Trying to locate correct thread-tap.

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butlersrangers
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Re: Trying to locate correct thread-tap.

Post by butlersrangers » Fri Jan 08, 2021 10:02 pm

Thanks 'Parashooter', that is very helpful. I planned to grind one of the extra 8-30 Taps to make it into a 'bottoming tap'.

The video has a useful approach. I will practice on a 8-32 tap first!

FredC
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Re: Trying to locate correct thread-tap.

Post by FredC » Fri Jan 08, 2021 10:25 pm

Well you never know till you try. For a very shallow thread this idea would work. I tried a deeper thread in brass and the first few threads looked OK. the deeper it goes the more the last thread needs to be pushed. In Krag barrels the first few threads are easy enough to rearrange. Deeper threads will take more plus they will only be partially tapped because of the taper on the end of the tap. The take off barrel from my uncle's Krag that became the 35/40 has the front hole plugged and a 8-32 tapped near receiver. Forming this thread took a lot of force and was only partially successful. The formed 8-32 hole did take one screw 1 1/2 turns and the other about 1 turn. I would need to make a larger former that would have marginal chance success anyway. I know I could make it work by using an Dremel tool with a burr to undercut the thread a few turns down below the surface. Not the thing i would want to do to a brand new Criterion barrel. The commercial forming taps that I have on hand have an unusual geometry and are designed to form from solid not push an out of place thread.
All that said, I went to the Criterion website and sent them a message to ask if they had Krag size 8-32 screws in stock to mount original sights, if not could they recommend a supplier? If no supplier exists do they make enough quantity of Krag barrels to justify my setting up and making them? I will report here if I get a reply.
Using a thread cutting tap on an 8-32 tapped hole with result in removing partial threads the deeper you go. Even a bottoming tap will do this. Seems like putting an 8-32 custom screw in would be the best solution.
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butlersrangers
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Re: Trying to locate correct thread-tap.

Post by butlersrangers » Sat Jan 09, 2021 12:58 am

FredC - Your photos will make a great cover for the book, "The Krag Screw-Thread Story".

FredC
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Re: Trying to locate correct thread-tap.

Post by FredC » Mon Jan 11, 2021 4:49 pm

carbon outlaw wrote:
Tue Dec 22, 2020 11:25 pm
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 ...
Just looked in the Brownel's catalog for something else and they have trigger guard screws for Krag and 1903 Springfields listed as 1/4 -25. I did check original and custom screws on hand and 1/4-25 is correct. I would not use the 1/4-26 tap on a Krag.

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butlersrangers
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Re: Trying to locate correct thread-tap.

Post by butlersrangers » Mon Jan 11, 2021 6:05 pm

Good catch 'FredC' !

A couple of days ago, I was looking at Joe Poyer's, "Krag Book", (page 110). He described the Krag Guard-Screws as 0.25 inch in diameter, with 25 threads per inch.
I noticed this was in apparent conflict with the 26 threads per inch, that 'Carbon Outlaw' mentioned.

I checked some guard-screws in my 'junk box', but, lacked a gauge for 25 t.p.i.
Neither the 24 or 26 t.p.i. blades on the thread gauge were a match, so, I presumed Poyer was probably correct about 25 t.p.i.
I didn't say anything, until I could check further. (You have confirmed it).

BTW - It is interesting that the standard Frankford Arsenal tap and die set (1902), apparently, did not contain a tap or die for 0.25" x 25 t.p.i.

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