What drill bits for drilling steel?

As a rough rule you need a slower bit speed the harder the material your drilling. Is your drill multi speed? If it's just a fixed fast speed you'll just blunt all your bits straight away, unless you are drilling wood or something soft like that.

If I'm drilling out bolts I'll start slow and increase the speed until I get some big bits of swarf coming away and then hold that speed, if the bit squeals then it's too fast. If you have a bench grinder you can re-sharpen your HSS bits, watch some youtube vids for instructions and you'll get the knack of it eventually!

Try some decent cobalt steel bits, got me out of many a mess

And the more inaccessible the bolt,the harder the steel .....

Titanium bits seem really good - used one when I had to drill out a stud in an alternator the other day.

If you're drilling out pressed studs from the balljoint, flatten the top with and grinder and then hammer them out.

You will be doing two things wrong with your HSS drills as they will do the job.
Too fast rotation and not enough force applied.

For speed, simple thing to remember for HSS into steel is 10,000 divided by drill diameter.

However thats a good approximation of speed in perfect conditions in a pillar drill or lathe with cooling, for jobs like you are doing you cant cool or lubricate enough and cant control feedrate well and the bolt material will be harder so just aim for about half of that.


Lets say you were going to drill first at 4mm diameter to put a pilot hole through, thats what I would do. 10,000/4 = 2500 / 2 = 1250rpm max. You can see that depending on your bolt size the final drill might be going very slowly ideally, a 10mm drill will only need about 500rpm for example. If in doubt go too slow, it will work better than too fast.

The more important thing is feedrate, which on a machine is no problem to control but for a hand help drill all you can control is force applied.
The key point here is that the drill must cut, you need to see swarf, if its not cutting its rubbing and will blunt very quickly as you have found.

The problem you might have now is that once you spend a time just rubbing and creating heat the bolt material can harden due to working, now you may need to get through that hard surface to make good progess again.



On the whole the things to remember are less speed and more force / pressure / feedrate to make sure you get cutting not rubbing and not much heat.
Pressing hard enough to cut will create far less heat than being gentle.

Hss bits are perfect for drilling out the bolt. But they need to be good quality set like sherwood etc. You do get what you pay for.
Learn how to sharpen them and you will not need to buy new drills for years.
As for coatings like titanium they are pointless for a home gamer.

Ben

Fixed that for you...😂😂😂
Sherwood and Wurth both use the same cheese for their drills, good enough for plastic,wood etc,but you can see by the sparks when you resharpen them, that they are soft.

Sharp bits and less speed, watch the swarf or lack of it as it will give you a clue if the drill is sharp or the speed is wrong, try stop start the drill with pressure, if it's a small drill you cant go mad on it or it will bend or break.