Drill Speeds & Pilot Hole Sizes For Metal?

[The Coal Man]

Hi,

Would anyone please be able to provide a small table listing the drill speed and any pilot hole sizes for mild steel and aluminium? In practice, I would only be driling up to 12mm diameter so any info re hole diameters between approx 6mm to 12mm for mild steel and aluminium would be very useful.

Thx

 

[Wedg1e]

The usual concept of going up in drill sizes is that the first drill should be a bit larger than the centre web of the one you follow it with.
The use of modern variable-speed drills makes the old tables a bit redundant since the best way is to fine-tune the drill speed as you go to suit the size, tip geometry and sharpness of the drill and the material you're working... unlike my boss who thinks that flat-out is the best speed for everything and then wonders why all the drills are blunt
In essence as drill diameter goes up, speed goes down. Bit of a pain on a pedestal drill with stepped pulleys, you might use 1200rpm at 3mm but that would be way too fast for 12mm which might prefer 500rpm or even less.

 

[Mee]

I like to go under speed and save my drill bits.

 

[knighty]

I tend to go pretty much as slow as possible

drill bits last way way longer like that, less heat so you don;t end up hardening the metal you're drilling, and you don't end up "polishing" it
(is polishing the right word?)

3 or 4mm to start with, tend to buy those by the box of 10 or so... used to buy really good ones.. but shifted to just good ones because every time someone else picked up a drill the bloody snapped them :-(

 

[p0689109]

ditto with Knighty

 

[brightspark]

small drills fastish speed larger drills slow its not critical as long as not doing loads of repetition work then it does count

 

[eSCHEn]

I use (for metric) size - thread pitch; so a 10 x 1.5 thread yields a 8.5mm tap. Not sure if that is a "normal" fit or not, SWK

 

[Mee]

small drills fastish speed larger drills slow its not critical as long as not doing loads of repetition work then it does count

Just tack loads of plates together and put them on the big drill, takes no time at all on autofeed.

 

[outofthefire]

I keep my pillar drill running slow mostly because it's a right faf changing the speed.

 

[outofthefire]

 

[The Coal Man]

Thank you for all your replies, thery are very helpful for a novice like myself.
Also, thank you for the table ("outofthefire").

Rgds

 

[The Coal Man]

Hi,

If I am using a pillar drill with speed of approx 450rpm to 500rpm to drill an 11mm hole in mild steel that is 3mm thick, should I drill a smaller size hole first or can I just drill the 11mm hole using some oil or cutting compund?

Thx

 

[knighty]

if you look at the very tip of your 11mm drill bit, the point doesn't really have a sharp edge to cut with... when you're drilling you're pretty much forcing the tip of the drill into the metal

past the tip, there's sharp edges to cut with

use a pilot drill which is slightly bigger than that tip - that way you quickly cut a small clean hole which lets the tip of the bigger drill pass through easily

(I normally use 3mm or 4mm)



you could use the 11mm straight away, it would probably be fine, but it's better practice to drill a pilot hole and it'#ll mean the bigger drill bit stays sharp for a lot longer

(the tip tends to blunt quickly, and when it is cutting it tends to get hot, which is bad)

 

[The Coal Man]

if you look at the very tip of your 11mm drill bit, the point doesn't really have a sharp edge to cut with... when you're drilling you're pretty much forcing the tip of the drill into the metal...

Thx for the reply.
I have an 11mm De Walt drill bit with a smaller section at the tip, I think it is the De Walt Extreme2 bit as it looks like the one in the picture below.

http://www.screwfix.com/p/dewalt-11...tracking url&gclid=CNqo8Zy17tACFeaV7QodGJ0Osw

Is this small tip just a pilot type of guide or does it replace the need to drill a 3mm or 4mm "pre hole" first? It's not an issue for me to drill a 3mm hole first, I just wondered what was the purpose of the smaller section at the tip of the De Walt drill bit.

Thx

 

[puffernutter]

I tend to use a Slocombe drill (centre drill) for some large holes as it centres well (no tendency to move as other drill bits do) and gives a really good 45degree hole to start the larger drills in.

Cheers

Peter

 

[Seadog]

The recommendation from Presto is to use a pilot that is 1.5 times the size of the chisel edge

 

[knighty]

yes, you can go straight in with that Dewalt drill bit


I've got a set of those too and really like them, especially for really thick stuff


bur you need to drill as slowly as possible, if you drill fast they heat up fast and then they get blunt really fast :-o

 

[SHogan]

What's this a screenshot from? It looks really useful!

 

[Seadog]

The Engineer's Black Book