What is causing these machining marks ?

compact8 said:
Yes, it was done with the side of the tool. The RPM was 2000 which is the max the machine can do.
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The pattern is from a resonance between each point of the end mill encountering the fresh aluminum and the rest of the machine bouncing back and forth in movements too small to see as chatter--but it is chatter nonetheless.

I would drop the speed a lot--I rarely venture north of 500 RPMs with my ½" end mill (12.4mm) in aluminum.

You said nothing about lubrication--put some WD-40 on it.
 
Linear knurling on a mill ? o_O All of the above posts are correct though , somethings not right there .
 
Mitch Alsup said:
...I rarely venture north of 500 RPMs with my ½" end mill (12.4mm) in aluminum.

You said nothing about lubrication...
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500 RPM ? I have been using 2000 because what I have read from the internet is that the appropriate speed for cutting aluminium is wayyyy.... higher. Are they valid for super-rigid machines only ?

I do not use any lubrication because I sucked the chips away with a vaccum cleaner when cutting. The use of lubrication will result in the creation of a harmful mist that will be inhaled.
 
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Buy some Anchor Lube if you are worried about fumes. Or use a respirator.

Don’t cut aluminum dry. It forms aluminum oxide.


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compact8 said:
500 RPM ? I have been using 2000 because what I have read from the internet is that the appropriate speed for cutting aluminium is wayyyy.... higher. Are they valid for super-rigid machines only ?
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Speeds and feeds are designed with the notion of high productivity of the machine (i.e., low production costs; even if it causes higher tool wear.)

When you have been cutting aluminum for several years, you, too, can use these higher speeds, but by then you will have found your machines weak spots and learned how to get around them.

I do not use any lubrication because I sucked the chips away with a vaccum cleaner when cutting.
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If you do not lubricate aluminum, the cutting edge (points) will get hot enough for aluminum to fuse to the cutting point. The points on your end mill might already have these little balls of aluminum stuck ferociously to them. Use an exacto knife point to gouge them off the tip.

WD-40 is kerosene without the nasal flavorings added to normal kerosene.

The use of lubrication will result in the creation of a harmful mist that will be inhaled.
Click to expand...

Perhaps machining is not really "in" your blood.............
 
Have to agree that it looks like chatter but that assumes a lot of things.
  • That the spindle and tool holding system is accurate. What is your spindle run out?
  • That the end mill is sharp and not excessively long or used near the tip.
  • That there is no excessive play in the table/vise/gibs.
  • That the depth of cut was deep enough to bite instead of deflect.
Sorry to disagree but a spindle rpm of 2000 is not excessive for aluminum. I mill it at 2800 rpm all the time with both HSS and carbide. Calculated rpm for aluminum with a carbide end mill is in excess of 8K.

If this is chatter then I would agree with Jim and try increasing your feed rate while also trying to increase your depth of cut. If a carbide end mill takes too shallow a cut it can deflect, especially if used up near the tip of a longish end mill; use the flutes as close to the shank as possible. I also agree with using some kind of lubricant. Relton A-9 works better than WD-40 but either will do and anything is better than nothing.
 
I run 3/8" alu-power 3 flute end Mills @ 4500rpm, feeding between 30 and 45 inches per minute in 6061 and get good surface finishes.

But, 6061 machines great. Some mystery aluminum machines like bubble gum. Try a known material first, then go through Mikey's bullet point list and check each of those items.

I've had surface finishes very similar to yours with loose gibs, especially when the column/head gibs need snugged on the CNC.
 
Updates included in the first post. Will appreciate you guys' opinions.
 
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