Woodworker's Journal 2007-Winter, страница 75
Always remember that when you veneer you need to create balanced panels. This means you must apply veneer to both sides of the core, keeping the grain running in the same direction so the finished panel won't warp.
Forming Cauls and Crossbearers
After much experimentation, we've come to the conclusion that oak makes the best crossbearers. Cut your crossbearers 1/2" thick, 2/2" wide and 36" long (or longer if you anticipate the need to clamp wider veneer). The number of crossbearers needed depends on the length of your veneer. You'll need a set of two crossbearers at each clamping position and enough to space the sets at 4" intervals along the length of the veneer.
Cutting uniform arcs on the crossbearers is critical so they distribute pressure across the width of the veneer evenly. Draw the large radius of the arc by tracing along a thin flexible strip of wood clamped at the center of the crossbearer and held back 1/4" from the edge at both ends, as shown in Figure 1. Cut away the waste and sand the sawn edge smooth. Use this finished crossbearer as a template for cutting out one more crossbearer. Clamp these two crossbearers together at the ends with their arched edges facing each other. Look at the joint between the
Figure 2: Clamp the crossbearers at 4" intervals and space additional clamps around the perimeter of the assembly to hold the edges.
crossbearers to see that there are no gaps and that pressure is being applied over their entire length. Make any necessary adjustments, then use these first two pieces as templates for laying out the arcs on the rest of your crossbearers. Cut out the remaining crossbearers and sand them to match in pairs.
The two cauls are cut from 3/4"-thick particleboard and are made 1" wider and 1" longer than the core being veneered.
Gluing the Veneer to its Core
When faced with clamping large sheets of veneer, use a slow-setting glue such as white glue to give you more assembly time. On smaller areas you can also use yellow glue for its fast-drying qualities. Have everything ready before you begin, including tools, glue, newspaper, clamps, cauls and crossbearers. An extra set of hands also helps for larger veneering tasks.
Pour glue onto one side of the core and on one sheet of veneer, and use a 3" or wider paint roller to spread the glue evenly. Position the glued veneer on the core so there is an equal amount overhanging all the edges. Place a piece of kraft paper on the face of the veneer,
then set one caul on top of the paper. Flip over this assembly and repeat these steps to glue veneer to the other side of the core. Remember to match the grain direction on both sides of the panel.
Clamp a set of crossbearers across the middle of the cauls and apply clamping pressure until the crossbearer ends touch the cauls on both sides. Check to see that the veneer sheets haven't slipped out of position. Working toward the ends of the veneer, clamp on the remaining crossbearers at 4" intervals. Place additional clamps between the sets of crossbearers near the edges of the cauls and use more clamps across the ends of the cauls at 4" intervals (see Figure 2).
Look at the joint between the veneer and the core to see if glue is oozing out its entire length. If there are dry spots, that probably means there's not enough clamping pressure, so add a few more clamps and turn the cranks a little further to bear down on the crossbearers.
After allowing the glue to cure overnight, remove the clamps, crossbearers and cauls. Next, peel away the kraft paper, trim off the overhanging veneer edges and sand the faces of the veneer smooth. Now you're ready to use your veneered panel for whatever project you've planned. p