Screwcutting Die Specification

[Donald MitchellParticipant @donaldmitchell68891]

Hi Engineers,

 

Can anyone tell me what the dimension should be for the three lock screw holes around the periphery of a 13/16″ die, in terms of, how many degrees apart are the holes?

 

I have done a bit of a survey among the die holders which I presently have, ranging from the so called junk Chinese ones right through to Dormer and Presto ones and I find the screw holes range anywhere, as far as I can tell, from about 35 to 45 deg apart.

 

Is there an established “standard” dimension ?

 

I’ve checked various books, including Tubal Cain’s workshop bible and can find nothing relevant.

 

I decided to make up a dozen or so tailstock die holders in order to leave dies permanently fitted and sized, instead of the constant pain in the butt resetting them as and when they needed changing.

 

I realise the dimension isn’t too critical but I’d like to get it about right if possible.

 

Donald Mitchell
Castle Douglas
Bonnie Scotland

 

 

[Donald MitchellParticipant @donaldmitchell68891]

[Alexander FairbairnParticipant @alexanderfairbairn46080]

Dear Donald,

 

Looking from head stock to tail stock drill holes in die holder to correspond to 9 o’clock, 10.30, 12 o’clock and 3 o’clock. This will satisfy a host of circular dies.

 

Regards,

 

Alex Fairbairn

[John Stevenson 1Participant @johnstevenson1]

Donald,

Silly question but if you are making these to leave with dies in why not mark each one out to suit the fie in question ?

 

John S.

 

[chris stephensParticipant @chrisstephens63393]

Hi Donald,

If you look at GHT’s book you will notice that he does does not use the two dimples on the die at all in his lathe die holder arrangement.

He has arranged for four screws, at 90 degrees to each other, only one of which is pointed. The other three screws are used to centralise the die in the holder. I can confirm from personal experience that the hole is frequently NOT in the middle of the die, and if you force it to be you will forever cut undersized threads and wonder why.

 

Die manufacturers do not need to think about whether the thread cutting hole is in the middle or not because their use is intended to be in a normal die stock, where the die rotates about its own axis. We want to extend their use to the lathe and have to take our special use for them into account.

 

So you are left with a couple of ways around the problem, one way is to have four jacking screw (or three if they are at 120 degrees to each other) or make your self a floating holder which would allow the die to centralize itself whilst still being held in line. (I would dismiss the three screws as being more difficult to centralize, with four you can loosen one and tighten the opposite, not so easy with three.)

 

I am surprised that this topic has not come up more often, can it be only GHT and myself who have the problem?

chriStephens

PS looking forward to being shot down in flames, I have got my Nomex romper suit on under my jeans and spoiling for an argument.

[Jeff DaymanParticipant @jeffdayman43397]

You’re not alone Chris, my dies are all over the road too with regard to dimple angle and hole in centre not being concentric with OD. It’s gotten worse in the past few years as dies are being sourced far and wide. Latest batch I ordered fom my usual suppliers was checked when they arrived and were from Macedonia. They did the job and cut lovely threads, and were well made and finished, but all dimensions of the dies themselves varied a lot die to die and were well off sizes to any “standard” / old ones I have. No idea whether the shops around the world making dies now follow any standard or convention (if one exists) for die body and dimple geometry.

 

Having seen this before I made my tailstock die holder with 4 screws in the OD but I had no idea GHT did it that way many moons ago. He obviously forsaw the need arising to adjust a die in the holder to run concentric, or maybe he got a couple of wonky dies too….

 

I also made only one screw pointed in my holder, because I examined/measured all my dies (about 80) before building it and found I have several dies with one dimple, several with two, and several with three, and angles differing all over the place! These dies vary in age from about 1917 to present as some are from my grandfather’s kit and some I have acquired from various sales and junk piles all over the place, and also from friends and co-workers. There are at least 8 thread systems in there. Obviously there are some I will never use, but it’s comforting to know that I have a die for say a left handed #12-24 USS thread ….

 

JD

 

 

Edited By Jeff Dayman on 06/02/2011 19:24:33

[John Stevenson 1Participant @johnstevenson1]

Good God, I must have close on 300 dies or various sizes and makes and I’ve just realised that in 50 odd years I have never checked any of them.

 

Damn, I’ll never be able to sleep nights from now on.

 

We need a committee to form a new British Standard for dies. How about BSDD for British Standard Die Dimple.

 

First thing we need to sort out is do Metric dies need to me measured in metric degrees and imperial dies in imperial degrees ?

 

John S.

[Gordon WParticipant @gordonw]

I always thought that threading dies are split for adjustment, to the final thread diameter. Solid dies are for cleaning up mangled thteads. Both types are for hand use, mass production on machines use all sorts of specials. How can a split die be adjusted and still be centralised ? I can only see a floating holder working in eg. a tailstock.

[chris stephensParticipant @chrisstephens63393]

Hi Gordon,

I can only see a floating holder working in eg. a tailstock.

Quite correct, but then that is what the OP is trying to do.

chriStephens

[John Stevenson 1Participant @johnstevenson1]

Posted by Graham Meek on 06/02/2011 20:25:02:

 

 

Bet you don’t have a 2mm pitch Trapezoidal 12mm O/Dia Die in your kit?

 

Graham

.

 

 

No, I tend to screwcut most things and collect more taps for the bits that’s hard to internal screwcut, usually because it weighs 3 tonne and is 20 miles away 😀

 

Might have a tap ?

 

John S.

[David Clark 13Participant @davidclark13]

Hi John

They might one day.

They take a long time to do.

Also quality won’t be brilliant.

All the ME on ine now is taken from the pdfs sent to the printers.

regards david

 

[WALLACEParticipant @wallace]

Tubal Cain in his book on Drilling and Tapping reckons the two locking screw should be ‘slightly less than 45 degrees’ from the central splitting one. . . whatever ‘slightly less is he doesn’t say . .!.

 

W.

 

[Frank DolmanParticipant @frankdolman72357]

Did you notice, Wallace, that Tubal’s diagram shows the variation from 45 deg

in the other sense from his words?

[Author]

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