What causes the pressure change of the bandsaw cut

[Susumu Mori]

Hi all,

There is one thing I have always been wondering and hope somebody has the answer.

The question is, as I resaw using a bandsaw, there is a time when the wood goes through without much effort and then somehow it start to require much more effort. It comes and goes and doesn't seem to related to the hardness change of the wood. When it runs effortlessly, the cut tends to be smooth and when it gets stiffer, it leaves a slight ridge.

I wonder if any of you experience similar things. I don't have this for ripping. So, it should be related to the higher pressure to the blade....

It doesn't cause much of a problem but I want to know how it happens.

[John TenEyck]

I've always thought it is due to a change in grain orientation in the wood, whether the kerf closes up a little, and probably a couple more things I haven't considered. But you are right, it happens, sometimes a lot.

John

[Myk Rian]

Kerfs are full of sawdust.

[John McClanahan]

Kerfs are full of sawdust.

That's what I was thinking. It will cause blade drift, too.


John

[Jason Beam]

The gullets are loaded...

[Myk Rian]

Yeah. Gullets. Not kerfs.

[Bill White]

What tooth count on the blade are ya using?
Bill

[Ted Reischl]

Ever notice that the dark rings in pine are harder than the light ones? Could it be that the rings in wood have differing hardness? You betchya!

[Susumu Mori]

I use 1-inch Resaw King with 3 TPI. It has very small sets. So, gullet clearance could be an issue.

I think the binding as John mentioned could also be a reason but if it is the gullet clearance, should I feed slower or back track a bit to release the blade pressure whenever I feel the resistance?

I'm not sure if it is related but before I switched to tue current ceramic guides, I also noticed occasional shrieking noise, almost like some blade pressure is released (like the release valve noise of turbo engines). Maybe from the thrust bearings, not sure.

There are still many mysteries about bandsaws for me. There are something going on that are not steady state and some transient events are happening. Clogged gullets or wood tension release could be it. Not a huge problem, but I would feel much happier if I could sail through the resaw with a smooth surface all the way through.

[John TenEyck]

When I experience this problem I find slowing down the feed rate helps eliminate it.

John

[John Lankers]

Could be a combination of feed rate, to many tpi., dry lumber vs. green lumber. When you notice sawdust buildup on the surface after you finished the cut it's a tell tale sign of gullets not being able to carry the amount of sawdust. I once thought the more tpi. the better, not so for resawing. Also if your cuts turn out warped this too could be a sign of feeding to fast not necessarily to little tension on the blade.
http://woodgears.ca/bandsaw/resaw.html

[Jim Finn]

I have noticed this myself when re-sawing 8" and 6" cedar. I wonder if a slower saw speed would help? I have a two speed saw but have it on high speed.

[Peter Quinn]

I resaw with a vari pitch 1/2 per inch, the gullets are the size of deep sea fish hooks, so no clogging but still binding when re sawing against the fence. I've always attributed it to tension releas when referencing a tall resaw fence. The blade is fixed, the fence is fixed, the keeper is against the fence and its bowing a bit as the cut proceeds so it acts as a clamp between fence and blade, mostly against the back edge of the blade. You get the rough marks when the fresh cut wood slice starts curling back into the blades teeth. You just never know what your going to get when shoving a board into a bandsaw. When I resaw off a uni point fence or kerf a board first on a table saw or just split a board freehand to a line this binding never happens unless the board really wraps around the blade, but the rough saw marks still do.

[John Lankers]

I have noticed this myself when re-sawing 8" and 6" cedar. I wonder if a slower saw speed would help? I have a two speed saw but have it on high speed.

The slower speed is usually for cutting metal not wood. Cedar cuts very easily and produces large amounts of "fluffy, stringy" sawdust which takes up more space in the gullets, which means even though it cuts so easy you might have to reduce the feed rate.
The biggest issue for me at least is (I have a Hammer N4400) a: feeding the stock to fast therefor overloading the gullets between the teeth, and b: a dull blade. Both can lead to excessive heat buildup causing the tips of the teeth to lose the temper. I am not enough of a saw blade expert but I do know a blade has to be sharp to be able to produce a decent cut.

[Rod Sheridan]

Hi all,

There is one thing I have always been wondering and hope somebody has the answer.

The question is, as I resaw using a bandsaw, there is a time when the wood goes through without much effort and then somehow it start to require much more effort. It comes and goes and doesn't seem to related to the hardness change of the wood. When it runs effortlessly, the cut tends to be smooth and when it gets stiffer, it leaves a slight ridge.

I wonder if any of you experience similar things. I don't have this for ripping. So, it should be related to the higher pressure to the blade....

It doesn't cause much of a problem but I want to know how it happens.

I think it's due to grain orientation and the resulting chip shape which impacts the ability of the saw blade gullet to carry off the waste without plugging.

You can check that hypothesis by running a coarser blade and seeing if that helps..............Rod.