View Full Version : Question about drilling Aluminum

11-11-2004, 05:14 PM
I need to drill a 17/16" hole through 1.5" of 6061-t6511 Aluminum.

I bought the correct bit. But should I start out with this bit? -

or should I work up to that size by using a few smaller bits first?

Also what should I use for lube? - petroleum base like WD-40? or Silicone based lubricants?


Cold Fusion
11-11-2004, 06:30 PM
I had to do something similar with a 25mm hole in 3" of aluminum. What I found works best is to predrill with something close to half the diameter of your larger bit. That way you won't be putting too much wear and tear on the first 1/4" of the flutes of the larger bit, which are normally the first to become dull. Be careful when drilingl the larger hole though, as the bit will want to feed itself down quickly and might jam. I used WD40 and it worked fine.

11-11-2004, 08:08 PM
Try Tap Magic Aluminium Cutting Fluid. Works great. The old timers (machinists) used kerosene. I think the Tap Magic works better though, smells better too :)

11-11-2004, 10:19 PM
Depends on what kind of hole you want. Sloppy, use a 1.5 inch drill, or a .50 BMG rifle. If you want it nice, step into it 0.25" or less at a time, close, then step drill and ream.

That's a deep hole.

Really deep. It's going to be hard to hold a close tolerance.

Use plenty of coolant.

11-11-2004, 10:20 PM
Invent...I thought I was the only one who loved the smell of Tap Magic LOL.

Can't get the wife to wear it. :p

11-12-2004, 12:24 AM
If it needs to be any where near precision you can forget a drill bit, or use a undersized bit and creep up on it. As Nervis1 says it will only be accurate if reamed, if you have a lathe you can bore it.

My favorite lube is a home brew of 25% WD-40, 25% JB-80 and 50% kerosene, this also is what I use to put a quick spray on equipment so it does not rust. BTW JB-80 smells great like WD-40. :)

11-12-2004, 11:08 AM
How much torque do you have available?

The problem with starting with a small hole and working up with larger drills, is the fact that the center chisel edge of the drill has no support. This makes it wobble and chatter until it gets far enough into the hole that the outside of the drill flutes start to steady it. So, if you are short of torque, then drill a starter hole, that is slightly smaller than the chisel edge of the drill: with a 1+7/16 drill bit, this would be only a 1/8 to 3/16 pilot hole. Then put the large drill in and drill down until it has fully engaged the work and the outer flute has penetrated by 1/16" or so. This creates a starter cone for all the rest of the drills to start in. Then you can revert to a 1" drill (or whatever) and drill out some of the material before you go all the way with the big one ;)

11-12-2004, 11:36 AM
Don't mean to be negative, but regardless of your drill technique, short of reaming (by first drilling undersize, then using a 17/16" reamer), your hole is going to be pretty sloppy. If that's OK, by all means go for it, but if you have a mill or lathe, boring is the way to go, IMO. What is the part for?

11-12-2004, 12:24 PM
The only thing That i could at to your Post, HuFlungDung, is to add a radius to the outside corner of the drill and this will act like a Reamer and hold the hole closer to size.

11-12-2004, 01:25 PM
I am partial to doing it like Hu suggests, pilot hole just big enough to allow the chisel clearance.
A good drill with an accurate sharpen shouldnt drill any more than 0.010" oversize.
Knocking the corners off with a stone as Donald says works extremely well too but if you only a couple of holes to do you have to grind the bit back quite far to re-sharpen when done ("read" not always ecomomical)

11-12-2004, 06:12 PM
DareBee, I understand what your saying about having to regrind the end of the drill back to get the radius out of the corners. But that was my primary profession for 15 years so I never had a problem with putting an edge back on a tool. And to do drill that hole properly one should drill it with in .005 - .015 of size and then ream it to size, but most don't have that kind of tooling laying around, so putting a radius on the drill would be the cheapest in my opinion.

11-15-2004, 09:12 AM
I was also suggesting a possible overdrill sizing scenario as reference. I had in mind that a lot of the drilling I do is very open tolerance clearance hole type work.