Aluminum chatter but only after depth

I’m running a Carbide3C #201-Z cutter (1.4", 3 flute, square) on 6061 aluminum that’s 1/4" thick. My cut parameters are:

Feedrate 500
PLunge Rate 50.7
RPM 10,000
Step Down 0.100
Ramp angle 3.0
Mill Direction: Climb

The profile is a bracket, with a simple 2-D shape that is 100% exterior profile. Basically, I just want to “cut out” a shape, without any internal geometry, or even any contouring. All passes will result in straight walls that go through the piece, to free it from the stock.

All goes well for the first 40 passes or so (4.0mm down) but then I suddenly get chatter, and the cutter hangs. I tossed my first piece, set a second one, and tightened my clamps more than the first time. The result was identical - chatter after about 40 passes, with 2.4mm of stock yet to be cut.

Do you think this is a clamping issue, or settings? I do get a tiny bit of chatter during the early (successful) passes, but only when ramping into the next lap around, and nothing hangs. The pass continues, and is otherwise successful.

Clamping is via toe clamps, in pairs, at ends of the 2x3" workpiece. I also have a registration pin on a short side, which just helps me align the stock quickly. My worry is that there is only around 1/4" of stock left in a few places, so the clamping force might be reduced if that stock starts to deform. Then again, the bit cutter seems to continue to clear fine, meaning the kerf hasn’t closed, so I feel like deformation isn’t the issue.

Any ideas what I’m doing wrong?

Do you mean you have clamps pressing into the workpiece from the sides? Or are these more like straps pressing on the top of the workpiece?

My bet would be that the main issue here is the plate buckling under the pressure exerted by the clamps as material is removed. I’d recommend you try alternative workholding, like painters tape and superglue or bolting it down. Painters tape and superglue in particular works wonders when it comes to cutting plates.

1/4" tools on the Nomad are difficult to get working, I’d recommend you put the 201-Z on the shelf and default to 1/8" endmills.

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Yes - I’m clamping from the sides, with lateral pressure. I was starting to think that buckling, vibration, or even a narrowing kerf were the issues. I think kerf is OK, because it doesn’t seem to bind. But the other two are possibilities.

Do you think that carpet tape is sufficient to hold aluminum while taking 0.1mm passes? Or maybe add that along with the clamps? I tried to avoid tape at first, so I could shim the piece off the aluminum table with a thin piece of cardstock, giving me 0.2mm of “spoil” on that last pass. Maybe that’s part of the problem? But if I keep the cardstock, then the tape becomes a tough setup.

Yeah - I might go to 1/8". Thoughts on the #102 cutter? That’s all I have on hand. It’s a 0.125", 2 flute square. Still OK to go with 0.1mm cuts, and 10,000 RPM? What feedrate?

0.1mm passes are nothing, basically any kind of tape should be able to hold that no problem, as long as your plate has decent surface area. If it’s a 1in square of course tape isn’t going to work.

I’d avoid the clamps. Application of lateral force to a plate is nearly always a bad idea unless the plate is quite thick, so able to take the force without bending.

And the Nomad is able to hold pretty tight tolerances. The tape itself serves as a kind of spoil board. If you’re really worried, just tape the card stock front and back. The card doesn’t take much away from the adhesion.

Think not so much about feed rate and more about chip load. On the Nomad in Aluminium you usually want something like 25um to 30um chip load, so at 10k RPM, about 250-300 mm/min/tooth. With your 2-flute endmill, that’s 500-600mm/min.

I’d take deeper cuts too. At least 0.2mm to 0.3mm depth should be no problem.

I use carpet tape for all my aluminum cutting. Its super strong and always worked well for me!

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OK - I guess I’ll try that then. Do you release it with heat, or just pry it loose?

I just pry it up after.

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A three flute 1/4 is a hefty tool to run, especially slotting. My opinion is to run a smaller tool, less flutes for better chip clearing action and do a roughing slot maybe halfway down the stock with a small stepover.

Also, can’t beat plain ol superglue and blue tape for ease of use, removal and minimum adhesive dingle-berries to deal with.

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Ohhhh yes, at least with the real Scotch blue tape

As for the zero, I put two layers of the tape on the spoilboard and zero off that, I rarely cut through the top layer of tape.

As Vince says, a smaller cutter will be doing less work, the one I’m using in that clip is a $12 4mm single flute at 22kRPM and 1,000mm / min feed rate at 1mm depth of cut, I’ve done much worse and still had trouble peeling the workpiece up afterwards. You probably can’t go that fast on a Nomad but it won’t be the tape slowing you down.

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I really appreciate all the tips. I’m doing slightly better, but still not quite the performance I’m hoping for. The carpet tape worked for a bit, but the workpiece started getting warm, and after a while, the tape released completely. With a 1/4" thick piece, I think there’s too much leverage when the cutter pushes at the top of the stock. That means I’m back to the clamps.

Is there a place to find recommended “recipes” for starting in 6061 with the Nomad3? Basically, I don’t care if the cutter is expensive (with coatings) or if the program takes forever. I just need to set it up, know it will run with confidence, and then pull my part out a few hours later if necessary.

I’m currently running a 1/8" single flute at 10k RPM, with 0.2mm passes and 250 mm per min travel. According to Fusion360, that’s 0.025 mm per revolution.

I seem to be getting a clean cut, and chatter is reduced (but still a little bit there). Wondering what I should tweak next (if anything) to increase my odds of pulling out good parts. I need to run about 8 of this part, so I’m willing to take time fussing to optimize so that the process is more automated, and I can concentrate on other stuff while a part is running.

Thanks!

That’s not a good sign, you really shouldn’t be getting a hot workpiece at these speeds. I’ve had high friction and heating on larger 8-10mm bits running at 20kRPM, which I should not have done, but the workpiece stays cold for me on 3-6mm size cutters at almost any speed.

I’ve run 10mm and 12mm thick workpieces on blue tape with no problems at all, so thickness shouldn’t be the problem.

Are you getting the chips out of the slot quickly and effectively?
Are you seeing any chips binding up in the cutter flutes?

+1 to these questions. A glaring oversight on the Nomad is chip evacuation and clearance. It’s super important, especially with slots and even more with deep slots. If you don’t have some kind of blower in your machine, now would be a good time to get one. I use a small compressor and I know some folks use airbrush compressors and others use fish tank air pumps.

check your dm’s

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Evacuation is pretty good. The 1/4" 3-flute was rubbing more than cutting, which I think caused the majority of the problems. The 1/8" single flute results in a barely warmer than room temp workpiece, with small chips getting tossed nicely. Some end up back in the slot, but only because they bounce back in.

Just took the piece out from the 1/8" cutter operation, and the result is great. I’m just wondering if there’s a better cutter than the 274-Z, which is a coated cutter, but single flute with a back-cut that’s intended for plastics. It worked fine here, but if I’m putting too much stress on a single flute, I’d rather get the “right” cutter for future work.

Also - I think my toe clamps were getting loose, from a small amount of flex on the remaining “frame” of material, and from vibration. I added top-down clamps in two spots, and that helped a lot.

So - what recommendations for a “workhorse” 1/8" cutter that’s hungry for a crap ton of 6061 chips?

I don’t recommend just one cutter, I recommend at least two:

  • 1/8" single-flute for slotting. I use these. They’re dirt cheap, DLC-coated (nearly impossible to get chips to stick to them) and I’ve eaten more Aluminium with them on my Nomadtron than most Nomads will cut in their lifetime.
  • 6mm or 1/4" 3-flute endmill for side cuts, facing, adaptive clearing and the like, where chips getting stuck isn’t really a possibility. I use these.

Of course it might be difficult to get those if you’re not in Europe. If you’re in the US or somewhere else I’m sure we can find other options.

One great (but expensive) option is DATRON, especially for the single-flute tools.

And whatever you do, I recommend getting some kind of air blast ASAP. I know it feels unnecessary when things are working but as soon as you get a clogged endmill and ruined workpiece (which WILL happen with multi-flute endmills) you’ll regret not having it earlier (I speak from experience).

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Consider using something like a 4mm single flute as well. The shank size increase over 1/8th offers a very noticeable bump in tool stiffness without needing that much more TQ to run.

I’m team no airblast here lol

Yep,

I also have had lots of luck with 4mm, I use these

I’m sure there’s plenty of generic vendors in your region too.

Nothing (except double sided tape) sticks to the DLC and they fling chips

Cool - thanks. I’ll see if I can find something similar on McMaster Carr. That’s the easiest place to order cutters for me.

For the air blast - would something like an aquarium pump with flex tubing and nozzle work? How do you route tubing and secure the nozzle to the moving carriage?

I use a standard compressor with a regulator valve but I think I’ve seen others mention an aquarium pump for evacuation.

For me, fitting it just involved cable ties:

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