View Full Version : Broken drill bit
02-17-2005, 02:03 AM
So I'm drilling into some W1 drill rod tonight and bam! Broke my drill bit. Think my speed was too slow but not exactly sure since I'm still learning. Any options before ditching the work piece? Import HSS bit.
02-17-2005, 02:36 AM
You may have to anneal it - it may have overheated and hardened as you drilled it. You should be using a 135° split point drill when working with hardeneable material and it is very important that you feed at least .003" per rev if possible as this will get the cutting edge under the work hardened layer (critical with stainless steel like 304 that work harden badly)
Get a better drill set when you can afford them (stubby drills are the stiffest) - import drills can be marginal at best - something you learn the hard way (by buying them) - false economy to buy "cheap drills" that never hold their edge or snap like glass.
Make sure that you have the W-1 securely clamped - if you were holding it yourself - you drill probably broke because the work moved or twisted.
FOLLOW SAFETY PROCEDURES ALWAYS - clamping work before drilling it is not an option - it is a requirement! I have a toolmaker friend (that should have known better) that got lazy once - the drill press nearly removed his thumb when it slipped down into a t-stot and the piece caught on the drill bit and swung around, and WHACK! Blood all over hells half acre. He almost died from blood loss...
02-17-2005, 12:15 PM
Thrud, thanks. Damn import drills and US drills look the same when your buying them in the typical 115pc sets. I can't tell the damn difference and I know some our the same. I do know that mine our 118deg. So should I heat this thing up cherry red and then let it cool? Then drill it out with another HSS bit? Actually I do have a few cobalt bits that I could use. Thanks for the tip on hardable material, drill rod is the hardest I think I've done. When I looked at my drilling speed I think it was too slow 500rpm with a 1/8" bit. I think it should have been much faster.
Actually, this is going to sound sadistic but I think that anyone who doesn't clamp down the piece should try drilling while holding the work in their hands. This would at least make them understand WHY the work HAS to be clamped to the table. When I was younger, I chucked a 1/2" end mill in the drillpress trying to mill a shallow slot in the top of a piece of wood (while holding it aginst the table). I'll never forget the feeling of that piece of wood being jerked out of my hands and across the room. After that I said "no more". I always clamp to the table.
[This message has been edited by kenrinc (edited 02-17-2005).]
02-17-2005, 12:45 PM
Ken A simple speed formula for tool steels and O1 ECT. IS TO TAKE THE NUMBER 160 AND DIVIDE THE DRILL DIAMETER INTO IT. wORKS FOR ME ON D 2 A2 AND SO ON. vERY IMPORTANT USE A GOOD WATER SOLUBLE COOLANT AND APPLY WITH A HAND HELD SQUIRT BOTTLE.
If the broken drill is HSS, you most likely aren't going to anneal it by just heating it up and letting it cool. You need a very precise heating/cooling curve (read: "computer-controled heat-treat furnace") to anneal HSS reliably.
You might be able to drill it out with a carbide drill or burr, but be really careful or you'll break the carbide.....
02-17-2005, 02:04 PM
You probably won't have any luck drilling HSS even with carbide. Any chance you can drill from the other side then punch it out or if it's not too deep you can try to chip it up with a punch. I did that with a 1/4x20 tap in an aluminum casting once. Its not good on the punch tho.
One other option if the workpiece allows it is to make a hollow end mill (see recent discussion about that), cut out a plug containing the broken drill, insert a solid replacement plug with Loctite 609, and re-drill.
02-18-2005, 04:21 PM
FWIW I thought I'd update you on what I finally did. The bit had started to go through on the far side. That's probably why it broke. There was a little tiny dimple on the other side so I hit it with a prick punch and that loosened the bit. I made a smaller punch with some 1/8in drill rod and then wailed on it somemore. After about 1/2 hour it finally broke loose. Work piece was saved.
I've noticed this drill rod I have is soft in places. All of a sudden I'll be drilling and I'll plunge away and then hit a hard spot and sit there forever...