Mandolin making pictures page 4
dude8.jpg 37) Now I have a reference for placing the tone bars. I take my measurements from the upper and lower points of the F holes. I'm marking the location of the treble bar here.
dude8.jpg 38) Fitting the tone bars can be quite time consuming. I take 1/4" wide spruce, position it over the line I've marked inside the top, and use a compass to transfer the outline of the top to the tone bar. I then take it to the bandsaw and cut off the excess.
dude8.jpg 39) Using a fingerplace, scraper, Exacto, and sandpaper, I fit the bar to the top. This often take a couple of hours. Not only is the countour changing along the length, but it the angle of intersection with the top changes as well. It has to be a perfect fit.
40) Once the tone bars are fitted to my satisfaction, I put a coat of hot hide glue on the mating surfaces and let it dry. This glue penetrates into the wood, and when more glue is added later, results in a very strong bond.
dude8.jpg 41) I've masked the location of the one bars on the top with tape and am applying the glue to the top also.
dude8.jpg 42) After the "pre-gluing" step has had time to dry, I apply more hot hide glue to the tone bar and the top and place it in position. I apply clamps to each end, then cam clamps along it's length. One nice thing about hot hide glue is it is that dried "re-activated" by the application of fresh glue. Hide glue is the adhesive used on postage stamps and envelopes. Your own body heat and moisture from your tongue are enough to "re-activate" the glue.
dude8.jpg 43) As you can see in this picture, the tone bars are glued on without shaping first.
dude8.jpg 44) Now I'm applying the gauze reinforcements to the inside of the F holes. A piece of guaze is cut slightly larger than the F hole and hot hide glue is /tdushed on. The gauze will be cut out from the F holes later after the glue is dry. I guess you could leave it on to keep the flies out!.
dude8.jpg 45) The tone bars are fairly small. Only 0.250 to about 0.300 inches high at the center. They really aren't structural members. I use a fingerplane and chisels to shape them to a kind of rounded triangle cross-section. They taper out to nothing just short of intersecting the headblock and kerfed lining on the other end. As they taper out, they get progressivly flatter.

All photos and content copyright 2001 Lynn Dudenbostel