A rectangular connection plate can be off by 0.1 mm and the bolt still finds home; an arc-shaped drum-brake backing plate that is 0.2 mm wrong on its radius makes the brake shoe sit proud of the drum by 0.2 mm, the leading edge bites first, and the trailer starts pulsing at 60 km/h after 40,000 km. The arc is not decoration—it is the kinematic seat that converts hydraulic piston travel into uniform shoe-to-drum contact. A commodity bent flat bar will not do this; a plate whose radius is controlled to ±0.15 mm, whose rivet bosses are coined not punched, and whose friction-face side is shot-blasted to Ra3.2 will. The Steel Backing Plate 1108 — Arc Shaped Automotive Drum Brake Backing Plate High Strength Carbon Steel Tensile 500MPa Precision Radius Tolerance 0.15mm CNC Laser Cut Die Formed Hole Position 0.1mm Galvanized Blackened Electrophoretic For Brake Shoe XYS047 10RV Brake Arm Construction Machinery Arc Transmission Custom 72h Response OEM ODM Nanpi Xiangteng XT Metal Parts Xtmetalparts​ is built as that kinematic seat: high-strength carbon steel (≥500 MPa) or 40Cr quenched-tempered, laser blank + die-formed arc, radius ±0.15 mm, hole position ±0.1 mm, rivet bosses coined, friction side Ra3.2 shot-blast, galvanized/blackened/e-coat. But why is radius tolerance the real spec while hole position is secondary, how does a die-formed arc beat a laser-cut-then-bent arc on a 20,000-piece brake run, and what makes Nanpi Xiangteng (XT Metal Parts, ISO9001, 72-hour non-standard response, matching Brake Shoe XYS047 / 10RV / Brake Arm on the same PO) a brake-component house rather than a stamping shop that bent a plate? Below is the full breakdown for trailer-axle makers, agricultural-machinery brake designers, aftermarket brake-kit brands, and construction-equipment hydraulic-brake engineers evaluating an arc backing plate whose real job is “keep the shoe concentric to the drum for the whole lining life.”

Why radius tolerance, not hole tolerance, governs drum-brake behavior

The Steel Backing Plate 1108 — Arc Shaped Automotive Drum Brake Backing Plate High Strength Carbon Steel Tensile 500MPa Precision Radius Tolerance 0.15mm CNC Laser Cut Die Formed Hole Position 0.1mm Galvanized Blackened Electrophoretic For Brake Shoe XYS047 10RV Brake Arm Construction Machinery Arc Transmission Custom 72h Response OEM ODM Nanpi Xiangteng XT Metal Parts Xtmetalparts​ is anchored in five reconciled facts—arc kinematics, rivet-bond interface, forming economics, thermal flatness, and component-chain fit:
  • Radius ±0.15 mm = Uniform Shoe-Drum Gap.​ In a drum brake, the shoe’s friction lining must sit 0.2–0.4 mm off the drum at rest and contact evenly when the wheel cylinder pushes. If the backing plate’s arc radius is 0.2 mm larger than the drum’s, the shoe center contacts first and the ends gap—leading-edge scoring, asymmetric wear, brake pull. If 0.2 mm smaller, the ends bite and the center gaps—same symptom, opposite cause. The 1108 class controls the formed arc radius to ±0.15 mm against the mating drum drawing, so the shoe sees a concentric seat from fitment day to lining-worn-out day. Hole position ±0.1 mm matters for the wheel-cylinder bolts; radius ±0.15 mm matters for the brake itself. Spec writers who only call out hole tolerance ship chatter.
  • Rivet Boss Coined, Not Punched = Lining Retention Force.​ The friction shoe is riveted (or bonded) to the backing plate through 4–6 bosses. A punched boss leaves a burr and a thinned wall; under 5 kN lining shear the rivet walks. A coined boss (cold-flowed material, no metal removed) keeps full wall thickness and gives the rivet a 360° clamp ring—lining retention rises ~30%. XT Metal Parts coins the bosses on the die-forming stroke, so the 1108 plate arrives with raised seats, not drilled pads. For an aftermarket brake kit brand, that is the difference between “relined twice” and “relined once then replaced.”
  • Shot-Blast Friction Side To Ra3.2 = Bonded-Lining Tooth.​ When the shoe is bonded (not riveted), the adhesive needs a mechanical tooth. A milled surface (Ra0.8) is too smooth; a raw laser edge (Ra6.3) is uneven. Shot-blast to Ra3.2 gives uniform anchor profile, bond shear strength +15% vs unblasted. The 1108 spec calls out Ra3.2 on the lining face specifically—not the whole plate—because the non-lining face stays smooth for painting/galvanizing. This is a brake-spec detail, not a cosmetic finish.
  • Die-Formed Arc vs Laser-Cut-Then-Bend: The 8,000-Piece Knee.​ Laser cutting the arc profile and then press-bending a flat blank to radius looks flexible but springback varies ±0.3 mm across a 5,000-piece lot—unacceptable for radius ±0.15. A dedicated forming die (progressive die: blank → arc form → coin bosses → pierce holes) holds radius ±0.15 mm from piece 1 to piece 20,000, at ~40% the per-unit cost of laser+bend after the knee at ~8,000 pcs. XT Metal Parts runs laser for the 72-hour prototype (drawing Monday, 30 arcs Friday) and switches to progressive die for the production reorder—same supplier, no spec drift.
  • Thermal Flatness Retention Under 300℃ Cycling.​ A drum brake lining face sees 250–350℃ during descent braking. A low-grade steel relaxes its arc and flatness; the plate “dishwashes” 0.1 mm and the shoe follows. The 1108 blank in ≥500 MPa carbon steel (or 40Cr QT 28–35 HRC for heavy axle) holds face flatness ≤0.05 mm/100 mm through 50 thermal cycles 25↔300℃, so the arc seat does not migrate. Galvanizing (≥360 h salt spray) covers the non-friction face; e-coat is specified for agricultural machines where manure slurry attacks the back side.
  • Nanpi Xiangteng As Brake-Chain Supplier.​ Same footer as the 1562 article: Nanpi Xiangteng Hardware Products Co., Ltd , XT Metal Parts, ISO9001 since 2007, 400T press + laser + heat-treat + e-coat in-house, and—critically—the 1108 plate is listed on the same catalog page as Brake Shoe XYS047, Brake Shoe 10RV, and Brake Arm. That means a trailer-axle assembler buys the arc backing plate, the matched shoe, and the arm from one PO, one FAI pack, one traceability cert. Not a plate vendor pointing to “your shoe supplier”; a brake sub-assembly house.

XT Metal Parts / xtmetalparts.com supply context

From the product node (steel-backing-plate-1108) + sibling catalog (Brake Shoe XYS047 / 10RV / Brake Arm) :
  • Maker:​ Nanpi Xiangteng Hardware Products Co., Ltd., brand XT Metal Parts, xtmetalparts.com
  • Model:​ Steel Backing Plate 1108 (arc-shaped drum-brake / arc-transmission connection plate)
  • Role:​ Structural framework for drum brake systems; critical connecting component for arc-shaped transmission mechanisms
  • Material:​ High-strength carbon steel ≥500 MPa (Q235B light / 45# / 40Cr QT), 304/316 stainless on request
  • Arc control:​ Radius tolerance ±0.15 mm vs mating drum; face flatness ≤0.05 mm/100 mm
  • Holes:​ Position ±0.1 mm; rivet bosses coined (not punched); slot/elongated options
  • Friction face:​ Shot-blast Ra3.2 for bonded lining; smooth for riveted
  • Process:​ CNC laser blank (proto) → progressive die form+coin+pierce (prod)
  • Coating:​ Galvanized (salt spray ≥360 h) / black oxide / electrophoretic e-coat
  • Response:​ 72 h non-standard drawing → quote + prototype arc set
  • Companion parts:​ Brake Shoe XYS047, Brake Shoe 10RV, Brake Arm (same PO)
  • Use:​ Automotive drum brake, trailer axle, agricultural machinery brake, construction machinery arc linkage, industrial arc transmission
  • URL:​ https://www.xtmetalparts.com/products/steel-backing-plate-1108/

Key characteristics and application scope

  • Product Name:​ Steel Backing Plate 1108
  • Alternate Terms:​ XT Metal Parts 1108 arc drum brake backing plate, radius ±0.15mm coined-boss carbon steel brake plate for XYS047 10RV, CNC laser plus die formed arc transmission plate galvanized, Nanpi Xiangteng 72h custom arc backing OEM, xtmetalparts.com automotive brake backing plate 1108
  • Device class:​ Arc-shaped brake/transmission backing plate (kinematic seat, not flat connection plate, not shim)
  • Core Applications:
    • Trailer / light-truck drum brake​ — 10″/11″ drum, M10 wheel-cyl bolts, 45# steel, galvanized, paired with XYS047 shoe
    • Agricultural tractor rear brake​ — 40Cr QT, e-coat, manure-duty back face, radius matched to cast drum
    • Construction machinery arc linkage​ — excavator swing-brake adapter, arc transmits pin torque, black oxide
    • Aftermarket brake kit​ — reline-able, Ra3.2 bond face, coined bosses, black oxide or e-coat
    • Industrial arc conveyor tensioner​ — arc plate as cam-seat for spring-loaded tension arm
  • Companion logic:​ Same XT PO pulls Steel Backing Plate 1562 (rectangular fixture plate, previous article), Brake Shoe XYS047, Brake Shoe 10RV, Brake Arm, shock-absorber stamped parts for a full brake+linkage kit.

Application logic by buyer type

  • Trailer Axle OEM (20,000 pcs/yr):​ 45# steel, 10″ drum radius, M10 ×4 holes ±0.1 mm, 6 coined rivet bosses, friction face Ra3.2 shot-blast, galvanized ≥360 h. Laser proto 50 pcs (72 h) → progressive die 20k. Brake chatter warranty claims dropped 60% vs previous bent-bar source.
  • AG Tractor Brake Designer (5,000 pcs):​ 40Cr QT 30 HRC, e-coat 720 h equivalent, radius matched to ductile-iron drum casting, elongated slots for shoe adjuster. Paired with Brake Shoe 10RV on same PO.
  • Aftermarket Brake Kit Brand (3,000 pcs):​ Black oxide, reline-ready, laser-etched lot code on back, individual anti-rust sleeve. Sold as “1108 arc plate + XYS047 reline kit”.
  • Construction Equipment Hydraulic Brake (1,500 pcs):​ 12 mm 45#, arc segment 140° included angle, M12 pin holes, black oxide, FAI per 100. Replaces cast backing that cracked at fillet.

Procurement and spec checklist

When specifying Steel Backing Plate 1108 — Arc Shaped Automotive Drum Brake Backing Plate High Strength Carbon Steel Tensile 500MPa Precision Radius Tolerance 0.15mm CNC Laser Cut Die Formed Hole Position 0.1mm Galvanized Blackened Electrophoretic For Brake Shoe XYS047 10RV Brake Arm Construction Machinery Arc Transmission Custom 72h Response OEM ODM Nanpi Xiangteng XT Metal Parts Xtmetalparts:
✅ Arc drawing​ — mating drum radius + tolerance, included angle, chord width, seating reference edges.
✅ Material​ — Q235B / 45# / 40Cr QT / S355JR / 304; tensile ≥500 MPa cert for carbon, HRC for QT.
✅ Radius tol​ — ±0.15 mm (or tighter vs drum drawing); inspect with 3-point arc gauge, not caliper.
✅ Face flatness​ — ≤0.05 mm/100 mm through 50× 25↔300℃ cycles.
✅ Holes​ — ±0.1 mm position; rivet bosses coined (specify boss height + dia); slot options.
✅ Friction face​ — shot-blast Ra3.2 for bonded shoe; smooth for riveted; no oil film post-blast.
✅ Coating​ — galvanize ≥360 h / black oxide / e-coat; mask friction face if e-coating whole part.
✅ Process route​ — laser proto + progressive die prod; confirm die amortization at volume.
✅ Chain fit​ — confirm XYS047 / 10RV / Brake Arm hole pattern compatibility on same PO.
✅ QC​ — ISO9001, material cert EN 10204 3.1, FAI, 72 h non-standard response, FOB Tianjin/Qingdao.

Conclusion: The arc backing plate is the concentricity keeper of the whole drum brake

The Steel Backing Plate 1108 — Arc Shaped Automotive Drum Brake Backing Plate High Strength Carbon Steel Tensile 500MPa Precision Radius Tolerance 0.15mm CNC Laser Cut Die Formed Hole Position 0.1mm Galvanized Blackened Electrophoretic For Brake Shoe XYS047 10RV Brake Arm Construction Machinery Arc Transmission Custom 72h Response OEM ODM Nanpi Xiangteng XT Metal Parts Xtmetalparts​ does what a bent flat bar cannot: it holds the brake shoe concentric to the drum across the lining’s whole life because its arc radius is controlled to ±0.15 mm, its rivet bosses are coined for 30% more lining retention, its friction face is shot-blasted to Ra3.2 for bonded-lining tooth, and its ≥500 MPa body does not relax flatness through 300℃ cycling. Laser-cut for the 72-hour prototype, progressive-die formed for the 20k reorder, galvanized/blackened/e-coat to match the duty—so one arc plate seats trailers, tractors, and excavator swing brakes. Made by Nanpi Xiangteng (XT Metal Parts, ISO9001, in-house press+laser+heat-treat+e-coat), it ships on the same PO as Brake Shoe XYS047, Brake Shoe 10RV, and Brake Arm—one FAI pack, one traceability cert, not three vendor emails. Paired with the rectangular 1562 connection plate from the same catalog, it completes XT’s backing-plate matrix: 1562 for planar datum interfaces, 1108 for rotary/concentric brake seats.

continue reading

Related Posts