Aluminum to Aluminum Interference Fit - ID 0.694"

I'm plugging a hole drilled off-center. I know the old adage: "A bad craftsman blames his tools", and as a general rule, I agree with that. However, when you buy a jig, you expect it to be true. The final responsibility falls to the machinist to make sure the jig is true, and I accept that responsibility in this matter. Nonetheless, I have to fix a hole that is 0.010" off center. It is my intent to use an interference fit to plug the hole.

The hole is 0.694" in diameter. There will be essentially no stress on the repair. I intend to use "green" Locktite as well as the interference fit to hold the plug in place as I drill and ream the new hole on center. Both pieces of aluminum are 6061.

Here are my questions,(and I have looked in the archives. I found no threads or posts on AL-to-AL interference fits, but then I may have missed one):

1) Can the difference between the 'sleeve' and plug be as large as 0.002" IF the sleeve is heated and the plug cooled?
2) If not, given the 0.694" ID of the 'sleeve', what is the largest plug OD can I get away with without using a press? (The "sleeve" is a relatively complex form as well as not particularly 'sturdy', so it doesn't lend itself to being held under a press without a LOT of fiddling. I COULD do it, but I don't want to unless I absolutely HAVE to.) I expect the Loctite to provide SOME, but minimal, lubrication.

Thanks,
Paul

PS - I see that Aluminum has an average coefficient of thermal expansion of ~0.0000125"/degree(F). If I need to have 0.002" of ID-OD difference, then it would appear to me that I need a temperature differential of no less than 160 degrees F.

0.002/0.0000125 = 160

Can someone:
1) Verify this (not mathematically, but practically), and
2) Does this "sound about right" to those that have done something like this?

Thanks,
Paul

Alu on alu galls like crazy, which IME virtually rules out press fits, heat/shrink fits can be very dodgey as the coldest part heats up VERY quickly and it lock up before the parts in place. ...if you're worried Loctite won't do the job you're down to threaded plugs.

I appreciate that. My concern with Loctite alone is the heat during drilling and reaming. Should I not be concerned with that? I considered a threaded plug, but as soon as I start drilling and reaming the new hole, the plug is going to turn in the sleeve. It's a through hole. Plus, it's only 0.010" off-center. Thread roots are going to be deeper than that.

Paul

PS - I suppose I could use a steel plug. But I don't really want to unless I have no other choice. I don't suppose heating the sleeve hotter for greater clearance would be much help as that would simply heat the plug that much faster.

Paul

Loctite green may not be your best choice for this (permanent) application. I'd use the high-strength (red) stuff, with a temperature limit of 550F. Make the insert roughly 0.004" smaller on diameter than the hole. You certainly can go for a closer fit, if that's more convenient for assembly.

If you must use low-temp (300F limit) Loctite, just slow down and/or peck on the drilling to keep the heat input down.

This online calculator is nice and very thorough.

Interference (Press - Shrink) Fit Calculator

-Tony

Pluging hole

sfriedberg said:

Loctite green may not be your best choice for this (permanent) application. I'd use the high-strength (red) stuff, with a temperature limit of 550F. Make the insert roughly 0.004" smaller on diameter than the hole. You certainly can go for a closer fit, if that's more convenient for assembly.

If you must use low-temp (300F limit) Loctite, just slow down and/or peck on the drilling to keep the heat input down.

Click to expand...

Use a threaded plug in a threaded hole and ping the plug in place. Then re-locate and drill the new hole in the threaded plug. Pressing a 6061 Aluminum plug into a 6061 Aluminum has almost no chance for success. OR Make a steel bushing and press it in the plate.

Roger 5/22/2017

Archer120x said:

This online calculator is nice and very thorough.

Interference (Press - Shrink) Fit Calculator

-Tony

Click to expand...

MMM? now apply the figures for aluminium to that calculator, then just for fun, try a bit of real world experience.

rogertoolmaker said:

Use a threaded plug in a threaded hole and ping the plug in place. Then re-locate and drill the new hole in the threaded plug. Pressing a 6061 Aluminum plug into a 6061 Aluminum has almost no chance for success...

Click to expand...

I agree. A press-in plug .694" in diameter isn't going to work. Even if you could get it in there cleanly when you ream a new
hole with only a .010" offset you're going to be left with a very thin walled partial sleeve--it's not likely to take much to blow it
out of there. The only way I'd try to fix this is with a threaded plug. Assuming there was room I'd make the plug large enough
that the new hole is well inside the minor diameter of the thread on the plug...

Thanks for all of the replies. It's done and dusted. Didn't trust the AL-AL, so I went with steel, red Loctite and somewhere in the vicinity of 0.0015" clearance. I'll post here once I get the new hole drilled or...

Paul

I said I'd relate the 'final details', and here they are. After contemplating cutting the new hole with the plug Loctited in place, I decided that the best course of action was to just bite the bullet and chuck the blasted piece in the 4-jaw, bore a larger on-center hole, and bush it. I just couldn't believe that the leading edge of the 'crescent' of the plug wouldn't catch either a boring bar cutting edge, a drill flute, or a reamer flute. Especially since I was cutting dissimilar metals. So that's what I ended up doing - chucking in the 4-jaw; boring a new, larger, round, on-center hole, and bushing it. Worked like I knew what I was doing.

Thanks for all the help.

Paul

Archer120x said:

This online calculator is nice and very thorough.

Interference (Press - Shrink) Fit Calculator

-Tony

Click to expand...

seems to be a nice calculator. do you use it? i cant make it work. im looking at "factor for safety against sliding" and its zero whatever i put in. or is something else indicating if the fit will work? besides you cant put in dimensions, just ranges, i wonder how to use that if aiming for the transmission of a given torque.

gitano said:

I said I'd relate the 'final details', and here they are. After contemplating cutting the new hole with the plug Loctited in place, I decided that the best course of action was to just bite the bullet and chuck the blasted piece in the 4-jaw, bore a larger on-center hole, and bush it. I just couldn't believe that the leading edge of the 'crescent' of the plug wouldn't catch either a boring bar cutting edge, a drill flute, or a reamer flute. Especially since I was cutting dissimilar metals. So that's what I ended up doing - chucking in the 4-jaw; boring a new, larger, round, on-center hole, and bushing it. Worked like I knew what I was doing.

Thanks for all the help.

Paul

Click to expand...

You fixed it before i saw your post. I was going to suggest making the hole big enough to install a filler plug big enough to take the correct size hole in the correct location with enough sidewall to be good, making a plug that just slipped in and was long enough to beat on with a hammer without hitting the rest of the part and then treating the plug like a rivet by installing it in the hole and swelling it with hammer blows. Then you can machine it down to the part surface. Done right, it takes a lot of effort and some luck to find it if you don't know it's there.

dian said:

seems to be a nice calculator. do you use it? i cant make it work. im looking at "factor for safety against sliding" and its zero whatever i put in. or is something else indicating if the fit will work? besides you cant put in dimensions, just ranges, i wonder how to use that if aiming for the transmission of a given torque.

Click to expand...

I have used it to make sure that the yield stress is not exceeded. Haven't had a need to determine the force transmission capability, yet. The ranges on diameters are or what will be the your part tolerances.