Drilling/Tapping Cast Aluminum

The Wire Nut

... we used to use them a lot at my former employer as screw inserts in some of the softer metals they machined... parts for satellites and the like. A great system for securing bolts, and very efficient from a weight point of view.

Mike T., Swampeast MO

I have a commercial popcorn popping kettle to repair. One of the bolt holes securing the bracket that keeps the thermostat in contact with the kettle is stripped.

Kettle is cast aluminum--presumably a decent grade. Have never drilled/tapped cast aluminum before.

What should I watch out for/do?

ALH_4

Insert

How about a Helicoil?

Larry C_5

Aluminum

It is softer than steel obviously. Use cutting oil and then "Tap-Magic" for aluminum.

Why did the hole strip out? Can the thermostat bracket be mounted using a larger bolt in the same hole location? Do you have enough depth for 2+ complete threads threads? If depth is an issue, you can use a bottoming tap to get another thread or two.

Joe_75

use only cutting oil for aluminum and plenty. Course threads are better then fine. Thread a nut onto the tap first use the nut as a guide to start the tap with a wrench on the nut and against the stock. then back the nut off, turn the tap one turn and tighten the nut to straighten the tap, back the nut off and repeat until you have a few threds started. This is the best way to tap a strait hole in thin AL. I would use a starter tap forst then run a bottom tap to clean the bottom of the hole. Use a small tap wrench too.

Mike T., Swampeast MO

I really don't know why it stripped out. The bolt is fine but just barely grabs at the very bottom threads and then it pops loose after a few heating/cooling cycles. Once the body of the thermostat is no longer in contact with the kettle, it starts cycling on air temperature and never gets hot enough to pop corn.

I should be able to go up one bolt size without problem. The bracket itself is quite a beefy piece of steel and I can enlarge the hole a bit if necessary. The other two mounting holes for the bracket are fine.

Might try making the existing hole a bit deeper, but it doesn't look like there's much leeway--the sides are slightly tapered and I don't want to risk drilling through to the inside of the kettle.

Mike T., Swampeast MO

Just may try that or similar before I attempt to drill and tap.

Mike T., Swampeast MO

This is at the perimeter of the cast aluminum kettle so it's quite thick there. Current bolts extend at least 1/2" into the kettle. Am afraid to go much deeper though since the sides are slightly tapered and the hole will surely break through to the inside of the kettle.

hr

After you re-tap

clean the oil out of the hole and off the bolt, with some contact cleaner, then use Loctite when reinstalling the bolt.

Aluminum threads strip easily when the bolt starts to loosen.

Or glue a stud in and Locktite on an acorn nut for a cleaner look :}

hot rod

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Mike T., Swampeast MO

THANKS EVERYONE!

Was able to make the existing hole about 3/8" deeper. Tapping seemed to go perfectly. Cleaned nicely and used Locktite.