Saturday, May 31, 2008

Carbon Carbon Everywhere

Look around, carbon fiber is everywhere. For only $269 you can get a decorative CF panel to stick on the pillar between the front and rear doors of your Scion! Yep it seems to be ubiquitous.

Only a year ago, prognosticators in the composites industry were predicting a major CF shortage. Looking around at suppliers, not all of them have all products in stock. That said, it's easy to find the materials I use in frame building. So that's a good thing.

A little known fact outside of the industry is that carbon fiber tubes cost about the same as high end steel tubes, such as from Columbus or Reynolds. True that. Oh and yeah, I said tubes. In fact I source my tubes from the same place as Trek. Did you know that Trek and many other bike manufacturers assemble their frames from tubes? For the consumer, that's not an important issue. But marketers have done a good job of selling the idea that CF frames are built of a a single carbon fiber monocoque - not assembled from tubes. So consumers don't like the idea of joined tubes and manufacturers don't talk about using CF tubes.

Well I'm not afraid to admit to working with tubes. The fact is, filament wound tubes can be manufactured to tighter specifications than a complex molded part. Which means that tubes offer the opportunity to build stronger and lighter! Yipee!

How these tubes are joined together is the real heart of the building process. And, for many manufacturers and frame builders, joining offers the potential for product differentiation. And I too have been working on my proprietary methods - with some success.

Most builders & manufactures use some form of wrapping the joint in CF and epoxy. Within this method, there are two primary approaches: a) wet wrapped CF vacuum-bagged until cured; b) pre-preg CF wrapped, heated under pressure in an autoclave until cured. The second approach is heavily used by manufacturers. It's an easier method to control the amount of epoxy in the CF (because it comes pre-impregnated), and pre-preg is relatively easy to handle while setting it up to cure. Two problems exist for this method in small volume production: a) Autoclaves are expensive; b) the product is molded - molds are expensive and limit dimensional flexibility. So, pre-preg is ideal for volume production.

Wet wrapping involves several steps. First, the layers of CF need to be cut out with the fibers oriented to plans. CF has little compression strength, so it requires fibers to be aligned in a variety of directions so that any force on the joint will be compensated for by fibers working in tension. In fact, if CF had the same strength in compression as in tension, we could make much lighter frames - using much less CF.

Anyhow, CF we use (except for cosmetic out layers) is unidirectional. That is, it isn't woven, all the fibers run in one direction. Various methods are used to hold the fibers together prior to being laid up with epoxy. None of these methods are perfect. So just cutting out the patterns on the dry CF can be difficult and requires a sharp scissor.

After the layers are cut out, we prep the tubes. This means lightly sanding the surfaces and then cleaning them with rubbing alcohol or acetone. The goal is to have clean bare CF on the tubes for bonding.

Then we mix up some epoxy. There are various approaches to mixing including: a) Electronic scales; Graduated cups; Calibrated pumps. Any of these approaches will work if care is taken. Once the epoxy base and hardener and dispensed, we have to mix them together thoroughly. This usually has the result of infusing oxygen bubbles into the CF - which we will address later.

The mixed epoxy has a limited pot life. By choosing different hardeners, and being sensitive to the ambient temperatures, it's possible to adapt the pot life for the task at hand. Note that there is a general rule that the longer the pot life, the longer the cure time. So we want to limit pot life to what we really need to assemble a joint and get it ready for curing.

Next we need a flat surface, which can be covered with saran wrap or wax paper (to keep the surface clean). We take our CF pieces and lay them down one at a time. Pour some epoxy on top and use a scraper or squeegee to spread the epoxy between the fibers. We want to avoid having the CF be soaked in and dripping with epoxy, but we want it to be full of epoxy. Depending on the setup, we may do this to all the CF pieces first, and them layer them on the joint. Or, we may apply each piece of CF as it gets wetted out. In either case, we end up with our tubes wrapped in layers of epoxied CF.

Over this we put a layer of material that won't stick to the epoxy. A mylar film can be used to get a very smooth finish, or a teflon coated polyester fabric can be used. The later gives a rough surface, but is better at allowing excess epoxy to flow through. And we want it to flow through to the next layer - which is a synthetic cotton batting. This batting performs two tasks. We will put this whole contraption in a sealed plastic bag, and use a vacuum pump to suck out all the air. The external air pressure will act as a giant clamp holding things together during curing, but more importantly, it will compress the layers of carbon fiber in the joint. In so doing, excess epoxy will be squeezed to the surface, and the batting will catch and hold this excess so that it doesn't enter the pump (which would be a disaster). Also, the batting provides a channel through which the pump can continue to suck air even as the bag collapes. Otherwise, the bag opposite the vacuum fitting would get sucked into the fitting and stop it from evacuating the rest of the bag - which would do us no good.

In the process of sucking epoxy through the layers, we hope to make sure that any voids in the CF are filled with epoxy and any air bubbles are pumped out. The reality is that this will never occur perfectly, but with good vacuum pressure we can eliminate enough voids and bubbles to ensure a strong, quality joint.

A key to making all of this work is holding the tubes together, in the proper position, as the CF is wrapped on, and until the epoxy cures. A number of approaches work, from fixturing the tubes to gluing them together.

I like the later approach, as it's possible to assemble a full front triangle and then vacuum the joints one at a time. But the bonds are fairly delicate and this got me thinking of a better way to join tubes. I've developed a proprietary method that I call full surface bonding. Without giving away too much, bond a solid surface, not a hollow tube to the adjoining tube.

How strong is this? Well, I wouldn't ride a bike so built without CF wraps around the joints. But, the point of failure is delamination of a tube surface. Think of it like this. We have a plain tube and one that is mitered. The mitered tube is bonded to the plain tube. When this joint fails, it is the surface of the plain tube that is failing - not the adhesive and not the mitered tube. In other words, this joint is as strong as it can be given lamination strength of the tube to which it is bonded.

One notable feature of this method is that it adds negligible weight to the joint. As implied above, I've been doing destructive testing of my joints. So far, with full surface bonding, I'm still using the same schedule of CF laminations on the joint. This ultimately produces a stronger joint, with a weight difference that is hard to measure. The goal, is to establish a joint that is as strong as a normal wet wrapped joint, but which has fewer laminations of CF and epoxy to save weight. When testing indicates that this is ready for market, I'll be sure to let you know.

In the mean time, I can miter and jig assemble my frames similar to steel frames, when these are set (and naturally in super alignment), I come back and vacuum one joint at a time - allowing for perfectly laminated joints.

Well, that's it for tonight. Gotta run, so we'll see you soon.

Saturday, May 24, 2008

I've missed you guys

How ya'll doing?

I'm back, in more than one way. Time to resume blogging. And I'm getting over a bad bug that's laid me low for a week - but gives me some free time to post.

The winter was slow, as it was hard and long weather-wise. Next year will require some better solutions to keep the shop fit for working. As those get sorted out, I'll be sharing them with you.

Being a slow winter gave me the opportunity to do a few other things, some of which have be referenced in other posts. One we haven't discussed much is reflecting on frames and frame-building. All my thinking hasn't lead me to many firm, absolute conclusions. But it all helps me refine my thinking and goals. So I'm going to share some of these thoughts starting here with something about which I feel strongly.

It's not for me to tell other builders what to do, so let's be clear about this up front. But my belief is that too many custom builders are working too hard to be visually different, or even to create visual art rather than bikes. Each of us has a different approach to our visual aesthetic. Some work hard to achieve certain common elements throughout their work. Others strive to make each build unique. And all of this is good, from where I sit. But, when the decoration appears to somehow impede functionality - it disturbs me.

This year's Handmade Bike Show offered many examples. I don't really want to point fingers at anyone in particular - after all some of the worst examples come from very capable and successful builders. And some of these touches looked cool. But if you go to, and look through the galleries, you can probably figure out I'm talking about. One bike, being shown for the second year in a row, isn't even ridable. Adding unnecessary, dysfunctional components or accessories, or significant (as in physically big, unnecessary, flashy) frame details aren't my piece of cake. Moreover, its likely to take buyers mind off of the more important aspects of bicycles and custom frame-building.

Richard Sachs probably represents the more Zen-like end of the scale. He's not into chrome or polished stainless. He works with a limited pallet of paint colors (or is that just his riders?), applied in traditional schemes. He doesn't do a lot of lug carving. But, he may put more than the average number of hours into a build - because he is obsessive about detail and functionality.

Farther down the scale are Curtlo's with their curved stays, or Kirk's Terraplane model with his curved stays. Without having ridden either, I'm comfortable conjecturing that these have no discernible performance effects. They do visually set these frames off, and don't impede the functionality of these frames. As such, they seem like fair approaches to incorporate style with functionality. Just like the Hetchin's curly frames that preceded them.

Personally I like a little flash in the form of polished stainless, and for dropouts, stainless is a functional improvement. Fancy paint is a cool thing, and long established as an aesthetic element of fine bikes. You, I and the next guy will have different opinions as to when these elements enhance or detract from the look of a bike - and I won't try to determine what other builders should do with these factors.

On the other hand, if you're building a fully equipped Rando bike, and can't fit the fenders concentric to the wheels, then who cares if you thread the dynamo wiring through the frame and rack tubes or not. And yet one respected name has advertising showing featuring such a bike. Schwinn (the real made in Chicago Schwinn) got this right, so top custom builders ought to as well.

Then there is the practice of penetrating tubes with tubes. The first time it looked kind of cool. And it probably didn't hurt too much other than to make the tube heavier (assuming the main tube itself wasn't very light,or that it had a very long butt). However, afterwards, repeating this practice is just derivative, non-functional, and a potential source of later problems for the rider. Some builders prefer to build exactly what the rider asks for - and if its pierced tubes, so be it - who can fault them for responding to their clients. But, the bike that Lance bought for his new store just wasn't likely to be ridden in any meaningful way, regardless of who purchased it.

I believe that all of this overlaps other behavior we see, such as the guys who buy a custom chopper and then trailer it to events. I just don't get this behavoir. If you're one of these guys, no problem - I'm not suggesting that you stop. But, it just doesn't make sense to me if either the rider or bike aren't up for the trip to the event - what are they good for? Showing off a fancy *purchased* chopper only says the rider was able to buy (finance?) the bike - it represents no skill in building, or aesthetic judgment, or riding ability. Look at me I have money?

The above isn't meant to pick on chopper guys, because this is just one example of a larger phenomena - that some frame-builders may have fallen into with their more outrageous designs.

The truth is that we live in a consumer society. Mere consumption doesn't ever satisfy anyone's needs. I can't prove this, and haven't done any scientific study of the issue. But, look around you and I think the statement proves itself.

If you doubt this, consider a few examples: We're drowning in the problem of too little oil. It doesn't matter if we're at peak oil of not. Prices around here are over $4/Gal. And most folks can't afford that - at least not without substantially changing their lifestyle. Should we be surprised about this turn of events when automotive sales for the last 10-15 years have returned to a focus on size of vehicle and amount of horsepower. No one needs 300-400 or more horsepower. No one can reasonably use that kind of power. Yet how many folks will stretch their budgets in order to have a huge powerful engine.

Yeah, we're putting a lot of emotional energy into our consumerism - trying to feel better, without consideration of functionality. And no, car sales aren't unique in this way. If they had any money left, American's would still be buying bigger and fancy houses - that they make less and less use thereof.

I'm a map freak - so Google Earth is just a great thing. It's interesting to look a rivers, lakes, and ocean front. Man, there's a lot of invested in boats, sitting in the water, with their covers buttoned up tight, doing nothing. Maybe the folks that take the pictures don't do so on weekends or holidays - but I bet even then, only a small fraction of the fleet is used on any weekend. This doesn't slow folks down from buying boats. And like cars and choppers, the bigger, fancier, and more powerful, the better.

It's long been said that the two best days for a boater are when he buys his boat and when he sells it. This suggests, awfully strongly, that the benefit of a boat is primarily the act of consumerism - and thereafter the best thing one can do clean their hands of their purchase. Now let's face it, there are folks who really use boats (and motorcycles/houses/cars). I'd suggest that in many cases, it is the owner of a small boat or a sailboat who is most likely to make significant use of their craft. There, the activities around using the boat are more accessible, and a source of enjoyment. When things get too fancy, boat ownership becomes just about posturing. And posturing isn't a very satisfying activity, if only because there's always someone who has more than you or I or the next person.

This probably sounds like a screed against consumerism - and likely it is. But, my point is that activity is where we find personal rewards. Hanging a bike on the wall doesn't really bring one much satisfaction. Riding a nice bike, properly fitted, is a joy. And by focusing too much on being visually different, IMO, some builders are helping push cycling too close to mass consumerism rather than pushing riders to be active.

Again, I'm not trying to bust anyone's chops here. But, this thinking does help me solidify the limits I impose on the builds that I do. Functionality has to be the driver for fine frame-building.

Hopefully I haven't PO'd all my readers. But, it is one of my convictions as a frame-builder - and I thought you should know.