by Alan Carruth » Mon Oct 30, 2017 1:47 pm
I've always used a strip of rubber cut from a truck inner tube. They do still make them, and you can usually get one that's beyond patching free. The trick is to get it cut up into a long strip that you can use.
You need to at least try to make a continuous strip of uniform width with smooth edges: notches make stress risers that cause the strip to break when you're wrapping the guitar. So far the best tool I've found for that is the rotary cutter that a lot of quilters and seamstresses use. It's like a pizza cutter, but 'way sharper. Regular scissors make too many notches. Also, cutting such a long strip of heavy rubber with scissors gets hard on the wrist.
I use a two step process to get a uniform strip. First, make a crescent shaped plywood insert that will go into the tube and hold a section of it flat. You need to cut against a backing with the wheel, and this provides it, as well as making it easier to get nice straight cuts. You don't have to stretch the tube tight, but make the cutout large enough to keep it pretty flat. I like to make it fill about 1/4 of the diameter of the tube. Mark off the inner diameter of the tube at, say, 1" intervals, and mark off the outer diameter with the same number of intervals at whatever width. Chalk works well. Now make a radial cut from one inside mark to one on the outside. Flip the thing over, and go from the end of the outside cut to the next inside mark over from where you began. You're cutting out a spiral that goes in and out along the radius. Note that this is easier if you only use, say, a quarter of the tube to begin with.
What you'll end up with is a long strip that gets narrower and wider. Use the cutter to trim it down carefully to a uniform width. Yes, you're throwing away a lot of rubber, but you didn't pay much (if anything) for it.
I just measured the length of one I use, and it's close to 90'. Hard to believe. That's long enough to go around a 17" deep body Jumbo, if you pull it tight. If the strips you make are shorter you can tie them together with a square knot.
Be aware that the rope overlaps in the center of the lower bout on the front and back, and can put a significant downward pressure on the top. So fat the only one I've had fail from that was a sandwich top, and that was due to the epoxy: they changed the formulation on me, and it didn't harden properly. Heckuva time to find out, but better that then after the strings were on, I guess.