Then click where the first fibre crossing sits. The net grows from there, and the cut shape comes out the other side. A STEP lets you pick which faces to cover first.
CARBON · GLASS · ARAMID
DrapeCut is a browser-based composite draping tool, free while in beta. Upload a STEP or STL model, simulate woven fabric draping over a compound-curved surface, see where the shear runs past the locking angle and the cloth will wrinkle, and export the flat cutting pattern as DXF. It runs on the server, so nothing is installed and the browser only draws the result.
An STL works straight away. A STEP is meshed on the server and lets you pick which faces to cover first, so a flange or a return edge can be left for another ply.
Click where the first fibre crossing sits, or let the tool suggest one. Set the weave, then the warp direction of each ply in the laminate; add plies to stack them on the same seed. The net grows outward from the seed across the surface.
The flat cut shape comes out the other side with the warp along x. Download it as DXF with fibre lines every 5th or 10th tow, ready for a plotter, a cutting table or a printed template.
A woven cloth is two families of tows, warp and weft, crossing at right angles. When it is laid over a doubly curved surface the tows cannot stretch, so the only way the cloth can conform is for the crossings to change angle: the weave shears. Draping simulation predicts that shear across the part and, from it, the shape the cloth must be cut to before it is laid up.
DrapeCut uses the kinematic pin-jointed net model. The cloth is treated as a net of rigid links pinned at the crossings, each link one tow pitch long. Starting from a seed point, two geodesic axes are traced along the warp and weft directions, then every other node is found by intersecting two spheres of radius one pitch with the surface. The method is fast, deterministic and gives the same answer as the published drape algorithms used in composites design. More on the model, and what it leaves out.
CAD flattening tools assume the sheet is isotropic and can stretch a little everywhere. Woven carbon, glass and aramid cannot: a tow is stiff along its length, so all the deformation happens as in-plane shear at the crossings. A compound curve, a dome or a saddle, is not developable at all, and a flatten will either fail or hide the distortion in a shape that cuts wrong. The draped pattern is different in kind: it is where each tow ends up when it cannot stretch, mapped back to the flat cloth. Carbon fibre over compound curves, in detail.
The colour on the part is the shear angle in every cell: how far the crossing has closed from 90°. Blue and grey is close to zero, gold is 45°, and red is past the weave's locking angle. Locking angle is where the tows jam against each other and the cloth can shear no further; beyond it the cloth buckles out of plane and wrinkles. A plain weave locks early, around 30°; a 2×2 twill reaches about 45°; satins go further. Choosing the weave in the panel sets both the locking angle and the tow pitch, and the statistics report the maximum shear and the number of cells past lock. Reading the shear map.
The flat shape is written as an R12 DXF with the outline, optional fibre lines, the seed mark and any cells past lock on their own layers. R12 is the dialect everything reads: plotter software, CNC cutting tables, laser cutters and every CAD package. Dimensions are in millimetres, the warp runs along x, and the seed mark shows where to start laying the cloth on the mould. A laminate exports as one file with a layer group per ply, each developed on its own mid-plane. When one piece of cloth cannot reach the whole part, the tool lays several pieces, trims each to its own ground plus an overlap, and exports them together or one at a time. The STEP to DXF workflow, step by step.
Each example is a real drape of a sample part: the net on the surface, the flat cut shape, and the numbers. Open one in the tool to change the seed, the warp angle or the weave.
DrapeCut is free while in beta. Examples export without an account; to download the pattern for your own part you sign in with an emailed code, and the part and its patterns are kept in your account. Signed out, your mesh is never written to disk, though the file name, settings, result numbers and a small image of the pattern are kept for 90 days so we can see how the beta is used. The model is kinematic: it has no friction, no tow bending stiffness and no ply-to-ply interaction, so treat the shear map as a map of where the cloth will fight you rather than a guarantee of what it will do. For predicting how a whole stack forms under pressure, a finite-element forming simulation is still the right tool; for cutting plies that fit the mould first time, this is enough.