Bent thread

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

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

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

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

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.

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.

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

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.

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

+1.

But if it is "severely blunt" how did it manage to cut the thread in the first post, apart from being wonky it's cut reasonably well and any tearing is possibly due to having to cut over depth on one side as it went off course.

I'm inclined to thing it is a problem with the method, Martin has had similar problems cutting threads in previous posts.

Although I don't reduce diameter and seldom chamfer an end if you put your second piece of metal back in the chuck and make the taper shallower you may get it to start, something like 20-30 degrees. Leave the tailstock loose on the bed and apply plenty of pressure with your right hand to the end of the tailstock while turning the diestock with your left,

Edited By JasonB on 14/11/2022 13:18:28

Right, some welcome further stuff. Apart from my technique which several of you have been kind enough to point out the correct way, I have found two other issues which at best won't help.

The adjusting screw on the die stock is badly formed at the point and the screw slot is far too shallow which rather makes it unadjustable, and more importantly I found the tailstock wasn't locking to the bed securely enough. Rotating the feed was pushing the tailstock away rather than onto the work so I've adjusted it to lock better.

I am also going to replace the die, whatever the circumstances around it there is no doubt it is poor. I will also see if I can fix the diestock or replace it. Has anyone a reputable supplier other than Drill Services, I was thinking Tracy Tools as I've had stuff from them before.

I will also look at single point threading as a separate exercise, some Youtube videos have helped explain things on that front.

Regards

Martin

Edited By Martin Shaw 1 on 14/11/2022 18:53:19

In order not to prolong your difficulties unnecessarily, Martin, it really would be beneficial if you could directly address some of the more salient points various people have raised:

Before attempting a cut, did you open the die to its maximum internal diameter [within the limits imposed by the diestock's own ID] by driving one of the die holder's screw points into the split and leaving the other screws loose?

How has the die managed to get into such an advanced state of wear? I find it hard to believe that Drill Service sent you a worn-out die instead of a new one. I've only ever ordered two items from Drill Service but they were first class. And, as Jason says, if it was in that state when you received it from Drill Service, how did you manage to cut the cleanly cut threads you've shown us in your opening post?

It looks to me like you've been trying to cut threads with it on something either very abrasive, or very hard, or very oversize, at some point after you cut the cleanly cut threads visible in your opening post's image.

This thread is about a bent thread. Please be straight with us.

"Before attempting a cut, did you open the die to its maximum internal diameter [within the limits imposed by the diestock's own ID] by driving one of the die holder's screw points into the split and leaving the other screws loose?"

Yes but as I explained above I have discovered a faulty screw in the die stock.

"How has the die managed to get into such an advanced state of wear?"

I have no idea beyond something I've done wrong. The two threads in the first post were done by hand in the vice on Saturday afternoon and thereafter nothing further beyond

"It looks to me like you've been trying to cut threads with it on something either very abrasive, or very hard, or very oversize, at some point after you cut the cleanly cut threads visible in your opening post's image."

I appreciate your trying to help but this is assumption on your part, and incorrect as well.

Dave said

"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"

I believe I did as well, that it hasn't turned out is what is being explored and I think a combination of useful posts has pointed me in the direction to take. My post immediately before yours detailed my further actions and having done them I will let everyone know the outcome.

"Please be straight with us." I very much have been and the other useful posts in return would suggest so, I'm sorry if I didn't explain things adequately enough for you.

Kind regards

Martin

So quite possibly the split remained closed while you cut the two threads you say are the only threads you've cut with that die from new.

Assumption can be perfectly logical and excusable when an adequate explanation for some event [in this case a very worn die after only two cuts in mild steel] isn't forthcoming.

Tracy Tools taps and dies have been good when I ordered them in the past.

Edited By Hopper on 15/11/2022 04:11:49

last few Dies I have bought have been from ARC but their M10 needs a 30mm holder so you may not want to spend out on both. And that will also open up the unsplit die debate.

Also bought a few metric ones from Rotagrip made by Volkel not their cheaper offerings.

Dormer from MSC is another option but quite spendy and again at least 90% of Dormer dies are solid like many makes these days.

It can be a pain to set up for single pointing a short thread on a hobby lathe. I find it a pain, as invariably (well quite often) I need metric when set up for imperial or vice versa. But the advantages of concentricity and parallelism, plus the savings on wear and tear on (relatively expensive) dies makes it worthwhile. A QCGB does help, mind - as reverting to a normal cutting feed-rate is easy.

Agreed, but hardly seems worth it for a 10mm thread though. Ordinarily you can whizz it on nice and straight and clean with a die and be done with it. I rarely bother with screwcutting unless it is something special or diameter over 1/2" (13mm) or so. But I have boxes of good old HSS dies and taps scavenged up over the years at rummage sales etc so no worry about wearing them out. And you can always sharpen them with a Dremel grinder.

Making a hand-crank for the lathe spindle for threading was about the best thing I ever did. Close second would be the tailstock die holder set and spring centre tap guide I made. You can just whip threads up in no time with no struggling with dieholder handles and spinning the chuck by hand etc etc.

Reading all the comments, It appears that the workholder er collet is very good,these collets grip and dont slip if tightened to spec, the material ie 1a leaded should produce good threads easily without the need for specialised lubricants ,the commercial die holder looks ok though I would prefer the type where the body holds the die firmly,i am not keen on separate inserts. the 45 degree lead is ok on this material a 30 degree is preferable on tougher materials. I think the problem is a rubbish die,it may be marked hss but its the manufacture thats the problem.Get a good ground thread hss die from a known manufacturer and the problem will disappear. Cutting a thread by hand with the work in a vice is difficult and takes a lot of practice and is to be avoided. Holding the die in the tailstock is the easiast method to cut a thread for the amature modeler, modern commercial tallstock holders are a bit too complicated and cost a lot of cash. During my training I spent a lot of time on a Boxford, the commercial tailstock die holder was simple, short length of 1/2 inch dia rod,possibly hardened to reduce wear was held in the tailstock chuck,the die holder about 4 ins long just slid onto the rod,no key ways or any method to prevent rotation, it had a heavy knurl along most of its length and a cross hole for a tommy bar , the die was held and adjusted by the usual 3 pointed screws. In use BA threads were cut with the lathe running and the holder gripped in the hand and pushed towards the work,when a shoulder was reached you just relaxed your grip on the dolder and then spun it off by hand ,on larger threads the tommy bar was used with the lathe spindle stationary. This type of holder can be home made using either mild steel or aluminium for the body and silver steel for the rod thatgoes in the tailstock chuck,no need to make morse taper shafts. I have a lot of these home made holders which cost nothing ,the largest holding 3/4 bsp as I thread water pipe when restoring full size stationary engines,I thread under power using a decent sized tommy bar which is prevented from turning by a steel bar held in the toolpost,Dont use the lathe bed.When I started my engineering work over 60 years ago ,there was never any problem with either carbon cut thread or hss taps and dies,though in the last 30 years i have sent a die and a number of taps back to suppliers as they would just not cut ,with duff taps some just start cutting and then just jam solid.Nowadays I rarely need taps or dies but if I do have to buy one I bite the bullet and pay a lot extra for ground thread HSS. A comment was made about why does a toolpost stud need to be relatively precise,well the nut needs to be square to the axis of the stud in order to maintain a firm grip. How would I do this stud,both my lathes have imperial lead srews so I would use a die , if it was imperial over say 1/2 inch i would screwcut with a chaser.

I only use die holder and vice for jobs like extending the thread on coachbolts or cleaning up damaged threads, I have a WD set of whit taps and dies 1/2 to 1 inch whit made in 1940 and typical goverment,no expense spared,solid metal case with hard timber insert in army green, a polished all over sliding block tap wrench and a die holder which has separate iserts to hold the dies,so the dies can be set to size and the setting held,each die holder has a built in guide to keep the thread square ,though it would take a strong soldier to cut one inch Whit threads ,it cost me £40 and I think the tap wrench alone was worth that as that is the most used part of the set.