Before we start tillering, lemme tell you what tillering is all about. Tillering is what turns a stick of wood into a bow. It's really the crux of the whole bow-building enterprise. The whole point of it is to get the limbs to both bend evenly, to get the shape you want, to get the the bow to the weight you want at the draw length you want, and to do it all without breaking it.
"Bending evenly" means two things. First, it means both limbs bend by the same amount. One isn't stiffer than the other. (Actually, a lot of people [myself included] like to have the top limb bending slightly more than the bottom limb). Second, it means the flex is distributed evenly along the limbs. A perfect tiller will look something like this:
Let's contrast that with a few examples of imperfect tillers. Some of them have names, but I don't know about this next one. I'm posting this one because for a long time, I had a bad habit of tillering bows this way.
The problem is that most of the flex is happening near the fades, and the rest of the bow isn't doing much work. This causes excessive set, puts too much strain on too small a part of the limb, and reduces the life of the bow. Of course if you're doing a reflex/deflex bow, this kind of tiller ain't so bad.
Since I mentioned "set," lemme take a detour here and explain the difference between "set" and "string follow." First of all, all bows have set. "Set" is when the belly wood gets compressed, and the limb bends more toward the belly than it did before. Now let's say you take a bow with 5" of reflex, and after tillering it, it has 3" of reflex left. That means it has 2" of set because it has been deformed by 2".
But such a bow has no string follow. String follow is the amount of deflex in the bow. If you start off with a perfectly straight bow, and you end up with 2" of set, it will also have 2" of string follow. But if the bow starts off with 1" of reflex and takes a 2" set, it will have 1" of string follow. If you start off with 2" of reflex and take 2" of set, the bow will be perfectly straight with no string follow.
And since this tutorial is idiot proof, lemme explain the difference between reflex and deflex. Reflex is when the limb (or part of the limb) bends backwards away from the belly. The belly is the side the string goes on, by the way. Deflex is when the limb (or part of the limb) bends toward the belly.
With that out of the way, let's look at some other bad tillers. This next one is called "whip-ended" because it's whip-ended.
This one has the opposite problem from the whatchamacallit tiller. Instead of bending too much near the handle, it bends too much near the tips. Some people like this sort of thing, though. It does reduce hand shock. Other than that, though, it has the same shorcomings as the whatchamacallit tiller.
This next one is just an example of a hinged limb.
Hinges are bad. It concentrates the strain on that one area of the limb, and it could easily cause your bow to break.
For this bow, I have chosen to go for 45# at 28". 50# is about the maximum I would be comfortable with for red oak. I have heard of other people going a lot higher, but they are probably better at making bows than I am. The lower the weight you go, the less chance there is of breaking the bow, so do give some thought to aiming for 40# if this is your first bow. If that's too light for you, you can always give the bow away or just hang on to it for sentimental reasons. I can almost promise you this won't be the last bow you make.
If you don't have a bow scale, then you can stick a bathroom scale under the tillering tree. When you pull down on the string, it will register on the scale. You just need to substract the weight of the tillering tree to get the right reading.
If you don't have any scale at all, you're just going to have to go by feel. I went by feel for my first 10 bows or so. You can sometimes find cheap bow scales on ebay. That's where I got mine.
Unless your CPU is a neuralnet processor, and you have machine-like rough tillering abilities, your bow is not going to be perfect when you first start bending on it. So let's start off by pulling it just a couple of inches and see what happens.
What do you know! The left limb is bending more than the right. We need to even that out. I do that by removing wood from the right limb, making it weaker so that it matches the left limb.
Now lemme tell you something really important. We're going to be moving gradually here. The farther you pull a bow, the easier flaws show up. So if you ever pull the bow to any length and notice a flaw, don't pull it any farther until you have fixed the flaw. Pulling it farther will just cause the bow to take excessive set. Take a hinge for example. Obviously, if you keep pulling on a hinge, that little area will take a lot of set. So remove that hinge before going any farther.
So far, I don't see any hinges or flat spots, so I just need to reduce the right limb some. Whenever I'm just reducing weight from a limb, I do it by holding the surform backwards, starting at the fade, and pulling the surform all the way to the tips.
I also count the strokes. Five at a time is about right. As you get some practice, you'll get a feel for how many you should do. If both limbs are even, and I just want to reduce the weight of the bow, counting comes in really handy. I would count how many strokes I did on one limb and then do the same number on the other limb. That way I'm taking off about the same amount of wood, minus my human error from not having a neuralnet processor.
There's something else I gotta tell you. Obviously, the harder you pull on a bow, the more the belly wood will be compressed and the more set it will take. Since we're shooting for a 45 pound bow, we don't want to ever pull the bow more than 45 pounds. There's just no reason to compress the belly more than necessary.
Until I get the bow braced, though, I'm even more conservative than that. I want to tiller with the long string until I get the limbs moving 10". As the string dangles there, I pull it taught and notice that the limbs just start to bend when the string is at 10". That means I want to brace the bow when I get the string to 20". And to be conservative, I'm going to shoot for 30# at 20". Don't you worry. That will leave us plenty of strength to get to 45# at 28" with a full brace. I'm just doing this to reduce strain on the bow and prevent it from breaking.
Here it is 30# at 17".
Oh, I forgot to tell you something. Your eyes can play tricks on you sometimes. You'll look at the bow and think one limb is bending more than the other or something, but when you flip it around, the problem goes away. So it's a good idea to sometimes put the bow on the tillering tree the other way and look at it. That way you can study it from different angles. That's what I've done here.
Now you have to keep track of which side is which. I just use a crayon and draw an arrow on the handle pointing toward the provisional top limb. That way I don't get mixed up.
Anyway, I've marked on the picture what needs to be done. For hinges, stay away! Don't touch that area. The only way to take out a hinge is to remove the stiffer wood around it so that it starts bending, which takes the load off the hinge. You can see how the wood on either side of the hinge is stiffer. Remove wood from the stiff areas to get them to bend more, and stay away from the hinges. When I look at the bow on the tillering tree, I use a crayon and mark the areas I intend to remove wood from. It helps.
That's another thing I should tell you about. You'd be amazed at how much more you see when you take a picture. When I took this picture, it all looked just fine to me. It wasn't until I looked at the picture on my computer that I noticed the flaws. The flaws aren't really all that severe, but they sure do show up in the pictures. So if you have a digital camera, you might keep that in mind. Of course it would take you a lifetime to make a bow if you took a picture and looked at it on your computer every single time you removed wood. So just take pictures at various milestones.
Whenever you remove wood from the bow, you should excercise the limbs. You see, the surface of the belly undergoes the majority of the compression. When you take wood off the belly, it removes the compressed wood and exposes some wood that isn't compressed as much. But it will be. So to show the true effects of the wood removal, you have to get that wood compressed so that it matches the rest of the compressed wood around it. You do that by excercising the limbs. Whenever I remove wood, I excercise the limbs 30 times. That is, I hold the string and go from relaxed to wherever I happen to be (in this case 17"), and then repeat. I do it 30 times. You should, too. Excercising the limbs also gets the wood used to bending and reduces the chance of breaking it later on. Bows are like shoes. You have to break them in, but not break them.
Since we're shooting for 30# at 20", we don't want to draw the bow more than 30#. Right now, I've reached 30# at 17", so I need to remove wood before I pull it any farther. Unstiffening that left limb and removing the hinge from the right limb will reduce the weight a little. I'm going to keep it at 17" until everything looks even. By then, it will be a little less than 30#. At that point, I'll pull it to 18" and see how it looks and check the weight. I keep doing this until I get to 30# at 20".
Here it is 30# at 19":
The hinge seems to be gone, but the left limb is still a little too stiff.
Finally, here it is 30# at 20".
It looks pretty good to me, so I'm going to brace it. Now I don't go for the full brace height at first. I shorten the tillering string using my handy dandy timber hitch, and I brace it just a few inches.
I apologize for the lack of constrast. I guess I need a different colour for the background to make these pictures turn out better. Usually you can see flaws as soon as you brace it that you couldn't see before. The most obvious flaw I usually see that I didn't see before is that one limb is a lot more stiff than the other. In this case, I got lucky. They seem pretty even to me.
When you brace the bow for the first time, you really should use a stringer. Remember this is a sensative time in the bow's life. Bows are like children. They are far more impressionable when they are young, and whatever you do to them in those formative years will stick with them their whole lives. So you want to be careful, and using a stringer is the best way to go. I made a stringer out of some braided nylon chord and some thick leather.
Maybe I'll post something on my web page some day about how to make stringers and how to string bows. For now, use google and learn how to use a stringer if you don't already know.
That's enough for today. On page 8, I'll tiller with a low brace. Page 8 may not correspond to tomorrow, though.