Don Stephan
Posts: 825
Joined: 2003-07-18
Location: Cincinnati, Ohio
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A vacuum bag can be used to press vertically, but allowance must be made so that the bag presses fully and evenly against the vertical edges. When the area of the bag falling down the side of the material being pressed meets the platen, there is always a "dead area" where the bag makes the transition from vertical to horizontal. This dead area will not apply full and even pressure against the bottom of the vertical surface, so some steps must be taken to elevate the vertical edge being pressed so that it does not fall within this dead area. (Darryl explains this concept much better than I.)
1. Cut a couple "spacers" from 1/4" plywood or MDF matching the shape of the veneered piece but about 3/16" narrower.
2. Cut a third "spacer" from the 1/4" sheet the same size as the piece being veneered.
3. Wrap these spacers in 4 mil or so plastic and tape the edges near the middle of one of the faces. (The plastic will keep the glue from sticking to the spacers.)
4. Cut your edge veneers about 1/2" wider than the piece being veneered.
5. Using clear packing tape, tape together across the edges NOT being veneered a 3 piece sandwich of the first two spacers and the piece being veneered, with the latter in the middle. I use packing tape because it seemed that blue masking tape, which is thicker, was leaving a dented area on previously veneered surfaces under the pressure of the vacuum bag.
6. Apply urea formaldehyde glue to the edges being veneered. Using clear packing tape, affix the veneer in place.
7. Add the third spacer to the bottom of the sandwich and tape in place.
8. Slide the assembly into the vacuum bag and draw a partial vacuum. Adjust the upper surface of the bag as needed so that it drapes down tightly against the veneer edges being pressed. The lower two spacers provide sufficient lift to the veneered piece to allow the vacuum bag so press fully and evenly against the (vertical) edges being veneered.
Chipping of the edge veneer during final trimming is much more likely with a wide allowance. I finally cut a small piece of cardboard backer from a pad of ruled note paper and taped to the back of a veneer saw. With good support of the edge veneer on the show side carefully cut the veneer about 3/64" to 1/16" proud and carefully sand flush with a sanding block moving from the show side towards the glue side. Depending on the radius of curvature of the shelf edge, it might be possible to flex a thin piece of MDF or plywood to match the curve and fully support the veneer while sawing it close.
It's not as simple as pressing a flat surface, but it can be done. The biggest challenge likely will be final trimming of the edge veneer, depending on the wood type used and its affinity for chipping.
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