To make a cardboard or phenolic tube stronger, it can be reinforced with layers of carbon fiber or fiberglass through a process called composite overwrap. It's a simple process that only requires a few steps.
- Prepare the surface of the tube. For a phenolic tube, this means sanding. For a kraft paper tube, remove the shiny glassine layer to allow better adhesion.
- Place the tube on something, like a rod supported on either end, that will allow it to rotate freely without touching anything
- Measure and cut the fabric to fit over the tube. Cutting it a little large is fine in order to cover the entire tube, but the material will stretch when wet. Make sure you have enough that the beginning and end of the fabric overlap to reinforce the seam
- Mix resin system and make sure to wear the appropriate PPE (personal protective equipment, including safety glasses, gloves, and probably a lab coat)!
- Place one end of fabric on the tube along the axis, and tack on with epoxy
- Spread more epoxy on the fabric to coat all of it - there should be no dry spots - but don't spread on so much epoxy that it oozes everywhere. Extra epoxy just adds weight, and reduces strength since it is not as strong as the composite fabric.
- Roll the fabric onto the tube and sparingly cover it in epoxy, repeating until the tube has been fully wrapped.
- Allow to dry (6-8 hours for fast dry, 10-15 for slow dry, but up to 4 days until max strength)
Troubleshooting:
- make sure that all of the fabric is wet
- work out any air bubbles by gently pushing them to the edges of the overwrap
- be aware of wrinkles - they're easier to work out of the layup if you have just laid that fabric, but can be removed with patience