The tools.
The app's tested math, run it here, take the numbers to the mandrel.
🧵 The stitch math
SPI to spacing (25.4 ÷ SPI), the thread's diameter (spacing ÷ 6), and the thread length for your seam, the app's tested shapes, on the irons' real sizes.
| stitches per inch (SPI): | |
| stitch spacing: | — |
| the thread's diameter: | — |
| the seam length (in): | |
| the stack thickness (oz leather, total): |
thread: —
Per inch of seam, the member formula the app checks: 2 + 2 × thickness × SPI inches of thread, plus backstitches, allowance and a tail, the app's sum, rounded generous. 8 oz total = 2/16 in thick.. the app reads oz as 1/64 in: 8 oz = 1/8 in per layer-pair of the stack.
View the math
stitch spacing = 25.4 ÷ stitches-per-inchthread per inch of seam = 2 + 2 · (oz ÷ 64) · spiTwo thread-ends per stitch, two thicknesses of leather taken per pass: the app’s saddle-stitch yield. At 7 spi on 9 oz: 2 + 2 · 0.141 · 7 ≈ 3.97 in of thread per inch of seam, before backstitches and tail.
🪢 The Turk's head
Bights and leads (Grid Maker's "parts") decide everything: the cords, the crossings, one cord only when they share no factor.
| bights: | |
| leads ("parts"): |
cords: — · crossings: —
cords = gcd(bights, leads); crossings = (leads − 1) × bights. A Gaucho's row coding runs over-2/under-2 along the cord; herringbone = the column coding. 9×5 shares no factor → ONE cord, the classic.
View the math
cords = gcd(bights, leads)crossings = (leads − 1) · bightsA turk’s head ties as one cord when bights and leads share no factor; otherwise the gcd is the cord count and the pass count. The crossings count the weave’s density, the app’s own pair.
📿 The bracelet's length
| wrist (in): | |
| the band's thickness (in): | |
| the fit: |
bracelet: —
length = wrist + π × thickness + the fit (Swiss Paracord's formula, the app's tests check its example: 7 in wrist, 0.320 thick → 8.005 in). Most makers just say "add an inch", the app's cobra defaults land there too. A king cobra's half-inch adds 1 9/16.
View the math
L = wrist + π · thickness + fitThe buckle-to-buckle length: the wrist’s round plus the weave’s own thickness through the buckle, plus the fit allowance. The app’s cobra defaults land at the same place.
🎗️ The handle wrap
| the handle's diameter (in): | |
| the handle's length (in): | |
| the cord: |
cord: —
A close spiral: turns ≈ length ÷ (cord diameter); the distance round = π(D + d); the cord ≈ length × π(D+d) ÷ d. The app's checks: 550 on a 1 in dowel over 4 in = 92.36 in; the gutted reads its flat width (3/16). The figure errs a touch generous, cord packs snug.
View the math
cord = length · π · (diameter + cord) ÷ cordThe helix unwound: each turn wraps π · (diameter + its own cord) of cord, and the length holds the turn count. Generous by design, the wrap tightens as it packs.
