Cable Runs

Something that new framebuilders should learn sooner rather than later is that planning and installing small bits (cable guides, brake mounts, H2O mounts, etc.) are better done up front rather than after the frame is built.

This is doubly true with carbon fiber frames where small bits present some special challenges. I don't like to put lots of holes through my tubing, and I like to keep the holes as small as possible. The biggest challenge comes when a rider requests internal cable runs.

Routing of internal gear cables is dependent on the crank axle design. Some, like cartridge BBs, are hard to fit a cable around while staying within the BB. For these, I exit the cable at the base of the down tube and use a normal BB cable guide.

Where more space is available, however, its possible to do some interesting things. There are still some challenges however.

Many external cup BB's use a sleeve running around the axle and between the two cups. This isn't compatible with having shift cables inside the BB's. I've developed a split seal for inside the BB, where each bearing cup is sealed separately from the other - leaving a nice smooth axle around which the cable can turn on its run.

This opens up some neat possibilities. A large hole in the front of the BB allows the cable to run inside the down tube and directly into the BB. Then a whole at the rear of the BB has a cable tube running part way down the chain stay where it exits. The cable continues to a pre-formed housing stop - and through the housing to the rear derailer. This makes a very tidy looking setup.

For guides, I like 0.125" O.D. brass tube. This is easy to handle and requires a minimal hole through the tubing and chain stay.

Here are some pix of the chain stay tubing exit that I'm working on. To begin, I build up a filet around the tube as it exits the chainstay.

The filet is basically a thickened epoxy which: 1) doesn't run while curing; 2) has better compression strength than plain epoxy. As you can see from the picture, its hard to get a smooth filet - it's too sticky.

The first thing we have to do is drill out the end of the tunnel and make sure that the cable passes freely through it.

Then we borrow some techniques from steel frame building. Out comes the file, and I file the filet into a smooth shape. It seems to be looking pretty good here, so now we can reinforce this area.

Frankly, this is probably not necessary, but this bike is being built to last and the chain stay encounters pretty significant forces on a regular basis.

In this case, I'm going to put on two longitudinal plys of uni-CF. Each will be split in the middle, along its length, for about half its length. One will be laid from each direction, splitting around the exit hole. The splits allow me to better flatten the CF down, where I want it. These plys will wrap about 2/3 of the way down each side of the stay.

Next comes a uni-CF ply running directly around the stay (at 90 degrees to the prior stays). This ply won't be split, so our exit hole will be covered. Not to worry, it's easy to see where the hole is under the CF.

Finally, I'm putting a full wrap of my double layer 2x2 12K twill. This has a toughening layer between the two plys of CF, making it good for reinforcing a chain stay. The total reinforcement is 5 layers of 150 Gr/SqMeter CF - 3 uni, 2 low-crimp. When it's cured we'll need to drill out the exit hole and make sure all is smooth. Then this guid will be done. A similar arrangement will be used for the front derailer, but we can't finish it yet for reasons that will be obvious later.

Meanwhile, we need to squeeze our CF layers together, and remove the excess epoxy. This is a complicated area to work with. The part is small enough to easily fit in a vacuum bag. Given the small diameter of the chain stay, holding the plys together with good alignment, along with peel ply and bleeder felt, is a bit of a challenge. So for this situation I prefer a different approach - wrapping with electrical tape.

Before I begin wrapping plys of CF, I put a ring of electrical tape around the chain stay, just beyond each end of the section to be reinforced. The tape is wraped upside down - so the sticky side is out. These sections of tape will be used to start and end the compression wraps of tape. Mounting them before things are wet with epoxy makes it a much easier and cleaner step.

Once the CF sandwich is in place, I take off my gloves (so I have clean dry hands), and begin winding the tape around the stay. This too gets wrapped upside down - the inner (usually outer) side won't stick to the epoxy and by pulling the tape tightly, we get good compression.

Ultimately I wind from one end to the other, then reverse and wind back to the original end. Along the way, it's important to keep the tape as free from wrinkles as possible. Every wrinkle will cause a pocket of epoxy that needs to be later sanded down. And a big wrinkle could actually lead to a hump in the CF which would be nasty.

With this done, its time to poke lots of holes in the tape. Actually, in the course of wrapping, excess epoxy was driven ahead of the wrap and out of the layup. But we want to do more and the holes will allow more epoxy to migrate up and out of the CF. The whole setup gets heated by a nearby incandescent lamp to thin the epoxy and facilitate it's flow. If you click to enlarge the picture, you should see lots of little bubbles of epoxy on the surface of the tape.

I won't be able to return to this before tomorrow - but hopefully then I can show pictures of the raw finish.

Cheers,

Done Baking

Here's the main plate. This is viewed from the top and looks much like the surface of the last piece. However, when we turn it over, we'll see a different finish.

Unfortunately, there are a couple of defects on the bottom. Most obvious, a corner got folded over, apparently while placing the layup in the vacuum bag.

While not visible in the pictures, a close observation shows the defect visible through the top layer as a triangular corner which is lower than the rest of the plate.

There is also a stray fiber that got caught - which is strictly a cosmetic defect. But there are also some depressions in the bottom - apparently the table had some defects in its surface which I didn't detect.

All of this leads me to consider a different approach for the next time. Rather than using a bag on a table, I'm going to try laying a piece of plate glass on the table. This should provide a smooth lower surface. The layout w/ peelplys and breathers will be laid on this. Then a lay piece of bagging material over this and seal its edges to the table with a special caulk-like tape. This will avoid the difficulty of sliding the layup into the bag.

Having said this, the majority of this plate looks good, and should make some fine dropouts.

All up this plate weighs 310 grams - so 40 grams of epoxy was squeezed out in the vacuum. That said, my ideal weight was 250 grams and my realistic expectation was 290 grams. So we're just a bit pudgy. It seems clear that I started with too much epoxy to hit my targets. Also, I need to check my pressure next time to make sure that I'm pulling as much as I think (possibility of excess leakage in the bag). Nonetheless, this plate came in with a lower epoxy weight than the last plate so we're making progress. And there doesn't appear to be so much epoxy as to reduce the strength of the plate.

More later.

More Carbon Plates

Pictures! Yea!!!!
Sorry for the quality, its a very old digital camera and the color is off because these were taken without a flash.

Anyhow, these are some more carbon fiber plates under vacuum. Last time, some heavy Kevlar was applied where the axle nuts rest. Two problems with this: 1) It doesn't cut; 2) It doesn't cut. A $35 ceramic tile blade died in the jig saw trying to cut Kevlar. Note, it didn't have any problem getting through the CF - slow steady cuts worked great. Moreover, the edges of the Kevlar end up fraying where the saw tore through them - very unsightly. Meanwhile, some of the CF elders suggested that I experiment without and protective layer over the CF - so that's what I'm doing here.

The last plates were cut up into smaller pieces and showed now voids or soft spots - clearly the epoxy soaked through just fine. After some careful weighing of my raw CF stocks, and some further calculations, it appears that I added nearly 70% epoxy by weight to the final product. That's fine, but not as light as it can be. It may be that for this sort of heavy layup, and infusion technique might be best. Something to explore down the line.


Back to the pix (you can click on them to enlarge), you can see the rough outline of the larger plate being vacuumed. In the one picture, you can also see a 2x4 clamped down on top of the other plate - squeezing it to the work table.

This time my layups looked much dryer than last - but after weighing everything, the main plate has 175 grams of CF and had 175 grams of epoxy added. Once its cured, we'll weigh the plate and find out how much epoxy remained in it. I'm hoping that this will be lighter (by volume) than the last.

The hidden (by the board) plate is just a lever about 1" x 7mm (finished thickness) x 12". It'll be used for some deflection testing.

The main plate will be used for some sample dropouts and the remainder will be used for a variety of tests, including impact & tensile strength.

For this set of plates, a release film was used on the bottom side instead of a peel-ply fabric. This should lead to a layer of smooth epoxy - although nothing like a jell coat. So it's just an experiment. Just as the clamps on the narrow plate are an experiment.

You can see the dark spots where the epoxy is oozing through. Apart from the edges, there's not too much. I gave the edges an extra drink just because I apply epoxy from the center and they looked a bit dryer. Maybe next time we'll do with out the extra.


Just FYI, there is a bleeder felt under the whole setup
(inside the bag of course), and one over the top. The long edges of the big plate got an extra layer of bleeder on top - you can see the ridges running across the top of the bag where these end. You'll also note that the bleeder is much wider than the plates - so there should always be an unobstructed path for the air to reach the outlets for the vacuum pump.

That's about it for this time. See ya around.

CF Drop Outs

OK,

I'm working on CF dropouts. I want to use a new brand of rear triangles, but they don't work with any prefabbed DOs. This is because the chainstays taper all the way to the ends, which aren't parallel to each other. So, a round plug that fits into the end, is way to loose at its front. And, a Do that follows the axis of the stay, without a bend, won't form a parallel platform for the hub.

Anyhow, the first step is to make a plate from which to cut out the DOs. Luckly, I've come into some samples of very nice CF fabrics. The one that will be the base of the plate has 9 plys of UNI Cf in 0/90/45/-45 degree orientation. Three layers of this are used, creating a base 27 layers deep. On the outside, I'm using some 2x2 12K twill that is doubled layered, so the total sandwich will be 31 layers. Kevlar tape goes on where the axle mounts to protect the CF from the bolts.

So here are some pictures from my first plate. This is the backside - nice and flat with a stray piece of CF in the laminate. Unless this stray ends up in an exposed place, I won't worry about it. Note, the Kevlar hasn't been mounted on this side yet. That will wait until the DOs are cut out.

The next view is an edge of the CF that has been cut. All looks good from this slice in terms of bonding and compaction.


You can click on the pictures to enlarge them.


No indications of voids or dry spots. This whole plate weighs 65 grams. I expect that the dropouts will weight less than half this - say 30 grams. After adding the hardware for the derailer - it'll probably be 35 grams.

Typical aluminum DOs the come with many carbon rear triangles weigh around 110 grams (on my scale).

The stainless plate DOs that these are based on weigh in at 125 grams.

So, 35 grams for these sounds pretty good to me.


By the way, Blogger is turning my pix sideways for some reason - sorry.

Here's the front. I've laid the stainless DOs on top of the plate, then sprayed it with some gray primer - to show where to cut.

The yellow is the Kevlar. One piece of Kevlar picked up a spare piece of CF - but this will sand out easily enough.

Notice on the derailer side how there is a shiny rectangle. There was a bit of tape on the end of the Kevlar tape to prevent fraying. The rest of the material was pressed against a woven peel-ply - leaving a flat finish. Where the tape was left a glossy finish.

That's it for tonight. See ya next time.

Fabric Pictures

Normally, I work with unidirectional CF, and sometimes a cosmetic layer of plain weave. Let me explain. In a plain weave, there are threads going both up and down, and side to side, each go over one thread then under the next. It's about as simple a weave as can be imagined. If you know that CF only exhibits strength in tension, then this might sound like a great idea, because one layer can deal with tension in two directions, each at a 90 degree angle to the other. Unfortunately, this doesn't quite work. In weaving the fabric, the threads get bent up and down - they don't lie in a straight line. So we can say that they are 'crimped' and these reduces their strength. In fact, the strength to weight ratio of CF is negatively impacted by the need add epoxy, to align with the vectors of stress (adding layers), and because of crimping. This latter factor is the reason that a woven fabric is usually reserved for an outer 'cosmetic' layer.

Uni-directional CF is an interesting beast and comes in several forms. Because it is uni (one) directional, it doesn't have crimps. Also, it's fairly easy to align with the force vectors, although multiple layers may be needed to pick up all the force vectors. Multiple layers aren't really a problem for us because we'll use enough CF to require multiple layers anyhow.

CF is held together in one of several ways. The first is to run a thread (generally of something other than CF) across the width of the fabric (which is sometimes narrow enough to be called a tape, or wide enough to be a cloth). The cross thread is held in place by some sort of glue. Another approach is to glue a veil (very thin layer of randomly aligned threads) of fibers to one or both surfaces of the uni. The later approach tends to be less visible afterward, but often doesn't allow as much bending of the uni to follow the shape of a structure.

The uni with the cross threads is more common, but the cross threads are thick enough that, even when they are turned in towards the work, they tend to print through somewhat as a ridge in the finished material. Also, its easier to damage the uni carbon threads by rubbing something (anything) across their surface. Each thread is made of very fine strands of CF, and abrasion starts to pull the individual strands away from the thread. With the veil, the surface is better protected, and often on both sides. However, with wider uni fabrics, the veil so limits bending that it doesn't seem to be used much. However, there is an interest form of CF tape made with a veil backing. A one inch tape will be divided into three strips of CF, each with a space between them. The veil runs edge to edge and so crosses these empty strips. Using this tape, it can be split length-wise along these gaps, allowing it to better follow contours. So where one tube joins another, the end of the tape can be split (as an example) allowing the middle CF strip to bend up along the length of the intersecting tube, while each of the other strips angles off and wraps around the intersecting tube. I'll probably have to add a picture of these later to illustrate this clearly.

Woven CF fabrics can come in a number of different weaves, which I won't try to describe here. But, some of the fancier weaves offer more flexibility than a plain weave, and often less crimping as well. This makes them better structural solutions, especially for more complex shapes. In a few moments we'll see more regarding this.

It should be noted that some of the challenges of handling uni-fabrics can be overcome using pre-preg CF. However, pre-preg requires a freezer for storage and an over for curing. Currently, my little shop has room for neither of these appliances - so pre-preg is out.

There are some other venues were pre-preg isn't the chosen solution. And for these
variations on uni-fiber have been developed. Most of these solutions are very high-tech, at least in terms of how they are manufactured. Only a few manufacturers have the facilities to create the best of these fabrics. And, these fabrics aren't generally available except on special order in very large quantities. Thus, they haven't readily been available to custom frame builders.

Recently I spotted someone selling 150 yards of such a fabric - which is much more than I can use over the course of several years - so the purchase was out of the question. But I made contact with the individual who is in the aero-space industry. He works for a major company that you've worked for, and my best guess is that his work is in the defense sector. But that's all I can share.

Anyhow, I asked questions because I wanted to know more about this stuff and it's applicability to framebuilding. He offered to sell me a small lot, so I bought 4 linear yards. Here is a picture of some in the raw:

If you look closely, you will see that there are two layers of uni CF. The top layer is clear, but look at the edge and see that there is a layer behind running at 90 degrees. What is this? It is non-crimped +/- 45 degree uni-directional carbon fiber. The stiching you see helps to hold its shape or body, but it allows the fabric to be very flexible and drape wonderfully around complex shapes (think of a bottom bracket where 3-4 tubes join together around the BB shell). Moreover, each layer of this fabric is about as heavy as one lay of my normal uni-CF - so only half as many layers need to be cut and applied. Naturally, each layer soaks up more epoxy, and more work has to be spent workign the epoxy thoroghly through the cloth. Also, I still need normal Uni to add a third major force vector plus occassionally other lesser vectors. This is very cool stuff and I hope to have some pictures for you soon of it in use.

My new friend also sent me samples of a couple of other interesting fabrics. Look at this:
When I first looked at this, I thought it was a 1x1 plain weave using 12K bundles - this is the now fashionable large checkerboard effect seen on a number of new bikes. Closer examination revealed that it is something else. First note that there is a veil above the upper surface. The backside has the same veil. Looking at the edges, this is 2 layers of CF, with the treads running at right angles. Because there is no stiching, I'm guessing that there is veil between the layers to glue them together. Also look at the weave, it doesn't make squares, but instead forms rectangles. This is a twill weave. Both directions of fabric run over 2, under 2 patterns, and adjacent bundles are staggered by one thread creating the diamond like pattern. My best guess is that when wet out, the veil becomes week and that this should form nicely over bends and curves. It has fewer crimps than a plain weave, but should still offer a nice cosmetic finish. Once I've experimented with it, I'll fill you in.

The next and last fabric is a bit more of a mystery to me. Here are two pictures, one where it has unraveled a bit, and another where the fabric is intact.
From the unravled edge, we can see that there's a whole lot of CF going on. Also, that the fabric is stiched through and has a veil on the top.

My best guess is that this has from 4 to 6 layers of CF. Looking at the edge in the second picture, you can get the sense of all the layers. Also, it looks like there may be some intermediate layers of veil. Without trying to take this apart a layer at a time, it's hard to get a clear picture of the internal structure. And because I only have a limited sample, its hard to investigate in a destructive fashion. Nonetheless, it looks like it has at least 3 directions of uni (0, +45,, -45 degrees) and possibly 4 directions (0, +45, -45, 90 degrees). With all of these layers in one cloth, very few pieces of this should need to be laminated together. Also, most force vectors should be addressed by this one piece of cloth. So it could speed construction significantly. It will take more effort and care to work the epoxy through this cloth. And, it may not drape as well as the other examples that we have. But like the rest, it's going to make for some fun play.

Well that's it for tonight. I'll probably take a cut at editting this a little tomorrow - meanwhile you can enjoy the pix.

Carbon Pix

OK, I promised some pictures and here they are. Hopefully I can format the page so that the pictures align with text.

First off, let's look at some CF bonded to an aluminum tube. In this case, it's a simple solution for a head tube. Use an aluminum head tube for structural purposes, wrap it in CF, and then bond the top and down tubes to the CF. First though, there is a layer of fine fiberglass followed by a layer of CF veil. The later is like a felt, only very thin and porous. Between these two layers, and the epoxy they hold, the CF will be insulated from the aluminum to avoid galvanic reactions.

On this sample, multiple layers of unidirectional CF tape are wrapped around the tube. These are wound at +/- 45 degrees from the axis of the tube, to cover a variety of forces that may be imposed on the joint.

For this demo, heat shrink tape was used to compress the sandwich while curing. Also, just to speed things up, I used a little heat. Around the CF, there is a release layer of plastic film (almost like less-clingy Saran-Wrap), which has a pattern of small holes that will allow excess epoxy to bleed off. On one side of the tube, a layer of bleeder material was placed over the release film. This is like a synthetic cotton batting, which will absorb excess epoxy. When a vacuum is used for compression, it also provides an air channel from which the vacuum can pull.

Normally, the bleeder layer would go all around the tube, but this is test to show you different options. After this was all wrapped, a heat gun was used to shrink the tape. As this was done, damp spots started to show in the bleeder material. The heat from the gun not only shrunk the tape, but also started to lower the viscosity of the epoxy - which helps to remove excess and helps to remove air bubbles in the fabric.

At this point, the whole shabang went into the over (the one in our kitchen), which was then turned on to 175. Once it was at temperature, this was held for about 10 minutes. Then the thermostat was raised to 225 and the timer set to 20 minutes. Approximately 7 of the 20 minutes were spent raising the temp to 225.

At this point, it was removed from the oven and allowed to cool enough to handle. The tape, bleeder, and release film were all removed - and the piece was essentially cured and ready to go. This is the state from which the pictures were taken. As always, pictures can be enlarged by clicking on them.

Here is the side that had the bleeder layer. Note that the lighting exaggerates the texture. The overlap in the layers of shrink tape leave a spiral outline on the CF. Also, most of the texture on the surface is an embossing by the bleeder and release film sharp wrinkles are from the release film and larger textures from the bleeder. Surprisingly, most of this texture can be removed with a layer of clear epoxy. Now here is the side without the bleeder. Notice how much smoother it is. Also, it has a deeper sheen to the surface. If you saw this in person, you would notice the depth provided by a clear coat. On this side, the excess epoxy had no where to go. Some is still distributed in CF (making for a weaker product), but some has risen to the surface forming the finish you see. The overlap of the tape spiral is still visible, but not as much as on the other side.

Now here is another head tube.
It's not an experiment - but a real head tube. It has cosmetic layer of plain weave CF on the top, and was created using a full wrap with the bleeder layer. Unfortunately I don't have a picture of it as it came out of bag, but believe me when I say it had a distinct texture. Less of the bleeder printed through with this, but the texture of the CF fabric was very nearly as strong as if it had never been epoxied. To this, I've painted on a layer of epoxy. This was undiluted, so it's rather thick. There were some runs, which have begun to be sanded out with 400 grit, none the less, you can see the depth of the finish - and when all polished up it will be very impressive looking.

Here's an experiment that didn't go so well...
The picture isn't well lit and you'll want to enlarge it to see what's going on. I tried to run a dart or arrow of plain weave from the BB out onto the chainstay - just for decorative purposes. The problem with plain weave (in particular) is that the edges tend to self distruct. Thread by thread fibers fallout of the weave. The smaller the piece is, the more this happens. I'm working on some solutions to this problem, but meanwhile take a close peak. Besides not having a clean edge to the plain weave layer, you can see a couple of other things: 1) signs that I used shrink tape on the chain stay; 2) the ends of the CF threads are unwinding under the press. The later is most noticable in the center of the picture - two threads on the bottom of the plain weave layer.

Now, this doesn't pose any structural problems - heck this layer isn't structural to begin with. But, it's not the result that I'm looking for - so back to the drawing board for this one.

Some of these issues go away when working using pre-preg (pre-impregnated) carbon fiber. The epoxy in the fabric holds things to gether when handled, and the tack of the fabric makes it easier to hold pieces in position as the CF is layered on. However, pre-preg needs to be stored in a freezer and then cured in an oven - and I don't have room in my shop for a freezer or a frame sized oven - so I stick to normal uni-direction dry CF and wet epoxy layups.

Tomorrow, however, I'll share some pictures of some rocket science that I'm sampling which starts to close the gap between those to processes.
Ciao