Bent thread

[Mike HurleyParticipant @mikehurley60381]

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

[larry phelan 1Participant @larryphelan1]

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

Just saying .

[Michael GilliganParticipant @michaelgilligan61133]

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.

[Martin Shaw 1Participant @martinshaw1]

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

[JasonBModerator @jasonb]

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.

[Nick WheelerParticipant @nickwheeler]

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.

[Martin Shaw 1Participant @martinshaw1]

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

[duncan webster 1Participant @duncanwebster1]

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.

[Nick WheelerParticipant @nickwheeler]

Are you using the correct side of the die?

[Bill PhinnParticipant @billphinn90025]

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.

[Simon CollierParticipant @simoncollier74340]

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.

[Chris MateParticipant @chrismate31303]

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.

[Anonymous]

Posted by Bill Phinn on 13/11/2022 20:31:15:

…. the section of bar to be threaded was first turned down to exactly 10mm ….

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)

[Martin Shaw 1Participant @martinshaw1]

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

[Bill PhinnParticipant @billphinn90025]

Posted by Bill Phinn on 13/11/2022 20:31:15:

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.

 

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.

Posted by Peter Greene 🇨🇦 on 13/11/2022 22:44:14:

Posted by Bill Phinn on 13/11/2022 20:31:15:

…. the section of bar to be threaded was first turned down to exactly 10mm ….

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).

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

[Martin Shaw 1Participant @martinshaw1]

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

[Bill PhinnParticipant @billphinn90025]

The die looks, Martin, like it's suffered the ancient Chinese torture called lingchi, aka death by a thousand cuts. Either that or it's been cutting very abrasive material. In your first picture of it, it looked seriously clogged with swarf as well. That's never going to make for easy cutting.

I've attached a picture of my own M10 die for comparison purposes.

ETA: I don't think my die is a Presto after all; I think I bought it from Turbine Jon, which may mean it's the same die as yours.

 

 

Edited By Bill Phinn on 14/11/2022 00:30:03

[Anonymous]

I've bought a lot of tooling from Drill Service over the years and have been pretty happy with the quality. Although, to be fair, I haven't bought many dies as I don't use them that often. In the picture FEW is the French Engineering Works which, despite the name, is in South Africa. I have quite a number of their taps and have no complaints. The die from TWT is by the Taps and Dies company in North Yorkshire. I have no experience of them. I'd be surprised if Drill Service sold poor quality as they supply to the commercial sector.

Andrew

[Bill PhinnParticipant @billphinn90025]

One more thing that occurs to me: can I take that in starting your threads you were taking full advantage of the split in the die by centering it on the point of one of the four screws inside your die holder and tightening this screw down firmly into the split, whilst leaving the other screws loose?

You can see a mark inside the split on my die showing that this is what I've done. I can't see the same kind of mark on your die.

Edited By Bill Phinn on 14/11/2022 01:55:04

[HopperParticipant @hopper]

Posted by Martin Shaw 1 on 13/11/2022 23:18:19:

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

 

Pic is a bit blurry so hard to tell, but that die does not look right. The flats on the tops of the cutting teeth look way too wide. Compare it with the pic Bill Phinn posted and see how pointy his teeth are.

With the set up you have used in the lathe and the lead-in spigot on the job, that die should cut a thread like butter. It is only 10mm diameter, a mere nothing to thread usually. But it may take quite a bit of force from the tailstock to push the die onto the job firmly to get it to start cutting a thread while cranking the chuck by hand slowly, (Purists look away now!) using the chuck key as leverage.

 

Edited By Hopper on 14/11/2022 03:31:51

[larry phelan 1Participant @larryphelan1]

Martin, the point I was making was that single point thread cutting is easy enough, even for a beginner [as I know only too well ]. A piece of HSS is dirt cheap, easy to shape, easy to mount. You dont need inserts, I would regard them as overkill for such a job.

The advice regarding a stocks with guide bushes is good, I made one long ago, but it only works for longer threads, no use for short ones.

I regret that you took exception to my post, it was not my intention to cause offence and I still think you should try it, if only as part of your learning curve as you may have use for it later on. As others have said, starting a die on a bar is never easy.

Regards.

[Mick B1Participant @mickb1]

That die is a basket case. If it's properly-hardened HSS, it's hard to imagine how the teeth could've become so severely blunted.

At railway where I volunteer, there are plenty of brutally-tortured HSS dies, but they're chipped and spalled, not bruised and swaged out of shape like that.

[Martin Shaw 1Participant @martinshaw1]

Larry

I didn't take exception to your suggestion so much as the way it was put, however you're quite correct that it is a skill worth having.

That was yesterday and the whole thing was frustrating me somewhat, today I have decided that a further try is necessary and perhaps a new die might be an advantage although the current one is all but brand new. Whilst I recognise that this should be the way to do this others are saying that single point threading is the better way, although it does seem a lot of faff for two short threads. As it stands I can't dismiss it as currently I don't have any threads at all.

I am very grateful for all the help and suggestions, this is not an overly complex task and certainly shouldn't be beyond me and the equipment I have. I'll post further if anything useful comes to fruition.

Kind regards

Martin

[Mick B1Participant @mickb1]

There are reasons for screwcutting to remove the bulk of material, then finishing with a tap or die – for example where the thread is large and deep, ends close to a shoulder and is short.

I'd agree that singlepoint screwcutting is well OTT for a couple of M10s, especially when there's a more underlying issue that needs sorting.

Looking at the original issue, I'd guess the die is loose-ish in the diestock and the tailstock's out of alignment, though I have to admit I can't remember having seen anything quite like it. The surface tearing in the shorter thread looks to me like angular stress.

A tailstock dieholder is certainly useful and quicker, but I'd been turning for 40 years before I stumped up for one. You can usually use the front face of the tailstock barrel or the jaws of a Jacobs drill chuck to square off a die adequately in a normal diestock.

[SillyOldDufferModerator @sillyoldduffer]

From what Martin has said, he did almost everything right:

• Known metal, leaded Mild-steel, easy to machine
• Diameter of rod turned down 5% less than M10
• End of rod chamfered to help start the die
• Bought a reassuringly expensive die from a reputable supplier
• Die backed off frequently to break swarf
• Undercut at the shoulder
• Cutting oil applied

Bad starting might be part of the the problem, however, the photo suggests the die is in poor shape, which would explain the result. A blunt die tears the metal rather than cutting it, needing considerable extra force, and tending to twist and bend the rod as the die is forced round.

What could possibly go wrong?

• Manufacturing error – the die was wrong from new
• Operator error –
  • the die was previously blunted by cutting a thread in a work-hardening material like stainless steel. Damage highly likely if the rod was oversized, the die didn't start at 90°
  • Failing to clear swarf (but it takes time to blunt a decent die)
  • the rod is fatter than 10mm diameter, not 9.95 as believed – faulty measuring
  • die back to front (unlikely)
  • Adjustable die too tight, ie not opened up by the holder's point screw
  • Die not centred in the holder (wrong sized holder)
  • poor start. This is easy to do! It's why many of us like to begin with a lathe cut spiral for the die to run in.
  • persisting with a bad cut, not realising something is wrong due to inexperience

When I started out tools got blunt remarkably quickly. Now they last a lot longer. I think the main reason is my technique has improved. Rather than forcing my way through metal I 'let the tool do the work', support the job properly, and avoid eyeballing angles and dimensions. I'm also much better at recognising when something is wrong, able to detect bad news by feel and sound.

I find threading by hand is far more likely to go wrong than when the job and tap or die are held mechanically. I don't think I've ever messed up a thread properly started with a lathe cut. I've blundered more than I care to admit by cutting the wrong pitch for the die though, blush…

Dave

Edited By SillyOldDuffer on 14/11/2022 11:48:34

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