I was doing a repairs on my friend Justin’s Specialized Epic carbon fiber hardtail frame this week. Justin is fast and knows how to play rough. Somehow he broke the drive side chain stay in two places. It was hanging on by threads. Fuck it. Fix it up and get it back out for more punishment! War horses.
There are some things that I like about carbon fiber frames. While they are delicate, they are very easy to repair at home with hardly any tools. You need a mass scale, a mixing stick, and a small brush outside of carbon material and epoxy. It’s a pretty nice thing to do, fix these when they break. More folks should learn to do it.
When I’m doing repairs for friends, the deal is that I don’t need to fuss to make it pretty or like it was never broke. I do a fix. It’s ugly but it works. That’s what no money buys you. This takes the pressure off me but also just lets me help a bro. This is not my job.
So, I was mixing the West Systems epoxy that I use; 105 Epoxy Resin & 207 Special Clear Hardener to be specific. These mix at a ratio of 3.7 (resin) to 1.0 (hardener) by weight. The manual is HERE.
I’m sure that mixing by volume is nice when working with large amounts of epoxy but at the scale of bike repair, mixing by mass is simply the only option. Often, only around 10 grams at a time are needed.
It’s easy to make this difficult and wasteful. Many people will aim for a target weight, hope they do the math right, over poor something, try to correct, and worry it’s all gone wrong. There’s an easy way.
- Tare your cup
- Pour in about as much resin or hardener as you think you need.
- This is best starting with the hardener as the greater quantity of resin will work in your favor in accurate dispensing.
- Take note of the weight.
- Some simple math and you’ll know what weight to bring the total to with resin (or hardener).
- Add the balance of the material.
- Stir the mixture
Total Weight = (Hardener Weight) * (3.7+1)/1
Total Weight = (Resin Weight) * (3.7+1)/3.7
This isn’t rocket science. This is just a nice quick and easy way of doing good mixing over and over with small quantities of material. I’ve looked for these formulas online but they are close to impossible to find. Sure, they are simple but look at how few people mention them or claim to use them. It’s fascinating how often simple math stops most people dead in their tracks.
