Find the combination of outer blades, chippers and shims that cuts a dado or groove to the width you measured. Enter your set’s inventory once and the calculator searches every combination for the closest fit.
A stacked dado set is a pair of outer blades with chippers between them. With ⅛ in parts you can hit any multiple of ⅛ in, but sheet goods are rarely a round fraction: “¾ in” plywood is usually sold as 23/32 in and often measures somewhere around 0.70–0.72 in. A dado cut to a full ¾ in leaves a sloppy joint; a dado cut to 23/32 may still be a few thousandths off your actual sheet.
Shims — thin rings in a few thousandths — fill the difference. The tedious part is working out which chippers and which shims add up to the number you calipered. That is what this calculator does.
Every part is a thickness, and the stack cuts a groove as wide as the sum of its parts, provided the blades are flat and the arbor nut is tight.
W = outer A + outer B + Σ chippers + Σ shims
The calculator tries every count of every chipper and shim size you have, from zero up to the quantity in your inventory, keeps the combinations within your tolerance, and ranks them: closest first, then fewest shims, then fewest chippers. You can restrict it to undersize-only (for a snug fit you can open up with a second pass) or oversize-only.
Results from the default inventory: two 0.125 in outers, four ⅛ in chippers, one 3/32, one 1/16, and two each of 0.002, 0.004, 0.005, 0.010 and 0.020 in shims. Your set will differ, so enter your own.
| Target | Width (in) | Chippers | Shims | Stack (in) |
|---|---|---|---|---|
| 3/4 in solid (0.750) | 0.750 | 1/8 × 4 | none | 0.75 exact |
| 23/32 ply nominal (0.723) | 0.723 | 1/8 × 3, 3/32 × 1 | 0.004 | 0.72275 |
| Ply measured 0.703 | 0.703 | 1/8 × 3 | 0.004 × 2, 0.005 × 2, 0.010 × 2, 0.020 × 2 | 0.703 exact |
| Ply measured 0.709 | 0.709 | 1/8 × 2, 3/32, 1/16 | 0.004 × 2, 0.005, 0.020 × 2 | 0.70925 |
| 5/8 in (0.625) | 0.625 | 1/8 × 3 | none | 0.625 exact |
| 9/16 in (0.5625) | 0.5625 | 1/8 × 2, 1/16 | none | 0.5625 exact |
| 1/2 in solid (0.500) | 0.500 | 1/8 × 2 | none | 0.5 exact |
| 1/2 in ply (0.472) | 0.472 | 3/32, 1/16 | 0.002, 0.004, 0.010 × 2, 0.020 × 2 | 0.47225 |
| 3/8 in (0.375) | 0.375 | 1/8 × 1 | none | 0.375 exact |
| 1/4 in (0.250) | 0.250 | none | none | 0.25 exact |
Measure the sheet, not the label. Caliper the plywood in three or four places and use the average. Sheets from the same stack can differ by several thousandths.
Example. Your “¾” birch ply calipers at 0.709 in. Choose “Custom”, type 0.709, and the closest stack is two ⅛ in chippers, the 3/32 and the 1/16, with shims of 0.004 × 2, 0.005 and 0.020 × 2: 0.70925 in, a quarter of a thousandth over. That is a slip fit.
Example. Half-inch plywood at 0.472 in: the 3/32 and 1/16 chippers with 0.066 in of shims give 0.47225 in.
Dado stacks remove a lot of material and can kick back hard. Use a featherboard or hold-down, keep the work tight to the fence, and never cut a through dado freehand. Many saw makers prohibit stacks wider than a stated width or prohibit them entirely — check your saw’s manual. A riving knife usually cannot be used with a dado stack, so take extra care.
The search is only as good as the thicknesses you type. Outer blades are sold as ⅛ in, but their carbide teeth are usually a little wider than the plate, and the cut they make together can be a few thousandths more than 0.250 in. Cut a groove with just the two outers, measure it, and enter half of the measured width for each outer. Do the same check with the full stack once: if the cut is consistently wider than the sum, lower the target by that amount next time.
For one-off grooves, two passes with an ordinary blade and the fence moved between them can be quicker than changing the stack. The calculator is most useful when you cut many dadoes to one sheet thickness, such as a run of bookcase shelves.
Outer blade teeth are wider than the blade body, chipper teeth can be slightly wider than their nominal size, and runout adds a little. Measure your actual cut once and adjust the target or the outer blade values to suit.
Yes. Inventory and target fields accept 3/32, 1 1/8 or decimals.
±0.005 in is a good default. Tighten to ±0.002 for a press fit; widen if the calculator finds nothing.
Every extra shim is another surface that can be dirty or bent. Fewer parts make a flatter, more repeatable stack.