fixing mis-drilled holes

Jim Keenan said:
When I was working as a gunsmith, we got that problem about once a month, as people who didn't want to pay for a proper drill and tap job used a hand drill or tried to have it done at a local garage.
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Heh, heh. Bubba and his Black & Decker can be a gunsmith's bread & butter. Almost as helpful as his brother who owns a Dremel tool.

The plug screw and re-drill fix needs the warning tossed in not to use a hardened set screw as the plug. Ideally, the steel should match so the next attempt at drilling doesn't walk the drill toward the softer of the two metals. This can apply to a weld-up, too if the filler is much different from the original material. A jig with correctly spaced drill guides is best for preventing the walking problem on the next go-around.

If you wind up needing to drill with an end mill, be sure to buy a cutter called an end cutting end mill. End mills without that designation won't cut down in the center.
 
I sort of alluded to that about the screws, but it needed to be clarified, and you did it very well. Some of those plug screws and mount screws are very hard and anything but a stiff carbide starter drill will try to wander.

Jim
 
He said the hole was 1/4 of a hole off. tapping it and plugging it won't work under those circumstances unless you drill and tap it large enough so that the new hole is entirely within the plug. With 1/4 of a hole off center you would end up with a tiny crescent moon shaped piece on one side, and it won't stay there if that's the case. In my work I have to fix this kind of thing sometimes. I'd take it to a mill with a DRO, use a center cutting endmill to center the hole oversize where it should be, which should still only be 1 1/2 times the original size, then drill that hole carefully, tap it with a fine threaded tap and drive in a threaded plug with permanent loctite. Then your new hole of the correct size will be centered within that, essentially you are making a threaded insert in place. Make sure and allow the loctite to set up well before drilling and tapping the plug. I've done this many times both with offset oversize plugs and with centered plugs, centered is better. In either case if done right it will never come out.

Or,,,, tig weld it. :)
 
...use a heat sink (wet cloths) to keep the heat from affecting the barrel...
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If one needs to prevent heat from affecting other than where one is welding, one should invest in the stuff that is made for the job and to which I can attest is better than other metods. To wit: Brownells Heat Stop Heat Control Paste, stock number 083-012-100
 
Lets do a comparison.

We'll look at a crankshaft in a circle track/road racing engine and a barrel.

The crankshaft accelerates and decelerates a 2500 pound car for the duration of the race. The dynamics of an reciprocating engine are pretty violent as one journal accelerates during the power stroke and the other seven struggle to keep up, then reverse the process during deceleration. Never mind that it also provides the motion for the camshaft/distributor and that alone consumes over 300hp when operating above 7500rpm.

These cranks develop cracks over time, regardless of how generous the radius is along the journal fillets. These cracks are welded, reground, chrome plated/nitrided, and then it goes right back into service.

Unless your a barrel on a machine gun deployed to Afghanistan your barrel with the buggered hole has a life that is quite easy by comparison. TIG/MIG the hole and forget about it. If your really that worried buy a copper rod that slips in the barrel, some heat exchange paste and stick it in the barrel for a heat sink. Overkill IMO but if it makes you feel good go for it.

I've done this repair and it works so long as the person running the welder doesn't turn the hole into Chernobyl or 3 mile island. It's worked on 1000 yard palma guns that have competed in world championships to magnum caliber elk guns. All of which were built over the last ten years and are still in service.
 
I used a DC inverter welder drilled and cleaned the holes out heat sinked the barrel and filled the holes back in with a nice weld.

Grinded them back smooth with a demel tool and cannot even see where they were now.

You can buy a flux wire welder or even a DC inverter stick welder for cheap now days and with some practice (A lot of practice I should say) on a bunch of scrap metal before you know it welding stuff onto a receiver or barrel will be no problem for you.

Having a stick welder and a flux wire welder has been one of the best investments I have ever made and both only cost about $300 including a auto helmet, gloves and a bunch of wire and 15 pounds of sticks or so.

What is funny once I got them all of a sudden people bring me all kinds of good scrap metal for free I can build all kinds of stuff out of.

Check out this heavy duty target stand I’m still working on now to add some more targets.

tstand.jpg


Boards slip into the top for easy change out and stapling targets onto and the steel targets are so heavy they will probably stop a tank shell :rolleyes:

That one steel target hanging on the left weighs 52 pounds LOL

All of the metal used in them was being thrown away unless I wanted it so I recycled that metal for a good use :D

I just picked up 60 feet or so of 1/4" thick x 1" angle iron the other day so I'm having fun with the welders today :D
 
I should have added if you are going to try that be sure to practice welding up a bunch of small holes on some thick steel stock first so when you put that weld on the reciever or barrel you know exactly what to expect.

Filling a little hole with a weld is not just a 1-2-3 operation unless you have had a lot of practice before hand.

I remember when I first got the welders I was going to do that then stopped myself for some practice before hand to find out I had to drill about 20 holes in that scrap steel stock as a way to get that weld just right.

Then when I did the weld to fill the reciever holes they were perfect :D

Practice made perfect go figure :p
 
If my welds were that bubble gummed up I would be embarassed to show them on a public forum.

It's easy to burn rods. It's even easy to run a wire welder. Anyone can have a welder, but not everyone can be a weldor. TIG welding is as much an art as it is a skill. Unless you are an experienced weldor that understands the effects of crystallization, and heat treating, welding a barrel can be dangerous. I would caution a beginner to use the tap and plug method instead.

His Soldier brought up a good point about the hole size. Drilling it larger and then using a smaller hole inside the plug would probably make it stronger. I think that 1/4 of the hole diameter off isn't too much to fill with the original size plug, but anything larger than that would definately be better to use a larger size plug.
 
+1

I can't help but cringe at the thought of buzzing on a barrel. Maybe on a .22 or something, but you WILL anneal the metal. I don't care how clever or awesome of a welder someone is, that spot will get annealed. That makes me nervous, personally. I wouldn't even CONSIDER buying a rifle that had a weldment on the barrel, personally, would you?
 
If the barrel has been heat treated properly you will never have a problem.

I have shot over 200 rounds out of the 7.7x58mm I fixed and it hits dead center bulls-eye every time.

I'm sure not going to sell that rifle when it is that accurate and even if I did someone would sure have a nice one.
 
I've been a toolmaker/moldmaker for over 32 years and have repaired a few things with the problem the OP described.
Here is what I normally do and it has worked out fine.

Make a plug of the same type metal you are repairing.
Make the plug .0002 to .0004 oversize...bigger than the hole you want to fix.
Make the plug about .015 shorter than the depth of your hole.
Heat the area with the hole up---use a hairdryer, heat lamp etc.
It doesn't have to be hot just fairly warm to the touch.
Put your plug in the freezer for half an hour.
Tap the plug in the hole and it should sit down from flush about .015.
Have someone that REALLY KNOWS how to tig weld fill up the remaining .015.
Smooth off with file and sandpaper till your happy---it will be invisible if done correctly.
Drill and tap any darn place you please, the repair won't affect anything if done properly.
 
this is going to sound dumb, but if he is only a quarter of a hole, and for probably a 6 screw, he's .025" off, so why not change the hole in the mount?
 
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