I’ll start off by saying I’m no expert and I’m just sharing my own recent experience.
Last week I drilled a 1” thick piece of plate steel 15 rows by 15 rows for 225 total holes with the Fireball drill guide. I used one Hougen HSS 3/4”x2” cutter for 220 holes and one “Steel Dragon Tools” carbide 3/4”x2” cutter for the remaining 5 holes, using only WD-40 as cutting fluid. The mag drill was a borrowed Hougen 904 which did not have speed control.
I found that feel is the key here as well as making sure the drill is sitting flat in relation to the drill guide. If the top is bowed or there are metal chips under one or the other, that slight misalignment would make the cutter not want to start cutting no matter how hard I pulled on the handle. Any slight misalignment wouldn’t allow the cutter to grab and it would just be spinning against the drill bushing. I had to move the drill guide and drill the hole from another angle. I speculate that could potentially wear out a carbide cutter quickly if the carbide is chipping due to bad alignment.
But when everything was good, you’d feel the cutter grab and you’d kind of know how much more or less pressure you need to sustain that cut. I’d start the cut with a flood of WD in the hole with moderate pressure and I’d retract the cutter every now and then to spray it with WD and then keep going til it was through.
Oddly enough, about 200 holes in I decided to try a thick cutting fluid like rapid tap on a few holes and the cutter wouldn’t even grab. I actually thought I had burnt out the cutter, I was hanging on the handle trying to get it to start cutting. Switched back to WD and it cut fine again.
I only bough the carbide cutter because the HSS one would not cut a few spots that had weld repairs and were thus hardened. It’s a cheaper cutter, got it on eBay for $30 and it worked very well. I can’t speak to the longevity of it but I was impressed given the price.
Long story short, if you’re cutting mild steel, HSS and WD-40 can work very well. If you’re burning through carbide cutters, I would imagine something else is the issue. As someone else said, too light of pressure is also bad and can wear out a cutter prematurely because it gets hot instead of cutting and also work hardens the metal as it’s just rubbing on it.
