Anyone who has machined much aluminum will sooner or later wind up with an endmill like the one shown in the photo (thanks Practical Machinist and Bobw):
Aluminum welded to and clogged the flutes of this endmill…
The same can happen to twist drills and inserts. Aluminum is a sticky material. You’ll need the right lubricant or coating on your tools to cut it successfully without the welded on aluminum, and even then, you can still get it if you push too hard. The aluminum comes out looking like taffy. Interesting to look at, but unless you’re real fast with the red button, it will break the endmill pretty quickly and possibly screw up the job you’re machining.
Supposing you did get to that button in time, how can you clean the aluminum off? Sometimes you can just pry it off with an awl or pick. But, it’s a lot easier if you drop the tool into a glass container of caustic lye. Use Draino or something stronger. Folks recommend the Purple Industrial Degreaser from Home Depot, for example. You’re basically looking for caustic soda or lye.
A related trick is dissolving a broken tap out of aluminum. Use a solution of alum and boiling water–it works great. No such luck when dissolving a broken tap out of steel.
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