JB Weld as a filler for steel?

[SZR48207]

Has anyone here had good results when using JB Weld to fill in holes in hardened steel? I would need to fill in some 1/8" x 3/4" pin slots on a gun barrel, only to go back and re-drill the same area but at a slightly different angle.

One of my concerns is shrinkage, although JB Weld's website says there is 0.0% shrinkage. Additionally, this area of the barrel will get quite hot, although not anywhere close to the 500*F rating of JB Weld.

I am worried that re-drilling may cause the JB Weld filler to crack.

 

[tig1]

As a welder for 35 years I have seen many bad results with JBW. Often applied, then when JBW fails it makes welding very difficult. Find a good tig welder in you area and do it right even though the cost will be greater. You get what you pay for. If you were close by I would be glad to do it as I have a tig welder.

 

[rclint]

I don't think any filler is going to be your answer here for pin slots... or anything on a gun barrel that will get heat cycled on a regular basis. Can you bore the hole out for the pin, then press in a made to fit pin ? If you have a lathe, or you could find a standard size shaft made from the correct steel of course (research here would be needed) then you could also blend the pressed in pin, if done correct you would never even see a repair. Also this would be the very best attack for any drilled/tapped hole.

Could you elaborate some more on exactly what gun/make/model and what part you are working on ?

 

[SZR48207]

I'm working on the front sight base on an AR15 barrel. I recently returned this rifle back to its "factory" state by reattaching the front sight, but completely forgot why I had customized it in the first place.

Sample Pic:

Basically, the front sight is canted about 3 to 5 degrees counter clockwise. While there is enough slack in the sight adjustments to compensate for this, it's very unsightly to have a front sight that is noticeably crooked. This is a common issue for this weapon platform, and some master builders have gone as far as purposely adding 1 to 2 degrees of clockwise cant because final assembly of the barrel into the upper receiver seems to induce some canting due to loose tolerances in how how the barrel indexes into the receiver.

Being a typical "gotta do it myself" kinda guy, I'm not about to 1) buy a brand new barrel with a straight sight because this barrel is still good and 2) throw away an opportunity to learn a unique skill.

 

[SZR48207]

To continue my post, you can see in the picture how there are 2 pins (taper pins) that hold the sight onto the barrel. You can also notice that these pins actually are in a position where they actually go through the barrel itself. These "slots" where the pins go through are what I plan on filling in with steel epoxy so that I can correctly align the front and rear sights and re-drill the pin holes.

Because I would be drilling into a path very similar to the original slots, I am not too worried about the "integrity" of the setup since the worst possible case would be that the epoxy fails and the front sight returns to the original pin locations. I am just not sure if a steel epoxy would hold up in this type of situation.

 

[SZR48207]

Originally Posted By: rclint
I don't think any filler is going to be your answer here for pin slots... or anything on a gun barrel that will get heat cycled on a regular basis. Can you bore the hole out for the pin, then press in a made to fit pin ? If you have a lathe, or you could find a standard size shaft made from the correct steel of course (research here would be needed) then you could also blend the pressed in pin, if done correct you would never even see a repair. Also this would be the very best attack for any drilled/tapped hole.

Could you elaborate some more on exactly what gun/make/model and what part you are working on ?


I could bore out the hole, but I am not positive this would solve my problem. Additionally, due to the location of the pin slots, I would not want to risk reducing the amount of steel between the pin slot and the bore of the barrel.

I may have to figure out some type of illustration to show what is going on, as I think that would make it more obvious why I am wanting to use an epoxy filler.

 

[SZR48207]

Here is a crude mockup of what's going on:

 

[morris]

what tig1 said. jb-weld is good for a lot of things, but not this app

 

[SZR48207]

I know it's rather quick, but I have good news to report. I received a tip from a gunsmith to try using set screws instead of the taper pins.

So, after finding out that Lowe's doesn't carry tap/drill sets, and driving across town to find out that Ace Hardware does, I managed to fix my front sight. I will be going to the gun range this weekend to zero the sights, but once they're set I'll be making the job permanent by using red Loctite on the set screws.

While the set screws are not as bulletproof as the taper pins, this would be the next best sensible option.

 

[rclint]

A word of advice, before making things permanent with set screws (locktite) order some good set screws from mcmaster, you will see a price difference between the cheap junk, and then quality made screws. I'm not sure what would be the best here stainless or regular steel, as steel can in most times be stronger than stainless.

Also these barrels get hot I have a Colt LE 6920 myself, one unfired in box, and have some experience with having range time with this platform. The barrel can get extremely hot, even hot enough to break the red loctite seal as that's what you use to break red locktite. You might also research the various locktite offerings I think they offer a permanent fix that makes the red look like nail polish. If you want to get real extreme you can use two set screws stacked on top of each other combined with a thread locker... and they make some short set screws just for this application, remember a soft setscrew with a cup will have maximum holding power, combined with surface area of the set screw.

Good luck, and my hat is off to you for coming up with a better alternative.

 

[another Todd]

Is it possible to find/purchase an offset front sight to compensate for this? If your barrel was drilled wrong, I am sure there were others. Also, put this question in the firearms section. Someone there might have a nifty solution. Would it be possible to braze up the hole and re-drill it?

 

[another Todd]

BTW, I would not use an epoxy. Most epoxies soften and fail at the elevated temperatures the barrel will see.