Let's see, where to begin? Ah yes. Concerning bamboo. (Can you hear the fiddle in the background from Lord of the Rings when Bilbo is writing about Hobbits?) You might like to know where I get my bamboo. I used to get mine at Master Gardens, but after getting a couple of bad shipments, I started getting mine at Frank's. It comes in 8 foot lengths, about 2 inches wide, and pretty thick. That means it needs some preparation.
For this build along, I'm going to make the bow 66" nock to nock. If I cut the nocks in an inch from each end, that means I'll need the total length to be 68". So let's cut the bamboo down to 68" long.
Before doing that, we want to center the nodes on each tip. That is, we want the distance between each tip and the first node to be the same. If we have an eight foot piece of bamboo, that'll give us lots of flexibility.
The nodes on bamboo are not equidistant. They are farther apart near the ground and closer together near the sky. Looky here at this picture:
These are opposite ends of the same piece of bamboo. See how much closer together the nodes are on the top than they are on the bottom? Well, ideally, we want the nodes to be as far apart as possible. The closer the nodes are to each other the more likely you are to get a hinge in your bow, or have other problems tillering. So when we measure out our 68 inches, we want to do it closer to the end where the nodes are farther apart.
To get the 68", take a piece of scrap wood or something that's more than 68". Use a tape measure to measure out 68" on it. Make pencil marks 68" apart. Then take that piece of wood or whatever and lay it down on the bamboo. In my case, I'm using a scrap piece of bamboo flooring. Once you lay it down on the bamboo, you can center it. Get it to where the nodes are the same distance from each pencil mark. In this picture, I've got the nodes on each end about 5 inches from the pencil marks.
I'm sorry that picture isn't more clear. The top part shows the left end of the bamboo, and the bottom part shows the right end. See how the pencil mark is 5 inches to the left on the top and 5 inches to the right on the bottom? Once I've got it centered, then I make pencil marks on the bamboo so I'll know where to cut. Then I cut off those ends with my band saw.
Then I want to find the dead center of the bamboo--the intersection of the center of the width and the center of the length. To get the center of the length, I put a yard stick flush with one end of the bamboo and make a pencil mark at the other end of the yard stick. Then I put the yard stick flush with the other end of the bamboo and do the same thing. Now I've got two pencil marks close to the center. I take a ruler and find the midpoint between those two pencil marks. That's the center of the length.
To get the center of the width, I just put a ruler across the width and find the center. Then I've got a + sign at the dead center of the bamboo, and I put a nice fat 'C' on there to remind me to SEE where the center is.
Next, we want to make sure the bow isn't warped from side to side. We want the tips to be lined up perfectly. To do that, let's run a string along the bamboo and hang weights from each end.
Since the bamboo is warped, it's kind of hard to tell when the string is really over the center, isn't it?
It all depends on how you look at it. That problem is easy enough to fix. Just stand there at the midpoint, stretch out your arms, and push down on each side. As you push down, the string will eventually touch the center point, and then you'll know whether it's running through the center or not. If not, then adjust the string on each end until it goes through the center. Once it does, make a pencil mark on each tip under the string.
Since I make a lot of bows, I have found it much easier to use a template rather than measure out my dimensions on each bow individually. I made my template out of a piece of poster board. I drew the lines exactly how I wanted them, got it perfectly straight, then cut it out with a box cutter. Then I used the belt sander to sand down to the line. Here's the dimensions of my template:
Don't wig out about the fact that it's 3/8" at the tip. You have to consider the fact that your pencil mark is going to be a little wider than 3/8", and then it's going to be even wider when you cut it out with the band saw since you'll cut outside of the lines. Besides, you can always put the end of the template an inch or so past the end of your bamboo so that you have a wider tip. Whatever works for you. I use this same template for my fiberglass bows. If for whatever reason I want to make it wider or more narrow, I simply adjust the angle of my pencil or where I put the tip.
Here's the template on the bamboo.
My goodness! Look how warped that bamboo is! Good thing I did that string thing, eh? You can hold the template on with squeeze clamps if you want, but I was just careful and did it with my hands while I traced around it. Put the template on the other end and repeat. Then cut it out with a band saw. Cut outside the lines, and then use the belt sander to sand the rest of the way to the lines.
Now isn't that better? If you don't have a band saw, there is another way. You can clamp the bamboo to the edge of your railing where one edge sticks up, and then use your Stanley Surform. That's how I did my first one.
Now you need to flatten the bamboo. I did my first one with a Stanley Surform, and although it was a lot of work, it worked just fine. But now I use a band saw and a belt sander, and I'm a happier person because of it.
I used to use a rip fence to do this part, but I've found it much easier to do it free hand. There are two reasons I don't use a rip fence anymore. First, most pieces of bamboo are kind of warped. Unless you've got really strong thumbs and can consistently keep that bamboo pressed against the rip fence, it's going to wander and make it hard to cut straight.
Second, if your bamboo is warped from side to side like mine is, you'll end up with a piece that's thicker on one side than the other. If you try to use a rip fence, you might run into this problem:
Do you see the problem here? You'll lose some of the width of the bamboo. As it turns out, I've got this very problem with my piece of bamboo.
I used to use a rip fence because I wasn't very handy with a band saw, and the rip fence was a crutch. But now I find it easier to free hand it. I can fix the above problem by just holding the bamboo at an angle and watching carefully as I cut it.
When your flattening the bamboo with the band saw, be careful not to follow the edge with the nodes. In other words, don't cut a dip where the nodes are. Just keep cutting in a straight line, leaving the node area thicker. You can follow the grain when cutting past a node so you don't get lost.
The closer to the rind you cut the bamboo, the less work you'll have to do with the belt sander. But however close you get with the band saw should be determined by how good you are with it. If you're not very good, you ought to leave yourself plenty of margin for error and just flatten it the rest of the way with the belt sander.
I use a 40 grit belt on my belt sander for just about everything, including flattening bamboo.
Since ipe is so stiff, the final bow will end up being pretty thin. Since the bow will be pretty thin, you'll want to make sure the bamboo is pretty thin. Think about it. Suppose you glue up a bamboo backed ipe bow with lots of reflex. Suppose the bamboo backing is 1/4" thick, and that the final thickness of the bow is 1/4" thick. Well, if that happens, then you won't have any ipe left. It'll all just be bamboo. But if it's all just bamboo, how is it going to hold any reflex? It can't! The reflex is held by the shear forces at the glue joint. You need that glue joint to be closer to the back of the bow. If the bow is going to be really thin, then you need the bamboo to be thin so that you'll have plenty of ipe left on the belly.
I make sure my bamboo is no thicker than 1/8".
Some people just sand until they get a knife edge, which causes a natural taper toward the tips. I don't recommend that method, because not all bamboo comes from the same diameter, which means some will have a higher crown than others. If you use "knife edge" as a rule, then some of your backing will be thicker than others. But it's all a matter of personal preference. My preference is to measure between the nodes and make sure nothing is more than 1/8". It's usually thinner toward the tips.
Do most of your sanding with the flat part of the belt sander. That'll keep you from having dips and stuff from the band saw. But if you have thick spots, you can work them down a bit with the elbow of the sander, then go back to the flat part.
Check both edges of the bamboo from time to time to make sure one edge isn't thicker than the other edge. If it is, just apply more pressure to the thicker edge until it's even again.
Once you've got the bamboo all nice and flattened, sand the back of the tips on both ends. Sand until you get the rind off and you get a flat surface.
The purpose is so you can glue tip overlays on.
Once you've got one piece of bamboo read to go, you can use it as a template to trace out the pattern on all your other pieces of bamboo. Just use squeeze clamps to clamp them belly to belly. That way, you can easily center it on the nodes, get the tips aligned, and trace it out in one shot without having to use a scrap piece of wood for centering, a string and weights for aligning, or a template for tracing.