Newbie questions - drilling holes in 6061

[radioactive]

A couple of questions regarding drilling holes...

I'm using HSS drills on my machine (4000 max rpm) and according to the machinist handbook I can run full rpm (4000) for sizes up to 7/16. I think the feedrate was listed as 16 ipm.

In general how should you drill a hole (for example 3/8" diameter)?

One time drill at this size? How far to peck at a time?

Or drill a small hole first, then step up in size until you reach the size you want?

Sorry for the simple questions.

Currently I'm using G83 with 0.050 pecks (no retraction though), should I have it retract to above the surface of the material? It seemed to work ok until my china drill chuck came off the taper

[Geof]

If your machine has enough power drill aluminum full size one time, no pilot holes.

If power is limited back off on the rpm rather than backing off on the feed, but keep the chipload more or less constant; i.e. if you go from 4000rpm at 16ipm down to 2000rpm for more torque reduce the feed to 8ipm or somewhere close.

You can probably go in at least 1/2 a drill diameter per peck but it is best to fully retract to clear chips and let coolant/lubricant into the hole.

Always use coolant or lubricant.

[radioactive]

Thanks for the advice, I appreciate it. So much to learn. I'm still working on a flood coolant system and using air now to clear the chips.

[djr76]

If you are drilling with a jobber length drill or longer, you will need to center drill the hole first. I use screw machine length drills as much as possible for rigidity.