Drilling Into Aluminium

[bungledust]

Hi guys,

I tried drilling into 97mm-thick aluminium sheet. This is the result:



Does anybody recognise what's happened here, and how it can be avoided?

[stallik]

Jokes about gunshots aside, it looks as if the plate was unsupported when drilled. Try backing it with some wood and drilling through both. Should help

Alternatively, drill a smaller hole then ream it out to size with a tapered reamer or try a step drillbit

[MüThing]

What type of bit did you use, and did you go straight for the full size or work up?

[Asymmetric]

You need to use a "step bit" like this one:

http://www.screwfix.com/p/erbauer-spiral-flute-step-drill-bit-4-20mm/8528D?kpid=8528D&cm_mmc=Google-_-Product%20Listing%20Ads-_-Sales%20Tracking-_-sales%20tracking%20url&cm_mmc=Google-_-Shopping%20-%20Tools-_-Shopping%20-%20Tools&gclid=CKGZwcny88wCFTUW0wodFzkE5A

It's the best thing I've ever bought. It makes drilling really easy as it coils the metal out and leaves ultra clean holes.

[bungledust]

Thanks for the tips, guys.

I used a step bit.

I will try backing it with wood, that might help.

Am thinking, is the aluminium sheet too thin?

My only other comparison is that I've drilled plenty of 1590A and 1590B die-cast aluminum enclosures, and I always get clean holes. They're a tad thicker, and I'm pretty sure they've got some kind of coating on them (powder coat?).  So, could it be that the 97mm-thick aluminium is just not appropriate? Should I try powder-coating it first, or a bigger thickness, or maybe even try steel?

Thanks again!

[stallik]

97mm is thick. Very thick. I'm presuming you made a typo. Thin stuff needs support, a sharp bit and moderate pressure. If you need a big hole, start small and work up.

In your picture, the metal has been driven out of the back of the hole rather than being cut off. It's likely that it can be salvaged by using a countersink bit to remove the burr

[bungledust]

Oh wow, yes 97mm is very thick! You're right - I mis-typed; I meant 0.97mm.

Will try your suggestions - thanks!

[Ben Lyman]

as mentioned above, start with a pilot hole (1/16"-ish) then a step drill. I also keep the torque set to a minimum so if the bit ever gets caught it doesn't rip shit up (or waggle me wrist). When it gets caught, throw the drill in reverse and grind away till it's all smooth again, then throw back to forward and keep on drilling. I only use a chunk of wood under mine for the pilot hole, not the stepper.
good luck!

[R.G.]

Aluminum is thought of as a "gummy" metal by machinists. It is prone to semi-welding itself to the cutting edge of tools and effectively blunting the edge, causing a lot of friction and even quasi-melting right at the microscopic cutting edge.

If you look at it the right way, that hole looks almost melted through.

You have to lubricate aluminum when cutting. There are aluminum cutting and tapping fluids, "Tap Magic" being one brand. That and a really sharp bit are nearly magic. The other bits of the incantation for clean drilling in aluminum is getting the speed of the cutting edge and how fast it's being fed into the material just right to cut more than locally melt.

But a backup sheet will help a lot, primarily in making the nearly sheared off half-melted bits get completely cut off, and even more preventing the feed from becoming too fast as portions of the center of the drill bit break through and the actual cutting edge get very short as the conical tip breaks through.

That last is one of the reasons that drills often grab in thin materials, and in turn why people who do not clamp sheet material in drill presses get horizontal slices across their belly when the bit grabs.

[digi2t]

Sharp tool, proper speed for the size of tool used, and the best cooling/cutting fluid for aluminium is Varsol (as recommended in the Machinist's Handbook). Easier to clean up after the work is done than any oil based topping/cutting fluids as well. First two points are the most critical though. Even a step drill can gum up and "melt through" if the two first criteria are not respected.

The other factor is the temper of the aluminium. Zero state (untempered) is the worst for machining, since it's so soft that any rotary action heat generated tends to melt the surrounding material, making for messy work. It's like trying to machine Camembert. Harder grades, like 3003, or 6061T6, tend to be easier to work due to their relative hardness. Again, tool quality, speed, and cooling are key.

[anotherjim]

After PRR reminded me of their existence in another post, I went and bought a hand-drill. That improves everything for me compared to trying to use power tools  on something as soft as regular ali' sheet. Hand drill & regular reversing of the bit to clear the tip helps.

Definitely drill thin sheet backed by scrap wood. Step drill speed ought to slow down as the diameter increases - not easy to do with many power tools.

Many choices of lube. Kerosene, WD40, cooking oil, water & all the proprietary cutting fluids. Depends how much smell/mess you can handle. Wash the workpiece well a soon as you can.

If the bit still clogs -  you can see it in the flutes just behind the cutting edge - scrape down the flute with a hard/square object such as the end of a file.

[Ripthorn]

I do a lot of metal working and machining.  Lots of good suggestions have been made.  Here are a couple thoughts:

- For cutting aluminum WD40 and kerosene are the most commonly used cutting fluids by home machinists because they are cheap and everywhere.  You likely already have one or the other.

- When backing a material to be drilled, try to back it with a material of the same hardness or slightly harder (such as thicker aluminum).  That prevents the mushrooming that can happen even when backed by a hardwood.

- Don't use tons of pressure.  Metal works best when you let the tool do the work.  Don't go too slow, as excessive rubbing creates friction that will prematurely dull the tool.  Too fast and you force material out of the way without cutting it.

- When drilling metal, especially sheets, clamp the material down.  If not for my nice watch, a piece of plexiglass would have severed the tendons in my wrist when I was drilling the plexi as a young 'un.  The bit caught and slammed into my watch, breaking the steel band and sending the watch flying.

[digi2t]

Hmmmmmmm.....

This....



versus this....



I say reach for the Winchester instead. Looks like it does a slightly better job. Quicker too. More fun as well.

OK... so precision might be questionable, but if you stand reeeeaaaaallllll close....

[bluebunny]

I'm sure Mike (haveyouseenhim) can give you some tips with this "technique".   

[kikey]

Are step bits any good for drilling in die-cast aluminum enclosures ?
They work great for alu plates but I have not tried on die-cast.

[bluebunny]

Yep, perfect.  Just make sure - as Jim says - that you clear the flutes of clogged Al after each hole.

[digi2t]

I'm sure Mike (haveyouseenhim) can give you some tips with this "technique".   

LOL!! That's exactly what I had in mind when I posted.

BTW, is it me, or has Mike been absent of late?

[bluebunny]

He has, although he did post a solitary vid fairly recently.  It did feature the, um, technique mentioned above.  Kinda...   

[davent]

I think i read Mike say he  was trading his lead melting gear for lead propelling gear.

dave

[tubelectron]

Oh, well...

Most of all, you need a well sharpened drill with the right cut angles (low rake angle ) and pre-drill a 1 or 1.5mm hole as a pilot. And obviously use a bench drill if you can access one,  and a flat wood shim... You don't need any lubrication for such a small job  , but only precision and quietness.

A+!