Guide · Yield and kerf
Linear Material Yield Calculator and Kerf Loss Guide
Type two totals for a quick yield %. For the real number, with kerf, trims, miters and the best bar mix, nest the cut list in the 1D nesting optimizer.
Formula
Yield = part length ÷ stock length
Yield = Σ part centerline length ÷ Σ stock length used × 100
Use any unit, as long as both totals use the same one. The prefilled numbers are the 80/20 frame: 37,610 mm of parts from 39,000 mm of bars, 96.4%. The remaining 3.6% is everything that did not become a part: saw kerf, end trims, miter wedges and every drop at the end of a bar.
For mitered pieces, use the centerline length, not the long point. A 1800 mm long-point piece with two 45° ends on a 60 mm profile has a 1740 mm centerline; counting the long point would overstate yield by the triangles that fall out between pieces.
Drops
Why yield ignores reusable drops
The reusable threshold grades drops; it does not move a single cut. On the machine frame job, a 300 mm threshold marks 1 drop as reusable and a 600 mm threshold marks 0, while yield stays at 95.2% in both cases. What changes is the remnant list and the labels you print.
That is deliberate: a drop on the rack is only worth something if a later job uses it. Enter it then as offcut inventory with Use offcuts first switched on, and its length counts as stock for that job, at $0.
Kerf
Kerf loss = cuts × k ÷ sin a
Every cut removes one blade width. At 90° that is k; at an angle the slot is longer along the bar, k ÷ sin a, which is 1.414 k at 45°. The machine frame makes 16 square cuts with a 3 mm blade: 48.0 mm. The window job with flip OFF makes 40 cuts at 45° with 2.5 mm: 141.4 mm.
Trims
End trims, quotes and what yield does not tell you
Trims and drops only lower yield through the stock you buy. The 80/20 frame trims 10 mm at both ends of 7 bars, 140 mm in total, yet yield is 96.4% with or without them, because the plan buys the same bars either way. Yield moves when the bar count or the bar mix moves.
When you compare supplier quotes, compare cost, not yield: a cheaper short bar can lower yield slightly and still win on the invoice. Use yield to judge the cut list itself, and the lower bound to judge the plan.
Reference
Blade kerf by saw
Typical kerf — check your blade. Measure a test cut with calipers once and type that number; it is worth more than any table.
| Saw / process | Typical kerf | Enter | Note |
|---|---|---|---|
| Band saw, bi-metal blade | 1.2–2.0 mm | 1.6 mm · 1/16" | Typical — check your blade; set widens with tooth size |
| Cold saw, HSS or TCT blade | 2.0–2.8 mm | 2.5 mm | Typical — check your blade; blade thickness printed on the plate |
| Carbide circular saw for aluminum (10–14") | 3.0–4.0 mm | 3.2 mm · 1/8" | Typical — check your blade; window and T-slot shops |
| Abrasive chop saw (14" wheel) | 2.8–3.2 mm | 1/8" | Typical — check your wheel; kerf shrinks slightly as it wears |
| Wood miter saw blade | 2.4–3.2 mm | 3/32" thin · 1/8" full | Typical — check your blade; frames and lumber |
| Plasma tube cutting | 1.5–4.8 mm | by amperage | Typical — check the cut chart for your amperage |
| Fiber laser tube cutting | 0.1–0.4 mm | 0.2 mm | Typical — check your nozzle and thickness |
| Tubing cutter (wheel) | 0 | 0 | Removes no material; allow a deburr trim instead |
Worked examples
Yield of the presets, computed by the engine
| Job | Parts (centerline) | Stock used | Yield | Cuts · kerf |
|---|---|---|---|---|
| Machine frame, 3 part types | 17140.0 mm | 18000.0 mm | 95.2% | 16 · 48.0 mm |
| 80/20 frame, mixed bars | 37610.0 mm | 39000.0 mm | 96.4% | 42 · 134.4 mm |
| Window frames, flip ON | 28800.0 mm | 30000.0 mm | 96.0% | 25 · 88.4 mm |
| Window frames, flip OFF | 28800.0 mm | 36000.0 mm | 80.0% | 40 · 141.4 mm |
| A500 tube railing | 206' 11 3/4" | 212' 0" | 97.6% | 36 · 4 1/2 in |
The window rows are the same 20 pieces: turning pieces over so neighbours share a cut lifts yield by 16.0 points and saves a bar. The railing reaches 97.6% because 36 varied pieces leave small gaps that short braces can fill.
Optimal
The lower bound and what Optimal means
Lower bound = ⌈ Σ (centerline + k) ÷ (longest stock − trims) ⌉
| Job | Lower bound | Bars bought | Verdict |
|---|---|---|---|
| Machine frame, 3 part types | 3 | 3 | Optimal |
| 80/20 frame, mixed bars | 7 | 7 | Optimal |
| Window frames, flip ON | 5 | 5 | Optimal |
| Window frames, flip OFF | 5 | 6 | +1 vs lower bound |
| A500 tube railing | 9 | 9 | Optimal |
For the machine frame: 17,188 mm of parts plus kerf ÷ 5,980 mm usable = 2.87, so no plan can use fewer than 3 bars. The planner found 3, so it shows Optimal.
The window job with flip OFF sits one bar above its bound, which is what the flip removes. The bound ignores that pieces cannot be split, so it is sometimes unreachable; a plan above it is not necessarily wasteful. The optimization software guide explains how the search proves it.
FAQ
Yield questions
Does a reusable offcut count toward yield?
No. Yield counts only what became a part. A reusable drop is real material you may use later, so the planner lists it separately; counting it now would make every plan look better than the bill you pay today.
Why is my yield lower with miters?
Each angled end turns a triangle of the bar into scrap, and each angled cut removes k / sin a of bar instead of k. Flipping pieces so neighbours share a cut recovers most of it: the window job goes from 80.0% to 96.0%.
What is a good yield for linear stock?
It depends on the list more than the software. Many short, varied pieces nest above 95%; a few long pieces close to the bar length may top out near 80%. Compare against the lower bound instead: if the plan meets it, no plan can use fewer bars.
Why does the calculator above disagree with the planner?
The calculator divides two totals you type. The planner works out centerline lengths for mitered pieces and uses only the bars it actually bought, so type the centerline total and the stock total from the planner's summary to match it.