Getting screwed again [7/32 - 28 BSF die]

Elric

Well-Known Member
Folks, I got the screws in from Marble's, and they are UNF 12-28, OD is .208 . It goes in less than a quarter-turn [finger-tips] into the Low Wall lower tang, then tightens up. My SWAG, the lower tang hole was tapped with a 55 degree Whitworth, and that screw was possumbly slightly undersize.

Now the new UNF 12-28 screws WILL turn into the tapped hole, and the screw threads get shiny. My guess the threads are being re-formed. Thankfully, the tang hole threads are stronger than the screw threads.

I want to re-cut the UNF 12-28 using an adjustable 7/32 x 28 BSF die. Since it is Whitworth, it's a British thing... Yup, Red Chinese, Indian, German, and Polish manufacturers are on Flea-Buy, but let's do British Steel... Any British sources for an adjustable 7/32x28 BSF die?
 
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RBHarter

West Central AR
I know this is a reach ......
Can you maybe do a cast of the threads ? Cerrosafe maybe ? Turn a soft bit of aluminum rod to ...... I don't know ......tapered from under minor dia up to 1/4 of the thread depth over the minor dia and get 3-4 turns for a measurement ?

Metric has 3 standard pitches per dia , SAE has 2 plus class fits and special pitches IE gun screws and pipe threads . Both also have an assortment of tapered , self locking and resistance fits .
 

RBHarter

West Central AR
The Italians had a bad habit of making their reproductions where possible from originals so some of those had all sorts of odd things in them not the least of which was odd ball screws because a black smith in po dunk 1902 Montana repaired a stripped screw hole with a filed single flute tap and made a screw hot formed out of a horse shoe nail .......
 

John G

Well-Known Member
List of Marbles screw sets on Buffalo Arms

Oohhh... lookee here... MAR995003 has 10-32 x .342 -AND- 10-36 x .355 with a 12-28 x 1.9

Ok I finally got my screw set listed above which comes with 10-32 X .342 and a 10-36 X .355 and of course the long screw 12-28 X 1.9.
The long screw at 1.9" is perfect. Goes right in and comes almost flush. Just slightly below grade.
Neither of the short screws did more then 1/2 turn then come up hard. The option was to tap the gun which did not make me happy. The 10 X 32 seamed closer so I gave it another turn then backed it out. Threads in the gun were unfazed. The screw was reforming itself, so I cleaned the threads lubed and ran it in again an additional turn, backed out cleaned and in again. Repeating until it came up hard on the sight. The threads in the gun look fine, the threads on the screw looks like it's been run into a die.
This is for my original 1885 High Wall. So all is good on my end, tang sight installed and looks good.
 

Elric

Well-Known Member
Taking this slow, since metal is harder to replace when you remove it.

For a gun probably over a century old, is it suprising that there is something not the same? The sear spring screw hole threads don't look smooth, but the lower tang screw threads look smoother. Ran one of the 12-28s in a few turns, and the threads did not look like they were changed, TPI-wise. Both thread flanks of the 12-28 look like they were reformed. Took a bit more force to turn the 12-28 in, not slot-stripping he-man, but you need a good grip.

John G, in my [un]professional opinion, the lower tang threads are quite a bit tougher than the screw metal.
 

John G

Well-Known Member
Yes that's what I found as well. I was very pleased to not be in danger of damaging the threads in the gun. New screws I can get, keep the rifle all original is valuable. I'm just glad when I got brave or more like foolish the that screw gave up first.
Now if I can make this new Marbles tang sight look 120 years old, or at least 80, it would blend in with the looks of the rifle much better.
 

Elric

Well-Known Member
Posted to the Practical Machinist forum asking where I can get a UK 7/32 x 28 BSF split die...
 

Elric

Well-Known Member
Ordered a 7/32 x 28 from the UK. A bit spendy, but BSF is not common. There is another Low Wall that most likely has 7/32 x 28 for the upper tang screw and it looks better. Not original, but a decent finish...