Major Chatter on First Pass for Aluminum

Beginner trying to mill T6061, got suggested feeds and speeds from a different thread.

1/16" 2F upcut going at 25IPM, 4ipm plunge, and .003 depth, I got major, major chatter and the surface was rough so I stopped it and gave it Easel’s suggested feeds which was 5IPM, 3ipm plunge, and .003 depth. I needed precision so I took it even slower at 4IPM, 3ipm plunge, and .0025d depth. Cut came out fine enough, but I realized that any pass that goes across the surface of the material get some serious chatter and rough surface no matter what speed/feed.

I gave it some WD40 every so often (1hr cut) and the bit basically goes quiet. Am I supposed to always keep the material lubed whenever cutting? Are the speeds not okay for dry cuts?

I very recently got all of the wobble out of my axes (dad didn’t calibrate it) so I’m pretty sure it’s not the chassis.

I can give mineral oil a try if that doesn’t seem dumb, I always use it on my knives. Thanks for the heads-up on that though I wasn’t aware of it.

And the chatter is coming from the tool I believe, the workpiece doesn’t seem to be the source, and I have the workpiece very securely clamped on all sides. I’m not entirely sure about the Z-Axis though, we just got it tightened down (though there might still be a slight bit of play in the bearing area, it’s just really, really annoying to tighten the nylock on the rod) and the chatter seems to be the loudest milling in the Y-direction though I forget which way.

Chatter also happens in the X-direction just not as loud, and I have the Dewalt at it’s lowest speed.

Is a 1/16th inch bit required to cut your project? I have much better aluminum cutting with a 1/4" bit…even an 1/8" bit would be better.

This works good for drilling and tapping.

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I started cutting submerged with soluble oil. Came out a lot nicer. Still a lot more chatter than I’d like, but that’s probably a stiffness problem that isn’t going to go away.

my experience:

WD-40 is fine and has saved many of my cuts. Maybe ‘real’ lubrication is better, but WD-40 does the job adequately.

I found that a 1/8" viper bit works best for me. Any smaller will break easily, any larger is overkilll and has given me headaches with missed steps and the like.

Using feeds and speeds off a forum is generally a bad idea, since every machine is different. I know it sounds cliché, but there is truth in it. Best is to start conservatively and work your way up to find a sweet spot for your machine. I use mach 3 which allows me to adjust feedrate on the fly, which is a huge help.

The first pass on metal usually is the trickiest, because of slight variances in stock thickness, and the flex in your setup. Especially on Y travel, the flex in the Z stage will either pull the mill slightly up (Y+) or push it into (Y-) the material, which will effect the DOC enough to potentially cause trouble. This is especially true on the first pass. If that one goes well, all following passes should be OK relative to the previous one. I typically stay put for the first pass and manually nudge the top of the router if I feel it digs in too deep.

hope that makes sense

WD-40 should work just fine for such shallow cuts. We would use isopropyl alcohol (99%) on aluminum and composite parts at work when specs wouldn’t allow for cutting or tapping fluid, with varied success.

I go fast and shallow and mine will quiet down a fair amount if dashed occasionally with WD40.
Use 1/8" bit as primary weapon.

Depending on the aluminum blanks you have, if the surface is anodised it is much stronger than raw aluminium. Also most surfaces are not 100% even so you may be cutting through a various amount of material for the first cut.

I know many may say that 1F or 2F end mills are good with alu, that is not my experience. I use 3F upcut helix bit and it work very well for for. I would suggest finding a high quality bit for metal work as it will save you a lot of headache. :sweat_smile: