Best way to drill an 8mm hole in alu?

Right, first of all I’m not a total dobber, I can drill holes in things. But what’s the best way? Got an 8mm hole to drill through a bit of alu round, about 30mm thick, got to be reasonably precisely in the middle and pretty neat. So, what’s best, start with a small pilot and work up? Small pilot then directly to 8mm bit? Usually I’d do an intermediate hole but that mainly seems to trash drill bits, having said that I’m more used to drilling holes in a couple of mm of steel rather than a couple of cm of alu…

(going to be using a small/toy milling machine as my pillar drill’s bearings are shot)

How neat? I normally just do pilot then 8mm drill bit. Bit more precise a 7.5mm bit and a reamer (but have to have the right reamer). Most precise a boring head on the mill.

2.4mm pilot hole. Then I would hit it straight away with the 8mm.

Start off with a centre drill then a 3mm is then 6 then 8mm

Runn about 800 rpm with coolant. Drill in a pecking motion.

Measure twice. Mark centre with a sharp object. re measure the mark. Pilot drill. Re measure. Drill final dia.

Christ, all these pilot holes going in.
You’ve not worked in a modern production CNC machine shop have you. 😀

Slow the drill down & use a firm thrust. What you don’t want is the drill spinning like mad rubbing the alloy away. Use a bit of oil & peck it every 5mm or so to break the swarf. What grade of alloy is it ?

10mm bit and gripfill.

pilot hole then wire erode it 😉

you have to drill it across the diameter?

put vice on mill. clock up back jaw in X. put round bar in vice. wobble the back of the bar. zero dro or zero your hand dial. wobble front of bar.

difference from back reading is diameter plus 1 diameter of wobbler. wind to middle of job (diameter/2 plus rad of wobbler), throw in an 8mm drill and drill your hole.

use a decent sharp HSS ti coated drill you dont really need to mess about with pilots.

You could put the alu into the chuck and the drill bit into a vice?

Pillar drill might help also.

You don’t say the diameter of the alu.

Only blokes could make such a hoo ha about drilling a hole in a lump of soft metal!

oh, in the middle as in it’s like a wheel. stick it in the lathe.

if you dont have a lathe put it in two v blocks in your vice and clock round it to find the centre, and drill your hole.

or just bring it to me tomorrow and i’ll do it for you

Being a toolmaker for over 30 years I find some of these replies quite funny.

Step1 . Drill the hole with an 8mm drill where it needs to be.

Step 2. oh….

Q to takisawa

Bit of a specialised machine your named after?

You any good at making pistons ?

Being a toolmaker for over 30 years I find some of these replies quite funny.

Spill the beans. I’d like to know the proper way. I thought larrythelathe sounded spot on but I really don’t have a clue.

Use the mill, use the v blocks with stops and clamps, clock up the centre and cut it with a 8mm 2 flute slot drill, nice even cut through, plenty of coolant or mill it 0.3 under and ream it.

Basically take it to Jamie porter or have a hole off centre that looks like you cut it with a noga blade

not sure i have an 8mm reamer… it probably wants to be a clearance hole though anyway

Cheers folks, seems like the concensus is definitely no intermediate drill… For me, the advantage of a pilot hole is as much about aim, I find it much esaier to get a little bit in the right place, then I can back up and fit the bigger bit. But then I could do that without actually drilling the hole eh.

My tiny lathe doesn’t have a tail chuck so not straightforward to spin the work- I could stick the bit in the vice but centreing that up seems like hard work for not much gain?

Porter_Jamie, have to say I recognise all the words in your post and yet I do not understand it at all 😳 cheers for the offer, I generally prefer a bad job done by me to a pro job but I appreciate it anyway!

Slow the drill down & use a firm thrust. What you don’t want is the drill spinning like mad rubbing the alloy away. Use a bit of oil & peck it every 5mm or so to break the swarf

wife whispered something similar in my ear last night.

Centre drill, 7.5mm drill using paraffin as a lubricant then ream to 8mm again using paraffin.

If its secured in place then just wap a 8mm through it, doing it in steps will give the same results but take a little longer.

My tiny lathe doesn’t have a tail chuck so not straightforward to spin the work- I could stick the bit in the vice but centreing that up seems like hard work for not much gain?

You can get a wotsit that fits into the tailstock on a morse taper, that has a v-groove on it – you clamp your round stock to the V, drill bit in the chuck, then feed in the tailstock to get the drill hole dead centre.

RDG Tools do them.

Hadge dropped a bomb then scarpered

Step1 . Drill the hole with an 8mm drill where it needs to be.

Step 2. oh….

You’ll never be a real engineer with an answer like that 😀

Hadge couldn’t be arsed lol. You need to make sure it’s clamped very securely as your drilling top dead centre on the bar and so it’s easy be off to one side and then your hole will wander off and be a mess. Make sure you are drilling it directly over the very centre and use a centre drill. Use paraffin as a lubricant as it is best for home use instead of proper cutting fluid. I would actually use an 8mm drill and drill it just so it’s got the full diameter in the bar and then I’d remove it and drill it with a 7.8mm drill all the way through and then you could either ream it 8mm or you could use a nice new 8mm drill and take it slowly and drill it and if you are careful you will be very close to your 8mm size but if you definitely need the 8mm a very good size then ream it. The reason for spotting it with the 8mm at the beginning is to give the reamer or 8mm drill a good start to cut with as if you leave too much material you’ll have trouble drilling or reaming it. But you must make sure your on the centre line of the bar when drilling okay. Is that alright for you? Oh and if I was doing this at work I would hold the bar in a vice on a milling machine, clock between the jaws so I could guarantee I was in the middle and then do the drilling process I gave above.

Hold the bar between your feet wearing flip flops

Get out your makita lxt cordless drill and stick in a 8mm drill bit.

Zip tie the trigger fully in and press hard roughly into the centre of the work piece

If you dont lose one or both of your feet you did it wrong.

* this may not be the best way but it seems to be how some of the engineers i work with would prefer to do things.

Cheers folks, very useful! I think I’m now at least 19% less likely to **** it up.