[Ed_R]

I'm running a Leadwell V25 with a Fanuc 21M controller and an 8K rpm spindle . It breaks every single bit under .0625 I use in it. I've had the runout checked on the spindle taper ( he said it was around 25 millionths of an inch) , checked the runout on the tool holders in question ( none are over 2 ten-thousandths ) , checked the bit shafts themselves ( under 5 percent of bit diameter in every single case ).
Bits break when I run a .0313 2-flute end mill at 10, 18, and 25 IPM at a depth of cut at half a diameter ( .015625 , a 64th of an inch ) in soft aluminum. This is the cheap extruded stuff you get at Lowes, the kind where if you yell at it too strongly it knots into a pretzel. It breaks in rosewood, ebony, and oak at the same or less IPM and the same RPM. I've run 5 IPM or less at 8K rpm through oak at a depth of a sixtyfourth of an inch on an engraving bit and chipped the tip off in the first 30 seconds.
So, anyone got any ideas? I'm thinking that the math for the right chip load for the aluminum at this depth puts the IPM at 24 for an 8K RPM spindle speed. Snap.


Am I really going to have to get a speed-up device just for the smaller bits?

[neilw20]

Sounds like jerk in the Z direction causing overshoot or erratic feed.
Put a dial indicator on the feed and makes sure the feed is dead smooth and changes directions only when it is supposed to.

[Ed_R]

I break bits when I cut fret slots in wood, starting the bit outside one edge of the workpiece and going through the workpiece completely. I think if there's Z axis jerk actiopn going on it wouldn't have any effect on this cut.
A guy I know whose opinion O trust says I have to cut aluminum at around 2 ipm with a DOC at around 10 thou or the chipload will be too high at 8K rpm. He suggests those settings or getting a higer-speed spindle. Now I'm on the lookout for a nice used MAC-ATC high speed air spindle in the BT-40 taper.

[Dylwad]

I would agree on the cut depth being too big and the feed rate too fast for your rpm, but the Lowes aluminum is pure crap to begin with, get a chunk of 6061 and try it again and it should work fine.

On wood I would keep the feedrates slow and DOC. Shallow too. Think and tinker (precisebits) has some good info on finding the right feedrates for small bits, it's mostly trial and error to find the sweet spot.

A kress or trim router might be a cheaper option than an air spindle.

Sent from tapatalk

[Ed_R]

Think and Tinker are telling me that at 8K rpm I should be able to run 35 ipm at a full diameter DOC through wood.
I'm thinking I need to figure out a cheap way to mount a trim router on the side of the spindle but there goes the ATC capability.

[bushwakka]

I break 1/4" bits in aluminium for the following reasons
* cutting too slow, and the heat welds the aluminium to the flutes
* the chips from a previous pass getting in the way
* chips not clearing easily (normally slot cutting deeper than 1 spiral depth).
* too much length of bit stickout past the collet.

I would try edge facing with your small bit (with a very small stickout). This rules out chip recirculation, as the chips get thrown out of the way, and there is always plenty of room for the waste to move.
If that works, then the spindle, runout etc are probably OK.

I've also found that in wood, 1/8" 2 flute bits break easily. I moved to 1/8" single flute bits, and can run up to 3-5 times (compared to 2flute) the cutting speeds (MDF, 3/4" single pass cut, 3000mm/min, 15000rpm).

Cheers
Bushwakka

[neilw20]

I use 1mm (0.025") and below all the time in steel and aluminum. If the surface is not perfect then the hole can start off center.
That's a good way to break them. Really fine feed until center is started, dead on correct position.
A tiny touch with a center drill works wonders.
As for the jerk, that gives a perfect opportunity to start off center, leading to breakage.
A spindle with ANY side play will allow the drill to start off center.
I have a proper spindle, not a floppy router nose, and drill down to 0.25mm (0.010") often, and occasionally to 0.2mm (0.008")
Always tiny center mark to start the tiny ones.
And I use all solid carbide below 1/4" nearly all the time.
A stationary point is a great way to make a center mark in wood. Just go down 1mm at each hole location first.
Starting in wood will almost always start off center due to variability in grain hardness. Fine MDF? no problem.

[Ed_R]

At what IPM/Depth of Pass can I run these .0313 2-flute bits through soft aluminum at 8000 rpm with full flood coolant ? Where would I go to learn this?