Overview
 GeoJig is a modular bike frame jig system designed for builders who need flexibility, accuracy, and scalability.
All GeoJig products share a modular design philosophy, allowing different configurations for frame width, length, and special requirements.

This listing includes three product types — Simple, Wall-Mount, and Modular — each serving different build levels while sharing compatible components.

Simple Frame Holder
A minimal and lightweight frame holder designed for basic frame alignment.
It does not include a main base; instead, the head tube holder and seat tube holder together define the reference plane.
  • Supports standard, wide, and long frames
  • Simple structure, easy to set up
  • Ideal for DIY builders and entry-level frame fabrication
Materials: Wood

Wall-Mount Frame Jig
A wall-mounted modular frame jig designed to save space while maintaining alignment accuracy.The head tube holder and seat tube holder define the geometric reference plane.
Materials: 4040 aluminum extrusion + modular holders

Modular Frame & Fork Jig

A full professional-grade modular frame and fork jig system.
All modules are connected through a 40120 aluminum main base, which serves as both the structural backbone and the geometric reference plane.

Materials: 40120 aluminum extrusion + precision modular components

About Frame Size Option

Standard: Regular road, gravel, MTB frames
Wide: Fat bike and extra-wide rear triangle frames
Long – Standard Width: Tandem frames with standard width
Long – Wide: Fat tandem or long fat bike frames
Custom: Any combination of width, length, and extra modules

Modular System Description

The GeoJig Modular Frame & Fork Jig is a professional-grade bicycle frame alignment system built around a rigid aluminum extrusion backbone.
Each module has a clear structural role and works together as one integrated system.


M01 – Main Base Module

System Backbone & Geometric Reference Plane
  • Aluminum extrusion: 40120
  • The structural backbone of the entire jig system
  • All other modules are mounted to this base
  • Provides system rigidity and global alignment accuracy
Geometric Principle:
The vertical plane defined by the center slot of the 40120 extrusion is used as the left–right symmetry reference plane for the entire bicycle frame.

Available lengths:
  • Standard Frame Base（1200MM）
  • Wide Frame Base (Fat Bike)（1400MM）
  • Long Standard Base (Tandem ) (2000MM)
  • Long Wide Base (Fat Tandem) (2200MM)
  • Custom Length
M02 – Bottom Bracket & Seat Tube Holder Module

Core Frame Triangle Positioning Module
  • Fixes bottom bracket and seat tube simultaneously
  • Connected to the side of the main base via a 90-degree pivot bracket
  • Allows:
          Seat tube angle adjustment
          Front–rear position adjustment by sliding along the side of the main base
  • Maintains precise alignment relative to the main reference plane
This module defines the core geometry of the front triangle, not just adjustment.

M03 – Head Tube Holder & Reference Module

Head Tube Fixation & Alignment Reference
  • Supports two fixing methods:
    1. Dual aluminum cone fixation (upper + lower)
    2. Fork-based head tube positioning using an M8 threaded rod
  • Allows builders to choose their preferred head tube alignment method
  • Ensures accurate head tube positioning relative to the system reference plane
This module defines the front-end geometric reference, not just a clamp.

M04 – Rear Dropout Alignment Module

Rear Triangle Reference & Calibration Module
  • Fixes rear dropouts in a stable and repeatable position
  • Once installed, it is generally not recommended to move this module
  • Serves as the rear reference origin when adjusting frame length
  • Both sides of the 40120 extrusion are marked with adhesive measuring scales to ensure:
    Left–right symmetry
    Accurate vertical drop between rear axle and bottom bracket
Rear dropout alignment is intentionally kept stable to reduce recalibration complexity.

M05 – Fork Alignment & Assisted Support Module

Fork Alignment & Structural Support Module
  • Used for:
    Fork alignment
    Assisted fork fabrication
    Supporting head tube positioning when using fork-based reference
  • Reuses aluminum profiles from the system
  • Can be integrated with frame jig configuration when needed
This module improves front-end accuracy and system stability.

M06 – Width Extension Module

Frame Width Expansion Module (Fat Bike / Special Frames)
  • Expands frame width without moving the system reference plane
  • Head tube, seat tube, and bottom bracket positions are shifted to one side of the main base
  • Standard expansion:
    4040 aluminum extrusion (+40 mm)
  • Optional expansion:
    4080 aluminum extrusion (+80 mm)
    Further expansion possible for special requirements
This design ensures the left–right symmetry plane always remains unchanged, even for wide frames.

M07 – Chain Stay Spacing Assist Module

Chain Stay Alignment Assistance Module
  • Cylindrical steel rod mounted in the center slot of the main base
  • Can slide freely along the slot
  • Provides accurate spacing reference during chain stay fabrication
  • Significantly improves efficiency and consistency when building rear triangles

FAQ

Q1: Are these three separate products?
A: Yes. These are three different GeoJig product types with different structures and module configurations.
This listing allows you to select and purchase one product type and configuration from the available options.

Q2: Can I upgrade later?
A: Yes. Modular components are compatible.

Q3: Does Simple or Wall version have a reference plane?
A: Yes. The head tube and seat tube holders define the reference plane.

Q4: What does Custom include?
A: Custom width, length, extra seat tube holders, and special modules. Please contact us before ordering.

Q5: Can I customize width and length at the same time?
A: Yes. Please choose Custom Configuration and contact us.

Q6: Can Simple or Wall-Mount versions be customized?
A: Yes. All GeoJig product types support custom width and length.