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Braid Transfer Calculator

The Braid Transfer Calculator models the transfer of pre-wound braid: braid ordered on a long spool mandrel is cut, slid over a catheter shaft of a different diameter, and stretched down until it grips. Because the wires can neither stretch nor unwind, the braid's picks per inch (PPI), braid angle, and coverage all change with the diameter the braid sits on. This tool predicts those changes in both directions — what a known spool braid becomes on your shaft, and what PPI to order the spool braid at to hit a target braid after transfer.

The calculator is opened from the Tools menu and works standalone — no model build is required, and the braid is defined with the same controls as a braid layer in the Catheter Setup tab. It applies to regular braids only (Coil and Triaxial Braid layers are not supported).

Goal Seek (Default Mode)​

Goal Seek answers the purchasing question directly: "I want this braid on my catheter — what PPI do I order the spool braid at?"

  • Goal Braid at Target: Define the braid you want on the finished catheter — pattern, number of carriers, wire material, wire shape, and wire dimensions.
  • Goal Parameter: Choose which quantity pins the goal at the target diameter: Picks Per Inch (PPI), Braid Angle (° from the longitudinal axis), or Coverage (%). The other two are computed as outputs. Switching the parameter re-expresses the current result in the new parameter (the value carries over), and the goal value itself is bounded so the goal braid can actually be braided at the target diameter — a PPI goal, for example, caps at the target's jamming limit.
  • Transfer Diameters: Enter the spool mandrel OD (D1) the braid will be wound on, and the target shaft OD (D2) it will be stretched down onto (the surface the braid lands on, e.g. the liner OD). Transfers are one-way (large to small), and the spool OD is the one input that adjusts automatically to stay feasible: it is kept above the target and below the diameter where the spool braid's weave would bind. A note under the boxes states the active constraint.
  • Required spool PPI (exact): The solved as-braided PPI on the spool that lands exactly on your goal after transfer, validated against the spool's own jamming limit (the braid must be braidable on the spool in the first place).
  • With integer PPI: Braiders set whole-number PPI on the machine, so the calculator also shows the nearest integer PPI and reads back what it actually achieves at the target — PPI, angle, and coverage — so you can see the consequence of rounding before ordering.
  • Import goal braid from design…: Copies a regular braid layer from your compiled catheter design into the calculator: its braid definition, its PPI as the goal, and the diameter it sits on in the stack as the target shaft OD. The spool mandrel OD defaults to 25% over the imported seat diameter — transfers run from larger to smaller — capped to what the goal braid can physically be braided at before its weave binds, so the import always opens on a feasible transfer. Adjust it to your actual spool. This button appears only after a catheter model has been compiled with Apply & Build Model; Coil and Triaxial Braid layers are not listed.

Forward Transfer​

Forward Transfer works in the opposite direction: define the braid as wound on the spool and see what it becomes at the target diameter.

  • Braid on Spool: The as-braided definition, including its spool PPI. Enter measured, relaxed (as-received) values — braid that has not been heat-set springs back slightly off the spool, so the braider's machine setpoint may not be what arrives.
  • The PPI input is automatically capped at the spool's jamming limit for the current wire and carrier selection, exactly as in the Catheter Setup tab.

Transfer Results​

Results are shown side by side for both ends of the transfer — the spool state on the left and the target state on the right.

  • Picks Per Inch, Braid Angle, Coverage, Fill Factor, Pitch: The full braid characterization at each diameter, computed with the same formulas as the Catheter Setup tab.
  • Status: The wizard's density language at each end — High Density (Process Limit), Near Binding, or Binding Likely (Jamming) — based on the fill factor.
  • Elongation on transfer: How much the braid lengthens as it necks down (greater than 1 when transferring to a smaller diameter).
  • Spool braid per finished length: The purchasing number — meters of spool braid to order per meter of finished, transferred braid.
  • Transferable OD range: The span of shaft ODs this spool braid can physically reach before the weave binds. Binding is two-sided: necking down drives the braid angle toward 0° until the wires crowd circumferentially, and expanding up drives it toward 90° until the wires jam in hoop.

A warning banner above the results flags anything that needs attention, such as a braid approaching its binding limit or a PPI outside the typical machine range. Infeasible transfers can't be entered in the first place: every input is bounded so that neither the spool braid nor the transferred braid can reach a bind state — the target OD floors at the smallest shaft the braid construction can sit on, the goal value stays within what is braidable at the target, and the spool OD auto-adjusts between the target (transfers are one-way, large to small) and its own binding limit. In the rare case where no spool diameter works at all — a goal braid pushed right to the target's jamming limit — the tool says so under the diameter boxes and tells you which input to relax.

Braid Previews​

Two rendered previews show the braid at each end of the transfer — the spool braid on the left and the target braid on the right, in both modes. Both panes are drawn at a common scale, so the wires read the same physical size and the mandrel diameter difference is visible. Hover over a preview to enlarge it.

Copying & Reporting​

  • Copy Summary: Copies a plain-text summary of the inputs, results, and warnings to the clipboard for pasting into an email or purchase order.
  • Export PDF…: Generates a single-page report of the transfer — inputs, results, warnings, and both braid previews. Disabled in Viewer Mode.
  • Export Excel…: Writes the same content as an Excel workbook — inputs, the results matrix, transfer metrics, the goal-seek block, and warnings. Disabled in Viewer Mode.

Both exports suggest a timestamped filename, so successive runs don't overwrite each other.

Model assumptions

The transfer model is the standard braided-sleeve kinematics: wire length and helix turns are conserved at the wire centerline, so the sine of the braid angle scales with the diameter the braid sits on. Predictions apply to the constrained mid-section of a braid whose ends are terminated — free cut ends unwind locally until they are tacked or banded. In practice a stretched-down braid seats at a friction equilibrium close to, but not exactly at, the kinematic endpoint, and the transfer is effectively one-way: a braid gripped on a shaft does not cleanly relax back to a larger diameter.

  • Catheter Setup Tab — the braid layer editor whose controls and formulas this calculator reuses.
  • Materials Library — the wire materials available for the braid definition.
  • Flowdown Calculator — pre-reflow stackup dimensions for the design the braid transfers onto.
  • CLI API reference — the headless braid_transfer command with the same forward and goal-seek modes.