Drilled holes aren't circular

[Rustyy117]

I'm trying to drill some 10mm holes in 1mm thick aluminium, I first drill a 4mm pilot hole and then use a 10mm HSS standard metal working drill bit but the holes are really misshapen

Here's an images to show what I mean (sorry for the low quality)



So my question is, what can I do in order to get perfect (or near perfect) 10mm holes?

Thank you!

[BillyGoat]

Was the drill skipping around?

You could clamp the metal between TWO bits of wood, drill through the top wood, straight into the metal - it will act as a guide and stop your bit skipping.

Make sure the bits are nice and sharp too....

BG

[Someone-Else]

All is not lost. You can still make them round.



Cone cutter

[Rustyy117]

Was the drill skipping around?

You could clamp the metal between TWO bits of wood, drill through the top wood, straight into the metal - it will act as a guide and stop your bit skipping.

Make sure the bits are nice and sharp too....

BG

Hey

No, it wasn't really skipping but it was vibrating quite a bit.

The drill bit should be sharp as its brand new.

I think I'd find it differcult to be millimetre accurate if I were to drill through a piece of wood and then into the aluminium

Any better drill bits for this type of work, or perhaps a 10mm hole saw bit for metal work?

[Rustyy117]

All is not lost. You can still make them round.



Cone cutter

Hmm... cool I'll look into those.

Thanks

[Someone-Else]

SCREWFIX £21.89

You can also get "stepped" cutters, but they cost considerably more.

[merlin50]

A pillar drill is best, but without one step up in sizes drilling a bit at a time and do not use cheap drills

[Hitch]

Grind the angle of the drill much shallower if you have a bench grinder.


Slow the speed of the bit down too I expect.

[Rustyy117]

A pillar drill is best, but without one step up in sizes drilling a bit at a time and do not use cheap drills

Yeah don't have a pillar drill so will try those cone drill bits

[Rustyy117]

Grind the angle of the drill much shallower if you have a bench grinder.


Slow the speed of the bit down too I expect.

Unfortunately I don't have access to an angle grinder, I don't do much DIY :/

I will slow down the drill speed though

[thescruff]

Don't look as though you drill right though

[Wee Eck]

Was the drill skipping around?

You could clamp the metal between TWO bits of wood, drill through the top wood, straight into the metal - it will act as a guide and stop your bit skipping.

I think I'd find it differcult to be millimetre accurate if I were to drill through a piece of wood and then into the aluminium

Drill a 4mm pilot in the wood and metal separately, align them (using the bit), clamp them then drill through all three with the 10mm?