Boy o boy my first decient pile of oak is sure showing how little I know and how much I still have to learn :P :o
In my short experence I have seen these marks (though not nearly as much) along with some waves telling me its time to change the blade ;D
But this time there are a lot of these marks and no waves so now I'm baffled ???. I read some articles talking about burn marks from the blade not turning fast enough, but I dont think thats the problem here?
when in doubt ask the professionals ;D :P
thank you
(https://forestryforum.com/gallery/albums/userpics/21479/002ff.jpg)
That wood looks dry and if you are adding much water it will make the sawdust swell which will cause the blade to heat up. While you are cutting reach over and touch the saw dust that has just hit the ground and see how warm it is. Those do look like burn marks from this angle.
i might not be much help. but anyway. do you only get this around knots? i dont know what you have for a mill. but it looks like your not moving along fast enough . the blade might not be sharp enough. or you have a bent tooth.
some knots can give yo a hard time. i sawed a white pine a few weeks back that had a large limb or crotch half way and every time i hit that area the blade wanted to cup or dive .i had to sawit just about creeping along to make it saw straight.
brent
I think it looks like the chemical reaction that Oak and some other hardwoods have when they come in contact with iron.
The iron contact in your case is the saw blade.
I don't know what to do in your case, but I think maybe reduce the water flow a little bit. Might help, might not!
Do you get the same color marks when the cant comes in contact with the metal (other than stainless steel) on your mill?
Those are the burn marks left by a band, well past its prime, as it wandered in the grain of a knot. It's time for a well-set and sharp band. The regularity of the pattern might even lead you to find a section of the band with tooth damage, or excessive dulling.
Tannic acids in the wood react to contact with metal. You should see chestnut go thru a mill that dose not have stainless contact strips, the stuff just bleeds all over everything. Your saw band has a damaged tooth causing side pressure so it is rubbing the wood causing the reaction, just like a nail in an oak log will. More set will help, washing the boards after milling will also help, in some cases it will stain the wood deep enough that planning it will not completely remove it. Either way a fresh saw out of the box will minimize it.
I agree with everyone on metal contacting timber leaving black stains, but direct from sawing... that's not from the metal contact we are talking about as contact reacting with the timber, if it was then chisels, planes, handsaws everything would stain the timber black all the time.
I'm not a band sawyer, but I figure the marks are from a dodgy band, swap the band, re-cut and you'll have no marks... let us know how you go
It could be the iron/tannic acid stain, I see it sometimes in bandsaw cuts. Iron tannate is a blue/black substance. In the case here it might form due to excess rubbing of the width of the band owing to lack of set, or maybe if the area is hard and the blade not sharp enough, the cut is wavy and the body of the band is rubbing. I think moisture facilitates contact between the wood and the metal which is why we see it commonly in freshly sawn wood, but don't see it commonly in woodworking with iron tools. Try binding a load of fresh oak with a chain, for delivery to your customer. :( >:( ::) If it is iron staining, you can apply a solution of oxalic acid in water to the area and after a minute or so watch the stain disappear (wash the area off then with water). Oxalic acid binds to iron displacing the tannic acid in the wood, and the metal is washed away as colorless iron oxalate, leaving the colorless tannic acid in the wood.