Explain causes for rising and diving

[kelLOGg]

I accidently started raising the saw band before finishing the cut. The end of log had a large wedge cut in it for felling and from operator's viewpoint the band had exited the log. It rose about an inch before I noticed; I dropped it back and finished the cut. (I have a spring tensioner.) I started the next cut and the band immediately rose in the cut. I was cutting clear RO with a new out-of-the-box band and was getting nice straight cuts for a couple of logs. I removed the band and inspected the teeth. The up-pointing teeth (when sawing) had a shiny rounding at the cutting point which can be explained (I think) by the increased pressure on them due to raising before exiting. The down-pointing teeth had no shiny rounding. The up-pointing teeth had a set of 0.012 and the down-pointing teeth 0.015. (I didn't check the set prior to using the band but even the 0.015 set seems low to me.

Here's what I don't understand: Why did the band rise? I would expect it to dive. The up-pointing teeth are dull so they can't cut well and the down-pointing teeth are sharp so I would expect the band to follow the path of the down teeth. The model I have in my head for a band is like an airplane wing - slanted up its gonna rise and slanted down its gonna fall) but it must be a bad model. ???

This must be real basic stuff but I can't find info on it in the knowledge base.
Bob

[bandmiller2]

Bob, did you check to see if the band is still flat.??You put alot of tension pulling the band around the wheels and probibly cupped it. Frank C.

[Magicman]

This is just a different twist.  Maybe not the case in this instance, but certainly something to watch for in the future.

You stated that you were sawing "RO".  If this was a fairly large Red Oak log and you were entering the butt end, there is a possibility that the blade rising had nothing to do with the blade.  Some butt log ends have a great amount of tension and hardness and will oftentimes cause a sharp and properly set blade to rise for about 6" and then settle back down for the rest of the cut.  The next cut will be a mirror image causing the board ends to all have the same profile.


  

[kelLOGg]

Bob, did you check to see if the band is still flat.??You put alot of tension pulling the band around the wheels and probibly cupped it. Frank C.

No I didn't but that is a reasonable thing to check. Perhaps stressing the band acutely cupped mit?

If this was a fairly large Red Oak log and you were entering the butt end, there is a possibility that the blade rising had nothing to do with the blade.  Some butt log ends have a great amount of tension and hardness and will oftentimes cause a sharp and properly set blade to rise for about 6" and then settle back down for the rest of the cut.

Nope, I exited the butt.

Bob

[isawlogs]

 Here goes ... the rising cut is due to the fact that the blade is dull on the upper teeth, they when cutting are creating a drag from lack of sharpness, the lower teeth having good edges and beeing sharp cut and so the blade rises because of the drag caused by the none cutting teeth...
Much like a chainsaw that pulls to one side , it will always pull to the side that is not sharp, try it   ;D  ;)  Next time your chainsaw needs sharpening , only do one side and try her out .  :P

[WH_Conley]

X2

[kelLOGg]

So, Isaw and Bill, the top of the band experiences more force from the wood because the teeth are duller. This pushes back on the upper teeth and and the band must flex somewhat causing the lower teeth to "cock" upward a bit so the band rises in the cut. Does that make sense as an explanation?
Thanks. So much for my airplane wing theory. Sawing ain't aerodynamics, is it. ;D

Bob

[PC-Urban-Sawyer]

I hear it's not rocket science either...  :D

Herb

[WDH]

I have had cases where i was "shaving" a cant such that only the teeth on one side of the blade were cutting.  On the next cut, the blade will not cut straight.  Sounds like the same dynamics that Marcell described.

[kelLOGg]

I have had cases where i was "shaving" a cant such that only the teeth on one side of the blade were cutting.  On the next cut, the blade will not cut straight.  Sounds like the same dynamics that Marcell described.

ditto!!

[POSTON WIDEHEAD]

I have had cases where i was "shaving" a cant such that only the teeth on one side of the blade were cutting.  On the next cut, the blade will not cut straight.  Sounds like the same dynamics that Marcell described.

ditto!!

Try Gillette. ;D

[5quarter]

Bob...you may have stretched the band a bit. If you didn't adjust the tension to compensate, your blade will tend to wander. I have done alot of skim cutting like WDH describes, and have had no issues with the blade not making a straight cut. also, you put a huge stress on the guides while you were raising the head in the wood. maybe check the tilt on the roller guides. One or both out of adjustment might cause the blade to climb in the cut. Putting on a new band will tell you if the guides are the culprit.

[kelLOGg]

Putting on a new band will tell you if the guides are the culprit.

I didn't mention it but I did change blades and the next cut was AOK.
Bob

[kelLOGg]

Bob, did you check to see if the band is still flat.??. Frank C.

I checked the band for curvature by placing a tool steel bar edge against the band and shining a flashlight behind it. The glint of light looked perfectly parallel so I don't think there is any curvature.
Bob