Hi,
I just bought a new blade for my miter saw, to replace the not-so-good blade that came with the saw. The new blade, a 90-tooth crosscutting Hitachi blade, is supposed to produce a clean cut with little tear-out. And on softwood the results are fine. But on wider pieces of hardwood (even not-so-hard hardwood, like poplar) the blade is producing a weird bowl-like indent on the cut face. It’s as if the blade is cutting a wider kerf at the top of the cut, and then gets on track and produces a narrower cut as it moves down through the wood. Not sure that makes any sense (sorry, it’s kind of hard to describe). The bottom line is that, if you look at the cut face, you see this very pronounced bowl-shaped indent at the top of the cut.
Any idea what could be causing this? The old blade, cheap as it was, didn’t produce this effect, and I’ve double-checked the setup of the saw, so I don’t think it’s a problem with the saw. Should I assume that the blade is flawed and send it back, or is there something I should try before doing that?
The blade is advertised as thin-kerf, but my understanding is that at 0.110, it’s not that thin, compared with other thin-kerf blades.
Thanks for any guidance you can provide.
Replies
I can suggest two possible things that may be causing your problem, providing that your arbor is not bent. First I would check the way you mounted the blade. Is it setting perfectly flat against the mounting plate on the saw? If you have a washer in behind the blade and the mounting plate it may be that you've bowed the blade when you tightened it onto the mount, with the outer cupped retainer. Believe it or not I've been a wood worker for 25 years or more and I've actually done this. Another problem may be that the blade is just too thin and distorts under the RPM's of rotation. Lift up the guard , crank it up and watch the blade from the front to see if it's wobbling, and be sure to wear your saftey glasses. Thinner, inexpensive blades do have a tendency to do this.
Thanks for the suggestions. I'm 99 percent sure that the arbor is not bent, because when I put on the old blade, the saw produces a straight (albeit, raggedy) cut. I tried remounting the new blade and the problem continued. So I'm assuming that either the blade is just too thin, or it's flawed. I'm leaning toward the latter, especially because I've noticed that after only a dozen cuts, there's a heavy buildup of resin-like stuff on some teeth but not on others. My interpretation, which is just a guess, is that the blade is bent or out of round. Whether that's right or wrong, I may never know, but I'm going to try to return the blade to the seller.
Thanks again.
Harmonics
From your description, it sounds like you are encountering what is called harmonic distortion, the blade vibrates like a struck gong as the cut is starting and then settles down after the blade is stabilized by the sides of the cut.
Watch when the cut starts, you'll probably see that the blade, where it touches the wood, blurs from the side to side vibration for a fraction of a second as the cut is started. Often times you will also hear the blade ring with a high pitched note. Could be a badly designed or badly made blade, although a lightly made or worn machine can contribute to the problem. The problem is generally worse with larger diameter and thinner blades. Unless your saw is underpowered I wouldn't use a thin kerf blade for precision cutting because they tend to do this. Was the blade meant for use in a chop saw and is it a 12" blade?
Sometimes you can minimize the problem by changing the feed rate, try a faster feed, and don't hesitate once you start the cut, and see what happens.
You didn't state what the diameter of the blade is, but if the kerf is 0.110" on a 12" blade, that's still fairly thin for such a large span. I've had plenty of good results from 10" blades with a kerf in the 0.098" range, but I typically recommend a full 1/8" (0.125") kerf for a 12" blade. Have you tried a stiffener at all?
Are you making an off-cut?
It could possibly be caused by blade deflection if your cut is just shaving off a little bit of the end and the cutting forces are not equal on both sides of the blade. Try cutting an inch or more off and see if the problem continues.
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