.225 dia x 40 tpi die

Can anyone help me, I am restoring and re making some aperture rifle sights for an old (1895) Enfield rifle, The original sight was made by Parker Hale, The thread I need to cut is .225 diameter x 40 TPI. The threaded spigot is 1/4" long, I have tried to open up a 7/32 ME die and close up a 1/4 ME dia but can't get a correct fit in the sight mounting.

I wondered of anyone has come across this problem. I could screw cut it but there is not much room, as I am making a number of these with different sized apertures it would be quicker and easier if I had a die or a 40tpi thread chaser.

Edited By Ian Lee on 04/01/2017 22:21:15

Hi Ian, I have made these in the past, original spec was supposed to be 7/32 x 40 Whit form but you will often find them over size and the only option is to screw cut a new one. Many of the PH and AJP sight threads were unique to them.

​Its the same with many old gun screws they are close to ???? BA or Whitwort but not exact the reason being as an apprentice they purchased a die plate this was used to ask their own taps thus even as the plate became worn or the years the parts still fitted together and interchangeability was not an issue in those days.

Thanks for the info, 7/32 x 40 whitworth thread form is now ME thread, and I thought it may be the case that over the years of manufacture the diameter altered, I only need a 7/32 die to open about 5 or 6 thou as 7/32 is .2187 dia.

Ian, try grinding or linishing the OD of the die a bit, it may not be opening wide enough because it's egg bound in the holder.

Are you sure its not just a 7/32x40 thread that has extruded slightly as it was cut, you can often find if the die is a bit dull that it pushes the metal into the shape rather than cuts.

Never tried it but I would think a 7/32" HSS die heated to cherry+ red complete with wedge protuding a little, gently squeezed in the vice, between some oak insulation, would open up enough without breaking ?

I am assuming this sight was not original equipment on the rifle, but was fitted for target shooting. The only thing I can remember about relatively early Parker Hale sights was that the thread provided adjustment in quarter-minute clicks - in other words roughly a quarter of an inch at 100 yards. From there on, the mathematics of solving triangles is beyond me - but it could give a clue as to the true pitch of the thread. Somebody please put me right if I am talking rubbish!

Need an old style two piece die really

Buy a 40 tpi chaser and screwcut the thread ,thats how an instrument maker would do it.Or set up a 40 tpi plug tap in the tool post and use it as a chaser,

It doesn't matter if a die breaks provided it breaks clean, see Jason's split dies above to realise that these will still work.

hi,

8mm watchmaker collets use a thread which is 0.275" x 40 tpi and you can buy a suitable die for that thread, I don't know if that might help you, though I suspect you might find yourself no better than you already are in that the die might not tighten enough to bring the thread down to 0.225". Might be worth a go if your other options come to naught.

RDG Tools have them in their Watchmaker Tools section under 8mm Boley lathe accessories.

Regards Tom

I have just looked at the Parker hale sight I have, it is 7/32 x 40 for the aperture mount. The aperture mount I have has a disc with about four aperture's drilled in it and you can rotate it

Another sight , the mounting hole is at least 1/4 inch dia.with a fine thread in it.

By the way these sights sell quite well and in the 100's of pounds. Much sought after.

Clive

Ive just been into the workshop and I can put a 7/32 x 40 tap through the mount for the aperture block, it fits but is slightly loose.

Clive

Tracy Tools might be worth a try.

Phil

Hi Ian, You could mount a die stock/holder in the four jaw to run true and machine out a few thou, just enough so that when the die is fully open it cuts the diameter thread you need. That way if you are unfortunate enough for the die to crack it will still be located in the holder. As JS said it doesn't matter if it cracks if it's a clean break it will still locate. The advantage of doing it that way is that you can have a dedicated holder set to size and have the repeatability you require. It also saves you having to set up for screwcutting every time.

Keith

Thank you all for your comments and advice, I actually took John Stevensons advice and linished to outside of the die, I went out and bought a Clarke Electric file from Machine Mart. It worked a treat, I turned a boss and threaded it to 7/32 x 40 tpi, I ran the die up to the shoulder, undid the die holder and left the die on the boss, put my lathe to 65rpm then used the new electric file to remove about 7 thou off of the diameter, worked a treat. I found that the grub screws in my die holder had a slight taper up to a flat end which was no good for opening the die up, I went to our local fastner supplier (BBN Fastnet) and bought some cone end grub screws, worked a treat at opening up the die.

To late now and I thought I had posted this.

During training I was given several die stock to open out. The number I was told I think was by 0.015". Any larger and the die might break. I would have thought that 0.010" would be enough for many dies.

I was told that after WWII they all started coming in on size. Before that there was always enough clearance so when new ones were bought they gave one of us the job of opening them out. No problem on bigger lathes as the handles can remain on.

The idea worked too. One of the early exercises was using a die to get a precisely sized thread. 5/16 bsw if I remember correctly measured with a mic. It tools several cuts and finished up with a nice shiny thread. I suspect the tallow they supplied had something to do with the finish but very light cuts would help too.

John

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When I worked in the engineering industry I used a lot of tallow, it was particularly good for threading, slotting and shapers. its just stank a bit, we tried all of the early modern tapping lubricants but they were not quite as good as tallow.