Aug 23

August 23, 2005

Bonded-in bottom bracket shells, frame thickening and bonding on the rear wheel well.

I bonded the right half of the rear wheel enclosures onto the frame because it makes getting at that rear wheel for maintenance a lot easier if I don't have to deal with two shells. Further, a good bond all the way around the perimeter of the dome would mean a stronger chain stay to hold that rear wheel solid and secure.

This shows the unfinished epoxy/micro that I used to fill in the edges between the frame and the wheel dome. It's so secure, it would probably hold water without leaking.

I also wanted to better distribute the load to the left hand wheel dome, so I thought I would bind some additional threaded studs to the frame. I wasn't sure about the best way to bond an aluminum bolt to the frame, so I made a little test part with some various methods of gluing bolts through carbon.

I used epoxy, Metl-Weld, and epoxy with micro. I also tested various ways of anchoring the bolts into the sandwich board. After they had cured, I tested the strength with weight:

They all held 75 pounds without even moving a bit - all except for the Metl-weld ones which snapped fairly easily. Metl-Weld is a two part metal bonding substance that is suposed to be as strong as a weld. I tested some of it on a couple of aluminum strips and I was able to break them apart by hand. Supposedly, it is compatible with carbon fiber and epoxy resin.

Regular epoxy resin works better than this stuff. And yes, I followed the directions for proper preparation of the metal first.

There are 4 aluminum threaded studs bonded to the frame + three steel through bolts - one at the top and two on each side. I am VERY pleased with the rear wheel - it is easy to adjust the track of the wheel simply by sliding the left hand wheel dome around before tightening the nuts and the quick release. It's very easy to get the rear wheel off and on again - less than a minute. Very solid and very light.

During ride tests I realized that I needed to do a better job of securing the bottom bracket shells for the cranks and the mid drive because I could see a bit of movement.

I sanded down the aluminum shells, cleaned them with acetone and covered them with epoxy. I placed the shells back into the holes in the frame which is a very tight press fit requiring the use of a hammer. Since the edges of the holes were routed round, there was a nice gap to pour more epoxy into. I filled these gaps with epoxy and let it cure.

Then I added 2 additional layers of 11 oz carbon fabric plus a final layer of fiberglass to build up the thickness of the frame to slightly more than the width of the aluminum brackets. While these new layers were still wet, I epoxy coated the aluminum bolts and brackets, and bolted the brackets into the frame squishing the wet frame to the same width as the brackets.

This should be pretty secure.

I continued the new laminate over the headtube area to build it up to the proper thickness also. I still need to deal with better securing the headtube in there - not exactly sure what I am going to do about that yet...


Still to do:

1. Add a rear caliper brake
2. Trace the real perimeter outline using an actual fairing half shell (when I get one!), and cut out the perimeter
3. Edge laminate the perimeter
4. Thicken the frame to avoid using the spacers on the brackets
5. Bond in the bottom brackets
6. Make new remote steering out of carbon and UHMW
7. Bond on the right hand rear wheel dome.
8. Bond fasteners to frame for the left hand wheel dome
9. add a thin coat of epoxy to the left hand wheel disc because it is not air tight


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