drill bushings are fairly cheap and could even be installed in a block of hardwood.
they are made from hardened steel (quite a bit harder than most stainless) and come in a variety of styles and can be replaced when worn or the jig need a different size
http://www.reidsupply.com/products/metalworking/drill-busings/
woodenspring
I have built a number of bows the same way with good results. I also use a spreadsheet for design.
When I change materials but keep the dimensions the same, obviously the poundages are different,
would you care to quantify some of the poundage changes you see using different woods in the same design?
willie
Willie,
I make my bows 68" long with a 4" handle and 2" fades... They are always 1/2" thick at the fades, and taper to 7/16" at the tips. (by doing this, you'll have very little wood to remove during tillering). Also, all of my bows have pin nocks.
I then start with a 2" wide fade and see where that poundage winds up.
(Note, I never build a bow to an arbitrary size and then tiller it to a certain poundage, I do just the opposite, I build a bow to a certain set of dimensions, and the bow's poundage is what it winds up being.)
This is always a starting point for me when I try a new wood. In the plan below, I have listed the bow wood and dimensions that I have built LOTS of bows to. There's not more listed just because I haven't made a large enough sample yet to call it "repeatable." But the bows listed are fairly repeatable, and easy to make!
Now, keep in mind, if you're using quarter sawn lumber for your belly wood, it's going to be a slightly higher draw weight. If you are using any other cut of wood where the grain is not perfectly vertical as seen from the end view, it's going to be a slightly lower draw weight.
1/8" hickory backing over quarter sawn red oak
> 2" @ fades - 40-45 pounds
> 1 1/2" @ fades - 30-35 pounds
1/8" hickory backing over jatoba
> 2" @ fades - 60-65 pounds
1/8" hickory backing over ipe
> 1 1/4" @ fades - 35 pounds
Let me know if you've got any questions...