fixing an oversized hole.

[Intimid8tor]

I feel like an idiot posting this considering I just posted a question about how to speed up milling the lowers.

For the record, this issue didn't occur because of being in a rush and had nothing to do with milling out the fire control pocket. That part went well.

After finishing my lower I cleaned it up and noticed the trigger pin hole looked too big. I measured it and sure enough it is .174. .018 over. Not sure exactly how that happened. I used the same process and drill bits I used on my first one where the holes came out perfect. It is oversized only on one side and it happens to be the side where the hole starts. The back side is perfect at .156. Nearest I can figure either it walked a little when the hole started or the bit bowed when I was drilling through. I didn't center drill this hole to start.

So, now I get to fix it. I found oversized pins up to .170 meaning I would still be .004 to small. Perhaps that would get taken up by anodizing and it would be a perfect fit. But, that means that one of my lowers would have different parts than the rest. I would prefer that not to be the case.

I guess I could have it welded and then redrill it? Or I could plug it and redrill.

What would the pros recommend on a good fix (i.e. no JB weld).

[kcstott]

I would recommend welding it up Or pressing in an insert and re drilling.
Anodizing will not build up enough to save it.

Now for the lesson.
One: you always center drill, Always, And you can only not center drill when you have a fixture with drill guides.
Two: you always ream a hole that has +/-.0015" tolerance on diameter and .004" on location.

[G-forceJunkie]

Drills will always drill bigger at the start since it has no side support untill its deep enough. Given the option, always center drill, then drill undersize, then ream to final size. I would just ream it for the oversize pin, the ano will take up a few thou.

[savs2k]

maby a bent drillbit or you forced the hole too much when you started it. I would just reweld it and drill it over. It would probably show up if you annodized so you might want to duracoat or some kind of paint that you bake. As for what to use to fix it... if you don't have a welder use this stuff. I have one stick left myself

http://durafix.com/

[Intimid8tor]

maby a bent drillbit or you forced the hole too much when you started it. I would just reweld it and drill it over. It would probably show up if you annodized so you might want to duracoat or some kind of paint that you bake. As for what to use to fix it... if you don't have a welder use this stuff. I have one stick left myself

http://durafix.com/

That stuff just got mentioned on weaponsguild. I was not aware of it. Have you used it on a milled lower? Is the temp any concern since a torch is used to heat the lower?

I have been thinking about getting a welder. This is one more reason to buy a mig with a spool gun.

[savs2k]

my buddy had to use it on a lower. worked fine but the stuff is hard to grind. The temp isnt an issue it takes alot of heat to melt. Its just a way lower melting point then alum. An ar will never get hot enough to come remotely close to melting the stuff.

[kcstott]

The thing is Tig welding 7075 is a pain and the welds can have a tendency to crack.
It can be done just not as for giving as 6061.
That said a mig with a spool gun may not be the best choice. Depending on your experience it can be a short zap and you're done good to go or it can turn in to a total fubar mess. And again if it's a 7075 forging you run the risk of the weld cracking.

If it's 6061 mail it down here and I'll fill it in $20 I have a tig welder and have been using one for twenty years.

[h0use]

fill it in with jbweld and re drill the whole.

[Woodworker2]

If you have a lathe, you might consider this approach:

Aluminum expansions with temperature. Heating the lower will make the hole larger. You could machine an aluminum plug to fit the larger size (plus a few thousandths for a friction fit). Drive the plug into the lower and once it cools, the plug will be locked in place. Then, redrill the hole.

You might consider buying a spotting drill, or a "ball" end mill to better locate the new hole. As others have mentioned, it is hard to keep a small drill from moving sideway. (Also, a drill bit will rarely make a truly "round" hole, a chucking ream would do a better job)

[Intimid8tor]

Well I filled it in with alumaweld and I will mill it clean tonight and see how it looks. I practiced a bit on a piece of 1/8" aluminum to get the hang of it then went to work on the lower. I center drilled the selector hole and even that one came out big so I filled it as well and will re-drill. I need to evaluate my process for drilling the holes. I will be drilling undersized from now on and then will use a reamer to finish them off. I haven't decided if I am going to continue using my center drills for spotting or if I am going to buy an actual spotting drill or 2.

[gunboat]

I guess this is asking the obvious, but do you center punch before drilling?
If your drill is drilling oversize resharpen or get a new drill. A chipped flute can be a bit of bother.

[Hilldweller]

Phew !

Wasn't sure when I read the title. I'm so glad this had to do with guns.....just saying....

[milotrain]

1. Tig weld it, no problem with a crack as long as you preheat the whole thing slowly and cool it slowly. Not enough length to the weld for a problem I think. You could OA weld it if you were a god among men.

2. I'd always always always ream trigger holes and take down pin holes. You can drill the rest, except the big holes but I'd just drill them under and throw an EM through them instead of a reamer, close enough for their tolerance and they are typical EM sizes.

[sonnyt650]

Anybody know how well the different options anodize?

I recently fixed a barrel hole that I cut poorly on a 10/22 receiver by boring it out oversized on a lathe, then plugging with a 6061 aluminum tube (same designation as the receiver) that was pretty close to the final inner diameter. I used reamers after both steps to tweak the sizing so that the insert required a heavy press fit while the barrel slid in with a little friction. Seems to line up great now with the scope near the middle of its adjustment range but I have to shoot it to be sure. I was hoping to anodize the results if it holds up to that test.

[Intimid8tor]

I guess this is asking the obvious, but do you center punch before drilling?
If your drill is drilling oversize resharpen or get a new drill. A chipped flute can be a bit of bother.

I don't center punch. On the first one I did I found the center of where each hole was to go and then drilled with no center drilling, no spot drilling and no punching. Holes came out fine and perfect.

On this one I did, I center drilled the selector hole and had all sorts of challenges drilling the hole. I believe that issue was due to running the spindle at too low of a speed. The 2 FCG holes were drilled straight through and went through with no problems.

Anybody know how well the different options anodize?


I recently fixed a barrel hole that I cut poorly on a 10/22 receiver by boring it out oversized on a lathe, then plugging with a 6061 aluminum tube (same designation as the receiver) that was pretty close to the final inner diameter. I used reamers after both steps to tweak the sizing so that the insert required a heavy press fit while the barrel slid in with a little friction. Seems to line up great now with the scope near the middle of its adjustment range but I have to shoot it to be sure. I was hoping to anodize the results if it holds up to that test.

your option probably has the best chance of anodizing. There might be a line or a slight color difference. I don't think mine would anodize well as it is a different metal. This lower will most likely get painted or coated in another way.