|Forum topic by Tog||posted 09-17-2012 02:25 AM||1272 views||0 times favorited||9 replies|
09-17-2012 02:25 AM
I just had a disturbing experience with a resharpened table saw blade and I’d like to know if my expectations are out of line or if it might have been damaged during sharpening.
I have a high quality 10” 40 tooth combination blade of a well known and highly respected brand. I’ve had it for about 20 years. It received light (hobby type) use for the first 10 years and has been unused, mounted on my saw for the last 10 years. (Finally got the time, space, and motivation to get my shop set up again after a move, career, etc.)
I sent the blade out to be resharpened at a facility recommended by the manufacturer. They replaced 2 teeth and resharpened the rest. I got the blade back and proceeded to mount it on my saw, doing what I always did in the past, which is putting a block of soft scrap wood on the back side of the blade to keep it from turning while I tightened the nut. While tightening, the blade slipped a couple of times, but I didn’t think anything of it. I didn’t think I was applying unusual pressure. When I was done, I noticed with horror that the two teeth that had slipped against the wood block were badly damaged. This wasn’t a failure of the braze; the carbide material itself was split down the middle; the back half was still attached to the blade and the front half had fallen off. (These were NOT the teeth that had been replaced.)
So I took the blade off and began examining the other teeth. I tapped each one lightly with a block of soft wood, about like you would tap someone on the shoulder to get their attention. With this light tapping, 3 more teeth split in the same way, right down the middle of the carbide.
I know carbide is hard but brittle, so it’s prone to chip and crack. When it slipped against the block while tightening, that was putting pressure on it in the opposite direction from the normal case when it’s cutting. That said, it still seems to me that these moderate forces shouldn’t be enough to actually fracture the carbide. Or am I wrong? Is C4 carbide really usually this fragile? Might the teeth have been damaged by improper sharpening (e.g. not enough coolant)?
I’m undecided about having the teeth repaired, not sure I would trust it again.