Okay folks, this is just a quick tutorial on mounting that end mill (or other cutter, etc) into an R8 collet in the mill, and getting it gripped correctly to prevent damage to your cutter, collet, workpiece, your face, your buddies face, etc. There are a few things to check on when mounting a cutter, so I'm going to step through it, one thing at a time. First off, you're going to need a mill, your cutter, and an R8 collet that matches the shank of your cutter. Here we go!
Up first, we have our (1/2", in this case) 4 flute double end mill, and an 1/2" R8 collet to match. R8 collets have a pretty small gripping range, so make sure you're not trying to squeeze a 3/4" collet down to grip a 5/8" tool, for example! A proper sized collet should 'just' slide over the tool. Also, NEVER EVER use a drill chuck for milling! Drill chucks won't put up with the side loads of milling, and will loosen up and possibly slip or eject your cutter while in use... Just think how exciting that could be!