Front triangle

Part of my design was a seat tube insert which I expected to mold independently, onto a 30,9mm aluminum seat tube used as a mandrel.

My idea was to get the internal diameter at the right dimension straight of the mold, so this would not need any machining to make the future seat tube fits inside.

The insert would then take place inside the front mold, and be part of the laminate.

See the end result here.

To create this seat tube, I started with a 3D printed cavities which I design with the correct offset, almost 2mm of carbon fiber thickness.

These printed cavities were placed inside 2 pieces of wood, before I brushed two layers of gelcoat and compacted the epoxy mold putty as the reinforcement.

I don’t have picture of the work during Prepreg placement and final mold , but basically the two cavities were bolted together so the pressure was apply on the laminate onto the seat tube mandrel.

I ended up with a tube a the correct length, and a perfect internal diameter 💪

For the bladder of the front triangle, I opted for linear inner tubes combined with epoxy foam - I went to this option after the research on how to do a bladder that I did along my project , more detail here.

First step was to create the foam inserts in the areas where the inner tube would not inflate enough.

For this I used wax sheet layers to offset the cavities in the desired areas.

Before to cast the foam inserts, I made sure the mold was protected with a cling film. Otherwise foaming epoxy would have bonded to the cavities.

I prepared some pvc tubes to create holes inside foam inserts, so the inner tube could enter by the head tube openings an follow the frame design.

Then the epoxy foam was mixed with its hardener and quickly cast in the cavities, before the mold was closed.

See here the foam inserts once mold has open.

The foam inserts needed a little of repair in certain area where it did not expand properly.

This was done with methacrylate glue.

Prepreg placement was another area where I would have needed some help....but no one could really help. So I decided to apply the basics of the technics learned during the training at Easycomposites.

First step was to define the cutting templates for Prepreg with the help of paper adhesive.

Then made these templates out of carton, cut the Prepreg and place it into the cavities.

The laminate is a combination of a 3K 2/2 twill surface ply, multiple crossed layers of UD and a 12k 2/2 twill backing ply.

After the last layer of backing ply, I did a one hour debulking of the whole laminate with a vacuum bag, so this ensure a better consolidation of the laminate

Once the two cavities were laminated and compacted, then I prepared the placement of fiber onto the foam inserts.

Having these inserts laminated was a way for me to connect one side of the mold with the other and ensure a connection ont the overall width of the tube section.

The inserts were placed inside one cavity, and linear inner tubes went through the inserts along the tubes.

All along the tubes, I placed some Prepreg which covers the overall width of the top and the bottom section of the tubes.

Once closed, the mold was bolted between two metal sheets made out of an old heater.

Once the bladders has inflate, then the whole thing was placed inside the oven to start the cure.

Because the epoxy mold putty whistand 90 degrees maximum, I opted for a low temp curing cycle.

Once the curing cycle was complete, the mold was left to cool down at room temperature.

Then It was open, and he first frame pop out of the cavities !

Swingarm

The same process was applied for each halves of the swingarm.

Below are the pictures of all the consecutive steps, from laying up the Prepreg surface ply, until the mold was closed.

After a similar low temp curing cycle, the mold has open and the part went out not too bad.

Same for the other half swingarm.

Next step was to finish the parts, bond the swingarm together, bond aluminum inserts and clear coat the whole things. Click here to see next steps.