Engraving Anodized Aluminum: chipping?

[Frogblender]

Howdy... I'm trying to engrave onto anodized 6061 using a .006" 15° carbide engraving bit @ 6000RPM @7ipm and around .001" DOC.

The anodizing is NOT hard anodized. In the picture, the letter "l" is .055" tall. You can see a fair bit of chipping between letters "a" and "l".

Any idea how to reduce the chipping? It seems the anodized black version of the same part is less susceptible to chipping than the blue part shown in the picture.

Without a microscope, it looks "not bad" - a tad fuzzy. But I want perfection.

[fatal-exception]

I've never had any luck engraving anodized finishes. I was looking forwards to it before I had the anodizing line setup, but several tries on my on anodizing has never been successful. Mine looked a fair bit worse than yours.

Any amount of anodizing is harder than the bare aluminum, and I think you will have this chipping regardless of what you do. I may be wrong though...

Paul

[M250cnc]

@ a depth of .001" you are only cutting the anodising

So you could go deeper with a more pointy cutter & drop the feed to 2" min & work your way up to find your max feed

Phil

[Frogblender]

Originally Posted by M250cnc @ a depth of .001" you are only cutting the anodising So you could go deeper with a more pointy cutter & drop the feed to 2" min & work your way up to find your max feed Phil

With a 15° cutter, 'tis about as pointy as one can get. I did try 10° (actual more like 12° when I measured it) bits, but the tip lasts "seconds".
Going deeper causes aluminum burrs. It also seems to cause more chipping.

Man, nothing is easy.

Am I wasting my time trying to engrave these on my mill? Should I just send it out for yag or CO2 lasering? I have a CO2 laser sample (done on one of them cheapo chinalasers), but the lettering seems more "dull" than the lettering done with the cutting bit.

[RomanLini]

If that is a 15° point and 0.001" depth the line width should be only about 0.001" but your line width looks about 0.007" or 0.008" (based on 0.055" height of the l) so you have 6 or 7 thou runout! No wonder it is mashing the finish.

Try cleaning the collet to improve runout or rotating it, or using a new collet or new bit. Then test the engraving with a magnifier to see your runout.

And 6000 RPM sounds way too low for fine engraving.

[Frogblender]

Originally Posted by RomanLini If that is a 15° point and 0.001" depth the line width should be only about 0.001" but your line width looks about 0.007" or 0.008" (based on 0.055" height of the l) so you have 6 or 7 thou runout! No wonder it is mashing the finish. Try cleaning the collet to improve runout or rotating it, or using a new collet or new bit. Then test the engraving with a magnifier to see your runout. And 6000 RPM sounds way too low for fine engraving.

It's a flat-bottomed bit with dia .006" - add to that my ~.0005" of runout,and your guess of line width is quite accurate.

6000rpm is all she can muster I do have a 30000rpm airspindle - perhaps I should try it. I've been avoiding it because of the huge amount of air it eats, with corresponding non-stop and defeaning compressor noise.

[M250cnc]

Maybe you have spindle slop

If the runout is repeatable, make sure the cutting edge is at the outermost extreme in the cutting circle.

Runout isn't the problem as you only have a single edge cutter

Is the cutter new, is it quality ?

Phill

[Frogblender]

Originally Posted by M250cnc Maybe you have spindle slop If the runout is repeatable, make sure the cutting edge is at the outermost extreme in the cutting circle. Runout isn't the problem as you only have a single edge cutter Is the cutter new, is it quality ? Phill

Yes cutter is new; quality is a crapshoot ($20 for 10 from ebay).

After lots of fiddling, reducing the DOC helps alot to reduce both chipping and aluminum burring. In fact, now it looks pretty damn good. The only drawback is now I'm working with fractions of a thou for Z height.