Miter saw blade runout is the side-to-side wobble a blade shows as it turns, and you can check it yourself with basic tools. That wobble is often the hidden reason a cut comes out off angle or uneven, even on a saw that seems fine. Knowing how to measure it helps you tell a blade problem from a saw problem before you spend money on parts.
The check needs only a square and a feeler gauge, and a strip of phone book paper can serve as the gauge. [1] You don’t need a shop or special meter to see whether your blade is running true. Most of the work is careful, patient measuring.
This article covers the check, what the readings mean, and how to replace the blade safely if it is the problem.
How do you check a miter saw blade for runout?
You can check runout by measuring the gap between the blade and a square at several points around the blade. You need only a square and a thin feeler gauge, and the whole check takes a few minutes.
Unplug the saw. Press the square tight to the fence so it cannot shift while you measure.
Slide a feeler gauge, such as a strip of phone book paper, between the back of the blade and the square. [1]
Move the square to the other side of the blade and compare the gap at the same spots. Keep the square pressed against the fence so the reference stays the same.
Rotate the blade by hand and repeat the measurement at several points around the blade.
For example, if the paper slides in easily near the top of the blade but grips tightly near the teeth, the gap is changing as the blade turns. That change is the wobble you are looking for. If the gap stays the same at every point, the blade runs true.
When does runout mean the blade or arbor needs replacing?
If the arbor, the shaft the blade bolts onto, has a visible bend, the saw needs repair or replacement. You can check this with the saw unplugged and the blade removed. Look along the shaft against a straight edge, and if you can see the curve with your eye, stop adjusting and get the saw repaired.
Before you blame the saw, check the blade itself. A bent blade is one of the most direct causes of wobble, and it is cheaper to fix. Lay the blade on a flat table and look for a warp or uneven spots around the teeth. If the blade is bent, replace it and run the check again.
Measure again after any change, whether you repaired the arbor or swapped the blade. Compare the new gap with your first reading at the same spots. If the wobble is gone, your cuts should line up again. If it is still there, the arbor or saw needs a closer look.
How do you replace a miter saw blade safely?
Unplug the saw before you touch the blade, and wear gloves, because the teeth stay sharp even when the saw is off. Then swap the blade in the order below.
Unplug the saw and put on gloves. Lower the blade guard so your fingers stay away from the teeth.
Lock the spindle so the blade cannot turn, then loosen the arbor bolt with the wrench that came with your saw. Remove the bolt and the outer washer.
Lift off the old blade, then take off the inner washer. Lay the parts out in the order you removed them so the new blade goes back the same way.
Slide the new blade onto the arbor with the teeth pointing in the direction of rotation shown on the blade and guard.
Put the washers and arbor bolt back on and tighten the bolt firmly. Turn the blade by hand to confirm it spins freely.
Repeat the runout check. The square should show the same gap at each spot you measured.
What to do after you find runout
Finish the runout check before you buy anything. The measurements show whether the problem is the blade, the arbor, or both, so you only buy what you need.
If the blade itself is bent, replace it with a new one. That is the cheaper fix, so start there when only the blade is off. If the arbor, the shaft the blade bolts onto, is visibly bent, a new blade will not fix the wobble. Have the arbor repaired or the saw replaced instead.
After any change, measure runout again. A quick recheck confirms the new blade or repair runs true, so your miter cuts stay square and accurate. Keep a note of the readings so you can compare them later.