Stuck cotter pin

Basically I have a cotter pin stuck and want suggestions on how to get it out, you can disregard the majority of everything else in this post, I just want to rant.

I recently took my bike into the shop as I thought the bearing were failing in the crank - the crank is the only thing I can't touch, I can work on the gear hub and everything else but I always mess cranks up - as it turned out they were fine and the metallic gunge could have been anything (The bike is probably around 80 years old now) so the crank was re-assembled and the existing cotters were re-used as the shop did not have any that would fit.

I had some cotters spare that would fit, I had used two in there earlier and I had three left. I removed the old one no problem (Using a hammer and a length of wood to support the arm) and picked up one of the new ones, I hammered it in but it jammed halfway and would not move. I managed to get this one out and found the metal was stripped on one edge - the axle is fine though.

I grabbed another pin and lined everything up again, I smashed it in as hard as I could and it got stuck halfway, I tried hammering it back out and it shifted by about half a centimeter and would not move further, I tried hammering it back in a little and it would no longer do that. I then heated the metal (ruining the paint somewhat) but it still won't hammer out, I then tried drilling a thin hole into the cotter pin with my strongest metal drill bits, but it will not go into the metal at all. Finally I tried hitting it again, but nothing happened. I should add that I have been feeding it penetrating oil constantly to ease it off, but no luck. Does anybody have any ideas? I don't want to replace the crank and I doubt I could find another chainwheel to fit (This is on the chainwheel side too which makes things very difficult).

I don't know if I can help, but:
First the axle is case hardened, and is harder than your drills.
The cotter usually is fairly soft. Normal fitting, tap cotter in gently to test the size of the flat, then file the flat to the required depth, keeping the angle.
It might be possible to ride the bike a little to see if it loosens.
If you have a round punch with a flat end up to about 1/4 inch, and can find something like a mole grip to hold it (keeps fingers out of the way) then hit it firmly with with a lightish hammer.
If drilling is needed use something like a 1/8 inch to start, and drill from either or both ends, bearing in mind where the flats on the axle are.

Thanks, I tried all of that, eventually, I gave in and found some stronger drill bits - as the ones I was using were apparently not good enough and would not go into the pin at all (I thought it was going in, but it turned out the cotter was filing the end of the drill bit off - kind of funny I suppose). I managed to drill into the cotter and remove what was left with a hammer and punch, but I have taken a little chunk out of my pedal arm (at the end the cotter is supposed to be hammered into) - I can not replace the arm, or at least, I won't likely be able to, what kind of negative effects can I expect to see? It's not large, but there will be a gap on the inside of the hole. Realistically I know I probably shouldn't ride it at all in such a state.

At least my crank axle is OK I suppose, but there was no chance of my drill going through that anyway. Incidentally, my drill is now ruined, it's been sick for a while and I don't think I'll be able to repair it again, I'll miss that drill.

Glad you got it out. The damage to the crank should not matter, just fit the cotter pins carefully, filing as needed. We used to frequently see cranks stretch the bracket axle hole, the cotter pin will pull it tight.