Making a 'Perfect' center-line glue joint on violin plates...
...The center line of two piece violin plates is an important joint. It is considered a point of quality if the joint is almost invisible when completed. To accomplish this, the joint must be exactly perpendicular and fit precisely all along the glue joint.
...This technique should allow you to make really excellent center joins in your violin plates...
...The first step in the process is to rip a straight line along the glue joint side. It must be just perpendicular to the bottom surface.
...This photo shows my jig for ripping this side glue surface. A flat steel plate with a metal bar bolted to the bottom rides in the table saw mitre gage slot. This bar should fit the groove tightly, just allowing for smooth sliding action.
...Two spring lever clamps, one at each end, hold the violin plate stock firmly in place during this cut.
... It is a good idea to run the bottom surface of the pieces over a belt sander to remove any hollows in the wood before this step.
...Next, we glue two strips of sand paper, say # 150 Imperial Eastman sandpaper, back to back. You may want to glue these two together laying them on a perfectly flat surface with a weight on top of them until the glue dries.
...The bottom edge of the sand paper is lowered into the slot of the table saw (for the mitre gage guide bar). As shown at left, each end of the sandpaper strip is clamped between two wood blocks which are in turn clamped to the ends of the table saw surface. Tension this sanding belt so it is tightly stretched, as well as held firmly.
...You may want to mark the glue joint edge with slanted pencil lines so that you can see your progress. Once the pencil lines disappear all along the joint on both halfves, then the joint should be perfect. Just blow off the dust, warm the parts and glue with fresh violin making glue. (Either hide glue or hare glue).
...To make this job easier, I fashioned two 'holder' boards with screwed on handles (the dark brown wood section). These in turn are screwed to the violin plate halves (be sure the two screws are in the waste wood areas!). Leave the surface to be sanded 'proud' (stiching out).
...The two halves are sanded at the same time by moving the two ' plate halves toward and away from you together at the same time (keep the two pieces in registar as you move them so that the two holders are exactly even at all times. Push the two plates together at the same time lightly. Let the sand paper do the work of material removal of uneven spots.
...Your sandpaper strip should last for many sets of plates.
...Now unscrew the plate boards and blow the glue surface dry of any sawdust.
...Here I am warming the two maple violin plate halves in a light bulb powered warming box (notice the thick foam insulation and aluminum foil interior lining).
...I like to pre-heat the wood parts to be glued to about 100 degrees F. This will help make a strong glue joint.
...Remember that this joint should be able to last for 300 years.
... My favorite glue method is to tightly tape a piece of waxed paper to a perfectly flat surface (here the top of my table saw).
...Quickly brush a covering layer of glue onto each glue joint (pre glue both surfaces) and then push them together, rubbing back and forth slightly as you align the pieces. Hold the joint tight together firmly with your two arms for about 60 seconds.
...Then gently release the pressure and let the plate lay undisturbed for several hours before removing the tape from the waxed paper and lifting the plate up and peeling the waxed paper away. Alow the plate joint to dry overnight at room temperature (say 70 degrees F.) before continuing work on the plate.
...You may want to wash off excess glue at the edge of the glue joint with a brush and some hot water form the water bath of the glue pot; drying with a paper towel.
...Some makers just rub the joint together with one half held vertically clamped in a wood vise as shown in this photo. No clamps are needed other than just hand pressure for a minute, if the joint is properly prepared.
...This joint is thus called a 'rub joint'.