Here we go again. I decided after string it that I would do the rest of the tillering with a scraper. I've never used a scraper before, but it sounded like the ideal tool for tillering because it would give you a lot more control than a rasp, a belt sander, or a drum sander. I made a scraper out of an aluminum sign I found laying on the ground, and I even posted a build-along for it. It didn't work very well, though, so I broke down and bought a set of scrapers and a burnisher from ebay. It was well worth it because this scraper works great! I love it! I should've gotten one of these a long time ago.
By the way, if you decide to get a burnishing tool from ebay, don't type in "burnishing." Instead, type in "burnisher." I got my burnisher and my scrapers all together.
You need to know how to sharpen your scraper, so here is a link showing how. They are really wonderful tools.
Anyway, I sraped on that right limb some and then brace it a little higher.
The left limb was bending about 1/16" more than the right. To measure there, I measure 9" from the center of the bow down one limb. From that point, I measure the distance from the limb to the string.
I do that on both sides and try to get them close to even. A 1/8" positive tiller (where the upper limb bends 1/8" more than the bottom limb) is good, so I'm not worried about a 1/16" difference. The right limb is provisionally the top limb, but I only say so to keep me from getting confused about which end is which. In the end, it doesn't matter. I'll choose whichever limb ends up bending a little more for the top limb when I'm done.
So...I pulled the bow about 10" (which came to the 16" mark) to see how it looked.
It looked good to me, so I pull it to 30# to see how far it would go. It went to 21".
I learned this neat trick from the fine folks on the Leatherwall. If you use Paint to draw lines from the middle of the handle to the tips, it's easier to tell if the tiller is off. In this case, it's obvious that the right limb is too weak. Pobably what happened was that while I was scraping the top limb, it didn't take enough set to really show the effects until I drew it to 21". That's why you have to excercise the limbs each time you remove wood.
I also thought the limbs ought to bend more toward the fades, so I scraped near the fades on both sides, but I did a little extra scraping on the left side. Here it is again at 21" after doing a bit of scraping.
The left limb still needs work. Oh, that reminds me. One cool thing about using a scraper is that you don't have to unstring the bow to use it. That makes tillering a lot less of a chore. Also, the scraper leaves a pretty smooth surface, and that reduces the amount of sanding you have to do later.
Here it is again at 21".
The left limb still needs work, but I also thought the right limb was bending too much at midlimb. It seemed to hardly be moving at all near the fade. So I worked on that a bit, too. Here it is again at 21".
I did this about six more times, just working near the fades and some close to the tips, but staying away from midlimb. Finally, I got a 1/16" positive tiller. Here it is at 21".
Up until now, I've kept the tips a little stiff on purpose. I want to narrow the tips, which will weaken them a little. If I weakened them too much before narrowing them, I could've ended up with a whip-ended bow. But I don't want to wait until the end to narrow them, because it could affect the tiller.
My goal while narrowing the tips is to get the string aligned. There are basically two reasons why a string might be misaligned. One reason is because the tips are misaligned. Another reason is because the limbs are twisting.
I'm going to show you four different ways to fix a misaligned string (a string that doesn't run through the middle of the handle). One way is to narrow the tips by removing wood on only one side. Here's a drawing of the belly of a bow with the string a little misaligned.
To fix it, I would remove the area in blue, which would narrow the tips and get the string close to the middle of the handle. Or you could just deepen the nocks on the blue side.
Another way is to narrow the handle in such a way that the string runs through the middle of it.
Some people leave the handle wide in the beginning for just that reason.
Another way is to cause the limbs to twist (or to untwist if they're already twisted). The primary reason limbs twist is because of the grain in the wood. But I've inadvertently glued in twisted limbs because the board I did my glue up on was twisted. Tips can also be misaligned because one side of the limb is more narrow than the other side. Lemme explain that a little. This is a look at the back of an unstrung bow with a centerline drawn down the back of the bow from tip to tip.
Notice that there is more distance between the centerline and the edge of the limbs on one side (the top of the picture) than there is on the other (the bottom of the picture). That makes the thinner side weak. Although the tips may be lined up when the bow is unstrung, they will not be lined up when you string the bow. When you string the bow, the tips will move in the direction of the arrows, bending toward the thinner (weaker) side, and the string will not line up through the center of the handle. You can fix that problem simply by removing wood from the thicker side until the tips line back up and the string runs through the center of the handle. Be careful, though, because doing so will affect the tiller some. You can use this same technique if your limbs are twisted--whether because of the grain or because you accidentally glued in some twist with a warped form.
Here is a look at the belly of a bow that is strung.
Either because of twisted limbs or because one side is thinner than the other when measured from the centerline to the edge, the string is misaligned when the bow is strung. To fix the misalignment, you can remove wood from the edge as indicated in the picture, and the string will line back up. I have actually experimented with this procedure quite a bit because I made several bows in a row with bad misalignments because I had a twisted form I used to glue the bows up on. So I know this technique works great.
There is one other technique mentioned in one of the Traditional Bowyer's Bibles. I can't remember which one. Basically, they recommend simply shaping the handle in such a way that it "points" toward the string. Lemme see if I can explain that a little. Let's say you've got a bow that is strung. The handle is still square because you haven't shaped it yet, and the string is misaligned. Viewing the bow from one tip, a cut-away would look something like this:
The black square is a cut away of the handle and the green dot above it is the string, which is obviously misaligned to the left. To fix the problem, you just shape the handle in such a way that it points toward the string, which is illustrated by the picture on the right. You'd remove the area in red, and the string would magically be aligned through the middle of the handle.
Don't feel like you have to use just one of these methods. You can use a combination of them if you want to.
Anyway, I narrowed the tips and afterward ended up with a 1/16" negative tiller. Keep in mind that it doesn't matter at this point whether my tiller is negative or positive since I'm free to decide later which end will be the top. I just want to make sure the tiller is within a 1/8" difference. Here it is at 21" after narrowing the tips.
Since the right limb was a bit stiff, I used the scraper near the fade and the tip. I ended up with a perfectly even tiller. Here it is at 21".
By this time, I had weakened the limbs quite and bit and worried that I wouldn't make my target weight. I inched the bow one inch at a time until I got to 27", and it was 30#--way off. Here it is, 30# at 27".
I ended up with 1.25" of string follow right after unstringing it.