Welding Question

[BJ42LX]

A buddy of mine is building an AR-15. He asked me to tack-weld a pin into the compensator that locks it onto the end of the barrel.

He had prepared the barrel with the pin in place - he used a piece of drill bit as the pin.

I shot a small tack on it but the drill bit didn't take the weld. My tack looked like a small donut with the drill/pin in the center. The pin sat less than 1/64" below the surface of the barrel.

He ground down the first weld and I tacked it again. This time I was successful in covering the drill/pin. Functionally, it will be fine.

Here's my question: why didn't the weld take to the bit? Does it have something to do with the type of steel in the bit?

 

[koditten]

Most likely the first attempt had a bad ground. This is the best I got. I think I'm picturing what you asked.

KO

 

[38Chevy454]

If the drill bit was HSS (high speed steel) it should weld fine. If it had some coating on it that could mess up your fusion.

 

[pfarber]

What state is he in? Some states will require a 360 weld, others you can just spot it.

Remember that MIG needs an electrical path to cause the wire to arc onto the part. You may not have had a good enough path (the compensator, being higher, had the least path of resistance, therefor got the arc started).

You may have simply not held the arc long enough to get the metal molten, cause a good path the to the pin, and thereby allow molten metal to fuse it.

 

[BJ42LX]

The bit was HSS - or at least that's what it looked like to me - not black phosphate, titanium or anything else off-color.

I was grounded right to the compensator. I'm sure I had a good ground there. But I guess the bit/pin could have been floating in the hole and didn't make contact. I any event neither the pin nor the compensater are going anywhere.

NYS - I don't know what the rules are. I was just helping himi out with the welding part. The way things are here if a full 360 is required they probably wouldn't let us buy the parts separately.

 

[brownbagg]

drill bit too hard, hard steel is diffulcult to weld.

 

[justanengineer]

drill bit too hard, hard steel is diffulcult to weld.

No, its not. Irregardless, I doubt he was welding the helical part of the bit but rather likely the shank which is usually soft.

 

[Engineer61]

HSS is much stronger at high temps and melts at a lot higher temp than standard steel alloys - that's why it's called high speed steel. You can use much higher speeds on cutting tools made from HSS than you can from tooling made from standard high carbon steels without burning off the cutting edge.
The first time you tried to tack weld the pin you probably backed off the heat once the barrel steel melted, and didn't get the HSS steel hot enough to melt.

 

[Tig Master]

A buddy of mine is building an AR-15. He asked me to tack-weld a pin into the compensator that locks it onto the end of the barrel.

He had prepared the barrel with the pin in place - he used a piece of drill bit as the pin.

I shot a small tack on it but the drill bit didn't take the weld. My tack looked like a small donut with the drill/pin in the center. The pin sat less than 1/64" below the surface of the barrel.

He ground down the first weld and I tacked it again. This time I was successful in covering the drill/pin. Functionally, it will be fine.

Here's my question: why didn't the weld take to the bit? Does it have something to do with the type of steel in the bit?

What type of welder did you use?

T

 

[BJ42LX]

What type of welder did you use?

T

Miller 211.

I was set at 6/60, which is the recommended setting for 1/8" steel and 0.030 wire and 75/25 gas. Using 120v power as it was more convenient where I was working.

I may try this process again with some scrap and an old junk bit just to see what happens. I probably should have done that before doing the barrel, but I didn't think there would be a problem in the first place.

 

[BJ42LX]

I just ran some tests with scrap metal and an old HSS drill bit. I made four holes and broke off four pieces of bit. I couldn't get a decent tack with any of them.

I'm able to make decent tacks small and large all over the test strip. But when trying to include a piece of bit in a hole - not so much. I didn't get the "dount" I did when welding the gun barrel. But the tacks with bits were very porous and popped open all over the place. I'm not sure what's up with that - it could be just me.

I ground down one of the tacks and I was able to drive the bit out with a light tap of a hammer - very little penetration.

If anyone ever asks me to do this again (I doubt it!) I'll be sure to use a piece of coat hanger instead of a drill bit.

YMMV.

 

[rodknocker]

Here's my guess, in order to harden steel, carbon is added. I assume this affects the molecular structure, and condenses it making it harder. In conclusion, there is an issue affected by metalurgy, that needs to be resolved.

 

[Zeke]

Use more current for tacks and clip the bead off the end of the wire before each one. The chart is for continuous welding.

 

[Tig Master]

Tig weld it and be done with it.

T