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!
Up next, mounting that collet into the mill spindle! But first, stick a finger up into the tapered bore it seats in, and feel around for any chips... It should be clean of any debris, coolant sludge, etc. If you find any, clean it up! A chip stuck on the collet taper when it tightens up will throw it off to one side... Making your .500" endmill act like it's, say, .517". Not a good thing when you're trying to mill an accurate slot, etc!
Okay, now it's clean, pop that collet up into the spindle, and hold it there with one hand (I use my left to hold it there, I find it's an easier reach for the drawbar in the next step this way). Reach up with the other (right, in my case) hand, and spin the drawbar threads down a few turns into the collet, capturing it and preventing it from falling out. Don't crank it all the way down yet, or you won't be able to get the cutter in!
Some mills use a protruding pin in the spindle bore to key into the slot on the side of the collet to keep it from rotating inside it's taper, so if it doesn't want to pop all the way in, try spinning it around until it easily slides in all the way. Our Jet mill here at menlo park techshop doesn't use one and the collet will pop right in at any rotation, but our older mills do, and will only slide all the way in when it's lined up correctly.
Don't panic if it doesn't want to slide all the way in, just rotate it around until it does!
Okay, we have the collet in the mill, now we're ready to mount the actual cutter!
But first, a quick note on *where* to grip on the cutter with the collet!
-the less tool stickout, the better! Basically, you want to use as short an end mill as practical for the job at hand, and grip it as close to the flutes as possible to minimize tool deflection, bending, chatter... Short = Rigid. BUT- don't "choke up" on an end mill and grip the flutes to 'fake' a short end mill! It chews up the collets, the tool, and is unsafe to boot. Don't do it!
So, you need to grip the round shank, somewhere above the top of the flutes, and below the groove / weldon flat (if it has one, but most do.) Take care to check all the flute lengths, I dug through our collection of end mills and found this classic example of one set of flute grinds extending farther up the shank than the other. You should make sure you're able to see the top of all grinds below the collet when it's installed. Or, to put it another way, you should see a solid ring of the shank between the top of the grinds and the collet. If you're using a cutter with a reduced or enlarged shank watch out for a chamfer or radius where the diameter changes, and make sure you're gripping on the round shank .
So, you should be gripping it somewhere between the second and third red marks from the left in the third pic, and between the two red marks in the fourth pic. Simple enough, eh?
Here's what it looks like mounted in the collet. Try to set it up just like the third pic.
So, onto loading the tool into the mill! It's a good idea to place a folded up rag under the spindle while installing any tool, in case it slips out while you're tightening it... There's nothing quite like chipping a brand new $30 carbide end mill, before you even get to cut with it! So, pad the spot it would hit if it falls, and slide it up into the spindle with your left hand to the correct height. With your right hand, reach up on top and tighten the drawbar with your fingers as much as you can, then switch to the wrench. Once it closes up enough and starts to grip the tool, it'll spin under the wrench instead of tightening. So, with your left hand, carefully let go of the tool and reach up and pull the brake, while you tighten the drawbar with the wrench in your right hand. Wrench it down nice and tight, but don't crank it down like superman... Remember, monkey tight, not gorilla tight!
A safety note is in order here: NEVER, EVER leave the wrench on the drawbar! If the machine turns on with it on the drawbar, it'll either twist the wrench into a pretzel, throw it across the room at somebody, or both! Just like a lathe chuck key, if your hand comes off the tool, the tool comes off the machine, EVERY TIME. Make sure you're not getting into the habit of switching hands with it still on the drawbar, or anything...
Alright! The collet is pulled up tight, the end mill is mounted at the correct height, and the drawbar wrench is back on it's storage peg (not still on the drawbar!)
It's time to make some chips!
When you're done, to remove the cutter:
-pad the 'landing zone' with a rag again, just in case it slips!
-pull the brake and wrench the drawbar loose several turns, but still threaded into the collet
-tap the drawbar down with the mallet side of the wrench to break the taper, drop the collet down, and spit out the tool... Don't forget to be holding onto the cutter with your other hand while you do this! If it doesn't spit it out, spin the drawbar out another couple turns, but make sure it's still threaded into the collet at least a turn or two. If the threaded end of the drawbar is sitting on top of the collet threads instead of engaged with them, you can bugger up the first thread on your collet, or heavens forbid your drawbar threads!
Have fun, and be safe makin' chips!