GeoJig Bike Frame Jig System – Simple / Wall / Modular, Standard to Fat & Tandem For Sale

OverviewGeoJig 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 HolderA 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 JigA 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.

• Wall-mounted 4040 aluminum base
• Supports standard, wide, and long frames
• Modular and adjustable
• Ideal for small workshops

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 framesWide: Fat bike and extra-wide rear triangle framesLong – Standard Width: Tandem frames with standard widthLong – Wide: Fat tandem or long fat bike framesCustom: 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.