As the answers suggest, this can be a complex issue. If you don't yet have a Wixey digital angle gauge to check for that 90 to the table, get one for about $30 on Amazon. You can use a combination square to check blade alignment with the miter slot by marking one tooth and checking the distance from slot to that tooth twice, once with that tooth at the front of the opening, once at the back. Different saws have different ways of adjusting this. If the blade is not parallel to the slot, you will likely have to loosen the table and shift if very carefully one way or another to align it. But then the blade may still be a problem.
I have switched to full kerf blades because the thin kerf blades may deflect from the tension in the wood, and who knows if a cheaper blade is really flat. If it isn't you'll get saw marks or burning. On good quality thin kerf blades, I have a 4 inch stiffener installed, which helps some. I learned a lot about blade deflection while
struggling to get a perfect 45 miter corner for frames, and finally gave up on thin kerf blades for exact cuts.
I popped for a Woodpecker dial gauge to check with more precision on blade alignment, but also use it to set the fence ever so slighly wider from the blade toward the back of the table. Mine is set for 4/1000ths out rather than exactly parallel. While checking this I discovered that my fence, although very good is not really perfectly straight, so setting the back end out slightly eliminates the fence pushing the leading edge of the workpiece to the side.
I do have a table saw jig I can clamp a board to to get a quick straight edge, but it does nothing to correct twists, bowing or other directionally stressed wood, particularly the stuff you generally find at HD. I've become extremely fussy about what I buy there and often find one piece out of 50 that's close enought to straight, and that has a grain structure that is straight enough not to warp on the way home.
Things got much better when I finally got a good jointer. Wish I'd gotten one with a wider blade, but what a difference it makes. One problem even with that is if you buy wood that's already dimensioned to your final size (as it is with big box wood) there is no way you can really plane it flat and have the same dimension. It will always wind up thinner. So you need to buy stock that is not only straight as you can find, with good grain structure but that is at least a quarter inch thicker than what you finally want. If its a truly critical build, the two step planing is necessary, with a day or so of climitizing in the shop before you do the second and final planing. And then you need to use that freshly planed wood within a day or so. This is a very fussy approach that is used for furniture and other very close tolerance builds.
Hand planing takes a little practice and learning to sharpen "wicked sharp." But planing itself is a very satisfying way to flatten and dimension wood. On top of that, it leaves a fantastic surface that is far more glassy that you can ever get with sanding, even with the finest grits. I now have collected 5 different planes, Wood River V3 planes do it for me, although I do have a Veritas router plane tucked away for cleaning up grooves and such. Most of the time I use a #4 jack plane, but I also have a #6 to flatten with. The extra length makes it better for flattening. But it's a lot of work to do a large number of pieces this way. Planes get in your blood after awhile, and sharpening and setting them properly takes practice. Worth considering is that a decent set of planes will cost nearly as much as a jointer and planer, and the two tools go together. Notice that nearly all skilled woodworkers have a set of planes handy.
There ARE lots of videos on YouTube on all of these methods, but I also found a lot of information in used woodworking books about specific tools on Amazon. The methods and techniques have been around forever so older books are still valie. Do remember that many of the finest antiques were built entirely with hand tools that were not near as good as we can get today.
Once again I've penned a novella, but I hope some of this is useful. How detailed YOU need to get depends on the project, your standards and pocketbook.
The more I do, the less I accomplish.
Last edited by DesertRatTom; 10-09-2016 at 05:03 AM.