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Anchor points and connections for xfoil: TPU hardware from the 3D printer for tarps, ponchos and more.

  • Apr 9
  • 3 min read

Those working with ultralight films like xfoil face the challenge of safely transferring forces into the material. Since tear resistance under point loads is rather low, mechanical solutions like eyelets are unsuitable. A stable solution is offered by the combination of full-surface bonding and 3D-printed reinforcements made of TPU 95A .


The mounting principle: gluing on the underside

A crucial factor for durability is positioning: The TPU hardware is always bonded to the underside of the film. When tensile stress is exerted by the guy line, the component is pressed against the film. The film acts as a mechanical barrier, meaning the load is not solely dependent on the adhesive but is physically supported. This significantly reduces shear forces on the adhesive tape and prevents premature peeling.


Material choice: TPU 95A

Among the available filaments, TPU 95A is the most suitable material for this purpose:

  • Cold resistance: It remains flexible and does not become brittle even at sub-zero temperatures.

  • Toughness: It is abrasion-resistant enough to withstand the friction of the cords in the hole without wear.

  • Adhesion: The surface forms a very good bond with LSE-based (Low Surface Energy) adhesive tapes.


Geometry: The 0.2 mm ramp

All components taper to a thickness of 0.2 mm at the edges. This flat geometry is necessary to ensure a seamless transition between the hardware and the film. Sharp edges would create stress concentrations where the film could buckle or tear under load.


The 4 hardware modules (OpenSCAD code)

Here are the code blocks for the individual components. The hole diameters are optimized to 1.5 mm to ensure a press fit for 2 mm shock cord.


1. Tension triangle (corners)

With rounded corners (radius 2 mm) to avoid notch effects on the film.


// xfoil_triangle.scad
size=30; tc=1.0; te=0.2; hd=1.5; r=2; $fn=60;
difference() {
    hull() {
        linear_extrude(te) offset(r) polygon([[r,r],[size-2.5*r,r],[r,size-2.5*r]]);
        translate([3,3,0]) linear_extrude(tc) offset(r) polygon([[r,r],[size-9-2.5*r,r],[r,size-9-2.5*r]]);
    }
    translate([8,8,-1]) cylinder(h=3, d=hd);
}

2. Surface lifter (round)

For guying points on the surface to create more space under the tarp.


// xfoil_circle_lifter.scad
d=30; tc=1.0; te=0.2; hd=1.5; $fn=100;
difference() {
    hull() { cylinder(te, d=d); cylinder(tc, d=d-10); }
    translate([0,0,-1]) cylinder(3, d=hd);
}

3. Locking toggle (Toggle)

Mechanical closure (T-shaped) for doors or poncho sides. The base is hole-free for maximum adhesive surface. You need to cut/punch a hole in the Xfoil at the desired location, insert the toggle from the back, and then glue the base in place. This ensures that the hardware is pressed against the foil when pulled, instead of just being held in place by the adhesive tape.


// xfoil_toggle_unten_schmal.scad
bd=30; th=8; tw=7; te=0.2; $fn=60;
hull() { 
    cylinder(te, d=bd-10);                      
    translate([0,0,1-te]) cylinder(te, d=bd);   
}
cylinder(th, d=5);
translate([0,0,th-2]) rotate([0,90,0]) hull() {
    translate([0,0,-tw/2]) sphere(d=5);
    translate([0,0,tw/2]) sphere(d=5);
}

4. Mini anchor (counterpart)

Small adhesive dot (20 mm) with central hole for the rubber loop of the toggle.


// xfoil_mini_anchor.scad
d=20; tc=1.0; te=0.2; hd=1.5; $fn=80;
difference() {
    hull() { cylinder(te, d=d); cylinder(tc, d=d-6); }
    translate([0,0,-1]) cylinder(3, d=hd);
}

Cord selection and elastic tension

Since xfoil film, unlike nylon, has very little inherent elasticity , shock cord (elastic cord) should be used at the guy points. A single strand of 2 mm cord is sufficient to absorb wind loads and protect the adhesive bond from sudden load peaks. A 2 mm elastic cord fits very tightly and securely in a 1.5 mm hole.


Manufacturing and assembly

Those without their own 3D printer can use the SCAD files to have the parts manufactured in a local makerspace or FabLab. The material costs for a set of hardware are minimal.


The bonding surfaces can be degreased with isopropanol before assembly. Information on choosing the right tape (e.g., filament tape or LSE-compatible industrial tapes) can be found in the detailed tape guide for xfoil projects .

 
 
 

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