Trouble boring in aluminum with small endmills

I am having some trouble boring in aluminum with 1/8" and smaller endmills. I can get them to work for about 10-15 minutes of cut time but after that, they usually snap. Here are the settings I have been using:

274-Z (1/8" ZrN coated single flute):
18000 RPM
25 in/min (0.00138" FPT)
0.01" Pitch
0.17" Max depth
0.18" Hole diameter

282-Z (2mm ZrN coated single flute):
18000 RPM
15 in/min (0.00083" FPT)
0.007" Pitch
0.17" Max depth
0.129" Hole diameter

I got to these settings by conservatively scaling the speeds and feeds listed in the aluminum material monday youtube video by Carbide 3D for single flutes and 18k RPM. I have tried decreasing the pitch and FPT by ~15% and neither had any effect.

Has anyone else had success boring small holes in aluminum? Anyone have any pointers? Carbide is expensive and I am really tired of breaking small endmills. My best guess is I have a problem with chip clearing but there are no chips in the holes when I look.

Hi Nick,

Not that I drill a lot of holes in aluminium, but I figured I would still contribute a few ideas.

  • What does your toolpath look like ? I like helical ramping down to max depth + one or two passes at full depth around the perimeter. You could try ramping in at a low(er) helix angle?
  • Consider using an air blast and/or a little lubrication ?
  • the 10-15min you mention, does that that mean you cut a number of holes correctly, and then at some point cutting the next hole goes wrong ? Have you been able to tell whether the tool break happens when the tool is at the max cutting depth ?
  • I assume you tried reducing stickout to the absolute minimum ?
  • have you checked runout ? it may be low enough that it kinda works, but high enough that it introduces enough extra forces/vibration on the cutter that it wears out quickly, and after 15minutes of wear it decides to call it quits ? How does the cut sound?

Would drilling endmills work for you?


That goes some way to explaining my urge to duck whenever I hear my machine run a boring toolpath :wink:

You don’t say what alloy aluminum you are using, but drilling or cutting aluminum is a challenge unless you have some flood coolant and bits that have only one or two flutes with high rake angles. Aluminum tends to be gummy at high speeds of travel or drilling. Try slowing the speed down and the travel speed. If you have access to coolant use this also. When it gums-up it coats the cuter and then cutting stops

Just got back in town, thanks for all the help. I think @Vince.Fab nailed it. I will adjust my speeds and see how it goes.

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