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Yesterday, I dismantled an old solid-oak desk. I had planned to rebuild it, which would have involved making a brand-new tabletop. But on closer inspection, I discovered that the structural design was flawed, which explained why the beat-up old tabletop had split in several places. So I decided to simply dismantle it, and salvage as much of the wood as possible.

Several #10 reinforcing screws that I had added about 25 years ago broke off during disassembly. So before storing the wood on my lumber rack, I marked the locations of all the broken screws, and set about slicing the wood into usable screw-free pieces. But then I got in a hurry, and ran the saw blade right into a screw that I was attempting to cut away.

Of course, my good glue-line rip blade was mounted on the Mark V, and I was sure that I had wrecked it. It's a Freud LM75R010 with triple-chip grind. And when everything is set up properly, it makes beautiful cuts indeed.
The funny thing was, I didn't even know that I had hit the screw until I saw it's shiny new surface in the cutoff piece. There was not even a difference in the cutting sound, at least that I noticed.
Fully expecting to find chipped teeth on the blade, I inspected all of them. No visible damage. Then I felt the edges for sharpness. Only the left side of the teeth hit the screw, and the left edges still felt exactly like the right edges. Then I made a couple of test cuts, and still found no sign of blade damage.

So the carbide was the clear winner in this contest. I'm accustomed to seeing carbide tooling cut all manner of steel in machine tools, but was still surprised that an ordinary wood saw blade could make a cut like that and come out unscathed. Score one for Freud's "TiCo Hi-density carbide with titanium"!

Glad to know that I can now blindly start cutting through my pallet stack .....

I am amazed that it didn't damage the saw blade. Do you think you dodged a bullet on this, or are these blades that tough?

Believe it or not, I bandsawed a screw, almost that bad, one time, and the bandsaw blade really wasn't that upset about it. But running MDF through the bandsaw was a different story: dull city!


Chris

rjent wrote:Glad to know that I can now blindly start cutting through my pallet stack .....

I am amazed that it didn't damage the saw blade. Do you think you dodged a bullet on this, or are these blades that tough?

It's hard to say. For starters, those screws are obviously made of very mild (read crappy) steel, or else they wouldn't have twisted off when I went to unscrew them.

Carbide is much harder than steel. But it's also pretty brittle, and it will chip under excessive pressure, especially if impact is involved. How brittle depends on the carbide formulation. And unlike a turning tool, the teeth on a saw blade are going to see a pretty significant impact each time they hit metal.

For industrial metal-cutting applications, one generally buys tools that are engineered for a particular application, and the tool manufacturer has already verified that the carbide is up to the job. In some applications, HSS is still used for production tooling simply because carbide is too brittle. So personally, I don't plan to perform any more steel-cutting tests with my good saw blades!

nuhobby wrote:Believe it or not, I bandsawed a screw, almost that bad, one time, and the bandsaw blade really wasn't that upset about it. But running MDF through the bandsaw was a different story: dull city!

Chris

That actually makes some sense. When using high-speed steel tooling in production machine tools, the abrasiveness of the workpiece material can be a better predictor of tool life than its hardness.

You got lucky. Don't count on that for all times and don't be surprised if you find that you have thrown some carbide in the near future. Just hope that if you do throw carbide that it goes into the saw guard.

That is why I keep an old cheap carbide blade around for cutting questionable material.

Even if you throw a tooth it can be replaced, this spring I took in my Freud 80 tooth compound miter blade for sharpening, the place I take it to exrays them and found a bad tooth and replaced it b4 it could break loose.

Well at least Dennis, you have a cutaway woodscrew/wood block to show everyone how a wood screw works ....