Five-cut method calculator
Square the fence of a crosscut sled or miter gauge to the blade. Make the five-cut test, measure the last strip at both ends, and this gives the fence error per foot, the angle, and how far to move the fence at its adjuster.
Measure with calipers, as close to the end as you can.
The length of the side you cut the strip from.
From the fence’s pivot bolt to where you will move it.
Error per foot of fence
0.002 in
- Angle off square
- 0.0095°
- Move the fence
- 0.004 in
Arithmetic: exact by definition
Move the fence by that amount at the adjuster, then cut the test again. If the error doubles instead of shrinking, it went the wrong way: move it back twice as far.
Why: Four cuts each add the fence error once, so the 0.008 in taper is four times the error: 0.002 in per foot.
Why these numbers?
The situation
The strip measures 0.508 in and 0.5 in at its ends, over 12 in.
From your input: the two widths and the strip length
What that means
Each of the first four cuts squares one edge off the one before it, so a fence that is off by a little adds that little four times over before the fifth cut measures it.
Arithmetic: exact by definition
The number
0.008 in ÷ (4 × 12 in) = 0.000167 in per inch, 0.002 in per foot, 0.0095°.
Arithmetic: exact by definition
So
At 24 in from the pivot that is 0.004 in of fence movement.
Arithmetic: exact by definition
How to make the five-cut test
- Take a flat piece of plywood or MDF, roughly square. A bigger board shows a smaller error, because the taper grows with the length of the strip.
- Number the edges 1 to 4. Put edge 4 against the fence and crosscut edge 1.
- Turn the board a quarter turn so the edge you just cut rides the fence, and cut the next edge. Repeat until all four are cut.
- With edge 4 against the fence again, cut a strip about 1/2 in wide off edge 1. That is the fifth cut.
- Measure the strip's width at both ends with calipers, and its length. Enter them above.
Why divide by four
If the fence is off square by a small angle, every cut the board makes is off by that angle. Because each new cut is made with the previous cut against the fence, the error adds up: after four cuts the first edge has been moved four times the error relative to the edge you are now cutting. The strip's taper over its length is four times the fence's own error, so dividing by four gives the real error. That is why the test is sensitive: a strip only 0.008 in wider at one end over 12 in means a fence off by 0.002 in per foot.
Moving the fence by the amount shown, measured at the adjuster, corrects it. If the next test shows twice the error, the fence went the wrong way. The same test squares a miter gauge's fence or a sliding table's crosscut fence. Blade choice and the rest of the saw are in the table saw guide.