Climbing blade.

[Brucer]

Think about this one for a bit if you like to solve puzzles. I'll give you the answer at the end.

Seven years ago my friend, John, figured he was going to have trouble operating his circle mill after he fell out of his hayloft and broke his back. So he bought a hydraulic LT40HDG28 just like mine. Three years ago he found out I'd bought a used sharpener and setter, so he asked me to sharpen his blades for him (for a fair price, of course). I somewhat reluctantly agreed, but it's worked out OK.

I was talking to John yesterday and he told me he'd opened up a brand new box of his regular blades (1.5", 0.050, 10°) and put one on the mill. It promptly tried to climb out of the log. He felt a couple of teeth -- still razor sharp. So he tried a second cut 3" deeper in the log. Same thing. So he set that blade aside, took another one out of the box, and it cut fine. Then he noticed that there were only 8 blades in the box instead of ten.

A quick call to Wood-Mizer and they said they'd send him the missing blades, but they'd like to have a look at the problem one to see if they could figure out what was wrong.

I drove out to his place today with a dozen blades I'd sharpened for him and he showed me the climbing blade. I took a careful look at a couple of spots and it sure seemed that the teeth were equally set on both sides. I scanned the blade from the side looking for broken teeth and they were all intact. I check a few teeth at random and they were all sharp as well. So I offered to bring it home and use the setter to measure what the exact set was on both sides.

What I discovered explained the tendency to climb and also gave a hint as to why their were only 8 blades in the box. Want to guess (or analyze)??

Here's what I found. With my old single tooth setter, I first checked the inside teeth, starting at the weld. I kept finding the same readings -- 0.026 to 0.027, tooth after tooth. The odd tooth would be another half thou either way, well within specs. But then, half way around the blade, I started getting readings in the 0.029 - 0.030 range. After a couple of those I was up to 0.031 - 0.033. A bit further on it was 0.034 - 0.035. The last three teeth before I got back to the weld were 0.037"  .

The outside of the blade remained consistent at 0.027 to 0.029 the whole way around. No wonder the blade was climbing.

Once I knew what the problem was, I could look at the blade on either side of the weld and see the difference in set on the inside teeth. But because I'd only looked at a couple of locations when I was at John's place, I didn't spot it.

I suspect when the blades were being set at the factory, the setter on one side started to get out of adjustment so it started bending teeth progressively further until the blade was finished (at the weld). When the next blade was put into the setter the inside teeth would have been way off to start with and somebody probably noticed. Perhaps the machine even checks itself at the start of each blade. In either case, the production line would have been halted while the setting problem was fixed. The blade that was only partly bad was the last one put in the box (and therefore the first one John removed). So somehow, the almost full box got closed up and sent on it's way.

I guessed a lot of things but I had to put the blade in the setter before I got the right answer.