drilling larger holes in aluminum

We do a fair amount of drilling holes in 1x2in tube stock. Sometimes many holes for lightening purposes. We’ve succeeded various ways - I’d like to know what is best practice with:

3/4in and larger diameter holes in 1/8in aluminum stock

Two specific questions when using a drill press:

a. what drill bit is best? hole saw bit, large drill bit, step drill bit, other

b. what is best technique? (pilot hole? oil? other recs.)

I’d like to settle on one tool and technique for my team and I would appreciate advice from experienced machinists.


For larger sized holes up to about 1" or 1 1/8", we always use a step bit for very accurate holes with a nice surface finish. Anything larger than that hole saws become basically the only option.

Step bits are very quiet and smooth when sharp, but it is best practice to use oil when necessary to cool it off for a little bit. If you had to choose one tool, I would go with the step bit.

My team actually uses a hand drill since most holes are applied after the robot is assembled. We created a block to clamp onto the side of the tube, giving a perfect located hole. I can’t remember what size we go up to but we use a stepbit also, just drill a pilot hole and run the step bit through and it’s very easy to make up to 1 1/8 holes atleast

Is it best practice to use a starter hole or does a step bit make it unnecessary?

And how does one achieve consistency on size of hole, if necessary, with a step drill bit?

I’m not sure if it is necessary, but it does make it easier in my opinion. Just a hole so when you start drilling, it doesn’t move around.

And a step bit has multiple layers usually, so after you drill with one, it kinda skips to a wider layer, and you can feel that drop. So you can either count the drops, or every once in awhile stop the drill and see what number shows up for that section you are in, if that makes sense.

We haven’t had to drill any lightening holes since our rookie year…best practice is to design the robot so it’s light enough.

Sometimes we use hole saws to make large holes, if we need them for functional reasons. But usually if we are using aluminum square tube, it will get brackets riveted to it, or maybe it will pivot on some bolts, or something simple like that, so it won’t need holes larger than maybe 3/8" diameter. We don’t even have a unibit.

We’ve been using these carbide hole cutters for bearing mount holes. I do recommend the hole cutter since it makes consistent holes in a drill press and bearings just slide right in there once you get the hang of drilling without applying a lot of force.

Set the depth stop on the drill press.

We’ve used cutters like those and they work very well in aluminum. Our approach for bearing holes is a bit different. We use a 28mm cutter (a couple thousandths too small) and follow up with an adjustable reamer for a light press fit of the bearing.

If you are using a step drill in a hand drill and making a lot of holes, put masking or painters tape around the step drill on the width above where you want to stop at, then just stop pushing when the masking tape touches what you are drilling into.

Will also recommend. It’s a lot better than the other kind of hole saws that we were using before. (Which apparently were intended for wood and not metal! They worked well enough though.)

Or just get something like this and drill all the way through.

Personally I favor these for up to 3/4" they do come larger as well

Layout all your holes first, and use a center-punch to guide the drill.

For drilling through 6061 Rectangular sections, I would also recommend a hole saw. The OD of the hole saw will keep it centered in the first hole, so it can cleanly go though and makes a parallel cut in the back side. A slower cutting speed, and liberal use of cutting fluid is the best method.

Cleanup with a deburring tool

Annular cutters are fabulous when a precise hole is needed. Our set has seen a lot of action since we bought it a few years back. Makes a great press fit bearing hole if done just right.

We also use annular/Hougen/Blair cutters quite a bit. We have small hole (up to 3/4") and large hole (up to 1-1/2") sets. The only issue with them is the cutter is often very difficult to remove from the arbor after use. We use the little spacer/washer but often it is a a real struggle getting the cutter off. Maybe we are doing something wrong? Does anyone have any tips or tricks to making it easier?

Our set has a small flat on the top away from the cutting edge and we just use a set of channel locks or a wrench to break them loose. Very much important to wait for them to cool down before doing this as that makes it easier too and prevents burns from touching a hot cutter. We typically just grab the arbor in a vise and then break it loose so we can finish removal by hand.

We do a lot of modifying of old parts so it is somewhat often that we have to widen a hole on a mount of some kind. To do this we use a half horsepower dremel with an aluminum cutting bit on it. This when well waxed will cut through aluminum like butter.

Thanks for all the tips and suggestions!