe this, then would you use a die to cut a leadscrew? If you would not, why wouldn't you? (because it cuts drunken threads of the wrong pitch).

[old mart]

One old method for individual sizes of thread was to turn up a top hat with a very thin brim to put in the diestock before fitting the die. The hole was just clearance for the male thread and helped to keep the die square on.
The quality pipe threaders had a set of scroll jaws on the other end of the body from the die jaws, used to keep the pipe square on when threading.

[epicfail48]

If you want perfectly concentric thread, you kinda need a lathe, anything short of single-pointing is going to leave some error, though whether that error is significant is another question
USing a mill would probably be the next best thing. So long as the process is set up properly, a cnc mill I would imagine would give results nearly as good as lathe turned threads with a thread milling cycle. Barring that, holding the tap in the quill of a manual mill would be fairly accurate I'd wager

if all you've got is hand tools, you can get pretty close with a tap. A tap guide will do a decent job of getting the tap running square to the face of the piece, and if you needed good concentricity you could go about making a tap guide that slips over your workpiece to both locate the hole and guide the tap. Picture a 3d printed pipe cap with a hole for the tap in, that's what I'm imagining here. Would it be good enough for suppressor threads? Probably not, but it would be better than running the tap freehand

[mickeyf]

This boils down to "How perfect do the threads need to be?" followed by, "How imperfect are the not-done-on-a-lathe threads?"

[Peter.]

I just made a gib adjuster with a 5mm thread on it. I turned the threaded length to the major diameter but with an added section turned to the minor diameter for the die to slip onto. To be doubly-sur eI used the tailstock to support the die when starting. The thread came out pretty true.

[The Metal Butcher]

The answer to perfect threads without a lathe is a bigger lathe and better fixturing. Not much can't be turned. A custom HBM with a leadscrew or a CNC one with threadmilling can do what can't be turned.

[BCRider]

If you're after the degree of accuracy that you are calling for with a thread into the end of a firearm silencer I don't think you really have an option. Wellll..... At least not without a custom threading tap or die. I'm thinking a special custom tap that has a long good fitting pilot on it to fit the hole that the thread has to align with so you force the thread into acceptable alignment.

It might be the same with a die where you'd have an external pilot hole that does the same thing.

For the die you might even fit the die into a tube with the proper ID to suit the job and make the seat for the die slightly oversize and then use one of the industrial adhesives to glue the die to the alignment tool using a master part that was single point turned to ensure perfect alignment.

I believe that piloted taps or guide jigged dies of this sort would provide the results you're after. But of course you need a lathe in the first place to make such tooling to start. Or deep pockets to order up such tooling. But once made you could make multiple parts that have single point like consistency and accuracy in much less time.

[Fasturn]

With a Die, I put a screw ( same thread as Die ) in lathe tail stock. With the Die on the screw butt it up against the part in the spindle. Now you have more control with the screw pitch guiding the die. Thread , smile and open a Beer. Happy new year !

[David Powell]

In my experience there is NO way you can produce really good threads without single pointing them in a lathe
Tailstock or turret mounted die holders produce far far better threads than you can get with freehand use of the usual sort of die holders, but they, in turn, are usually slightly inferior to those single pointed in the lathe.
For threads which need to be good, but not perhaps" Perfect" I have found that single pointing to about 70 % of nominal depth and then running a die held in a tailstock or turret holder over the already partially formed thread gives an acceptable result nearly every time, and is much quicker than single pointing to a finished size.
I would add that most" Box Store" taps and dies are rubbish, and that to get good threads,or even reasonable threads one needs good quality, known name taps and dies , and proper lubricants for the materials being threaded ,regardless of the ways they are presented to the work.
Hope these hints help. Regards David Powell,

[Rich Carlstedt]

I think some of the responses are over complicating the posters question so let me rephrase it if I may.
What methods are available without a lathe to make die cut threads straighter ?

This is not a argument for what perfect threads are, or whatever, but a straight question
Joelee, Peter, and Fasturn mentioned a couple of techniques and the point about using a quality die is paramount to making acceptable threads

Personally , I use JoeLee' s method , but also have a very old style die holder that came with a cam operated shutter that closes around the stock before the die engages it whiuch controls the face of the die and the work piece

Rich

[JoeLee]

I think some of the responses are over complicating the posters question so let me rephrase it if I may.
What methods are available without a lathe to make die cut threads straighter ?

This is not a argument for what perfect threads are, or whatever, but a straight question
Joelee, Peter, and Fasturn mentioned a couple of techniques and the point about using a quality die is paramount to making acceptable threads

Personally , I use JoeLee' s method , but also have a very old style die holder that came with a cam operated shutter that closes around the stock before the die engages it whiuch controls the face of the die and the work piece

Rich

My old die holders also have the cam adjustable three finger guides but I never found that to be the best design. It helps some but it's flimsy.

If you really want to check the die for squareness I suppose you could use a thread plug gauge. Or cut a thread on the lathe and check it for squareness against the die.

JL............

[J Tiers]

The guides of whatever sort are certainly better than nothing.

Essentially, if you want really good threads square to the axis of whatever it is, you have to lathe cut them, or the equivalent. That's the way to get the threads on-center, square to the axis etc.

If you just need threads, a die used by hand or with a guide, are OK.

There are dies and machines that cut very good threads, but most have no access to them, so they are irrelevant.

A good die holder in the tailstock will do a better job than any guide etc. In fact, in some materials, the actual threads, without considering how straight and square they are, are better with a die, which cuts "full profile". That is where the idea of partly single pointing, and finishing with a die comes from. You get a combination of characteristics.....and a lot of flak from purists who will tell you to "grow a pair and do it right".

There are "single point" threading tools that cut the full profile, and they are worth considering if you need very good threads, and do not want to have to deburr the threads after cutting them. Those are not cheap, plus you need the one for the exact pitch and class you are cutting.

[JoeLee]

The guides of whatever sort are certainly better than nothing.

Essentially, if you want really good threads square to the axis of whatever it is, you have to lathe cut them, or the equivalent. That's the way to get the threads on-center, square to the axis etc.

If you just need threads, a die used by hand or with a guide, are OK.

There are dies and machines that cut very good threads, but most have no access to them, so they are irrelevant.

A good die holder in the tailstock will do a better job than any guide etc. In fact, in some materials, the actual threads, without considering how straight and square they are, are better with a die, which cuts "full profile". That is where the idea of partly single pointing, and finishing with a die comes from. You get a combination of characteristics.....and a lot of flak from purists who will tell you to "grow a pair and do it right".

There are "single point" threading tools that cut the full profile, and they are worth considering if you need very good threads, and do not want to have to deburr the threads after cutting them. Those are not cheap, plus you need the one for the exact pitch and class you are cutting.

I discovered the full profile inserts a long time ago. That's the only way to go if you want clean threads. The best part is they don't leave the burr and you can get some pretty precise fits when you don't have to mess with that nasty burr.

JL...............