Spider

Description

Forged Aluminum Bicycle Spider (Flat): Five-Arm Chainring Carrier

The forged aluminum bicycle spider is the five-arm carrier in a crankset that holds the chainrings. It has a central round hub with five arms extending outward, each machined at its tip with a bolt hole for the chainring. This flat version keeps the arms roughly in the same plane as the hub for a simple, light structure.

The spider carries pedaling torque from the crank to the chainrings, and the arm roots are stress concentrations. Al Forge Tech (AFT) hot forges the spider so grain flow runs continuously from the hub into all five arms, with a recessed hub to save weight. After heat treatment, the central spline or mounting bore and the arm bolt holes are CNC-machined, and the bolt circle diameter (BCD) and indexing are confirmed on CMM.

Key Features

Five arms and hub forged in one piece with continuous grain flow at arm roots
Flat design for a simple, light structure
Bolt circle diameter (BCD) and indexing CNC-machined
BCD and flatness verified on CMM

Forged Aluminum Bicycle Spider (Flat) Specifications and Manufacturing Capability

Item	Details
Product category	Aluminum Forging Bicycle Parts
Application	Chainring carriers for bicycle cranksets
Primary process	Closed-die hot forging (hot forging presses 600T–8,000T)
Material	Selected to customer specification; 2xxx, 5xxx, 6xxx and 7xxx series aluminum alloys available (e.g. 2014, 6061, 6082, 7075)
Heat treatment	In-house T4 solution treatment (8 units) and T6 artificial aging (7 units), set by alloy and strength requirement
Secondary machining	CNC machining (52 machining centers, 30 lathes), deburring, vibratory finishing
Surface finish	Anodizing (including hard anodizing), shot blasting, e-coating or painting, as required
Inspection	Zeiss CMM (4 units), hardness testers, spectrometer, fluorescent penetrant inspection line
Dimensions and tolerances	Per customer 2D/3D drawings
Quality system	IATF 16949:2016, ISO 14001:2015

Forged Aluminum Bicycle Spider (Flat) Manufacturing Process

Drawing review and DFM: we confirm alloy, load direction and critical dimensions, then run QForm simulation to predict metal flow and defect risk.
Die design and manufacturing: the number of die sets (for example, blocker and finisher dies) is planned around part complexity, and die contours are checked with a portable 3D scanner.
Hot forging: closed-die forming on 600T–8,000T hot forging presses creates a continuous grain flow that follows the part contour.
Heat treatment: T4 solution treatment and T6 artificial aging are performed in-house, with parameters set by alloy and strength requirement.
CNC machining and finishing: holes, threads and mating surfaces are machined, followed by deburring, vibratory finishing, shot blasting or anodizing as required.
Inspection and shipment: dimensions, hardness and chemical composition are verified with CMM, hardness testers and a spectrometer, with lot traceability kept under IATF 16949.

FAQ

Why is spider BCD accuracy important?

The BCD (bolt circle diameter) is the circle on which the chainring bolt holes lie and determines whether the chainring mounts correctly. Errors in BCD or indexing can make the chainring wobble, affecting shifting and chain running. AFT machines all five bolt holes in one CNC setup and measures BCD, indexing and flatness on Zeiss CMM.

How does the flat spider differ from the stepped spider?

In the flat spider the arms lie roughly in the plane of the hub, suiting single-ring setups or designs where the chainring sits flush on the spider. The stepped spider has a deeper hub and arms with a height change, giving a specific offset between chainring and hub to suit different chainline requirements. AFT can develop either style to the brand’s drawing.

How does a forged aluminum Forged Aluminum Bicycle Spider (Flat) compare with casting or machining from billet?

Forging shapes aluminum in the solid state under pressure, so the grain flow follows the part contour and the porosity and shrinkage common in castings are avoided. Compared with machining from solid billet, a near-net-shape forging removes less material and shortens machining time. For a Forged Aluminum Bicycle Spider (Flat) under repeated loads, forging balances strength and weight; the final choice still depends on design loads and volume.

How do you keep the Forged Aluminum Bicycle Spider (Flat) consistent from lot to lot?

Al Forge Tech runs incoming (IQC), in-process (IPQC) and final (FQC) inspection under IATF 16949:2016, supported by 4 Zeiss CMMs, hardness testers, a spectrometer and a fluorescent penetrant inspection line. First, middle and last pieces of every lot are checked against the die; when wear causes dimensional drift, the die is reworked to keep the Forged Aluminum Bicycle Spider (Flat) stable across lots.

Can the Forged Aluminum Bicycle Spider (Flat) be anodized or given other surface finishes?

Yes. Al Forge Tech offers anodizing (including hard anodizing), shot blasting, vibratory finishing, e-coating and painting, plus pickling and ultrasonic washing lines to clean parts after machining. Please note the finish type and film thickness on the drawing so machining allowances and cosmetic standards for the Forged Aluminum Bicycle Spider (Flat) can be evaluated together.

Request a Quote for the Forged Aluminum Bicycle Spider (Flat)

Developing a new Forged Aluminum Bicycle Spider (Flat) or converting an existing part to aluminum forging? Send us your 3D/2D drawings, alloy and temper, annual volume and finishing requirements. Our engineering team will reply with a feasibility review, die plan and quotation.

Online inquiry: Contact Us
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To compare similar parts, browse Aluminum Forging Bicycle Parts and our automotive aluminum forging applications, or visit About Us for our equipment and certifications.

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