July 6

July 6, 2005

Joining PETG

The fairing mold is slightly over 10 feet long, and I can only buy PETG plastic sheets in 8 foot lengths. This means that in order to vacuum form a 10 foot long fairing, I would need to either split the mold into two halves, vacuum form each half, then bond them together - or, figure out a way to bond two 8' long flat sheets of PETG together and vacuum for one entire fairing shell.

I decided to see if I could figure out a way to bond the PETG together that would stand up to the heat and pressures of vacuum forming. Since my join would be around 8 feet back from the nose of the fairing, I am not concerned with a visible seam, as the air flow would most certainly be turbulent that far back from the nose.

I tried a variety of different ideas, and the only one that worked was to heat weld two sheets together while pressing them firmly together using pliers. Like this:

1. Stack and clamp two sheets of PETG together

2. Pass a heat gun back and forth across the exposed edges of the PETG until they get soft

3. While keeping the PETG soft with the heat gun, press the two edges of the plastic together using a pair of pliers

4. While still hot and soft, split the two stacked sheet apart (like opening a book), place down onto a flat surface and press down the seam with weights and a flat bar

5. Here is a side-view of the seam

6. Here is what the seam looks like in the vacuum mold


Training update: I officially hung up my road bike and went out for my first long ride on the M5 with Greg. It's tough riding with someone on a road bike because it's more difficult to talk due to the different altitudes, and the M5 is way faster. At 200 watts I was averaging about 34 - 35 kph on the flats leaving Greg way behind. In fact, comparing the SRM data after the ride showed a way higher than average speed with a way lower than average watts output. On the longer rides, I am not that concerned with the lower power output. My plan is to do one long ride a week starting at 4 hours and add a little distance each week slowly working my way up to 18 hours in one ride.

Additional inter-week rides are for faster sessions - one intervals session, and a couple really quick hour to 90 minute workouts.


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