Drilling Mild Steel

[jsg612]

I need to drill a series of eight 10mm holes in some fairly hefty 5mm mild steel. What is the best way? Drill slow and steady with a drop of oil or flat out full speed with a lot of oil? Can you also recommend me a good drill bit to buy that will last me for this project - it will probably be blunt afterwards and go in the bin, so not too expensive, but not too cheapo!

Thanks,
-jsg612

[Globs]

Use a pilot hole, not a punch.

[XG332]

10mm metal drill bit?
I would just go for it.

[miniman]

Handheld drill? How is the metal held / fixed down?

10mm would be fairly slow with some oil for me.

[Robb F]

Pilot a small hole. Around 850ish rpm, push firmly.

Mild steel isn't tough material so it won't be as hard as your think.

[B17NNS]

Pilot first, nice and slow with some oil.

[pikeyboy]

I'd procede as follows :- mark out with a scribe, center pop each hole position and then drill a pilot hole, then go through with the final size. Generally as a rule of thumb large dia drill means slower speed and vice versa. Buy some quality drill bits from an engineering merchants, good quality HSS will be fine for mild steel, use some oil as you say and apply steady pressure dont make the drill smoke, if it does its going too fast or you're loading it to heavily. Good luck you're not doing anything too tricky

[spikeyhead]

I'd go with a 4mm pilot hole.

HSS drill bits, buy a few unless you're capable of sharpening them properly. It's much easier to change the bit than try and carry on with a blunt one.

[993AL]

A 3mm or 4mm drill first. Your drill shouldn't blunt unless your'e running at too high a speed. WD40 will do as a lubricant/coolant.

[lewes]

I wouldnt use WD40 as a lubricant as its flammable !!!

[Big Al.]

lewes said:

I wouldnt use WD40 as a lubricant as its flammable !!!

Agree WD40 should be avoided, Rocol cutting compound, light engineering oil or at a push engine oil, just drip a small brush into it and tap the the drill with the brush when it's revolving.

My suggestion re drilling would be if your doing it free hand i.e. hand drill centre pop and successively drill with a series of drills about 2mm Dia. apart. If using a pillar drill then you should get though using a couple of sizes after the pilot.

As a general guide small drills fast & big drills slow.

HTH.

[redeye]

i drill 13mm holes in 10-15 mm steel in one go with dewalt extream bits and WD 40 as a lub ,hand drill no probs ,these bits have a small pre drill point
the best i have ever used

[ANS2vrs370]

When you are cutting through the metal look at the chips (bits) of mild steel coming out if then are blue/black you are going too fast and it is all too hot and your drill will be blunt in no time.

If you get one long spiral you are have the feed and speed about right and your drill edge will last a lot longer.

As stated a decent HSS drill bit will do if it was a pack of 10 from the car boot then you might as well throw them at the steel. Disclaimer as general rule of thumb this applies you can occasionally get a decent set but 95% of the time they are utter ste

[The Black Flash]

Big Al. said:

lewes said:

I wouldnt use WD40 as a lubricant as its flammable !!!

Agree WD40 should be avoided, Rocol cutting compound, light engineering oil or at a push engine oil, just drip a small brush into it and tap the the drill with the brush when it's revolving.

My suggestion re drilling would be if your doing it free hand i.e. hand drill centre pop and successively drill with a series of drills about 2mm Dia. apart. If using a pillar drill then you should get though using a couple of sizes after the pilot.

As a general guide small drills fast & big drills slow.

HTH.

I would definately do it in a number of steps, will be a lot easier.

[Incorrigible]

In order of preference

take the steel to an engineering shop

borrow a mag drill

DIY (where all the above advice is fine, although WD40 will be fine IMHO for such a small hole)

[richyb]

I was drilling out some holes on some chainsaw bars recently using a pillar drill and I found as slow as possible worked best.

[zcacogp]

redeye said:

i drill 13mm holes in 10-15 mm steel in one go with dewalt extream bits and WD 40 as a lub ,hand drill no probs ,these bits have a small pre drill point
the best i have ever used

Not having a pop at you redeye, but DeWalt Extreme drill bits remain one of the most disappointing DIY purchases I have ever made. Pack of 5, from screwfix, the only two I used burned out within minutes of using them.


Oli.

[.:ian:.]

I got a set of cobalt steel bits from screwfix, awesome things, they just carve straight through iron and steel. Stainless is a bit tricky but ok once it gets a "bite".

ETA low speed, mild pressure, job jobbed.

Edited by .:ian:. on Thursday 13th January 16:02

[Globs]

pikeyboy said:

I'd procede as follows :- mark out with a scribe, center pop each hole position

No, punching a hole work hardens the metal in a cone shape below the punch, which is exactly where you do not want a cone shaped hardened piece of metal.

Just drill a pilot hole, then the main hole.

[davepoth]

Definitely pilot hole. I think I used three or four drill bits to make the hole progressively bigger, it cuts down the amount of cutting the bit needs to do and as a result reduces the heat buildup massively. I reckon it was quicker that way.