No More Scratches: Nylon Bending Blocks for Sheet-Metal Brakes

If you bend thin-gauge metal for cosmetic parts, you know the pain: a perfect blank goes into the brake and comes out with witness marks, scuffs, or die lines. Nylon bending protection blocks—3D printed in SLS PA12—give you a reusable, quick-swap way to create a soft, consistent contact surface on your brake so parts leave the station scratch-free. They bridge the gap between disposable urethane films and full custom steel tooling, especially for aluminum, stainless, brass, and pre-finished sheets. (thefabricator.com)

What Exactly Are Nylon Bending Protection Blocks?

Nylon bending blocks are drop-in, non-marring “soft jaws” and radius inserts that sit on (or replace) your lower die face. We 3D print them in SLS PA12 (Nylon 12) for a tough, dimensionally stable, and low-friction working surface that resists gouging and protects sensitive finishes.

Why PA12? In laser-sintered form (often called EOS PA 2200 or equivalent), PA12 delivers a balanced property set for tooling fixtures: typical tensile strength around 48 MPa, modulus about 1.6–1.7 GPa, Shore D hardness in the ~75 range, density about 0.93 g/cm³, and a heat-deflection temperature that depends on load (approx. 64–90 °C at 1.8 MPa and 150–170 °C at 0.45 MPa, depending on supplier and print parameters). (EU - EOS Store, EOS GmbH, Materialise, formlabs-media.formlabs.com)

Friction also matters. PA12’s dynamic coefficient of friction against steel typically falls around 0.32–0.38, which helps reduce sliding scuffs compared with bare metal-on-metal contact. (apm.matweb.com, lookpolymers.com)

When Nylon Blocks Make the Most Sense

Use nylon protection blocks when:

• You’re bending thin to medium gauges where cosmetic quality is critical (common from ~30–16 ga, depending on alloy and die opening).
• Parts have decorative or pre-finished surfaces—brushed stainless, anodized aluminum, painted/powder-coated, or bright copper/brass.
• You need repeatable radii without metal witness marks.
• You want a reusable alternative to disposable urethane films for day-to-day work. Urethane films are great for quick protection but are consumables and need frequent replacement; nylon blocks give you a durable, shaped surface you can standardize across jobs. (thefabricator.com, wilatooling.com)

Consider standard urethane films when you’re in a rush, need a temporary barrier, or are bending profiles the nylon cannot match; films are a proven way to eliminate die marks, placed between sheet and die, and widely used for cosmetic work. Many shops keep both options on hand: films for odd jobs and PA12 blocks for repeatable work. (thefabricator.com, Polytec Solutions)

Design Options We Offer (Quick-Swap by Print)

1) Scratch-Free Contact Surfaces

Flat or lightly crowned pads that cap your lower die shoulder or V-opening entry, spreading contact pressure and eliminating sharp hard points. The low friction of PA12 reduces slide-induced scuffs during gauging and the first degrees of bend. (apm.matweb.com)

2) Bend-Radius Inserts

Snap-in or screw-down inserts that present a defined nose radius (“R-bar”) to the sheet for consistent inside radii in air bending. We can provide families of radii (e.g., 0.5 T, 1.0 T, 1.5 T, 2.0 T) you can swap in seconds without re-tooling the brake. (Match the radius to your alloy specs and finish requirements.)

3) Finger-Brake/Leaf-Brake Caps

Clip-on profiles that convert finger edges into broad nylon faces for box/pan work where panel cosmetics matter.

4) Quick-Change Backing

Dovetail rails, magnet cups, or countersunk 1/4-20s so you can lock a block onto a steel carrier and hot-swap profiles between jobs. No adhesives, no wrap tapes.

How Nylon Blocks Protect Finishes (and Your Schedule)

• No metal-on-metal: Nylon provides a compliant, damage-absorbing interface that prevents hard contact from imprinting grain, rolling mill marks, or die lines into soft alloys or polished skins. Urethane films do this too, but they wear out; nylon blocks are reusable. (thefabricator.com)
• Lower friction: PA12’s modest friction against steel reduces sliding scratches during back-gauging and part repositioning. (apm.matweb.com)
• Pressure spreading: Shaped contact surfaces distribute load to avoid stress risers at the die shoulder, which is where witness marks usually appear on thin stock.
• Process discipline: Standardized, printed radii reinforce good practice (correct R for the material), keeping you in stable, low-tonnage air-bending regimes. (thefabricator.com)

Bending Tonnage & Process Notes (Read This Before You Order)

Nylon blocks aren’t a substitute for proper tonnage planning. Keep your job in the safe window and you’ll get both clean cosmetics and long block life.

• Use standard air-bending tonnage formulas to estimate force from sheet thickness, V-opening, and material strength—then confirm against your brake’s limits. Industry references use a 60,000-psi baseline and constants like 575 for imperial calculations; adjust for your alloy’s tensile strength and V-opening. (thefabricator.com)
• Avoid coining or bottoming with nylon in place. Coining forces concentrate at the punch tip and can exceed what any polymer interface should see; stick with air bending when using protection blocks. (thefabricator.com)
• Watch temperature: SLS PA12’s heat-deflection temperature at 1.8 MPa is typically in the ~64–90 °C range depending on supplier and print setup; at lower stress (0.45 MPa) you’ll commonly see ~150–170 °C. If your parts run hot from rapid cycling or thick sections, pause to cool or use film temporarily. (EOS GmbH, formlabs-media.formlabs.com)

Rule of thumb: If your tonnage math says you’re creeping toward narrow V-openings and high line loads—or if you must coin—use conventional steel tooling (with or without film) for that operation, and reserve nylon for the cosmetic-critical bends. (thefabricator.com)

Compatibility

• Press brakes (air bending): Lower die V-openings, flat dies, or shoulders.
• Leaf/box-and-pan brakes: Clip-on caps for fingers.
• Back gauges & support: Auxiliary bumpers and gauge-contact pads reduce back-gauge scuffing on soft anodized or mirror finishes.

Not sure which profile fits your machine? Email [email protected] with a phone snapshot of your die setup and the part print—we’ll recommend a starting kit.

CAD & Printing Guidelines for Better Blocks

• Edge conditioning: Add 0.5–1.0 mm (0.020–0.040 in) fillets on working edges. Avoid knife edges; nylon likes rounded load paths.
• Wall & ribbing: For general pads, 6–10 mm (0.24–0.40 in) walls with cross-ribs keep things stiff without overbuilding.
• Countersinks & hardware: We’ll insert heat-set brass threads or specify through-holes for 1/4-20 SHCS per your preference.
• Fit tolerance: Target ±0.2 mm (±0.008 in) on critical mates; SLS surface is micro-textured, which actually helps grip dies.
• Orientation: We orient parts to align layer knit with load and to keep wear faces smooth.
• Finishing: Bead-blasting to a uniform matte is standard. If you want an even slicker face, we can vapour-smooth or tumble—ask during quoting. (Note: higher gloss may slightly raise slip; choose based on your part handling.)

Maintenance & Expected Life

Wipe blocks between jobs (IPA or mild soap), especially after bending galvanized or abrasive finishes. Deburr parts before bending; burrs act like sandpaper on any protective interface—film or nylon. Replace blocks when the face shows grooves deep enough to telegraph on sensitive parts. Urethane films remain a great consumable for odd geometries and can be combined with nylon blocks for edge cases. (wilatooling.com, thefabricator.com)

Specs Snapshot (Typical Values for SLS PA12)

Values are representative, not guaranteed. We’ll optimize print parameters for durability on your job.

Ready-to-Print Profile Library

• Flat pads (shoulder caps for V-dies)
• R-bars (0.5 T, 1.0 T, 1.5 T, 2.0 T) for aluminum and stainless air bends
• Hem offset shims for pre-hem relief passes
• Finger caps for box/pan brakes
• Gauge bumpers for back-gauge contact points

Tell us your die dimensions and material stack (alloy, thickness, finish), and we’ll match a starter kit.

Ordering & Custom Work

Email [email protected] with your part drawing (PDF/DXF), machine/die details, and a brief description of your finish goals. We’ll propose a block set (contact pads + radii + mounting) and send a firm quote. Need unique features—slots, magnets, carrier rails, part-number embossing? We 3D print on-demand, so customization is straightforward.

FAQ

Will nylon blocks deform under load?

Used for air bending within standard tonnage limits, SLS PA12 holds shape well thanks to ~1.6–1.7 GPa modulus and Shore D ~75. Avoid coining/bottoming, and verify tonnage with your material and V-opening. (EU - EOS Store, in3dtec.com, thefabricator.com)

What about heat from fast cycling?

If a run heats the interface beyond ~64–90 °C at 1.8 MPa equivalent stress, slow the cycle, add cooling breaks, or use urethane film for that step. (EOS GmbH, formlabs-media.formlabs.com)

We already use urethane film—why add nylon?

Films are perfect as a universal, consumable barrier. Nylon blocks shine when you want repeatable geometry (defined radii, quick-swap profiles) and a reusable surface that doesn’t need to be cut and replaced each shift. Most shops use both. (thefabricator.com)

References & Further Reading

• EOS PA 2200 / PA12 typical properties (tensile, modulus, density, HDT). (EU - EOS Store, EOS GmbH)
• Materialise PA12 (SLS) datasheet—Shore D and HDT references. (Materialise)
• Formlabs Nylon 12 Powder TDS—HDT ranges at 0.45 MPa/1.8 MPa. (formlabs-media.formlabs.com)
• MatWeb/LookPolymers PA12 data—dynamic COF versus steel. (apm.matweb.com, lookpolymers.com)
• Steve Benson, The Fabricator: tonnage fundamentals & cosmetic bending. (thefabricator.com)
• WILA knowledge article: protecting sheet material to minimize part marking. (wilatooling.com)

Questions or a print-ready CAD file? Email [email protected] and we’ll help you choose the right block set for your parts.

Disclaimer: If you choose to implement any of the examples described in this article in your own projects, please conduct a careful evaluation first. This site assumes no responsibility for any losses resulting from implementations made without prior evaluation.