doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Thread size of Brit shotgun rod ends

Rocketman,
Yes I am deadly serious about the thread form being 26 2/3rds TPI.
I travelled the road that you are now on some years ago and all I was met with was blank stares and obstruction.Well to me that is like a red rag to a bull, so I got my old friend Phil Heighway, senior designer for the Coventry Tool & Guage to run some checks and he confirmed with the use of a shadowgraph printout that the thread form was 26 2/3rds his comment was that whoever invented that threadform 'was a miserable b****rd' with nothing better to do.
The Parker Hale accessory business was bought out by the company who make the 'Bisley' range of cleaning kits and rods,called John Rothery Ltd., the most unhelpful company I have ever had the misfortune to deal with.
Like all problems they have a solution if you persevere.Once I had sorted out the thread form and pitch, I just made my own tap and die out of tool steel, hardened and tempered and 'viola' after all I am only cutting brass or aluminium with them so they work great.
As regards 26tpi BSC & BSF, yes Roy is correct and I also checked this out early on and was extremely frustrated to be near, yet so far. With short thread engagements you are so very nearly there but it just does not feel right, especially if you are trying to make a nice 'posh' set of ebony rods.

Thanks. Will have a look at this situation - again - when I get home. 26 2/3 TPI!!!! Reminds me of a "learning" problem a drafting professor gave our class wherein the obvious solution was a sprocket with 44 1/2 teeth. It was surprising/disappointing how many guys settled for that solution. Prof claimed to have found this as a real life problem on a troublesome ag machine in his early career; couldn't figure out why it kept breaking chains!!!

"Once I had sorted out the thread form and pitch, I just made my own tap and die out of tool steel."

I'm curious on how you cut 26 2/3 TPI. Are these threads double lead? Stanley Planes made some weird threads on their early block planes for adjusting the blade depth. These threads were double lead, 180 deg from the other.

In 35 years as a machinist I don't think I ever saw a lathe which would chase 26 2/3 tpi. Even if it were a double lead 13 1/3 would be no better. These threads would simply require a special set of change gears. It also does not convert to any metric thread lead so no dice there. Most lathes will cut 26 or 27 tpi but nothing in between.

If Coventry Tool and Gauge Checked it out as you descibed Its time for me to eat crow!

I promise you guys the information I have supplied is correct.
If I can find all the details I will post it here.
Obviously anyone who has doubts can measure the pitch of a genuine PH brush thread! ! !

2-Piper is correct; with the right combination of change gears you can cut any number of t.p.i you desire including 26 2/3 t.p.i. The formulae/method for calculating the change gears for,cutting fractional threads, is detailed in the Machinery,s Handbook under the section on, "Thread cutting".The gears required may vary from lathe to lathe because the constant gearing of lathes [Drivers over driven]Used for cutting standard thread pitches dose vary depending on the lathe manufacturer.