Building a Bike in Montana

First Stop Introductions
#1

Hello Cyber-compositiods,

I am a wrench in my local bike shop and am starting my first bike related composites project. Using a oxy-acetylene rig and a TIG machine I have made a few steel frames off and on since my first one in High School. When I lived in sunny San Diego I shaped and glassed a dozen or so surfboards. I have always thought it would be cool to make a composite bike so now I am making the leap.

The frame is a ‘fatbike’ (4+inch wide tires for those not in the know) that I’ve drawn up in my full version of BikeCAD Pro. I plan to use the same jig that I did the last 7 steel frames in because if it is out of spec I can’t measure it. I considered a tube-to-tube build very similar to the steel frames, but I really want to take advantage of the opportunities for interesting shapes allowed by using composites. I plan to use a blue foam core that I will hand shape after hotwiring out the outline. May or may not burn out the core, shouldn’t matter much either way as I will NOT be internally routing any cables (Mechanic, remember.) Bottom bracket is steel threaded but I have carbon dropouts, head, and seat tubes in the plan.

So far, I have managed to cobble together a working vacuum pump from an old minifridge, a '77chevy vacuum advance and a switch. A car battery charger and a dimmer runs my hotwire foam cutter. I have some uni and some twill, some resin, bagging supplies and a bunch of carbon learning yet to do.

A practice foam core is cut out, and I am trying to make some type of decent seat tube at the moment using a mandrel made from an alloy seat post.

Anyhow, I am definitely up for suggestions from those that have been there and done that. Thanks Leif.

#2

Watch a bunch of Youtube and Vimeo videos on one-off carbon frame builds using foam core and perforated shrink tape. Both bike and recumbent builds. You’ll learn a lot that way.

#3

I have been doing just that. (watching videos) also I’ve been playing around with some test pieces. Having a hell of a time with wrinkles. Just building that ladder of success with my wrinkly carbon rungs. LL

#4

Key to wrinkle-free layups: “One word: bias”

(say in your best Mr. McGuire voice)

“enough said…that’s a deal”

#5

I think that my bagging technique is just not right somehow, I have been doing my layups on the bias and still having lots of wrinkling. It seems like when I pull vacuum the bagging material is always ‘pinching’ some of the breather into a ridge which leads to a wrinkle in the carbon. Is there something I can do to avoid the pinch? LL

#6

The breather should never pinch, only the bag. In fact you want the bag to pinch to avoid bridging.

So flatten your breather, pull a partial vacuum, pleat the bag so that it is nice and orderly, use a screen roller tool to get the bag tight into all the corners, and then finish pulling full vacuum. You may have to do a couple partial vacuum pulls to get everything in place.

The key is to use enough bag that you can pleat it to take up the slack and avoid bridging and pulling your layup out of position.

In fact if you have a really busy layup that wants to come apart you will probably need to debulk it before you even place your breather.

Like most advanced manufacturing operations it’s 90% setup and 10% process so take your time to do a really nice setup and you’ll be rewarded.

Give this a try and let us know how it goes.