What causes this surface, grain or blade ?

[GeneWengert-WoodDoc]

I also support the idea of harmonic vibration of the blade.  (It is the same thing that causes an antenna on the car to vibrate and a specific pattern at a specific speed...the old, long antennas.)  The frequency (and therefore the vibration) can be changed by increasing the blade tension.  Also, if the blade is heating, then cooling (using a lube or even cold water) will make it stop.  Oftentimes, real fine dust will spill out of the gullets and rub the blade causing heat.  This is why a faster feed speed (if you have the power) will help or using a band blade that has a "skip tooth" will also work.  The width of the blade will change the frequency.  Also, keeping the guides as close to the log as possible will change the resonant frequency.

[5quarter]

  

[MartyParsons]

Hello,
I have seen this, I removed the blade and used a different hook angle and it went away. I think I was running a 7/34 and went to a 9/29. I  was getting lots of sawdust on the log with the 7/34 and the lines like on the picture. I had a 29 hp Kohler on a LT40 and I needed to saw faster to get ahead of the sawdust spill over.
The 9 degree solved the issue. The 9 degree has a lower tooth height and the set is lower, back angle would be 29 degree. The next log I put the 7/34 back on and the marks were gone. Different log species and smaller.
I dont think changing the mill alignment would help.
Hope this helps.
Marty

[Okrafarmer]

Some of you may have skipped right over my remark about "power hop" but I believe it is another example of harmonic imbalance. Seeing (or feeling it) in/on a 4X4 vehicle will help you understand how these kinds of things can happen on a larger scale.

Power hop is caused by the perfect storm of just the wrong tire pressure, just the wrong tread pattern, just the wrong ground surface consistency and texture, the wrong speed, poor weight distribution, and often, uneven terrain allowing one or more wheel to come off the ground at some point, along with the front and rear axle being direct coupled to each other (no mid-chassis differential or fluid coupling). The combination of all these dynamics causes the bucking bronco sensation that is known as power hop, and is experienced by ATV riders on up through articulated four-wheel drive tractors-- sometimes making a frustrated farmer have to stop and let some air out of his tires.

In aircraft, these kinds of phenomena have names like "flutter" and "compressibility"

[jackpine]

 I had never seen the type of saw marks that Tom  showed run the full length of the log before, until yesterday. White pine log that had been laying for three years on the ground, crooked and with a twist. Sawed 5 old logs before that one with only random marks but changed bands after slabbing because band was getting dull and leaving more of those marks. I had just set and sharpened some 10° bands so put a fresh one one and the marks ran the full length of the log. Pulled that band and put another on, same result. Tried more tension, less tension, more water, no water and at best got about 12" of smooth cut. Pulled that band and put a new one on, smooth  cut with only a few marks at random.

Today put one of the bands back on and cut some fresh red pine. Sawed great with no marks.

My conclusion is the same as some of those earlier, a combination of log properties and harmonics in the band coupled with the fact that the older bands have lost some of their beam strength.

[5quarter]

Hmm.

[Satamax]

Guys, i'm not a sawyer, but pretty sure i've seen this resawing wide planks with the bandsaw, with blades which had unequal set. Due to a problem of the toolsetter of the guy who sharpens my blades.

[Jay C. White Cloud]

Hi Satamax,

Sorry buddy, "tooth set" couldn't do this even if you wanted it to, the physics wouldn't work.

I use certain "hand set teeth" and "filling patterns" on both bandmill and chain saws mill to make "unusually kerfing patterns."  The challenge with any band mill, is if you your teeth are set "unequal" you can't saw a straight line because your blade will "dive" accordingly in the cut, rendery the job useless.

You could have seen it in a resawn board though; that is very possible because "harmonic kerfing patterns" can happen on any band saw blade, vertical or horizontal.  In vertical ones, tension and "push speed" are typically the solution as the blades cannot take the harmonics for long before they break or something else happens.

Regards,

jay

[Jay C. White Cloud]

Sorry, I am having troubles with my edit and load features on this laptop.  I forgot to ask if you had been doing the resawing yourself?

[frye]

 Had the exact same problem twice with some ash logs a month ago that had been cut down for 2 years.thought it was my blade! changed blade no more problems.but like what everybody else said I used the blade on another log, no problems. Thought it might have been bad set  like they say. Or the blade heats  up causing bad blade harmonics and expands and you have to retention your blade after you cut a few logs.I did find my roller guides where out of wack about 1/8" in a 6" span. Still don't know...good luck