Drilling aluminium

[E-wan]

Hi

I'm building an extension for my car roof rack and I need to drill a series of 8 mm wide holes in 6 mm thick aluminium t section bars with my pillar drill

Any advice appreciated in particular

When drilling metal with a pillar drill is it still helpful to use a centre punch?

Would a pilot hole be helpful or working up in gradually increasing sizes of drill bit

Does aluminium benefit from a cutting lubricant when drilling

Many thanks for any help

Ewan

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[novocaine]

centre punch. yes
pilot hole, maybe, but it's only 8mm.
cutting fluid, no harm, helps clear the chips.
drill speed, fast as you like.
you could change the profile of the cutting face of the bit, but meh, not worth it. crack on.

 

[porker]

You can use WD40 as a cutting fluid with Ally. I use it all the time on the mill.

 

[AES]

Centre punch - yes (make sure it's sharp)

Lubrication - yes (paraffin or WD40 - ali is "soft/low melt point" and swarf tends to get stuck on the drill )

Pilot hole - if you need great accuracy yes, if "normal" don't bother

IF you have VERY many holes to drill and can do so, change the drill angle from "standard" (118 deg included) to about 100 deg or a bit less. But if you can't do that accurately, and/or have only a few holes to do, don't bother.

Make sure to debur, particularly on the underside of the hole.

RPM - for 8 mm dia, not full speed but about mid/+ (assume your pillar drill has 4 or more speeds)

Feed - not heavy, but maintain light/mid pressure

 

[E-wan]

Thank you for all your suggestions

Best get drilling

Would a half round file and sandpaper be the best method of deburring drill holes?

Ewan

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[MikeG.]

Not unless you want them bigger. The easiest way is flat, with a flat file or some sandpaper on a block.

 

[chaoticbob]

The 'snail' type countersink bits - eg these Fisch jobs are good for deburring. Maybe a bit spendy for a one-off job, but (depending on what you do obviously) handy things to have around.
Rob.

 

[LancsRick]

Definitely lubrication, aluminium is quite sticky.

 

[julianf]

You can use kerosene as a cutting fluid for alloy. It's nice as it does not require all the clean up that other oils will.

 

[AES]

I forgot, even though 6 mm thick ali isn't all that thin, do be prepared for the drill to grab just as it breaks through, especially if you haven't used a smaller pilot drill first, and/or changed the 118 degree drill angle.

If it does grab it may well tear itself out of your hands, especially if the work piece is quite small. And your reactions will NOT be quick enough for you to react, I promise you (DAMHIKT)! And that HURTS. (DAMHIKT either)! So use a machine vice, drill press vice, or even just a drilling vice (the simple hand-held jobby). If none of those available, used double-sided carpet tape and stick the job to a piece of scrap wood.

Re deburring, as above, definitely NOT a round file! As suggested already, a flat file (fine cut), sand paper on a block, a snail-type countersink bit, or used GENTLY, even a small rose-type countersink bit (small dia, not much bigger than the 8 mm hole). If you're going to do a lot of such holes in ali, a hand-held deburring tool is handy (looks a bit like a hook-shaped knife blade but circular mounted in a handle, with the cutting edge on the inside of the hook). Not expensive but usually only found in model engineering suppliers I think.

Countersink bits or the above hand-deburring tool especially recommended if you're worried about not getting scratches on the ali surface.

 

[novocaine]

stick a bog standard countersink in a file handle. you turn in the hole and your deburred and ready to rock.

a deburring tool is great if you do a lot of stuff, useful on the lathe on occasion for me but really not needed for an 8mm hole on a bike rack.

yes to clamping it down if you can, if you haven't got a drill press vice then 2 bits of wood and g clamp will do just fine.

seriously, it's an 8mm hole, unless you are trying to lighten it by drilling hundreds of holes then it's a five minute job.

 

[autotrans]

use a step bit?

 

[E-wan]

Thanks for your suggestions I think I'm set up now

Ewan

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[Aquachiefofficer]

I have to agree with auto trans - use a step drill and save yourself the effort of de-blurring the holes by simply going slightly deeper so that the next (10 mm step) takes the burr off. Turn the piece over an repeat de-blurring on the other face.
I did a few bits of aluminium drilling last year and it worked fine for me.

 

[E-wan]

Eventually got everything marked up and ready for drilling

Made a jig bolted to fence made from a piece of 2 by 4 and clamped underneath the drill table

As the T section bar I'm drilling is fairly long I've angled the drill table so as to be able to support the other end of the bar in my vice

The Jig has a clamp screwed into the top of it which I can simply release slide the bar along and re clamp to drill holes consistently the same distance from the edge

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[AES]

Thanks for posting your results E-wan. Good looking neat holes. See, it wasn't hard really, was it?

(OK, apart from working out how to hold that long lump of T angle firmly)!

MUCH better (IMO) than paying someone else to do it, well done.

 

[Robbo3]

Well thought out & nicely done.
I like the way you added the tea for automatic stirring.

 

[OscarG]

Love your drill press!

That a Meddings?

 

[Lazurus]

I like the vice to.