Bent thread

It's wonky because trying to start it with a die is rarely successful for straightness, plus you have to use a lot of force to cut 100% of the thread

So above 6mm it tends to be a lot easier if you get the lathe to do 80% of the work and the die does the last 20% kinda thing

The bigger the job, 8 10 12mm, the less successful a die will be at the start

If you want to do a straight start with a die then put the job into the lathe chuck and hold the die with the tailstock barrel when you wind it on

A lot of very useful info here and proof if it were needed that agreement between engineers about the way forward is often not forthcoming. There has also been raised some questions regarding my options which I will try and answer.

I was an electrical engineer before retirement so mechanical skills are being acquired by practice on its own, which is not to my mind entirely the best way of so doing. The workshop is primarily for enjoyment and to keep my mind active, activities that become overburdened with stress tend to get left by the wayside, however otherwise beneficial they may be. I rarely have any need for threads bigger than M6/0BA and mostly tapping at that so I have never identified a need for learning the skill of thread turning on the lathe, dies in stocks usually works and will so going forward now I know a bit more about things.

The M10 die and 1" stock cost me £14.58, quite enough for two threads. I have no doubt that a suitable holder and insert may well cost a similar amount however such an approach requires me to give up a significant quantity of spare time to learning the skill to an adequate level. It may be useful but I have loads of other activities which I consider more important. I am never going to know everything about mechanical engineering, or indeed a lot of other things but you have all kindly given me enough info to hopefully enable me to sort this problem.

I'll give it all a try on some suitable scrap and let you know.

Kind regards

Martin

Let me be totally honest, if the threads had been straight in the first place, the matter would not have reached the forum. The turned section is a nice touching fit in the toolpost, the threads just hold it down. Obviously I want to do the best job I can hence my request for help to which the response has been most generous.

Martin

Although (as I previously commented) I like lathe cut threads, as Nicholas Wheeler says it can sometimes be a hassle to set up for a relatively quick 'one-off' job.

Something I knocked up years ago (which has a relationship to electrical conduit threading tools) is great for getting common threads started and aligned perfectly staright - was quite easy to make (can't remember where I saw the plans originally) and works a treat if the thread isn't going to be too short. This has a set of common metric bushes for 4,6,8 & 10mm. Other sizes can be knocked up in 5 mins as required.

One big advantage is the work can be held in your bench vice, avoiding the chance of slippage you get sometimes (particularly on bigger thread sizes) when holding in a lathe chuck when using tailstock die holders etc..

There may be commercial versions available? But quite easy to make for free from odd stock lying about

regards Mike

But you might get them right first time ????

Just saying .

Me … In the circumstances, I would have probably drilled and tapped the body, and inserted ready-made studding, cut-off bolts, or whatever, secured with a retaining compound.

Much less hassle, and decent taps are cheaper than decent dies.

MichaelG.

Larry

I presume your comment is aimed at me, just what is it that your saying please, for the avoidance of doubt. Presumably lacking skills and asking for help is not a condemnatory act?

Michael

After a wholly unsatisfactory afternoon not cutting threads I'm inclined to agree with you. I have come to the conclusion that I'm going about what I'm trying to achieve the wrong way, as has been suggested by others and single point cutting is the way to do it.

For some reason I cannot get the tailstock die holder to start cleanly, why I know not but I think something to do with pressure against the stock and adequate rotation. I've tried half a dozen times with no success, the lack of a brick wall is an improvement.

Plan B is a 13mm sleeve with M8 tapped holes each end and studding Loctited in. It is I suppose marginally less strong than a turned from solid stud, but I can do it and it will likely work. Plan C involves finding a small engineering shop to make something from a drawing which will cost about the same as a toolholder and inserts and be a lot quicker than my learning curve.

I didn't anticipate that cutting an external thread would be so difficult and I will learn how to do it properly in due course but other things have to have priority, but thanks everyone for your valiant attempts to help me.

Best wishes

Martin

just one thought as to why you may still be having problems even with a tailstock die holder. What diameter (OD) is the die and what is the dieholder designed to take? It's not unknown for people to put a 25mm OD die into a 1" holder which throws the die off to one side and makes it difficult to start.

Martin, you could remake the stud with each thread longer with a short lead in to steady the die. Once the threads are satisfactory, cut them to length. It's also worth checking that you're starting with a suitably sized workpiece.

In reality, the only moderately tricky bit about cutting M10 threads with a die is holding the work securely.

Ok

A couple of pics, this is where I started,

a piece of 10mm bar with the end reduced to 9.8mm and bevelled. I subsequently turned a spigot to just under the minor diameter of the thread to centre it all. The next shows the horrible end result,

I have a suitable tommy bar for the collet chuck and the tailstock die holder is a bog standard Arc product. It's a brand new 1" die and I measured the holder at 25.4mm so I think they are intended for each other. I don't disagree with you Nicholas, this really shouldn't be difficult but for some unexplained reason it is. I'm not the most expert mechanical engineer but this is basic stuff isn't it?

I've had enough today, a further look at this in the week.

Martin

You don't need an insert and holder, just grind up a bit of tool steel. As you can finish it with a die the exact form doesn't matter. If your lathe won't go slowly enough wind it round by hand. A decent undercut to run the tool out into helps a lot.

Are you using the correct side of the die?

Martin, can you tell us the brand of die you're using, what it's made of and whether it's split or solid?

The picture below shows an M10x1.5 thread I've just cut on some EN3 mild steel using a woodturning lathe. The bar was held in an ER20 collet chuck in the spindle and the thread turned using a bog-standard two-handled die holder held square against the start of the thread with my drill chuck.

The die was a Presto HSS split die, and the diameter of the section of bar to be threaded was first turned down to exactly 10mm using a hand-held piece of HSS rested across the lathe's banjo.

I wouldn't want to have to do this sort of thing this way very often, but it is perfectly doable all the same. There is no discernible bend in the turned section.

I've tried cutting M10 on EN3 using the wood lathe in the past without success. The only difference in my set-up then was I was using a solid Aldi carbon steel die; it just wouldn't cut. It's that kind of situation that can tempt you to use too much force and then cause things to bend.

Having said all this, I can't see how you can have arrived at the result in your second picture using any kind of M10 die. If I looked at the second picture out of the blue I'd say someone has used a file with the intention of turning a dog-point.

I think Martin said above that he was using the correct side.
I sometimes use steel hex bar to cut big threads with a die so it can’t spin in the chuck and also it seems to be free cutting. Screw cutting in the lathe can be very satisfying if you have a gearbox with the desired pitch. Setting up change wheels is a pain.
I agree with Hopper: turn the bar down to 9.8 mm or less. Commercial threads are usually well under nominal size over the crests.

I just thought about something reading this. I made a dieholder for my lathe that fits/slides from the tailstock.
Now the type I got might work, just thought about it had not tried it yet, and that is to use a steady rest clammed on in my case about a 2 inch smooth round part just after the 4x tightning screws for the die onthe holder's tip, that will hold the die+dieholder in position to start, and in my case it can work for say 10mm or so before it run out of space, just a thought.

I would commonly turn it to a slightly lower dia (ref Tubal Cain in "Drills Taps and Dies) giving negligible performance loss but much easier threading (with a die).

(.... and to suggest thread-cutting as others have done ...up to a shoulder at that.... for someone who, by his own admission, is inexperienced in threading is unhelpful imo)

Two more pics,

a pretty standard M10 split die by TWT UK whoever they may be but bought by me from Drill Services Horley along with the die stock. My understanding is that we are looking at the trailing face of the die and the thread is started on the other side. I do hope I've got that bit right.

The general set up for illustrative purposes only. Right back in the first post I showed the stud with threads cut with the same die, which was fine except for the bend in the thread at both ends. They were hand done in the vice and it was necessary to apply some force to the diestock to start the thread and it was by no means easy to cut. Is it possible that its just a cheap and nasty die? The narrow spigot was turned, it's not a result of the die, I was trying out an earlier suggestion.

Regards

Martin

The penny has dropped. I see on closer inspection that you tried to start the thread beyond the dog point but basically got nowhere.

If you were using the same die as the one you cut the complete but bent thread with, then, in the case of this initial and complete failure, I'd say there was not enough force constantly applied pressing the die on to the work to get the thread properly started.

So would I; my purpose was to demonstrate that even using a wood lathe and a hand die holder, and threading bar at the full diameter a useable straight thread can still be cut.

ETA:

Looking at your die, I can't help seeing almost non-existent teeth on it.

Edited By Bill Phinn on 13/11/2022 23:06:26

I think that's the angle of the photo, is this better?