Using large dies

I cut a lot of large whitworth /unc threads usually on the lathe and then run a hex nut die down them to clean them up.

Sometimes its hard work just cleaning the thread up removing a small amount of material.

On a woodworking forum someone has a 1.5inch 6tpi split die and they are wanting to cut threads just with this.

is it at all possible on steel?

what would the forum say is the biggest thread that you can cut with a die from scratch on sized steel?

I suppose it depends on how long the die holder handles are.🙂

When you say a split die, do you mean the usual single piece die or do they have a proper split die (2 pieces), so far more adjustable. Plumbers used to cope with 2” pipe threads and more.

I have a pipe threading set which goes up to about 2 inch but when I did larger sizes I would hire a threading machine. I would also get an apprentice to thread the pipes Usualy used for airlines mainly.

David

Cutting a pipe thread - even at quite large sizes - doesn't mean taking all that much metal off because the thread pitch is constant. For 2 inch nominal bore pipe the thread it (from memory) 11tpi so cutting this is a different ball game to cutting 6TPI on a 1-1/2 diameter work piece - that's nearly twice the depth of cut.

Who needs a gym subscription when you can cut threads for a living and get paid for it.

I've tapped 2 inch BSPT in 316 stainless with the biggest tap wrench I could hold. You'd need to go and have a lie down afterwards.

I employed a kiddy once upon a time - we installed air compressor pipe work for a living. He was enormous - 6 foot 4 and built to match, in his early twenties. He told us all sorts of stories about how fit he was and how he went to the gym three times a week.

He left after the first month, couldn't hack it.

Happy days.

Simon

Of course the depth of the thread is at least as important as the OD.

It depends on the steel and the state of the die. I've got 8-off 1" 8TPI BSW dome nuts to make for the railway, and because the taps are in decent condition and the steel is quite good BDMS, I can do it if I cheat a few thou on drill size to give meself a bit less metal to shift. And it's lucky there's no particular time pressure.

But I can remember trying to die-cut some 1" BSW external threads on EN8 using chipped WD dies that might've gone through the desert with Montgomery. I ended up with a ricked neck and horrible galled threads.

I'd say if you've got good freecutting MS, 10 thou or a bit more undersize, a nice sharp die, a long-handled diestock, some Rocol or suchlike and you've had good coffee and an eggy breakfast, you might have a chance with 1 1/2" BSW.

But don't be doing it with difficult material, worn dies and wonky diestock at the dog-end of a rough day.

Edited By Mick B1 on 18/05/2020 20:22:48

Yes i meant a round split die so it could be opened up a little to start it off

the large dies i have are all hex nut type so i generally use a big pair of stiltsons to run them down

I just cant imagine trying to do a 6tpi whit over 1” from scratch or even trying to tap with a set of 3 taps

I think trying to cut the thread true would be even more of a challenge than turning the die especially if he wants to use it for chuck mounting.

So far as I'm concerned die-nuts as you describe are purely for cleaning up slightly damaged or rusty threads, not cutting them from scratch.

Ian, when you have gone to the trouble of setting up your lathe to screw cut the thread why not just cut it to size and you will have a better more accurate thread than finishing with a die ! Measure it with wires or a thread mic if you have one or use the mating part as a gauge.

John

I had difficulty cutting a thread with a 3/4” UNC Tap In aluminium alloy recently.

I was always taught this, but I've noticed on several videos I've watched on YouTube, the Americans seem to have proper thread-cutting dies in a hexagon shape. Has anyone any further information on this?

My first employer had a big collection of taps and dies in wooden boxes all ex War Department and US Army.

Although we used most of them there were a few boxes of large pipe taps and dies i.e up to 6" Whitworth Pipe. We never really looked in to them until the time came to clear them out with the metal going to the scrappy and the boxes were used for home projects. One of the tap boxes was built from 4" thick by about 18" wide by 36" long bits of wood hinged together to make it 8" thick! There were a couple of boxes of tap and die holders about 7 foot long and it wasn't until we were scrapping them that we realised that there were extensions to go on each end of these die-stocks. The total length of the die handle must have been nearly 20 feet! Needless to say they were still in the protective grease and had never been used. There was a ratchet system on the die holder to allow a back and forth action to cut threads in situ.

It made you wonder at the sanity of someone who organised to get these made at what must have been enormous expense when the money would have been better spent on armaments or even food imports. They were obviously not engineers. One of my old workmates had a workshop bench for many years made from one of the boxes and another had a very robust kennel that outlived a few of his dogs!

The limiting factor practically speaking as far a I am concerned would be the ability to stop the workpiece turning.

regards Martin

The McMaster website shows Hex Dies as thread repair as per UK practice but they do show the conversion holder in the clip below.

Would be easy to mage similar at home

Steve

Done that way as a result of painful military experience. For want of a nail the shoe was lost etc. The young men who had to repair artillery pieces on Guadalcanal in 1942 did so with minimal training and experience. You'd be amazed what military men break by accident, never mind what the enemy are up to. The last thing soldiers need is to find replacements damaged in transit or rusty in the tropics due to inadequate packaging, or that the only set is 2000 miles away due to shortages. So the military overstock and box to the extreme to guarantee stuff will be available when needed. Not insane, just extremely wasteful.

Dave

Nevertheless I can remember one factory I worked in getting such a large order for 'Wands, Marshalling' that we were convinced there was someone on an aircraft carrier somewhere shovelling 'em over the side...

John f

I do screwcut on the lathe to size but i run the hex nut dies down after just to make sure they are the right fit

i make chuck adapters for woodworking lathes and its surprising how many dont fit even though I’ve used my spindle or sample threads or nuts so I’ve found that running the tap/die down my cut thread makes them work.

the other day i had a chap send me a commercial 1 3/8 6tpi whit adapter that would not go on his lathe he sent it to me it wouldn’t go on my dummy spindle but running a tap down it cleaned it up..didn’t seem to remove any metal..but afterwards it went on my spindle and the customer was happy.

My original post was about someone agin on a woodwork forum who wanted a die holder 3 1/8” dia to use his round split die to cut a male 1.5 “ 6tpi on a steel bar... I dont think that would be possible at all...but ill stand corrected if someone says they can do it...

Hi, I made a couple of round to hex adapters out of a couple of 30mm nuts, 15 years or so ago when we had a breakdown at work and the only way to clean up a couple of threads was a couple of hex dies which we didn't have in those sizes at the time. Never had seen any adapters before.

Regards Nick.

Edited By Nicholas Farr on 19/05/2020 19:05:07

A professional pipe threading machine has sets of adjustable dies in a die box, they never use split dies. Back in the 70's I used Rigid and Facom machines. Production threading on lathes before cnc's came out was mostly carried out using die boxes rather than single pointing, as it was much quicker.

The pipe thread set I have has separate blades which are adjustable and when I worked on a lathe this style of threading head was used for larger threads over 1 inch and were fitted to tailstock MT 4 which released when the tailstock was stoped by saddle which was hit by sliding tailstock.

David