Quote:
Originally Posted by Cory
Are you using carbide or HSS? With HSS I could see 6 IPM being reasonable, but you should be running at about 0.003 IPT or more with a good carbide end mill, which would be a baseline of double what you're currently running. With a cutter that small and a top speed of 3600 RPM I would never run slower than max speed. We were forced to run our machine no faster than 2500 RPM recently and were slotting 1/4" plate at 23 IPM with a 3 flute end mill. You have a less rigid machine, but 1/4" Al plate isn't very taxing and I would expect similar performance.
As Scott mentioned, with a chip load of 0.0015 IPT you're coming closer to smearing material off as opposed to shearing, which will dull your tool and cause premature breakage. This will be a bigger problem if you're conventional instead of climb milling as chip formation begins with zero thickness and increased rubbing.
If you find that you're breaking tools it's almost certainly a chip evacuation problem. We can slot 1/4" plate with a 3 flute aluminum specific end mill indefinitely as long as the chips are cleared out of the path of the tool. As soon as you start re-cutting chips you run the risk of dulling/snapping the tool or welding the chips to the flutes.
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Most of our cutters are HSS, but I believe we have a few carbide tools. We tend to really only push up to that 3600 limit when using 3/16" end mills or smaller and small diameter number drills.
This whole discussion of our cutting rate leaves me rather wondering if our mill has been incorrectly displaying units for cutting or something... I was always told that the units for the feed rate readout were in inches per minute. Like I said, we usually cut with that in the 2-6 range. I think we've pushed it up to 10 or 12 in the past, but that introduced some very serious vibration, and I believe even some tool deflection. Cory, maybe you're right, maybe this is all caused by a less rigid table, and our low cutting feed rate is just a product of vibrations occurring when we get near "normal" cutting speeds.
We have experienced some dulling and tool wear. Perhaps this is due to the lower cutting speeds we use wearing instead of cutting. When we increase spindle speed and cutting speed, though, we tend to start melting chips onto the tool. I always attributed this to poor cooling (even with the mist coolant) rather than chip evacuation or low cutting speed. We always (well, except for a few special cases) climb mill.
Granted, when I'm talking about tools breaking, I'm talking about a couple of 3/16" or smaller endmills breaking when they took too deep a cut at too high a feedrate.