minimum wall thickness for drilling aluminum?

I have an aluminum part that I need to drill out to install an EZ-Lok insert. It's an M6x1 insert, which requires a 3/8"-16 thread to install. That needs a size Q bit (.332"), but it's going into a boss sticking out from the main body of the casting that's only got an OD of .480". If I can get it centered in a 4-jaw chuck on the lathe, should I be OK to do that, or is the wall thickness going to be a problem? There's already a "pilot hole", it's the original hole with trashed M6x1 threads.

Also, if I did the math right, it looks like the recommended RPM for drilling aluminum is 3600+, does that sound right? I don't think my lathe will even do that, so I'll just have to set it on the highest gearing and let it go.

Note: I'm pretty much either going with this method (preferred) or filling it with epoxy and drilling and tapping. Those are about the only available options, for reasons that are too long to go into right now. Welding, etc., are not options. Other types of inserts (Helicoil, Timeserts) do use smaller drills, but for the cost of a full kit to install one of those I could buy a whole replacement part.

One thing for sure is you don’t need to worry about the rpm, you’re just drilling one part. The other questions asked are hard to answer not knowing what the part is used for.

jml74 said:

...Other types of inserts (Helicoil, Timeserts) do use smaller drills, but for the cost of a full kit to install one of those I could buy a whole replacement part...

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If a Heli-Coil is a better option perhaps you can find a local jobbing shop that has a kit on hand and get them to fix your
part. We have a variety of thread repair kits on hand and we'll occasionally do "onesie-twosie" repairs for customers...

OK, here's some more info on what I'm trying to do and a couple of pictures. I posted this to a group on FB and got a bunch of "just make a new one!" and "weld it closed and drill and tap!" replies, which is what I was trying to head off here. This is a motorcycle camshaft holder, so anything that might affect the bore on the bottom, even slightly, is not an option. I think the only viable options are either an insert or epoxy.

The hole that needs an insert is the center hole on the boss; it's for one of the valve cover bolts and doesn't have to be torqued down very tight (6-9 ft-lbs), but it's a specialty bolt, so I can't just drill and tap it for a bigger one, either. If I snap that boss off, though, I'm pretty much screwed, which is why I'm hesitant. The hole does go down into the body of the casting past the boss, if that makes a difference. It's about 18mm from the top of the hole until it bottoms out.

LKeithR said:

If a Heli-Coil is a better option perhaps you can find a local jobbing shop that has a kit on hand and get them to fix your
part. We have a variety of thread repair kits on hand and we'll occasionally do "onesie-twosie" repairs for customers...

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That may be the best option, actually.

Sorry I have no useful or helpful information; But I am laughing my balls off that a metric thread insert has an imperial thread for it to fit in...

Plenty of meat below in the body of the part.

Not sure if there are long inserts or if one could be made.

If the insert could go further into the body it would be stronger.

Real crazy thought...make an insert that threads into the existing hole below with left hand threads and is larger at top threaded for special bolt.

Would be pain to make but if yours maybe option. ..test with scrap.

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jml74 said:

OK, here's some more info on what I'm trying to do and a couple of pictures. I posted this to a group on FB and got a bunch of "just make a new one!" and "weld it closed and drill and tap!" replies, which is what I was trying to head off here. This is a motorcycle camshaft holder, so anything that might affect the bore on the bottom, even slightly, is not an option. I think the only viable options are either an insert or epoxy.

The hole that needs an insert is the center hole on the boss; it's for one of the valve cover bolts and doesn't have to be torqued down very tight (6-9 ft-lbs), but it's a specialty bolt, so I can't just drill and tap it for a bigger one, either. If I snap that boss off, though, I'm pretty much screwed, which is why I'm hesitant. The hole does go down into the body of the casting past the boss, if that makes a difference. It's about 18mm from the top of the hole until it bottoms out.

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Boring with small internal boring bar would be better than drilling for a crooked and chewed hole like that.