Five Cut Method Calculator

Five Cut Method Calculator for crosscut sleds and miter fences. Enter both strip widths, strip length and pivot distance to get the fence adjustment, its direction and screw turns.

Squaring a Crosscut Sled With the Five Cut Method Calculator

The Five Cut Method Calculator turns two caliper readings from a test strip into the exact distance to move your crosscut sled fence. It also shows which way to move it and how many turns that takes on an adjuster screw.

It is for woodworkers building or tuning a crosscut sled, a miter gauge fence or a panel sled. A fence set with a framing square is close, but the five cuts expose errors of a few thousandths of an inch that a square cannot show.

How the Five Cuts Magnify a Tiny Error

You cut all four edges of a square test board, turning it a quarter turn after each cut so the fresh edge rides against the fence. The fifth cut slices a thin strip off the first edge. If the fence is out of square, that strip is wider at one end than the other.

An Instructables guide to the method explains why the difference is divided by 4 and not 5. The first three cuts each carry the fence error, the fourth corner ends up holding three times that error, and the fourth cut adds its own. The strip therefore shows four times the error of a single cut.

The Math Behind the Fence Move

The method was popularized by William Ng, and woodworkers on LumberJocks and in Matt Cremona's crosscut sled build write the math the same way. Divide the width difference by 4, divide by the strip length to get the error per inch, then multiply by the distance from the fence pivot to the adjuster.

$$E=\frac{A-B}{4\times L}$$

$$M=E\times D$$

A and B are the strip widths at each end, L is the distance between those two readings, and D is the pivot-to-adjuster distance. E comes out in inches per inch, and M is the move at the adjuster end in inches.

The default numbers come from William Ng's own example, as recorded on Kevin's Workbench. A strip reading 0.842 in at one end and 0.896 in at the other, 24 in long, on a fence with a 28.5 in pivot distance, calls for a move of about 0.016 in.

Why the Measuring Points Change the Answer

Most calculators use the full strip length for L. Calipers never grip the very end of a strip, though, and the span that matters is the distance between the two spots you measured.

The Five Cut Method Calculator asks how far in from each end you took the readings and subtracts that from the length. With readings taken 1/4 in from each end of the 24 in strip, L becomes 23.5 in. The same 0.054 in difference then calls for a move of 0.0164 in instead of 0.0160 in.

That gap is small on one round, but it grows on short strips. On a 6 in strip measured 1/2 in in from each end, using the full length understates the error by about 17%.

Using It as a Table Saw Fence Calculator

The same five cuts work on any fence the stock slides against, so the tool doubles as a table saw fence calculator for sleds and miter gauges. The Sled Layout section sets which end of the fence you adjust, which side of the blade the board sits on and whether the fence is nearest you or farthest away.

From those three choices, the hero states the move as toward you or away from you. The fourth card turns the move into turns of a threaded adjuster. A 0.0164 in move on a 1/4-20 screw, which advances 0.05 in per turn, is about a third of a turn or 118 degrees.

If you fit a threaded adjuster to the fence, the Drill Bit Size Calculator gives the tap drill for 1/4-20 and other threads. For setting the blade itself, the Blade Height Calculator covers how high it should sit for each kind of cut.

How Square Is Square Enough

The third card compares your error with a target in inches per foot. On a Sawmill Creek thread about a new sled, one woodworker calls 0.001 to 0.002 in per foot quite good and very doable, which is why the default target is 0.002.

The card also shows the widest difference your strip can have and still pass. At a 0.002 in per foot target on a 23.5 in span, that is 0.0157 in between the two ends. The default strip's 0.054 in difference works out to 0.0069 in per foot, about 3.4 times over the target.

Offcut widths can run up to 12 in, and the strip length and pivot distance up to 120 in. The readings must be at least 1 in apart. If the two widths differ by more than 5% of the span, the tool stops and asks you to recheck, since that usually means one reading came from the main board and not the thin strip.

Checking That Your Last Move Worked

The Last Round Check compares this strip with the one from before your last adjustment. If the same end is still wider and the gap grew, the fence went the wrong way. If the gap barely changed, the fence likely crept back as the screw was tightened.

If the other end is now wider, you overcorrected, and the tool shows how far past square you went. An error over half a degree gets a separate warning to rough-square the fence with a framing square before running five more cuts.

Setup Slips That Throw Off the Result

Mixing up the ends is the most common one. Mark the end of the strip that sat against the fence before you pick up the calipers, since the direction of the move depends on it.

Moving the pivot end is the second. Loosen only the adjuster end and keep the pivot screw tight, or the fence shifts sideways as well as turning. The pivot distance you enter only holds if the fence swings around that one screw. Bike City Woodworks advises putting the correction point as far from the pivot as you can, since a longer lever turns the same angle into a larger move that is easier to measure.

The third is trusting the screw alone. Matt Cremona clamps a block to the sled and sets the gap with stacked feeler gauges before he tightens the fence, which keeps a slipping clamp or loose thread from eating part of the move.

Five Cut Method Questions From the Shop

Why divide by 4 when you make five cuts?

Only four of the cuts carry the fence error into the strip. The fifth cut just separates the strip so you can measure it, and its two long edges come from the first and fifth cuts.

On a Sawmill Creek thread, a 0.020 in difference is worked through the same way. Dividing by 4 gives 0.005 in over a 20 in strip, or 0.00025 in per inch, which is 0.003 in per foot.

Does the length of the fence matter?

Only through the pivot distance. The error per inch is fixed by the angle, and a LumberJocks member points out that what shows up on a real part depends on the width of that part.

At the default error of 0.000574 in per inch, a 3 in wide face frame part is off by about 0.0017 in, while a 24 in panel is off by about 0.014 in. That is why the third card shows the error across the widest crosscut you make.

How do I move a fence just a few thousandths?

Clamp a stop block against the adjuster end of the fence, then slide feeler gauges between the block and the fence to the thickness the calculator shows. Matt Cremona stacked gauges to 0.097 in for his first move this way.

A threaded adjuster makes later rounds easier. At 1/8 turn on a 1/4-20 screw, the fence moves about 0.006 in, which is fine enough to sneak up on square.

What if the second round shows the same error?

Either the fence did not move or it moved back when you tightened it. Enter the last round in the Last Round Check, and the tool tells you which pattern your numbers match.

After any fix, tighten every screw and run all five cuts again on a fresh board. Judging the move before the fence is fully tightened is how a good adjustment gets lost.