When diagnosing a machine that is not cutting straight look at the guides. If the rear guide is touching the blade even when not cutting, then the rear guide is probably set too far forwards. This is forcing the blade forward of its natural position on the blade wheels and can cause poor quality cuts.
RECAP. Use sharp pencil lines, start on track, and go slow until the blade is all the way in. Then, always watch your cut line, let the saw stay on its straight course, and don't stop or readjust too much unless you have to. Those are the essentials!
Focus on the point where the blade is cutting into the workpiece and never stop pushing through the cut. This will also contribute to slight shifts side to side resulting in a wavy edge. Plan the cut so that you have continuous access to get all the way through without stopping.
band saw won't cut straight Could be a number of things. Blade guides not properly adjusted, blade tension, dull blade, blade width and feed rate are the usual culprits. Have you watched the Alex Snodgrass video? It helped me. Especially about centering the gullets on the crown of the top wheel, not the blade itself.
If the blade tension isn't correct, the downfeed pressure can cause the blade to cut on an angle or wander. Virtually all modern band saws have blade tension indicators, and many machines with electronic tensioners will not even run unless you have the correct blade tension.
As noted previously, blade speed, feed pressure and feed rate are all required to be in balance for the particular material being cut. If any or all of these are not near recommended specifications, then crooked cutting will most likely result.
The teeth aren't sharpened correctly along one side, perhaps because they were improperly filed, without maintaining the same sharpening angle. The guide bar rails are unevenly worn and therefore asymmetrical, insofar as one is lower or thinner than the other.
Buildup of sap on the blades, insufficient set, dullness and unguided cuts, can all cause an overheated blade and kickback. Never set a blade deeper than is required to cut the work piece 1/8 in. to 1/4 in. greater than the thickness of the stock is sufficient.
If your chain is not sharpened properly, then chances are that one side has teeth longer than the other. If the teeth are longer on one side, then your chainsaw will most definitely not cut straight. This condition could be caused by your chain hitting a rock, nail, or dirt while it's running.
Your Blades LOOK Dull
If you see jagged edges, bent teeth, or simply an overall dullness even after cleaning, you'll quickly know the answer. When blades look dull, it means they've lost virtually all of their true cutting power.
Because a circular-saw blade cuts on an upward rotation, the bottom face, in which the teeth enter the cut, will almost always have a clean, tear-out-free surface.
To get straight cuts with a circular saw, use a straight edge guide or a saw track, ensure the blade is sharp, and maintain a steady hand. Clamp the wood securely.
Chain Not Cutting
If the chain is sharp, but doesn't feel like it is cutting then the depth gauges or rakers need to be lowered. This is the “shark fin” shape directly in front of each cutting tooth. It's purpose is to limit how deep the cutting tooth dives into the wood.
The most common cause is not properly clamping down the material you're cutting. Other possible reasons your cuts aren't straight or accurate include a damaged blade, an unstable fence (the flat piece of material mounted on the saw table), a broken bevel gauge, or some sort of malfunction with your miter gauge.
When diagnosing a machine that is not cutting straight look at the guides. If the rear guide is touching the blade even when not cutting, then the rear guide is probably set too far forwards. This is forcing the blade forward of its natural position on the blade wheels and can cause poor quality cuts.