Repair threads on screws?

[romulus]

As I began to reassemble my Ithaca 87 shotgun, I noticed that the large receiver screw that holds the trigger group in place has threads that sort of look "peened". They aren't sharp. The threads of the mating hole on the receiver looks similarly peened down. This screw has been removed only once, so it's not a matter of abuse. I noticed I can get the screw in fine, is there a danger of it slipping out? Can I rethread these or "clean" them with the appropriate tap and die?

The older Ithacas, as well as the newer ones, sure seem better machined than the interim Ithaca Acquisition models...

Thanks in advance

 

[jrhines]

Without examining the threads it is hard to tell if they have been peened over or if they were cut that way to start with. Can you get to a similar gun & take a comparative look?
Given the specs on the screw and an appropriate tap, yes, you can clean up the threads. Taps come in standard sizes and each size comes in several tolerances, from H1 to H3 or H4. The H number denotes the number of half-thousandths (0.0005"), over the tap basic size. If you use an H1 tap you will cut the minimum thread. Check out MSC Industrial supply for a source.
You might also consider replacing the screw with a new one.

 

[romulus]

Gracias, jrhines...will look into it.

 

[P95Carry]

Thing that occurs to me Romulus - is, going by your description .. it would sound as tho both the male and female threads are shy of the full crest and root dia ..... in other words ... the male max dia is reduced and also the female a tad plus on dia. may be wrong but if this is the case no amount of work with tap or die will improve matters IMO.

Just pondering, that's all!

 

[romulus]

In looking at matters with a flashlight I'd reckon you are correct...I'm also wary of doing this especially in light of the fact that the screw seems to hold well...I'l just be careful not to strip it...btw, what the solution should the hole in the receiver get stripped? I can always replace the screw...

 

[4 eyed six shooter]

The factory makes the screw and threaded hole that way to make it easier to start the screw into the hole. There are severaI other firearm manufactures who do the same thing. I would not attempt to run a die over the screw or a tap into the hole as you could remove enough material to make the screw sloppy in the hole. Best wishes to all - John K

 

[jrhines]

4 eyed six shooter - Where did you hear/see/read this info? I'm not disputing it; it sounds OK to me. Just wondering what your source is. Could you name some of the other manufacturers or some specific guns you have seen this on? Again, I do not doubt what you are saying, just trying to get smarter in my doting years.

romulus - Torque is what generates the friction that keeps a screw in place. If you can't use the proper amount of torque the screw will backout with use. Some would recommend Loctite or the like to keep the screw in place, but in this situation, where I know I'll be removing the screw on a semi-regular basis, I use white shellac thinned 1:1 with wood alcohol. Just a drop on the threads and snug 'em up. To remove, use a toothpick to put a drop of alcohol around the screw head, wait a bit & it will come out. Before you start, try a drop of alcohol on the finished surface of the gun where it won't show, to check for possible staining