Farmerford
Platinum Member
- Joined
- Dec 9, 2006
- Messages
- 733
- Location
- Columbus, Georgia
- Tractor
- Kuborta B2400, L2900, L4330; Caterpillar D3B, John Deere 455D
I used to work for a company that made cutter blades, and we heat treated them all to about Rockwell C 40-44. I imagine the newer blades are about the same hardness. I now modify those blades by sawing off the cutting edge and drilling 5/8" holes in them to attach stump grinder teeth.
I can saw the blades with high speed steel metal cutting band saw blades using light pressure and plenty of cutting fluid, although the band saw blade dulls noticeably after cutting several.
But I have never had much luck drilling them with steel twist drills, even the better brand cobalt steel coated ones. The cutting edge of a twist drill is so sharp and thin (relatively) that it overheats and dulls before penetrating the surface (which is sigificantly harder than the core).
I finally bought a straight flute carbide tipped drill bit (McMaster Carr, about $60 for 5/8"). You must use a drill press, and a reasonably tight one, but if you do (and are careful) the carbide drills without significant dulling. I have drilled at least a dozen holes in 1/2" and 5/8" thick hardened blades and the drill is still sharp. If it dulls, it can be sharpened by a standard drill sharpener with a diamond wheel.
A word of caution if you use a carbide drill. Tungsten carbide is very brittle and you must avoid localized pressure. For example, if you withdraw the bit half way through the hole and a metal chip falls into the hole, do not restart the bit without removing the metal chip. If the chip is caught under the edge of the bit and you apply much pressure to cut through the chip, you may crack the edge of the bit where it contacts the chip because all of the downpressure is localized at the chip.
I can saw the blades with high speed steel metal cutting band saw blades using light pressure and plenty of cutting fluid, although the band saw blade dulls noticeably after cutting several.
But I have never had much luck drilling them with steel twist drills, even the better brand cobalt steel coated ones. The cutting edge of a twist drill is so sharp and thin (relatively) that it overheats and dulls before penetrating the surface (which is sigificantly harder than the core).
I finally bought a straight flute carbide tipped drill bit (McMaster Carr, about $60 for 5/8"). You must use a drill press, and a reasonably tight one, but if you do (and are careful) the carbide drills without significant dulling. I have drilled at least a dozen holes in 1/2" and 5/8" thick hardened blades and the drill is still sharp. If it dulls, it can be sharpened by a standard drill sharpener with a diamond wheel.
A word of caution if you use a carbide drill. Tungsten carbide is very brittle and you must avoid localized pressure. For example, if you withdraw the bit half way through the hole and a metal chip falls into the hole, do not restart the bit without removing the metal chip. If the chip is caught under the edge of the bit and you apply much pressure to cut through the chip, you may crack the edge of the bit where it contacts the chip because all of the downpressure is localized at the chip.
. That said, even with it, your bits will only be as good as the steel they're made of. So if your using Big Box store bits,or worse..Horrible Freight bits, now would be a good time to invest in some quality bits. Having a sharpener, you'll get YEARS out of a box of good bits.