A bandsaw blade does not always track square to the fence slot. Make a long freehand cut, measure how far the kerf walked, and this calculator returns the angle: atan(deviation / length). Skew the fence to match that drift so the blade is no longer fighting the fence. Different tool from blade length.
A bandsaw blade does not always track square to the fence slot.
Use it when rip cuts wander off the line even though the blade is sharp and tracking well. Draw a line on a straight scrap, freehand a cut along it, and measure how far the cut runs off over a known length; the page turns that into the angle to set the fence so it matches the blade’s natural lead.
Drift is a right triangle. The cut you made is the adjacent side. The sideways miss at the far end is the opposite side. The fence needs to sit along the hypotenuse — parallel to the path the blade actually wants — not parallel to the table edge.
drift° = atan(deviation / length) × 180 / π
Inches of drift per foot = (deviation / length) × 12
(If length and deviation are in millimetres, per-foot still uses the same ratio × 12 in.)
Skew the fence by that angle, the same way the kerf wandered. From the infeed, move the infeed end of the fence toward the side the cut drifted (or kick the outfeed end the opposite way). The fence should run parallel to the drifted kerf. Then feed a test board with the blade in the kerf; it should neither pull into the fence nor climb away from it.
This is not a blade-length calculator. Tracking, tension, guide-block side clearance, and a dull set will all change the number. Re-check drift when you change blades. A blade that drifts an inch in a foot is telling you to look at guides and tension before you crank the fence that far.
| Length | Deviation | atan(dev/len) × 180/π | Drift per foot |
|---|---|---|---|
| 12 in | 0.0625 in (1/16) | 0.298° | 0.0625 in/ft |
| 12 in | 0.25 in (1/4) | 1.193° | 0.25 in/ft |
| 24 in | 0.125 in | 0.298° | 0.0625 in/ft |
| 12 in | 0 | 0° | 0 |
| 6 in | 0.125 in | 1.193° | 0.25 in/ft |
Those angles use the same math as the calculator (math.degrees(math.atan(dev/length))). Default example: 1/16 in over 12 in → about 0.298°.
Mark a straight line on a scrap at least a foot long. Cut freehand down that line for as far as you can keep the blade on the start of the line, without steering. At the far end, measure how far the kerf is from the line. That pair — length and deviation — is this calculator. Then rotate the fence to the angle it returns, parallel to the kerf you just made.
The same way the blade wandered. If the kerf walked left of the layout line as you face the infeed, the infeed end of the fence moves left (or the outfeed end moves right). The fence is no longer square to the table slot; it is square to the blade’s actual path. A test rip should feed with even pressure, not a fight.
No. Blade length is a tracking/tension install number from wheel diameter and rise. Drift is a fence-skew angle after the blade is on and cutting. Use both. Length does not tell you drift, and drift does not tell you which blade to order.
A quarter inch in a foot is already a lot of skew (~1.2°). An inch in a foot is a blade or guide problem: tension, side-guide clearance, a twisted blade, or worn tires. Skewing the fence that far will still cut, but you will fight every resaw. Fix the saw, then re-measure.
Same triangle. A tall resaw fence just makes a bad skew more obvious because the face is a longer reference. Measure drift the same way, set the tall fence to that angle, and keep the face in line with the drifted kerf from bottom to top.