[tbaker2500]

I was hoping to get some advice from the experts around here. I have a few project where I drill hundreds or thousands of 1/16" holes in 6061 aluminum sheets. Sheet it usually 1/8" or thinner. Invariably, I get flashing on the bottom side of the hole. It almost feels like the bottom has a skin on it which pushes and deforms, rather than cutting. The bit is new, HSS 118deg jobber, using flood coolant on a CNC.

Are there suggestions as to how to prevent the flashing from occurring? The best I've done is resurface the flashed side with an end mill, but it still leaves bits of flashing stuck in the hole.

Thanks for any help!
Tom

[Sinistersam]

You could try using an end mill instead of a drill bit. Split point bit might work as well. A solid backing material would help also. Feed rate could be to high, and pushing rather than cutting.

[weibelmarco]

An aluminum tooling plate may be an option as you would drill constantly in solid material.
That can cause problems on larger sheets which can only be clamped around the edges as it may bulge up towards the center as you drill along.
I made a spring loaded arm bolted to the spindlehead that pushed down on the sheet while drilling and i stacked five high. Worked like a charm.
For that job it was economical to reface the tooling plate after each run about 15 thou. It may not be for you tho.
Good luck !

[holbieone]

for thin sheet like that try brad point drill

[txcncman]

for thin sheet like that try brad point drill

+1

Also options: Use carbide drill. Peck drill. Use slower feed for last 0.015" when drill corners break through. Water jet.

[tbaker2500]

All good suggestions. I will start trying them, thank you!
About the carbide drill- does it have a sharper cutting edge?

[Bob La Londe]

I drill 1/2" 6061 regularly and have the same problem if I hurry. If I peck and clear and feed slow the last little bit the back comes out almost smooth. Hard to judge on my drill press, but you can program it if you are doing it CNC.

[txcncman]

Carbide is not sharper out of the box than HSS. But, it will hold the sharp edge longer.

The sharpness of carbide depends on the grain size. I think micro-grain carbide has a 0.002" spherical radius grain size. That means the sharpest carbide would have 0.002" radius on any edge. Where as HSS can probably be ground to have edges down to the ten thousandth radius or less.

[tbaker2500]

Thanks!
I'll post how it turns out.