Die defeated by mild steel

[RainbowsParticipant @rainbows]

I was trying to make part of a mini lathe toolpost by turning 16mm bar to 12mm and threading one end M12 and tapping the other M6.

I turned the bar and tapped it easily enough but the last operation was to thread the M12 screw.

After 5mm the die bound up like a nut tightening on a screw. At first I thought maybe the steel had work hardened, thought I was pretty certain it was just mild steel I had picked it out a scrap bin. I took a blowlamp and heated it till the metal turned black and let it cool thinking that would anneal it. After that it still would not let itself be threaded.

Anyone know what made the die fail to cut?

[RainbowsParticipant @rainbows]

[pgk pgkParticipant @pgkpgk17461]

Oddly i had a similar problem on some silver steel but then I was aware that mine are cheap carbon steel dies I've had for years. I solved my problem (after assorted bog-ups) by partial threading on the lathe and chasing with the die when roughly down to size. (Usually i test my threads with a nut but this time didn't have one of the correct size and didn't want to compromise the tapped part)

[David JuppParticipant @davidjupp51506]

Perhaps starting diameter was a little large, especially if the soft steel is extruding a little and not simply cutting. M12 major diameter for male thread is a little less than 12mm.

[davebParticipant @daveb17630]

I suppose it is possible but M12 is a bit big to thread with a die, anything over M8, I screw cut and finish with a die.

[Nigel McBurney 1Participant @nigelmcburney1]

Possibly a cheap M12 die with no cutting clearance,or a worn die they will bind on the thread, regarding annealing,steel should be heated to red heat,held at this temp for a while then allowed to cool SLOWLY, mild steel round should not require annealing, drawn mild steel flats and square may need annealing as there is a lot of stress built up when drawing sharp corners through a die. The advantage of screwcutting in the lathe is that the threads are true to the axis of the round bar,they can either be finished to size ,or left oversize and then finished to size by a light cut with a good die.

[Roderick JenkinsParticipant @roderickjenkins93242]

As the posters above have alluded, cutting an M12 thread with a die needs a lot of heft. Very difficult to do in the lathe – if that's where you are doing it. I suspect that the die is just getting as far as the end of the lead in before the effort of cutting the full depth is too much. I would need to get both hands on a hefty die stock to thread M12 from scratch in steel. Just holding the blank in the vice without twisting is difficult enough. I always partially screw cut anything over 6mm or thereabouts with a coarse thread.

HTH

Rod

Edited By Roderick Jenkins on 03/02/2016 23:29:24

[RainbowsParticipant @rainbows]

The die was a fairly decent presto, first time I ever cut M12 on a die so it would make sense that it is too big to cut by hand. Lathe I was using only had fine feeds with no srewcutting but I can probably figure something out,

[Ady1Participant @ady1]

Screwcutting on the lathe also means your thread is perfectly square with the rod, all the die does is tidy things up

[HopperParticipant @hopper]

Were you leading with the end of the die that has the tapered teeth? Try turning the die around and using the other end of ut tto clean up the thread and get going again then go back to leading with the tapered teeth.

And +1 on make the diameter a bit under 12mm. (about .005" -.010" in old money.)

Using a die on 12mm should be a doddle, in or out of the lathe, if all is set up right. (Try threading 2" pipework if you want a workout.)

[Ian S CParticipant @iansc]

Does your die have a split, if so open it out and take two goes at getting to size, make sure the die is the right way round, take say a 1/4 turn, then back off, continue, use a lubricant, even if its only engine oil. Don't rush it.

Ian S C

[Chris Evans 6Participant @chrisevans6]

I always buy HSS taps and dies but I recently bought some new old stock Presto dies thinking I was buying my usual quality. However when they arrived they did not have HSS on them and the package had CS, from that I assume Presto also make carbon steel dies. I will put them to one side and only use them for cleaning up existing threads.

Edited By Chris Evans 6 on 04/02/2016 08:56:20

[Rik ShawParticipant @rikshaw]

From 8mm upwards I usually – like others – rough out the thread on the lathe with a single point tool then run a die nut down in my tailstock holder to finish to size. Even doing it like this a 12mm thread that you intend completing in your lathe needs to be roughed out fairly close to size otherwise you'll still be struggling to finish the thread with the die / dienut.

Rik

[Roderick JenkinsParticipant @roderickjenkins93242]

I wouldn't get hung up on the fact that the dies are made from carbon steel. Carbon Steel is considerably cheaper than High Speed Steel and it is undoubtedly a fact that cheap dies, inevitably made from CS, can be poor quality. In principal, CS dies can be harder and have a finer grain size than HSS. The downside is that they tend to be less tough (will break and chip) and you have to watch the speed at which you cut threads to prevent them getting hot and over tempering – not usually an issue outside of production use. From a premium supplier like Presto I would expect that, for amateur use, CS dies would be excellent.

That's how I see it, anyway,

Rod

[davebParticipant @daveb17630]

As Hopper said, 25mm conduit and 2" pipe CAN be threaded by hand, if there is no other option and you have the correct tools to do it. I have done a lot of this, hard work! Never had the same success with mild steel bar, even with a long taper to start the thread, it's difficult to start it straight. Old fellows in days of yore, when men were men, mighty thews etc, did the job by hand but used a die holder with a guide (similar to a conduit die holder). It IS possible but there are much easier ways to do the job. Tallow is the best lubricant for this if you want to try it the hard way.

[Roderick JenkinsParticipant @roderickjenkins93242]

It's the depth of thread, not the diameter of the tube, that is the issue. I have no problems cutting 40 tpi direct on to 1/2" steel, 12 tpi or 1.75mm is a different matter.

Rod

[CirclipParticipant @circlip]

Ever measured commercial metric threads? On smaller sizes -M4 to M8, I always turn o/d before threading to 0.1 lower in diameter, 0.2 would be good for M12.

Regards Ian.

[MWParticipant @mw27036]

I would recommend prestos' range of split HSS thread cutting dies. I once owned a set of non split carbon dies and theyre only good for the bin to be honest because you cant adjust the overall diameter, theres no start to the thread basically. I know they cost alot for what they are but they definitely work.

I don't have a particular issue with carbon steel itself, it's a pretty durable steel but i suppose it could blunt quicker than HSS and thus have a shorter lifespan, just make sure you get the split ones or you'll be cursing and swearing for england.

Michael W

[Tim StevensParticipant @timstevens64731]

It could be that the curls of swarf from your first attempt jammed in the die, because you forgot to turn back half a turn to break the strands.

Cheers, Tim

[MWParticipant @mw27036]

It would be a good piece of advice since plunging in with a die without turning back can make small threads look awful,

Michael W

[Ian S CParticipant @iansc]

You can split unsplit button dies with a narrow cutting wheel on a Dremel, you could even do it with a 1 mm thick disc on a disk grinder.

Ian S C

[AdrianhParticipant @adrianh95127]

As stated earlier, the top diameter of a metric thread is actually less than the designated size.

Cutting with a M12 hand die straight onto commercial bar will probably only work if you have a very good/new die and use quality thread cutting oil. It is also difficult to get a straight thread over a length.

Why not start with a piece of studding ( threaded bar) or cut a suitable bolt or capscrew up and tap the end of that

[Mike PooleParticipant @mikepoole82104]

HSSGT are the letters that have become associated with a quality die, however these letters are not a guarantee of a quality product just as carbon steel has become associated with a low quality item. Making a die for hand threading from HSS is surely s bit of overkill as the major selling point of HSS is that it retains its hardness at red heat, not a condition likely to be encountered when hand threading. A well made CS die is likely to provide all the performance required in a home workshop. Presto was a brand that had a strong reputation but I wonder what has happened to it in recent years, Britool was a brand that was made in Britain but now seems to be applied to products from Taiwan. I went shopping for a 3/8 drive socket set in 1978 but baulked at the £130 price tag. I do own a 1/4 drive Britool socket set but it should be called Taitool, It is a nice set but a tragedy it is no longer made in Britain but I doubt it would cost £40 which is all It cost in 2012 if it was made in Britain. It is difficult to be sure of what you are buying these days when even famous brand names have been traded and the new owners may not aspire to the standards that originally built the brand.

Mike

[KWILParticipant @kwil]

Britool merged with FACOM of France, who then merged with Stanley Tools, who than merged with Black & Decker, so there you have it, all part of Stanley Black and Decker Industrial and Automobile Repair Division. [For merge read takeover]

[Nigel McBurney 1Participant @nigelmcburney1]

Why not use a tailstock die holder,with a long tommy bar,if the work slips in the chuck jaws, then grip the work in an ER collet, on rough work that slips in the chuck a dab of weld will stop rotation (it stops against the chuck Jaws) the weld can be ground off later. Or make a die holder, with a guide,that works ok provided its not too close to a shoulder. I have a virtually unused set of ex WD whit taps and dies,a circular guide also holds the die,the assembly then fits into a die holder about two foot long. the advantage each die can be set to size and not loose that setting, the set has 1939 stamped on it. Only used the dies once,though the taps have useful,best feature is the superb tap wrench ,it a sliding V and is bright steel all over and that gets used a lot.

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