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Engraving metal:

"An Amana solid carbide 60 and 90 degree bits works, but the tip of them goes dull very quickly it seems, which then turns the lettering muddy. We tried a nice 'Engraving' bit made for metal work from Onsrud, a 60 degree single-flute with a very very sharp tip. And that tip snapped right off on the second plunge. We were running it at 1.333 ips cutting, with a plunge of 0.6, at 13K rpm. While it's obvious that I need to take slower and shallower passes, can anyone chime in on what they use for plunge and stepdown?"

A 90° Drill/Mill works well & is always exactly 0.500" in diameter. Try to get one with a coating on it...and test your zzero plate if you get the coating. Sometimes it acts as insulation & the zzero routine won't work.
As far as speeds go, reduce the speed to X and Y move speed to 1.0 and the Z move speed to 0.4 and use a shallower stepdown. Set your safeZ height low to reduce Z travel times. V-bits do not really cut in the center of the Vee. Use air cooling to reduce the smearing effect, AND the grade of Aluminum makes a big difference on machinability. Some alloys are harder/denser and these reduce smearing/melting of the AL when it is heated up during cutting. The idea here is to keep the tool moving at all times, reduce Z position positional loss by reducing Z speed and blow 20 psi of compressed air on the bit while cutting to keep things cool. Lubricant or liquid coolant is not necessary or advised since it wicks into your spoilboard.
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