doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Whitworth threads

I am missing a bolt for an old English gun. It had been badly buggered. But I have to plead stupidity because I put my damaged bolt in a safe place so I could recover it. Now I can't find it. I hate when that happens but I was knocked pretty dippy by the accident and the bolt probably needed to be replaced anyway as tig welding a new head and reshaping the bolt is an iffy enterprise. I'm going to try a machine threaded bolt, but I presume the thread is a British Standard Whitworth. All I know about Whitworth came while I was restoring a MGTD using Whitworth tools.I know nothing of the treads. 1)Will a modern machine thread bolt work in a Whitworth threaded hole? 2)Does any one know of a dealer who sells Whithworth screws or bolts?

The area the bolt screws into is on the tang and there is not much metal there to oversize drill and cut new machine threads. I am to not too crazy about drilling and re threading anyway as the fit is critical and if I don't line things up just right I'm going to have a problem with the gun.

Good luck, but I don't think you can presume anything about the thread on an old British gun necessarily conforming to any standard... What's the gun?

It's the Army&Navy I've been working on.

I would be most surprised if that is a Whitworth thread.
More likely to be a British cycle thread.
Depending on the date of manufacture, early like 1860 - 1900 could be anything because there was no standard threads & they made screws & taps from a screw plate.
O.M

Damn!! Things keep getting worse.

It's not getting worse, just more expensive.
O.M

I doubt that you will be able to find a US thread that will work in a Whitworth threaded hole. The US threads are cut with a 60 degree angle and a sharp vee top and bottom, while the
Whitworth is cut with a 55 degree angle, and the tops and bottoms of the threads are rounded. You probably can find taps and dies to cut Whitworths on the internet. A good investment for anyone who works on mechanical things is a book called "Machinery's Handbook". For your purposes, a used one several years old is good enough, as the basic info you need has not changed in the last 50 or more years.

Assuming you have a typical dial caliper, measure the ID of the screw hole. It will likely be near a fraction minus the thread depth times two. We can probably guesstimate a good fit of a standard bolt from this measurement. You may want/need to run a modern tap through the hole to make sure the new bolt fits reasonably. This is not the most technically "pure" repair, but a very practical one. Post the diameter and we will begin the rumination.

DDA

I'll do that! Thanks! I don't have a modern digital mic. I still use the old fashion calibrated mic which I have to put my glasses on to read. I keep thinking I ought to get a new modern mic, but I'm use to the old one.

I was thinking Whitworth used a 45 degree V, but there are many things I am wrong about.

I'm going to get that book.

When you get it back together don't forget to share what you learned on the DIY Gunsmithing forum. Photos are especially appreciated.

Steve