The Jig: A Practical, No-Nonsense Framebuilding Fixture

Building frames can be costly if you need to get a €3,000 professional fixture and you can not trust wood or MDF to remain straight and true in heat and moisture variations.

“The Jig” is our answer: a highly accurate, affordable fixture designed specifically for prototyping and small-scale production. By pairing standard aluminum extrusions with our custom CNC-machined fittings, you get a rig that is heat-resistant, structurally rigid, and easily adaptable to any tube shape and size.

Transparent Pricing: The total cost to build this jig is around €400 / $430 USD. To save you from massive international shipping fees on heavy metal, we only sell the custom machined fittings (the kit). You source the heavy aluminum profiles locally, keeping your costs down. Plus, if you ever move on from framebuilding, the extrusions can easily be repurposed for other workshop projects.

What’s New in Version 4.2 (2026)?

We are constantly refining the design based on real-world workshop use. Version 4.2 includes several major structural and usability upgrades:

• Improved Rear Axle Rigidity: We completely redesigned the rear dummy axle configuration to prevent unwanted deflection, making it much easier to keep dropouts perfectly aligned.
• Versatile Steering Angles: Easier setup and adjustment for steering angles that are non-parallel to the seat tube.
• Modern BB Compatibility: Designed to easily accommodate wider (73/92 mm) bottom bracket shells.
• Universal HT/ST Fittings: One stepped fitting covers all common external and zero-stack (EC & ZS) headtubes, while a conical fitting covers the rest. The seat tube fitting is identical to the HT fitting for maximum versatility.
• Better Accuracy & Setup: Improved trigonometric calculations for precise setups, plus easier physical measurement of rear spacing.
• Streamlined Build: Adjusted the design to use cheaper aluminum extrusions without sacrificing any functionality.

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What is included in the kit

Our fittings are CNC machined from high-strength 7075-T6 aluminum alloy and use standard metric M8x1.25 threads for fastening.

Hardware:

• 1x Stepped Headtube Fitting: Covers all EC and ZS standards.
• 1x Conical Headtube Fitting: Covers all other headtube standards.
• 1x Conical Seat Tube Fitting: 20–59 mm (identical to the HT fitting).
• Bottom Bracket Fittings: Covers BSA68/73, PressFit86/92, PF30 (68/73 mm), BB386/BB30, BBright, and T47.
• Gauge Blocks: For easy alignment of the center plane for road or MTB bottom bracket widths.

Digital Access (Customer Portal):

• Detailed user manual on how to assemble and build with the jig.
• Access to our improved spreadsheet calculator (or simply use the interactive calculator at the bottom of this page).
• 3D printing files for custom gauge blocks to help set your center plane distance perfectly.

Important Note: The aluminum extrusions are not included in this kit. Sourcing standard extrusions locally is significantly cheaper than paying international shipping rates for heavy, bulky items.

Price and how to buy

Inside the EU: €119 (Free Shipping)

Outside the EU: €119 + €20 Shipping

For instant purchase, you can order directly through the RD Physics Etsy shop. Alternatively, you can purchase directly from us by sending an email to ideas2cycles@gmail.com or by using the contact form below.

Calculator

You need the manual to make full sense of this, but we include a quick reference here below:

BB drop: This is the vertical distance from the axle line down to the bottom bracket. Typically 30-70 mm.

CS length (c-c): The distance from BB to rear axle. Typically 430-460 mm.

(Effective CS): The horizontal distance from BB to rear axle. Some prefer to use this dimension.

ST angle: Angle of the seat tube in degrees, typically 70-75 degrees.

HT angle: Angle of the head tube (steering angle). Typically 65-75 degrees.

BB fitting diameter: We machine the components to 49 mm.

HT/ST fitting diameter. We machine the components to 59 mm.

Rear spacing: Over-locknut-dimension (O.L.D.), typically 120, 130, 135, 142 or 148 mm.

BB shell width: For road (68 or 86.5) use 68 mm. For MTB (73 or 92) use 73 mm.

Center plane position: This is where you place the HT and ST fittings (see manual). The gauge blocks we provide set the spacing to 58.5 mm (Road) and 61 mm (MTB). Other distances can be used depending on needs and brackets used.

Profile size: This is the stacked dimension when assembling the aluminum extrusions. Typically 40, 45 or 50 mm square extrusion profiles are used.

Profile length: This is for ajusting the head tube angle if not parallel to seat tube. DX_HT dimension is calculated from this value. Typically 1000 mm.

Rear axle from bottom: The vertical distance from the bottom of The jig to where the rear axle is drilled through. Typically 300 mm, but others are possible.