So as I started a small project
A Chicago Screw to addapt my current Tool Post Stud to be used with the new QCTP
Cool project... Anything named after Chicago just sounds better....
So I have a 1/2” bolt grade 8 which I annealed.
It doesn't really matter here, but you shouldn't need to (and probably don't want to) do that. Plain old cheeze grade drill bits will cut that bolt in it's as delivered condition just fine.
I started with a basic set of drill bits Bosch started with 3/16, 1/4, 5/16 and finally 11/32
There's the first problem I see. Step drilling has a place, but for basic drilling, stepping up a sixteenth at a time, that's one thirty second per cutting lip on the drill... There's not enough engagement to keep it centered up and working as it should. The last step, one thirty second on the diameter, one sixty fourth on the cutting lips, it's gonna act up if the slightest breeze picks up two towns away from you.
Everything went fine until I got to the 11/32 bit , screamed like a banshee
I've never heard a banshee scream, but I'd bet the drill bit was moving, the fluts digging in and popping out unevenly... Basically chatter.
, so I figure old bit I will run and buy a new one. I come back and the new bit cuts worse?
Even the slightest (absolute slightest) difference in a drill bit in a bad situation will act very differently. That sounds about right. You can actually use that to your advantage sometimes in a pinch.
I have my spindle speed right at 1000 rpm
At the moment. All other bits cut fine to a depth of 2-1/2”
I'd probably back that speed off a little, but at 11/32, it should be very doable at that speed. It'll want a fairly quick feed rate though. And some meat to cut. For a one time setup, no production line pieces, I'd probably pick a speed at five or six hundred for the whole thing and never look back. If I was making a dozens I might worry more about finding the most productive speed with each drill size.
Well yeah.... Same thing I'm missing every time things don't go my way.... And if you ever figure out what it is, I want to know....
This is one off those things where there is a lot of ways to skin a cat. And they're not all wrong. My way, were it me, and were I taking this project on from scratch, I'd "dimple" a center with whatever center drill was handy. (The drill point, NOT the actual center profile). Just enough to cradle the web/split point of the drill I was going to use. I'd be inclined to grab a 5/32 pilot drill, because that's what I keep for that use, and plow that in as far as it comfortably goes. Or maybe 3/16 if I had to pick one out of the index, as I think that's the first one that'll hit your two and a half inches. Then I'd go right to the 11/32 drill bit (which probably won't be deep enough to have a pilot all the way, and it won't matter at that size). And just feed it steady, stopping to clear the chips as needed. That 11/32 drill bit should be plenty able to plow it's own hole from scratch, it'll easily follow a pilot in that range, and by the time it "bottoms" if the pilot is short, it'll be well supported and guided by the time it gets to the bottom of the pilot and starts to clear it's own center. Getting the majority of the cutting lip engaged makes the whole thing go a lot smoother. And your drills last longer.
You can indeed work harden grade 8 bolts if you try to "careful" with them too much, but they're usually not bad. Keep chips coming out (not dust from a one sixty fourth depth of cut/one thirty second on diameter), and they're usually pretty decent to work with. I doubt you actually did that here, as with that small of an engagement, I honestly think you'd have wrecked your drill if the metal turned hard on you.
