OK, I've machined a fair bit of aluminium with my X2 now but today was the first serious attempt at cutting steel. I achieved what I wanted but it took a long time (as expected with a small machine and no flood coolant). So, to help things go better next time I'm looking for some advice on the following scenario. How would you go about drilling a 10mm hole in a piece of 10mm mild steel. What are the drill sizes, rpm values and feeds that you would use?

e.g. (and please note, these numbers are made up)
1: 5mm drill, 800rpm, 10mm/min
2: 10mm drill, 400rpm, 10mm/min

I'm sure its been covered many times before but what would you use for coolant/lubricant when drilling like this? I'm using CRC at the moment.

Steel generally takes a long time and isn't much fun, in my experience. I usually start with a drill around half the size of the final hole (maybe a 5-6mm in this case) and step up from there in 1/16" or 1mm steps. I will usually disconnect the Z and just use the CNC to position the workpiece and then run the drill by hand. For steel I try to use good cobalt bits. It takes a good deal of pressure to cut well, otherwise it just rubs, work-hardens the steel, dulls the bit, and creates heat. Make sure to have a couple extra bits of each size too. I can go months without breaking a bit in aluminum but steel is a whole other game.

My 2 cents worth.
Mild steel is not that hard to work with.
There are many ways to drill or make a hole.
For holes 1/2 or smaller step up drilling might work and might not. What i mean is as your stepping up in drill size the drill bit could shift or flex making the hole more and more off center. What you could try is drill a 1/8 hole first. Then make sure its centered. Then drill to size or just under final hole size and use a reamer.
As you are drilling/reaming holes try a sulfur base cutting fluid.
For holes larger than 1/2 inch a boring bar cutter or drill & reamer.
If your drill/cutters are sharp. You don't need that much pressure to cut/drill steel.
If its heating up/smoking use less rpm & pressure. More cutting fluid.

I,d center drill it first, then with rpm's down to around 280 to 300 just go with the 10mm and peck it down. And use coolant!

I,d center drill it first, then with rpm's down to around 280 to 300 just go with the 10mm and peck it down. And use coolant!

Thats another way of what i mean in my last post. Thank You:)
But if you want a good hole use a Reamer.