Drilling anodized aluminum...

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I'm about to start the process of drilling into an anodized aluminum chassis purchased via Par-Metal and I'm looking for tips on the dos and donts with this particular chassis.

A few thoughts on the process:

• I'll be using a 10" bench top drill press for drilling. So at least it'll be easier to make precision holes.

• I've bought an automatic center punch for initial hole drilling.

• When doing design phase of this project, I used AutoCAD for drawings. I plan on printing out drawings at 1:1 scale and then applying to chassis. Any tips or tricks for this?

• I've heard it's best to drill a pilot hole first - at least for the larger holes.

• I've also bought cutting fluid to keep bits in shape and heat down.

• I got some scrap aluminum to practice feed and speed on. RPM on drill press is adjustable from 530 to 3100. I've heard RPM for aluminum would be at slowest setting.

• For the larger holes e.g. Neutrik panel mount holes I was going to start with a smaller hole and use a stepped bit to get to close to the final ≈1" holes.

Some questions:

When drilling the holes should I do from within chassis to keep a cleaner look? Not sure if this makes sense or not.

Am I missing anything?

Not rocket science, but here's a few things.

You DO want cutting fluid. With mild steel I'd say you can get away without (coolant makes a bigger difference with steel) but on aluminum it is critical. While aluminum is soft, it is very prone to chip-welding- it sticks to cutters. WD-40 or kerosene works well for aluminum.

530 RPM might even be a bit fast for larger cutters, but for small drills you may want to bump it up. Speeds and feeds for AL are available online.

Take care to avoid scratching the finish. Chips getting underneath the workpiece is the fastest way to do this. You'll want to have a piece of sacrificial wood underneath your workpiece while you drill it (this helps to minimize the scratches).

If you can, good clamping can really help with the holes. That can be hard with a chassis, of course, but it does make a huge difference.


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I don't see you say this, so I have to point it out....


You can go 99% of the way through with ease and no reaction. Then the drill grabs and spins four sharp corners at you. Let off the pressure and it flings the panel through your tummy.

I have scars, they could be worse. When I drilled 2" holes in steel (no drillpress) I figured oak backers, clamps, and psyched myself for days.
H713 - the advice on scratch prevention is sound. Will look up speeds and feeds settings online.

Thanks PRR. Good to know about the effects of not clamping!

I know it's typically for wood, but I did get in addition to the drill press a drill press table. I figure it'll make it easier to hold my work in place. Otherwise, I could go out and get a drill press vise, but I figure the table should suffice. Ultimately, need to figure best way to clamp things down here with the shape of chassis taken apart.

So for the larger holes, because I can't go slower on RPM, should I use handheld drill instead?

BTW... what are oak backers?
If you do not have a lower speed then you can drill very slowly or as I do with the drill when it hits the surface let it take some material and then remove the drill then I do the process again. There are large drills that apply to this eg hole saw.

When drilling, I always use a wooden board or piece of wood underneath masking tape on the side which is to be drilled allways with double layer masking tape as protection WD-40 that lubricate do not forget protection glasses. But this has already been told by others and some other good tricks mentioned in the thread take it easy and think about the next step and you will get a good end result.

PRR you are right, it is so easy to injure yourself because you think that you can hold it wiith your hand. I have seen injuries looks similar to minced meat after a piece of metal was stuck in the drill and rotated. It looked bad, please be safe.
I print cad drawing at full size then stick to item with pritt stick.
On the drawing, the centres of all holes are also indicated with a small circle for the pilot.
This way, you can see if your pilot drill is running off and correct as you go.
A dot for the centre mark is obliterated as soon as the drill touches.

My bench drill is such low torque that any item large enough to be gripped firmly will stall the drill if it grabs. Don't forget though that the drill will try to lift the workpiece as it breaks through due to the spiral flutes.
I would though deburr edges as required before drilling so I wasn't gripping a sharp edge. Also, gloves can be useful for protection from sharp edges.
Lots of great tips here already.

Aluminium needs to be drilled much faster than steel.
If using Carbide instead of HSS, double the speed again.
The aim is to create 'chips' and not spirals.
As H713 mentioned, lubricant/coolant is critical for aluminium to prevent the cut metal from welding to your bit and prematurely ending the life of your drill bit.
WD40 is perfect for this and you can often flow it from the top of the drill bit right where it needs to go.

If you want something that professional aircraft sheet metal workers recommend, also try:


Pilot holes are good. Step drills are awesome. Greenlee punch/dies are the tools I wish I had! Knockouts | Greenlee

The technique K.A.B describes is called 'peck drilling', look that up.

Finally be certain you want to drill that hole. Is it in the right spot. Is it the right size. Is there enough clearance behind whatever goes into that hole? Write the hole size and purpose next to the intended spot.

Nothing worse than finding out that 10mm hole actually needed to be 8mm....
I have had the three sheet metal punches for many years but for the last five years or so I have been using the three step drills for holes in aluminium. The step drills are much easier and quicker to use and give a cleaner finish to the edges of the holes. The limitation to both types of tool is the thickness of material that they can be used on. With the step drills, each "step" is only 5-6mm so any material thicker than that needs to be conventionally drilled. The current fashion of 10mm front panels is a case in point.


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I use ipa (that alcohol stuff) for drilling and drill at quite high speeds. Looking up the speed is best advice (beside clamping the piece and using a piece of wood.)
Be aware that the drill (even big ones) may ‚oscillate‘ when speed isn‘t good, thus cutting a pentagonal pattern around the hole.
If you aren‘t after /100 mm precision, cover the whole piece with masking tape for scratch-protection...
None round holes occur when the tip of the drill has exited thin material before the outer diameter has located. The traditional way of avoiding this is to grind the drill tip in a special way, rather like a brad point wood bit. However, step drills with their large land relative to flute avoid this problem, they wouldn't be much use if they didn't.

Just a safety suggestion. If using flammable fluids for lubrication, keep a fire extinguisher close by.

WD-40, Kerosene, Alcohol and such are flammable and the heat from drilling will cause them to go to give off vapor and thus be quite ripe for ignition at the slightest cause.

Alu is soft as butter. Centre punch, use a sharp bit, and go. Pilots are a good idea for larger holes. I doubt you need any cutting fluid.

But aluminium _alloys_ are hard. There's a huge difference between pure aluminium (absolutely impossible to drill neatly unless sandwiched between harder layers), and standard precipitation-hardened aluminium alloys (which are much more common).

Most Al alloys are free-machining and easy to work, and although hard are not steel-hard.

Pure Al is a pig to machine, clogs up the tool, sticks to it, burrs really badly (just like copper).

Always drill from the front, the exit hole is less neat (alloy), heavily burred and distorted (pure Al).

If its thin sheet large holes ideally need to be stamped/punched, not drilled, as sheet may buckle. You'll never get a neat finish in very thin sheet unless laser cut or etched.

For thicker sheet/plate the neatest holes are drilled from the front till the bit starts to emerge, then finish from the back, but not all the way through. Ream afterwards for ultimate quality.

Alternatively chamfer the hole edges slightly with a countersinking bit after drilling.

Diecast aluminium as in Hammond boxes cut and machine really easily, feel almost crumbly, and do not burr. They are more brittle than most aluminium alloys though.

And the other bit of advice is do not remove any protective plastic film until final assembly :) If your sheet has no protection you can add masking tape onto it for marking up and protection during the process.
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BTW I've only seen soft Al as highly polished sheet, intended for decorative purposes rather than structural. I suspect that anodized panels are usually alloy as softer pure Al would be too easy to bend and this would crack/craze the anodizing layer - but a suspicion is only that.

I do remember Eurocard cage systems from ages back that came with precut sections of anodized front panel in several widths corresponding to 1/2/3/4 card slots in the cage - they were very nice 3mm sheet heavily anodized.
So I took a look at the Speeds and feeds and at Par-Metal’s website. It looks like they are using 5052-H32 alloy aluminum in their product. Looking at the calculator it specifies an average tool speed aka surface speed of 200 for 2024 and 280 for 6061. I’m assuming 5052 is somewhere in between. Based on the calc it’s saying 955RPM for a 1" bit. I’m starting to get the gist here other than feed part. When it spits out a number like 4.3, does that mean just bring the press down slowly? Or is that meant for something that can be programmed like a CNC machine?

I am doing a CAD drawing based on a DWG that Par-Metal provided me. I have a plotter at work, so I can print out at 1:1. Does any glue stick work to apply the drawing to the chassis? or is Pritt Stick the only way to go here? I’ve got markings for the center point for all holes and the press has a laser on it, so I’m hoping it’s fairly smooth sailing here.

My bits are TiN coated HSS from Dewalt. Good, bad, ugly? I’m guessing to run them at same speeds as HSS. I’ll have a look at peck drilling via YT to get the gist. I bought some Rapid Tap for my cutting fluid. It’s good to know WD-40 works just as well.

I do have one 1 1/2" punch that I acquired years ago. They are pretty awesome. I think it’s too large for this project though. I’ve been looking at the greenlee punches for future projects. It seems for the larger holes it’d be easier to go the punch route.

The tip about drilling from front (or exterior) of chassis is great. Didn’t think about that. I do plan on chamfering or reaming edges. I’ve noticed that hand held tapered reamers don’t come in a size larger than 1/2". My guess is I’d have to buy specific tapered reamer bits instead. If I'm going for the whole polish look then it looks like I’m going to have to add countersink bits to that shopping list.
You can use much slower than recommended speed for Al, especially with a low-power drill(!). The feed rate is good to follow though. Remember speeds & feeds assume enough power and that you are doing production where time costs money!

Some metals are much fussier about speeds/feeds. Most precipitation hardened Al alloys are similar, you'd not worry about the difference unless going for large-scale production and wanting to optimize throughput. The heat-treatment and aging will change the hardness anyway, some alloys reach full hardness slowly at ambient temperatures, others need a soak at 200C. Aircraft fuselage/wing sections are stored in huge fridges to delay any hardening until all the major manufacturing forming steps are done.

TiN coated drills will eventually lose the ceramic coating as it wears, but HSS is fine anyway, will last a long time with just Al alloys to cut.
Speeds and feeds are more for hole quality/finish than anything else, so go with the recommendation you have, or as close as possible.
You can use the printout you have to make markings onto painters tape, remove the template after, then the paper won’t haunt you after that, and your layout won’t wiggle around like a sheet of paper can often do.
A way to help stabilize the part and help prevent any stupid and dangerous mistakes is to check the longer end of the part against the post of the drill press.
The high speed steel is sharper than the coated bits, but you should be fine. Just about any oil will do with aluminum, cooking oil, hand lotion, whatever...
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