I work for a printing company, and our paper cutter has developed an unusual problem-- the blade cuts OK at both ends, but not in the middle. I think the sharpening service is suddenly not grinding them straight anymore. Before I accuse them of screwing up our blades, I'd like to know what a typical tolerance would be for a blade that's 43" long and
3/8" thick.I measured one of the blades with my Chinese digital caliper, and found that it was .02" wider at both ends than it was in the middle. Even assuming some error in my measuring, that seems like too much, considering that some of our paper is only .003" thick. The blade cuts into a sacrificial plastic "cutting stick" which is replaced frequently-- I found a note that says it should cut into the stick by about .004". I'm sure we're setting it deeper than that to get a clean cut, and it's making the blades get dull faster.
The blade is adjustable for angle, so it's OK if it's slightly tapered, as long as the edge is straight. The last person who changed the blade told me that when she adjusted the angle so it cut at both ends, she could still see daylight under the middle of the blade. I haven't checked the cutter's table with a straightedge, but I'd be surprised if it was warped that much.
Any guesses as to how they managed to grind a curve into our blades? If I'm right, they've done this more than once, over a couple of months.