Blade Chatter

[rmack]

 

  Is there a simple explanation why, at the same cutting speed, some parts of the board will be smooth cut while other parts have a rougher surface?

[POSTON WIDEHEAD]

Have you tried a different blade?

[rmack]

Have you tried a different blade?

The blade is brand new out of box, did it from the first cut. still don't understand how it could cut fine and not in the same cut.

If you notice, it cuts nice through a knot on one piece, and chatters through the knot/crotch on another.

[Peter Drouin]

Blade is slowing down at the end of the log , be my guess

[MartyParsons]

Hello,
I see this with a new customer, most times sawing to slow. At the start of the cut and the end of the cut. Increase sawing speed. Some hook angles seem to make this occur more offten.
Marty

[tyb525]

I agree with Marty, sawing too slow. What I usually do, is enter then log slowly, and once the body of the blade is in the log, speed up as fast as I can to the normal speed.

Sometimes in a really wide cut when I can't go fast enough, I will get chatter like that. You might check your blade tension also. I set my blade tight enough that it doesn't flutter or vibrate at operating speed.

Really that chatter won't hurt anything if you're going to plane the boards, but I would try to avoid it.

[Tom L]

I get that when I start too slow with 7 degree blades. seems like the only blade angle that chatters like that at the start. I don't have the problem with any other blade profiles

[rmack]

guess I'm going to have to man up and giv'er some speed. 

I imagine the broken blade report will be soon to follow  :D

[drobertson]

If you have'nt already, check the blade roller clearances, and the top set screw between the band wheels, set it with a 1/16th clearance,

[tyb525]

Too much speed shouldn't break the band, you'll hear the engine lugging real bad before that happens. As WM says, you should cut as fast as you can while still maintaining a straight cut.

[pineywoods]

Yer drive belt is slipping.. probably on the crankshaft pulley. I have found I can duplicate the problem at will by deliberately slipping the drive belt. If the belt is tight within specs, try a shot of belt dressing...

[thecfarm]

No expect by a long ways. But breaking blades is the least of my worries. I have not done a lot of sawing,but I think I have only broke one blade in 8 years. I have probably gone through only 50 blades too.

[5quarter]

I always enter the wood at or near regular sawing speed. It feels counter-intuitive at first but becomes second nature after awhile. If you are already in the habit of sawing too fast, pineywoods would be right. the harder you push your saw, the greater the demand for power from your engine. A loose drive belt lowers your available HP and will cause that intermittent blade chatter. same conditions with a tight drive belt will pull down the rpms if you're trying to saw too fast. Another thing to concider is that if a log has been sitting around for awhile, the ends will be drier than the middle. By itself probably not enough to make a significant difference, but can definitely change the calculus depending on your saw and sawing style.

[Brucer]

That's a classic pattern caused by the blade resonating. Think of a guitar string -- it vibrates at a certain frequency which is called the natural frequency.

On a sawmill, the blade's natural frequency depends on the blade tension, it's width & thickness, and the length between the "supports" (which would be the blade guides in most cases). That's exactly the same factors that affect the frequency of a guitar string.

If you were to rapidly pluck a guitar string at exactly it's natural frequency it will start to resonate. It will flutter (and get louder and louder) until it distorts (or breaks).

What's happening here is something is forcing the blade to vibrate at close to its natural frequency. There's a whole bunch of factors involved.
- blade tension.
- thickness & width of blade.
- distance between blade guide wheels.
- tooth spacing.
- carriage travel speed.
- width of the cut.
- resistance to cutting (wood species, sharpness of blade).
- tooth hook angle.
- dryness of wood.
- density of wood.
- amount of set.
- amount of lubrication.
- amount of buildup on the blade.

So what you have is a combination of factors that just happen to cause the blade to resonate at certain places in the log. Change some of the factors I mentioned and it will go away.

Usually I try to kill off the vibration by changing the blade tension and the rate of blade lube. Up or down doesn't matter.

[rmack]

thanks for the suggestions, I started with increasing the speed and that does seem to help in the drier wood. I'll check the belt tension tomorrow just to refresh myself on how to do it if nothing else.

It is just starting to dawn on me how fast this saw can be 

  run through a log. 

I did manage to get some dunnage cut, and though the crooked end cuts make the cants look out of square, they are actually pretty close. 

[tyb525]

I always enter the wood at or near regular sawing speed.

That's interesting, if it works for you then it works, my WM manual says to enter slowly until the blade is in the log, then speed up.

[Brucer]

A Super with a 35 HP diesel should move through the wood pretty darn quick. It took me quite a while to realize I could push the cutting speed until the motor started to bog down a little.

Given sharp blades, properly aligned and properly set, the most likely cause of wavy cuts is the blade slowing down in the wood. You don't want the motor speed to drop enough for that to happen. On the other hand you want to keep your carriage speed up so each tooth is making the fewest possible number of passes through the log. That way you get the maximum BF before your blade starts to dull.

The main reason for slowing down when you enter a cut is to avoid the blade slowing down too much when it first hits the log. It takes a half second or so for the governor to get the motor back up to speed and during that time you can get some ripple at the start of the cut. A gas engine is much more sensitive than a diesel to this. Electric is even less sensitive.

How much you have to slow down also depends on species and width of cut.

[Tee]

This post has helped me as well. I've had this in the first inch or two of most cuts and now know somethings to look for. I think the blades I have are 10 degrees and cutting SYP.