I may have mentioned before that it’s really hard to drill a hole through composite steel, since (sometimes) the metal hardens from the heat of drilling through the layers. Thus, you get a ways into the piece and think “this is going well” and suddenly all activity ceases until you re-anneal the work.
Now that I understand what’s going on, I can handle it predictably, but it’s still not a lot of fun. The last carbide bar I made, I had a brilliant idea: “why not drill it when it’s red hot?”
Here’s why not; this is something you probably have never seen before:
It’s thermodynamics 101: the contact-point between the drill and the hot steel is small, but it’s going to transmit heat fairly quickly. At that point, the smallness of the drill kicks in – it can’t shed the heat very quickly, either. Then it starts to melt.
This was a hand feeling I have never experienced, before. Everything was (apparently) proceeding fairly smoothly but suddenly the drill went forward quickly and I pulled it back, thinking it had pierced through the work-piece. Imagine my consternation when I looked at the glowing red-hot bar and couldn’t see any sign of a hole. Then, I looked at the drill.
By the way, I was wearing welding gloves, so if I had whacked a knuckle on the bar, it would have alerted me to that fact when my gloves started to smoke.
Deploying patience allows you to give the steel an annealing cycle or two. Drill it a bit, heat it and anneal it, drill it a bit, etc. Then, when the hole is all the way through, it’s time to run an 8-32 tap through it. Normally, tapping annealed steel is easy, but in this case there are randomly located layers of hard stuff as well as soft stuff. It took me about 1/2 hour with a hand tapping wrench to carefully tap the hole. I managed it without breaking a tap. Breaking a tap is not merely a badge of dishonor for a machinist, it’s a nightmare: now you have a piece of ultra-hard tool steel threaded into your work-piece and if you’re not extremely lucky in how the tap breaks, so you can get pliers on it and get it out, you’re left trying to drill a hole in the tap for a screw extractor. Basically, it’s time to break out a diamond drill. Or, you grab a chop-saw and cut the end off the work-piece, fire up the forging press, and make a new end. “Knife-makers don’t make mistakes, they make shorter, thinner knives.”