Feb 17

Feb 17, 2005

How to learn

You don't learn by doing things right, you learn by doing things wrong (well, I do anyhow).

I think I have made almost every mistake in the book with this fiberglass molding process! This is a good thing because now I know from first hand experience WHY you have to do what the books say, and WHAT exactly happens when you don't.

Mistake #1: Spending too much time on the surface finish of the wheel fairing plug. Since I was going to use the male plug to mold the fiberglass onto with vacuum bagging, I failed to realize that the exterior of my finished glass piece would still have the fiberglass weave pattern on it (print through) and would require some additional post finishing. To spend all that time getting the plug super smooth was a waste of time. Also a mistake related to this mistake is to use Bondo on Styrofoam. I know Bondo reacts with styrofoam, but you can use it if if coat your foam plug with epoxy resin first, which is what I did. The problem with bondo over foam is the foam is soft and the bondo is hard and the bondo cracks and indents really easily.

Mistake #2: Spending too much time on the surface finish of the Female fairing plug mold. Since I'm not spraying on a gel coat, the print-through from the fiberglass cloth shows up on the exterior surface of the finished part anyhow.

Mistake #3: Using painters poly and duct tape to make a vacuum bag. WRONG!! I completely wasted the good part of a day trying to locate leaks in my crappy plastic bag that wouldn't hold a vacuum. I think it's OK to use thicker weight of painters poly, but you need to use the double sticky vacuum bag tape.

Mistake #4: I tried taping the edges of my vacuum bag down to a plastic table top which did not work out very well. What happens is the plastic needs to wrap around your mold and press into grooves and crevices in the mold. When the bag it taped down to a table, it needs to stretch too much to fill the spaces in your mold. The best way I have found is to made a vacuum bag and put your part into the bag, then seal it. That way the bag can freely form to the part.

Mistake #5: Not making a solid support for your female mold! At 20 inches of mercury there is a lot of pressure on your mold. Enough to bend it out of shape. I made this mistake twice - first using a styrofoam edge around my female mold which bent apart, then I made another and used heavy weights to hold it down - but it STILL bent out of shape! For male molds, this isn't an issue.

I think in the end, unless you are producing multiple parts, you are far better off making a styrofoam male mold and either leaving it in the part, or dissolving the foam after the resin cures. Spend a minimal amount of time with the surface finish of the mold, and more time finishing the part. If you need to make more than one or two copies of your part, and want to go the female mold route, do the surface finishing on the mold surface, then use gel coat and make sure your mold is MDF wood so it won't warp under vacuum. Either that, or make your male plug out of MDF wood, pull a STRONG fiberglass female mold from that - reinforce it with wood structure, and make your final part from that. I think the work involved in the female mold process only makes it worth-while if you plan on producing more than one part - other than that, there is far less work involved with a one-time styrofoam male plug, and a bit of post surface finishing.

Following is photographic evidence of my schooling:

I put 5 layers of fiberglass cloth onto my dented up foam and Bondo plug then added loads and loads of resin - I couldn't believe how many double cups of resin I dumped over that thing to saturate it!

After vacuum bagging and curing, I ripped off the breather and peel ply revealing my new fiberglass wheel fairing.

The wheel fairing. The black lines are black felt marks on the glass cloth I used to cut out the patterns.

The wrinkles are caused by the vacuum bag wrinkling up around the edges. These can be sanded or ground off later, but I'd like to try to do a better job of planning my bagging so I don't get those ridges.

I used my Dremel cutting tool to cut a line around the whole fairing.
When I pulled the fiberglass off, the entire foam plug ripped apart. In fact, the fiberglass pulled off the thin layer of bondo on my plug.

I had planned on using the plug twice to make both wheel fairings, so now I have to use the fiberglass part as a female mold and make my second set with that instead of the plug.

I had to scrape off the bondo which was stuck to the PVA mold release.
This is my vacuum bag test using painters poly and duct tape. For some reason, I was able to get a pretty good vacuum using this set-up
My cheap-o vacuum bag test
Here are both halves of the wheel fairing sanded smooth, waxed and ready for PVA mold release agent
I laid in 4 to 5 layers of glass cloth using my contact cement spray glue technique.

The flange was built with styrofoam and duct tape holds the fiberglass mold to the flange.

Ready for about 3 1/2 tons of resin.
This is a disaster. First, I'm not getting a good vacuum, and second, note how the edges are warping up.
I ripped it apart and made a traditional vacuum bag which worked very well. I used 25 pound weights to hold the mold flat, but it still warped enough that the two halves do NOT fit together.
The parts popped out quite easily.
Since my two new wheel wells don't fit together because they are too warped, I am going to put the original two back together and use it as a new male plug mold. I will pull another entire fairing off of that and cut it inhalf to get it off.

4 3/4 hours on the M5 yesterday inside in front of the TV.


1. Strut slot sliders - Simplify to a folding cover
2. Canopy Bubble - make a sliding convertible top
3. Front wheel well - Make glass version
4. Wingnuts for fairing mounts
5. Electrical - rechargable battery with a panel with switches for rear strobe and front headlight
6 Add a second front caliper brake
7. Make a portable wind trainer using the (mini-rollers)
8. Look into painting the fairing
9. Find a helmet that fits in the bubble
10. Add second brake
11. Install sound system
12. Rear add-on lighting system

TOTAL distance on TCR1
866 km

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