"David De Vuono" wrote in message
om...
This machining thing is getting expensive. I broke End Mill number 2
and 3 of the four I bought for my combo mill\lathe today. I can
understand the first one going last weekend as it was a 1/8" end mill.
Then today I broke a 3/8" end mill. Was using it to cut through a
chunk of aluminum when the drill chuck (MT2 taper) or something like
that came loose on the taper when using the power feed from the lathe
lead screw. The end mill went crooked and snap. Guess I need to get a
proper End Mill holder and make sure it is snug more often. I ended up
using a skill saw with 40 tooth carbide blade to cut through the
aluminum, it cut like butter. Then I spent about 3 hours cutting fins
into the aluminum heat sink I am building. I was using a 1/4 End mill
and manually feeding it so it did not break. I then was cleaning up
the groves with a brand new 3/16 Ball End mill and snap. Guess I was
so used to the pressure of the 1/4 inch. Oh well, when I factor in
the cost of end mills, this heat sink is starting to get expensive.

Dave D.

What Jim said. Normal drill chucks DO NOT grip hardened objects well enough
to be trusted.

The chuck coming out of the spindle is but another of the problems related
to that type of holding system.

If you have no alternatives but to cut with your chuck, do these things:

Wipe each off with a dry cloth, until there is NO oil present, nor any lint
or dust, the arbor and the socket in the spindle.

Using a block of wood against the table, or what ever you have below your
spindle, set the chuck by bringing down the spindle hard against the wood
block. Don't break anything, just tap it sharply a few times to insure it's
well seated.

With the end mill in the chuck, tighten each of the holes repetitively.
Each one tilts the scroll slightly differently and tightens the chuck ever
so slightly better. Go around the chuck a couple times, using each hole
alternately.

Try to not take full width cuts with the finish size end mill. Your rough
cuts with the saw were a great idea. You are far better off to finish a
1/4" wide slot with a 3/16" end mill than you are using a 1/4" end mill. By
using an undersized end mill in a roughed opening, you can cut one side at a
time, preventing any climb milling. Climb milling is the most desirable
way to take finish cuts, but not on a weak setup. It encourages problems,
including breakage, when the end mill pulls the table along. You can
always go back over a cut, climb milling, to clean it up after conventional
milling. That usually works fine.

Make sure you lubricate the aluminum well while cutting. Use kerosene, or
many guys recommend WD-40. I haven't used it, but it appears to have a
solvent base with dissolved paraffin wax in it. It's bound to be good for
aluminum. You can brush apply the lubricant, or use a spray dispenser.
Brush is generally a little cleaner than spray, for obvious reasons.

Run your cutter as fast as possible. When cutting aluminum with such a
small cutter, it's nearly impossible to over speed the cutter, and too slow
is bad, really bad, where it comes to breakage. Very fast tip speed
discourages grabbing and yields a much better finish, plus will accommodate
higher feed rates.

Good luck. Don't give up, you'll get on to it. It requires that you
become familiar with the characteristics of cutting tools, and your personal
machine. You'll discover things that work and you'll have better luck in
the future. My hat's off to you for trying.

Harold