Best drill bits for drilling into steel beams

[Roger928]

Cutting oil is almost always pointless unless you're in a machine shop

I would always use a water soluble cutting oil/ coolant even on site as it extends the life of the broaching cutter or drill bit.
Most mag machines have a facility for applying the coolant direct to the centre of the broaching cutter.
Though I would just use a small hand held pressure pot sprayer.
The best mag drills have an auto feed / retract and power off function.

 

[Deleted member 174758]

I tend to use what I have with me - generally 3-in-1 oil as I'm a chippie, not a steel fabricator. Either way a bit of lube eases the cutting action and prolongs drill bit life. I find that drilling modern electro arc furnace steel UBs (RSLs in old money) and extruded structural steel tube takes M42 (cobalt) HSS steel bits and that they don't last all that long beceause of the hardness of these arc furnace steels. I generally find Milwaukee drills to be reasonable, although Dormer are superior (though nowhere as readily available - Toolstation stock the Milwukees and they are like budgies - cozthey go cheap!). Used to use Heller, but the Milwaukees have been better - I was getting 40 to 50 holes out of 4 and 5mm in 6 to 10 mm wall steel last year.

I suspect that this fast blunting is down to the (accidental) inclusion of hardening alloys such as molybdenum, tungsten or manganese in electro steels which can be incorporated into some scrap loads such as car gearboxes, back axles, etc. When these end up in the mix the mild steel turns into a tool sttel and manganese in particular is bad news because it work hardens - he morer you driil it and heat it, the harder it gets (which is why it's used in steel for tipper and big waggon bodies)