MANDRELBENCHGet the app

The tools.

The app's tested math โ€” run it here, take the numbers to the mandrel.

๐Ÿงต The stitch math

SPI to spacing (25.4 รท SPI), the thread's diameter (spacing รท 6), and the thread length for your seam โ€” the app's tested shapes, on the irons' real sizes.

stitches per inch (SPI):
stitch spacing:โ€”
the thread's diameter:โ€”
the seam length (in):
the stack thickness (oz leather, total):

thread: โ€”

Per inch of seam, the member formula the app checks: 2 + 2 ร— thickness ร— SPI inches of thread, plus backstitches, allowance and a tail โ€” 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.

๐Ÿชข The Turk's head

Bights and leads (Grid Maker's "parts") decide everything: the cords, the crossings โ€” one cord only when they share no factor.

bights:
leads ("parts"):

cords: โ€” ยท crossings: โ€”

cords = gcd(bights, leads); crossings = (leads โˆ’ 1) ร— bights. A Gaucho's row coding runs over-2/under-2 along the cord; herringbone = the column coding. 9ร—5 shares no factor โ†’ ONE cord, the classic.

๐Ÿ“ฟ The bracelet's length

wrist (in):
the band's thickness (in):
the fit:

bracelet: โ€”

length = wrist + ฯ€ ร— thickness + the fit (Swiss Paracord's formula, the app's tests check its example: 7 in wrist, 0.320 thick โ†’ 8.005 in). Most makers just say "add an inch" โ€” the app's cobra defaults land there too. A king cobra's half-inch adds 1 9/16.

๐ŸŽ—๏ธ The handle wrap

the handle's diameter (in):
the handle's length (in):
the cord:

cord: โ€”

A close spiral: turns โ‰ˆ length รท (cord diameter); the distance round = ฯ€(D + d); the cord โ‰ˆ length ร— ฯ€(D+d) รท 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 โ€” cord packs snug.