Introduction: Repair Carbon Fiber Bicycle Frame - CNC Made Insert

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If you have and Carbon fiber bicycle frame that had been damaged by the rear axle shaft, here you have a good solution that will transform your damaged bicycle in an aluminium indestructible one!

Step 1: The Problem of Carbon Bicycle Frame

Carbon fiber frames are very light and trong, but the rear axle shaft can damage the frame due several reasons:

  • Lack of tightening torque
  • Tolerances play
  • Hard hits
  • Ect.

The removal of material on the frame will lead to misalignment of the wheel with the frame, causing noises on the rear brake, on the drivetrain, tires hitting the frame, ect.

This can be repaired with carbon fiber and resin, but for this project I prefer to make an Aluminium insert that will be much more robust to erosion.

Step 2: Fusion 360 Modeling

Since Fusion 360 is a powerful and simple to use CAD/CAM software, I used it to create the 3D model.

I started by measure the dropout and frame dimensions with a paquimeter to create a draft of the part.

Next step was to make a sketch with measured dimensions on Fusion 360, after that with some extrusions and holes the part was ready for CAM.

Step 3: Fusion 360 CAM

After Model the part Fusion 360 was used to generate the Toolpaths for the CNC.

  1. - Facing of stock with 6mm tool
  2. - 3D Adaptative to remove material with 6mm tool
  3. - 3D adaptative to finish with 3mm tool (since I didn't have a small diameter tool was not possible to finish the part)
  4. - Ramp to remove material for screws on the backside

Tools used:2 Flute Carbide end mill Amazon link

-Diameter 6mm, Flat end mill, 2 flute, carbide

-Diameter 3mm, Flat end mill, 2 flute, carbide

Step 4: Milling the Part on the CNC

The milling of the part was performed with my homemade CNC, if you want to see the specs are in this video.

The G-code from Fusion 360 was used upload to GRBL controller of the CNC and the party started, as planned.

I don't want to get in detail for speeds and feeds, because this will be specific for each machine.

Tools used: 2 Flute Carbide end mill Amazon link
-Diameter 6mm, Flat end mill, 2 flute, carbide

-Diameter 3mm, Flat end mill, 2 flute, carbide

Step 5: Preparing the Frame

The insert was made in a way that is necessary to remove some carbon fiber of the frame to be possible to assemble the part to be glued.

  1. Carefully was removed the excess of the frame until the milled part is possible to be inserted.
  2. The position of the part was verified to make sure the wheel is aligned with the frame
  3. The part was glued with Araldite to the bike frame

This part of the work was critical, so I didn't took to many pictures. (sorry)

Step 6: Finished Job

At the end the bike was rideable again, already made +400km of MTB without problems.

Thanks for reading the Instructable and check my youtube channel:

Youtube channel Laranjas3

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