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Is bronze grabby?
- Thread starter NCjeeper
- Start date
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- Jun 7, 2013
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- 10,111
Quality bits do not untwist ---
- Joined
- Sep 2, 2013
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- 378
Resharpen that one and you'll have your self a good stubby drill.
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- Feb 1, 2015
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- 9,640
Getting the right temper on steel has always been a problem. Manufactures with legal beagle looking over their shoulders will error on the side of being too soft which can result in the drill unwinding. Those that are looking for a hard cutting edge have drills that can shatter as in the first post. These usually are found in products with inferior grades of steel where the window for a tool that is both tough and hard is narrower.
Many years ago, I had a flat blade screwdriver that twisted with a reasonable amount of torque. The screwdriver was made by Stanley which was formerly Atha Tool Works, a respected tool manufacturer 100 years ago. I wrote to the company, stating I would rather have the tip fail by breaking (as my Craftsman screwdrivers did) than twisting into a corkscrew. I got a new screwdriver in reply.
Fast forward some forty years and my wife bough a dozen office chairs for her business. They came disassemble and required assembly with a 5mm Allen wrench which was provided. Even though I was using judicious force in assembly, they would round the corners and /or twist the shaft. I managed to get the dozen chairs assembled and even had a couple of unused wrenches left over.
Some time later, I was going to make some custom wrenches and decided to try to reharden and temper the wrenches. The result was a wrench that performed as well as my name brand wrenches. My guess is that plain medium or high carbon steel rather than more exotic is being used and the manufacturers are not properly hardening and tempering for whatever reason.
Many years ago, I had a flat blade screwdriver that twisted with a reasonable amount of torque. The screwdriver was made by Stanley which was formerly Atha Tool Works, a respected tool manufacturer 100 years ago. I wrote to the company, stating I would rather have the tip fail by breaking (as my Craftsman screwdrivers did) than twisting into a corkscrew. I got a new screwdriver in reply.
Fast forward some forty years and my wife bough a dozen office chairs for her business. They came disassemble and required assembly with a 5mm Allen wrench which was provided. Even though I was using judicious force in assembly, they would round the corners and /or twist the shaft. I managed to get the dozen chairs assembled and even had a couple of unused wrenches left over.
Some time later, I was going to make some custom wrenches and decided to try to reharden and temper the wrenches. The result was a wrench that performed as well as my name brand wrenches. My guess is that plain medium or high carbon steel rather than more exotic is being used and the manufacturers are not properly hardening and tempering for whatever reason.
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- Nov 14, 2020
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- Joined
- Sep 28, 2013
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- 4,318
a good rule of thumb when pre-drilling holes is to drill a hole the size of the tip or web of the main drill. Reduces cutting force but keeps the whole flute length engaged in the cut. Pre-drilling bigger than that allows the drill to walk around the hole, leading to chatter and oversized holes.
- Joined
- Nov 9, 2011
- Messages
- 253
Brass and bronze like zero-rake tools, because yes, they do grab. I have a set of drills modified by grinding a flat on the two cutting ends, they work great in brass, bronze, and some plastics. (The flat is ground to provide a small surface parallel to the length of the drill, ground in the cutting edges.) Drills will also grab when drilling into a hollow cylinder, where the outside edges take all the torque as the drill breaks through. I once had a 3/16" drill grab and shatter in such a cut, shot a piece of drill thru my lip and took out a tooth. I bought shields for my mill and lathe after that.
It looks to me like a couple of things going on.
Number one, a glass hard drill bit. Too hard (glass hard), or too soft of a drill bit is kind of a common thing in the cheapies. Some do work OK, but there's a very high occurance of what I believe to be heat treat failures. I've never had a broken drill bit look like that, but any time I've had one shatter that far along the flute (not a flute, opposite of flute... The only way that you couldn't brake a drill bit if you tried...), any time I've decided to science that, I've never had one fail to fail the hammer test. Set it on an anvil (even the back of a vice is an adequate anvil), and smack it with a hammer. You could break about any good drill bit, but if a good sharp hammer blow literally shatters the drill.... I'd bet yours would fail that test too. Then you know that that set isn't a candidate to drill important things with, unless you're OK with having half of a drill bit as a permanent feature of that project.
Number two, I'm looking at the cutting edge. I could be wrong, but it looks "normally" sharpened. Bronze, like brass, kind of likes little to no rake on the cutting edge. Otherwise the drilll wants to "thread" into the work. Not as bad as brass, but same idea. It leads to chatter, grabbyness, and general displeasure during the operation. Although a quality drill bit will usually get the job done as is.
Number three, and this might very well be situational, with technique, drill grind ("brassed" drills or regularly sharpened drills), but I have a lot better luck drilling a smaller pilot hole. Just enough to comfortably clear the web, and thereby engaging more of the cutting edges on the final size drill bit.
Number one, a glass hard drill bit. Too hard (glass hard), or too soft of a drill bit is kind of a common thing in the cheapies. Some do work OK, but there's a very high occurance of what I believe to be heat treat failures. I've never had a broken drill bit look like that, but any time I've had one shatter that far along the flute (not a flute, opposite of flute... The only way that you couldn't brake a drill bit if you tried...), any time I've decided to science that, I've never had one fail to fail the hammer test. Set it on an anvil (even the back of a vice is an adequate anvil), and smack it with a hammer. You could break about any good drill bit, but if a good sharp hammer blow literally shatters the drill.... I'd bet yours would fail that test too. Then you know that that set isn't a candidate to drill important things with, unless you're OK with having half of a drill bit as a permanent feature of that project.
Number two, I'm looking at the cutting edge. I could be wrong, but it looks "normally" sharpened. Bronze, like brass, kind of likes little to no rake on the cutting edge. Otherwise the drilll wants to "thread" into the work. Not as bad as brass, but same idea. It leads to chatter, grabbyness, and general displeasure during the operation. Although a quality drill bit will usually get the job done as is.
Number three, and this might very well be situational, with technique, drill grind ("brassed" drills or regularly sharpened drills), but I have a lot better luck drilling a smaller pilot hole. Just enough to comfortably clear the web, and thereby engaging more of the cutting edges on the final size drill bit.