Kris: It's hard to nail down a "recipe" for board bows, self bows, etc. You can get pretty close, but there's always a margin of error both ways because you're dealing with an organic material. Now, the more control you have over the components of the bow, the closer you can get to a recipe. For example, you can make a laminated wood bow and get really if not exact every time because you're laminating, which gives you more control over the make-up of the wood. You can even choose different woods for the back, belly, and core based on their characteristics. On the far end of the spectrum, you hear builders who use glass in their bows talk about recipes all the time. That's because they utilizing wood laminations PLUS the consistency of fiberglass (a non-organic material).
That being said, I can offer you some suggestions on getting close to your intended weight per draw length, and encourage any bowyers with pyramid bow specs to offer them up for comparison. But first, I wouldn't make your bows 56"-60" long. Here's why. As I stated in my previous post, I use the following formula for determining minimum bow length:
Bow Length=((Draw Length x 2) x 1.15)+1
For 30# at 26" bow, I'd make it 61" long MINIMUM (60" ntn). For the 45# bow I'd make it 64" long MINIMUM (63" ntn). Now, say you come up short in weight and need to pike it (shorten it to increase draw weight.) Generally you shorten both tips 1" to gain 5# in draw weight. It you've built the bow at the margin of safety, you don't have much to play with. Plus, we're working with unbacked red oak, not osage or hickory, both of which can take more abuse.
BUT (ah, the exception) you can always use the glue-one recurve to add a few pounds (up to about 5#) at the given bow length if you come in too low. So, you've built the bow at the margin and come in under weight but haven't done the glue-on recurve tips, simply the add them and your weight will go up. If you've already rounded the edges at the tips on the back of the bow (which would not lead to a good joint) just bevel them like you would when adding tip overlays, only over a longer run.
So, for my overall recommendations (which I hope others can chime in on). Again, I have a hard time nailing a draw weight/draw length out of the air. These are specs from bows I have built; but again, they're GUIDELINES! Adjust as necessary.
30#@26" = 62" overall (61"ntn), 2.5" at the fades, 1/2" at the tips, 13/32" thick. If you come in heavy, you can just scrape the belly evenly on both sides to drop the weight. Too low? Pike it a little (assuming you haven't added the recurved tips yet).
45#@28" = 66" overall (65" ntn), 2.5" at the fades, 1/2 at the tips, 7/16" thick.
Both of these assume the same riser/fade layout as shown in the build-along.
Sorry this got so long. I hope it answers your questions and gets you started in the right direction. If you don't hit your target weight, then don't hit me either!
Heck, as cheap and quick as it is to build these things, you'll have a rack full of bows to give away if nothing else!
PS The specs for my son's bow you inquired about are: 47" ntn, 2 7/8" at the fades, 1/4" at the tips (yikes!), 9/32" thick, 25#@22". The glue-on recurved tips are more like miniature siyahs (found on a horsebows).
Topic: The "So You Wanna Build a Bow?" Build-Along (Read 20002 times)
