Trying to locate correct thread-tap.

[butlersrangers]

Does anyone have a source for a 5/32" X 30 TPI tap?

(Arsenal tap was .156" X 30 TPI - United States Form).

I am restoring the front sight-screw hole on a Krag barrel. The original hole was 'removed' by a 'dovetail' cut.

I have fashioned a steel 'patch' to fill the dovetail. When I drill & tap the new sight-screw hole, I would like to use an original sight-screw.

[FredC]

SpamHaus reply: This SpamHaus thing is nuts. After you type a reply it disallows you from posting and reports the wrong IP address. I post again in a couple of minutes and it allows it?!?! Is this happening to anyone else?

I looked in my MSC catalog for special taps and they did not have a #8 -30 tap. That would have been too easy. Carbon Outlaw had mentioned finding some arsenal taps I think. Not sure if the person he got them from had more.

I have some questions about what you are doing. Are there no threads period left in the barrel under the dovetail cut? Is the dovetail blank you are intending to use have enough thickness that there is no need for any threads in the barrel?

Do the S&S screws sold to replace original screws duplicate the old 30 TPI and rounded thread form or do they match the new Criterion barrels 8 32 threads. The 30 and 32 threads are so close in pitch diameter and threads per inch the threads would conform if the wrong screw is used once. If you went back and forth between the 2 thread styles you would eventually ruin the threads. Today many internal threads are formed instead being cut. Form taps displace the metal instead of cutting. If done correctly with the right tap drill and proper lubricant a formed thread can be considerably stronger than a cut thread. All that being said using a wrong screw that has been gently applied with a good lubricant and used forever after that could work.
Depending on the strength of the material in your insert one could use a 8-32 tap to make initial threads and and a hardened screw blank could be used to rearrange them so that an original screw could be used afterwards. Let me know if you want me to make a hardened form screw/tap for you.

[carbon outlaw]

I will look today and get back to you ...

[carbon outlaw]

I did a post about using a 8-32 tap or 8-32 screws and I found they work fine ... I made some sight screws to try and they worked fine ...

[FredC]

Carbon Outlaw,
Sorry, I thought it was you that found the #8 30 tap to cut the rounded crest style of threads. Do you remember who that was?

I sent BR an email and we are thinking that I will make a threaded tool to rearrange standard 8-32 threads to fit original Krag screws with no damage to the soft screws that are threaded in after the modification. Your trick with the brass screw is the same principle, the moderatedly strong barrel steel with form the brass threads to fit. In case you want to try it there are ways to color the surface of brass almost black. I think my Machinery's Handbook mentions how I can look it up in case you want to know.

[carbon outlaw]

I tried to find a 8-30 tap for a long time ... I found a company that said they could make any size tap and die you could ever want the only problem was they were expensive ....

[carbon outlaw]

when i was looking I found some very interesting size taps ... 1/4-28 ... 1/4-30... 1/4-32 and 1/4-26 this die 1/4-26 is the one for the Triger guard ...

[FredC]

Yeah, having a 8-30 tap made with modern high speed steel and the old rounded crest thread form would cost a very pretty penny. With a screw cutting lathe one can make a tap from high carbon tool steels and file the relief by hand on the lead angle. But that is the problem with out the machine generated cam relief on the cutting surfaces they do not cut a very pretty thread. I found 2 specials I built myself, one for shotgun cleaning jags and another large metric special to make an accessory for a Taiwanese built machine. Both worked but I would be real hesitant to sell the work produced or the taps as they do not meet my usual standard of work.
Be careful with that 1/4 26 tap. It was probably produced when thread standards were changing quickly and may not match the arsenal threads. If you had a damaged receiver that nothing else would help, give it a try but you may need to cut a special screw to fit. Not too hard if you have a lathe, but an extra step none the less. If it does try to remove metal cutting through the case hardened material may be problematic.

Which brings us to a decision for making these sight screw threads. Which is easier, better, faster, making a special screw cutting tap or a forming tap to rearrange the threads cut with an off the shelf 8-32 tap? I will think on this a couple of days then probably make one or the other this weekend.

The shot gun cleaning jag tap is .296 - 27. No wonder it had to be custom made. It must have cut a fairly clean thread as I remember the customer wanted to give presentation grade custom cleaning rods to his friends. After 40 years the details get a little foggy.

[butlersrangers]

Fred, your Machinist Knowledge and Expertise is always enjoyed!

[FredC]

BR,
I took out the screws to measure from of my dad's rifle and the sight has 3 C stamps! A very small one one on the sliding piece and one the ladder and one on the ladder base. What gives here? My grandfather bought this rifle during the depression. My dad hunted all over the Fred Harvey ranch with it before he was mobilized for WW2. An uncle stored it for my dad when my grandfather died. My dad kept it as a keepsake since he bought a 1917 Enfield to hunt with after getting back from the war. This Krag has never been out of the immediate family's possession. I guess sometime soon I will need to post photos in the US Military Krag section. This thing has turned into a puzzle for me. Please tell me this sight is worth a bazillion dollars and I can trade it for a pristine ladder sight and hand guard plus six figures cash! Blacklisted by Spamhaus again!

I did clean the screws and and put them on the optical comparator. Show the rounded thread form very clearly.

Are these the screws I want to measure for 1901 sights or are they carbine sights?