Is this a common problem? On my cast iron job I was using a nice
new just bought 3/4" rougher end mill that I put in an ER32 collet and
it pulled out over 1/2", put a nice mark in my previsouly virgin table
and then broke. Got another new end mill and went back to the end
mill holder to finish the last part.
Cat40-er32 was about 1" shorter than the cat40--3/4" end mill holder
so I went with the less stick out is better aproach, and it backfired
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*Always* use std holders for roughing, especially hogging tools. Collets
were not designed to take that kind of load. That is why the flats are
ground into large end mills, you need the fixed screw to lock in the
tool, creeping and pulling out will happen even then if you push the
tool hard enough, only the screw acts as stop to limit the tool from
exiting the holder.
Always clean the spindle taper and check the tool's taper to keep
running as true as possible. If the tapers are clean and the draw bar
pressure is correct, things should be good. And then remains how you are
feeding the tool, is the cut interrupted, is the iron good (high chrome
content, bad Brinnell hardness all come into play, lead screw slack is a
possibility. Sheesh, with all these considerations it is a wonder we
ever get anything machined right, LOL!
HTH, if not, just disregard all of the above and reduce the feedrate
Have a nice day Randy!
3/4" is near the very max. that an ER32 can hold also. Roughing in an
ER collet is dicey enough, but at the max. capacity it really pushes
things too far. We rough with 1/2" end mills (in aluminum) in ER
collets, but we don't do it with an ER20, we do it with an ER32.
ER collets are made for precision; but not for maximum grip. TG and DA
collets are made for
neither. They're just cheap and convenient. Slippage during milling is always
a problem with any
of these types.
Set-screw type endmill holders are generally better for rough nilling, or
even for finish work
with cutters bigger than maybe 3/8". Here's a tip, though: When you install
the endmill in the
set-screw holder, tighten the screw just snug, then back it out maybe a quarter
turn. Then, pull
the endmill out of the holder as far as possible, so that the end of the
endmill's flat that will
actually prevent pull-out is engaged with the screw. Then tighten the screw
fully. If you do the
opposite, and push the endmill into the holder, it will still pull out a bit
during cutting because
the flat on the endmill is wider than the diameter of the set-screw.
When you need a good grip, but can't stand the runout that a set-screw
holder creates - like if
you're into serious roughing where runout will warp your chip loads and cripple
performance - then you'll want to look at milling chucks. These are specially
designed collet type
holders that give good runout, bunches of grip, and excellent rigidity and
They're more expensive than normal (TG, ER, etc.) collets; but the difference in
dramatic. Here are a couple examples.
Heat-shrink holders are probably best; but the cost and trouble make them
less than attractive,
in my personal opinion.
Everybody has their own preferences, of course. And sometimes, what works
best depends a lot on
what you're used to, and how well you use it. I can't deny that there are lots
of people who get
good results with TG's. I just don't happen to be one of them.
With the shallower angle on the TG series they really grip in my
opinion. The smaller size shanks, under 3/8" dia. don't go deep enough
into the collet for good concentricity, even the single ended ones. For
3/8 and larger collets I haven't had problems with either concentricity
or pullout. I've also seen TG collets with a plug that will engage the
Weldon notch on endmills, this would effectively eliminate pullout problems.
As you say, different strokes for different folks.