If you cut enough wood, you’ll eventually encounter situations where the saw blade is burning the wood. This usually happens with ripping operations but can also happen with crosscuts. If the burning is really pronounced, it may be accompanied by smoking and a noticeable increase in feed pressure. Although there are a number of causes for burning, the underlying cause is heat buildup due to excessive friction of the blade against the wood. Reduce the friction and you reduce or eliminate the burning.
In troubleshooting wood burning during cutting, one of the first things to check is that the rip fence is parallel to the blade. If the fence alignment is ok, a dirty or dull blade, the wrong blade, and a slow feed rate are the next most likely culprits. Other causal factors include a warped blade, a blade that’s too low, a missing or misaligned splitter, or “problem” wood such as warped wood, reaction wood, and improperly dried wood.
Each of these possible reasons for wood burning is described below.
Blade not parallel to fence
A misaligned rip fence is a common cause of wood burning and fortunately, is easy to fix. If the rear end of the fence is angled towards the blade, the board will get squeezed against the fence and the back end of the blade will tend to burn the left edge of the board that rides against the fence. If the fence angles away from the blade, burning may occur on the cut off piece.
The solution here is to adjust the fence so it is parallel to the blade. Any decent fence has adjustment screws built into it. My Excalibur fence has two little Allen screw adjusters on the locking handle mechanism. It’s a matter of sequentially loosening and tightening the screws until the fence shifts into position.
Note: Before adjusting the fence, you might consider doing a quick check to ensure that the blade is parallel to the miter gauge slot. If it’s not, make it so or other problems will crop up. Rip fence alignment is much easier if the miter gauge slot is parallel to the blade.
When a blade starts to burn, the first thing I check for is pitch build-up on the blade teeth. Pitch causes burning because it slows down the feed rate, plus the pitch heats up very quickly, heating up the wood faster than if the metal teeth were in direct contact with the wood. The solution here is simple – clean the blade.
If you’ve cleaned the blade and it’s still burning wood, chances are that the blade is dull. I read some where that about three-fourths of the time when wood burns, it is due to a dull blade. This seems about right to me. You should be able to tell if the blade is dull by a quick visual examination of the teeth. If the teeth are dull, their edges will reflect light and look shiny. Some of the teeth will also likely be chipped or pitted.
A blade that is warped will wobble, resulting in extra friction and burning. A warped blade is also dangerous because of the increased chance of kickback and should be replaced immediately. It’s likely that the blade got warped because it overheated during a previous cutting session.
I know you’re not using a rip blade to cross-cut or a cross-cut blade to rip. Right??? Just double-checking dude. Of course, you mounted the blade correctly with the teeth facing towards you.
Feed rate too slow
If you feed wood into the blade too slowly, burning can result. This is most likely to occur if you’re a novice or if you’re cutting a “burn prone” wood for the first time. Something like Sugar Maple or Purple Heart. When you feed wood into a blade, try feeding it as fast as possible without bogging down the saw and try to avoid slowing down in mid-cut to reposition your hands. The optimal feed rate is something that woodworkers learn with experience. But there are other less-common reasons. These are discussed below.
Blade height too low
Low blade height increases heat buildup because there are more teeth in contact with the wood at any one time, thereby increasing the amount of friction. Raising the blade reduces the friction since there will be fewer teeth in contact with the wood. It also directs the force on the workpiece more in the downward direction so kickbacks are less likely to occur. I generally set the blade height to an inch or so above the workpiece.
No splitter or splitter misaligned
A table saw splitter keeps the freshly cut wood from pinching together and binding against the blade. Without the splitter, you’re asking for trouble in terms of burning and kickback, especially when cutting wood that is warped or has lots of internal stress. If the table saw splitter is installed but is not directly in line with the blade, burning and kickback can still occur because the wood gets forced against the back side of the blade.
If the burning occurs with certain pieces of wood but not others, it could be that the wood in question is warped. This is easy to diagnose: lay the wood on a flat surface and see if the board rocks when you push down on any of the corners. If it does, that baby is warped. A warped board tends to bind as it passes through the blade, contributing to burning and possibly a dangerous kick-back. Not a good thing… Before ripping a board, make sure it’s milled flat.
Reaction wood / Improperly dried wood
Wood with internal stresses in it may burn during ripping because as the internal stresses are relieved, the wood may warp or twist, resulting in binding against the rear edge of the saw blade. Even if the wood is milled flat prior to ripping. The fix here is to use a splitter and try to avoid using reaction wood and improperly dried wood.
It’s not always easy to identify reaction wood but telltale signs are a pronounced sweep in the grain and fuzzy wood fibers that are very dense and hard. Indicators of improperly dried lumber include numerous checks or splits in the grain as well as various forms of warping such as bow, crook, cup, and twist.
Burn Prone Woods
Certain species of wood are more prone to burning than others. These woods are typically hard and dense; examples include cherry, mahogany, maple, purple heart, and walnut. With such woods, try increasing the feed rate to reduce heat buildup and burning. This should clear up the problem, assuming the blade is sharp and the saw is properly aligned.