How (not) to drill metal sheet?

As it will when you put your weight on a pedestaI drill so much that it begins to squeal! This has happened to me plenty of times when trying to utilise bits of scrap that looked the right size but turned out to be made of the wrong stuff. I've melted cheap drill ends more than once, as I'm sure others here must have done.

think you are confusing this with the bit polishing

Wot: not try the proper approach in advance!?

Your info on drill types is welcome and handy, in making that choice, but most of us don't have much of a selection, and have to make best use of what we have. In many cases we will just have a box of drills and are lucky enough if we have one the right size that still works, let alone one of the ideal material. The OP probably just picked up what looked like a handy sized piece of scrap for the job, and only found its properties beyond his equipment once started. Grinding out the hole he has may get him out of trouble - and it certainly has for me on a number of occasions. Also, most of the common tool sources like Screwfix tell one precious little about what one is actually buying (Shudder to think of the number of use once and throw away masonry drills I've bought afer reading ads that simply lie about what they can do!)

Your handy list will help me choose my next set of drills.

An HSS twist drill, which has been ground correctly

You will find that C1150 and D 200 very hard to source. I have tried two engineering suppliers and they hadn't even heard of them. I suspect you would have to contact Dormer for info on them.

John wrote: Alternatively, use one of the TCT wonder drills that

Sounds interesting. Got any brand names?

they are the metal cutting carbide drills that I mentioned in the earlier post,don't know the brand.

Most seem to be tiny drills and burrs for the jewellery purposes but there are more links such as: