help drilling 500 .375" holes 3" deep aluminum help

[vz58]

Greetings. I have been drilling .375" holes through 3.1" of 6061 aluminum on my lathe (flood coolant and diy cnc conversion) using high helix drill bits. It is slow and I often get a poor finish (spiral lapping marks).

I want to step up my speed and hole quality. The lathe can go about 2000rpm max.

I was looking at some of the $50 drill bits like guhring but hate to spend money blindly with so much knowledge available here.

I use a collet for the drill bit and the stock is mounted in a cross slide fixture.

I can put a cross hole in about half way through before or after the 3" hole is drilled. That might allow coolant in and chips out.

Advice?

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[Cknoble1]

I would look into yg dream drills. (Carbide) they you could probably feed 30IPM or more at 2000rpm. while maintaining a good surface finish.

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[rcs60]

you could try the hss msc brand -interstate not as good as yg1 or gurhing but gets you started for about 20.00
most parabolic drills you should be able to go about 10x dia before pecking
with the limitation of your machine i would stick to HSS as it is maxed out at about 200 sfm

[vz58]

should I run the cross hole to help get coolant in or just go? I ordered the yg dream and some interstate to try.

[rcs60]

i would try it with out the cross hole and no pecking to start
if the chips do not seem to be flowing down the drill and out i would add a single peck
most manufacturers recommend 200sfm and about .007 ipr for the 3/8 drill ----yg1 maybe more aggressive than this
but this should be a good starting point

[SchortBus]

135 degree High helix bits. I usually use Cobalt with air to keep chips moving and lube with periodic squirt of spirits - flood coolant might not be what you want here. If finish is perpetual issue - drill undersize and ream.

Ever consider using 7075? 6061 is gummy to begin with, it can dull a bit fast and chips virtually sieze to bit - leaving marks in woirkpiece(s). Comes at cost - but machines much easier, leaves higher quality finish too IMO.