What
Just because you align the blade at 90 degrees doesn’t mean it will stay that way when you tilt it to 45 degrees. On most table saws, the entire blade carriage rides in semi-circular tracks called “trunnions”. The blade is tilted as the assembly travels along these tracks. The “axis of rotation” for the blade tilt mechanism is supposed to run along the surface of the table where the blade comes through the table insert (throat plate). This way, the table insert won’t interfere with the blade even when it’s tilted. However, inaccuracy in machining, or stress relief in the castings often causes this axis of rotation to shift so that it no longer runs along the surface of the table. So, as the blade is tilted, it gradually gets out of alignment with the miter slot. Fortunately, this process should only be required once for the life of your saw.
Why
The following symptoms are common when making bevel cuts on a saw when the trunnions are not properly aligned:
- Burning of the cut edge
- Board wandering away from the fence during a rip cut
- Sawdust being thrown up at the operator
- Kickback
These are the exact same symptoms that occur for normal (90 degree) blade alignment. If you see any of these symptoms when you tilt the blade (making bevel cuts), then you need this procedure.
How
First, make sure that the standard blade alignment (blade at 90 degrees) is accurate. Then, tilt the blade to 45 degrees and check the alignment.
The measurements
The best way to do this is to tilt the dial indicator as shown in the photo above. The most accurate readings always result when the plunger of the dial indicator is at right angles to the surface being measured. Use the same method that was described for standard blade alignment - mark a dot on the blade and take all measurements with the stylus of the dial indicator on that spot - rotating the blade as necessary. The error measured in this step will represent a combination of horizontal (90 degree) and vertical (tilt axis) misalignment. If you don’t perform the standard 90 degree blade alignment accurately, then it will influence your readings when the blade is tilted and invalidate the procedure.
Measurements can be made with the dial indicator horizontal as shown above but I don’t recommend it. Many sources of error can creep into your readings making them inconsistent and very frustrating. The dial indicator will have a tendency to lift during the measurement process so be sure to check that the jig remains flat on the table. Since the dial indicator is not perpendicular to the surface being measured, the readings will be exaggerated by 1/cos(45). This turns out to be equivalent to the vertical (tilt axis) misalignment so no further correction is needed.
Make a note of the change in reading between your two measurement points as well as the direction of the change. In this case it’s about 0.006 inches and it’s higher at the trailing edge of the blade. To determine the vertical (tilt axis) component of the misalignment, multiply the measured error by...
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