Saturday, June 21, 2008

Veneering Curved Aprons

A few days ago I veneered the curved aprons for the table I've been working on.  Veneering curves along a large radius can be tricky, especially when there is no practical way to accomplish the task using a vacuum press.   I decided to break the veneering of each apron into several separate glue-ups.  This way I only worked about 1/4 of each apron at a time.  More on this in a moment.  

In the meantime, the photo below shows the set of tools I used for  this process.  In the picture you can see regular PVA glue, perforated veneer tape, a glue roller (or brayer), an Exacto knife, packing tape, a glue pallet, and a piece of sandpaper.  It's important to have all of the required tools close at hand before any glue is spread.

One of the most important tools in any veneering operation--but especially when veneering curves--is the caul one selects.  The caul helps spread clamping force equally across the entire surface of the veneer, ensuring good adherence to the substrate.  The trouble with cauls is that they almost always accomplish this task imperfectly.  Some people use thin packing foam, others use plain poster board, and many people use a layer of cork.  I've tried all of these with mixed results.  I was all set to buy a length of cork at the hardware store last week, when I saw a roll of the material pictured below.  It's sold as "floor liner" and appears to be the stuff you wipe your feet on before entering a building on a rainy day.  I immediately thought it would make a terrific caul.  The rubber material has just the right ratio of rigidity to give, and the "kerfs" along the backside allow it to follow a curve well.  Besides all of that, it's marvelously inexpensive and it resists glue.

I attached a piece of the rubber caul material to a length of 1/4" plywood with one centered piece of packing tape.  I had made sure earlier that 1/4" ply would bend around the radius of the apron without cracking.

Long before I spread any glue on the apron, I cut and taped my 3" lengths of veneer.  I had purchased quarter sawn maple veneer which came in three 8' lengths.  I used two of these lengths, cutting 3" pieces from each one, numbering as I progressed.  Thus I had two #1's, two #2's, and so on.  I then taped together four pieces, bookmatching the edges.  

Perforated veneer tape is still my choice for building-up any kind of veneer panel.  Getting the moisture level just right for the tape can be difficult, but I find that a sponge with as much water wrung out of it as can be done by hand provides just about the right level.

My next step was to figure out how to hold the apron substrate in position so that I could apply as many clamps as possible to it without causing it to twist and break.  I decided to clamp it on blocks to my work table in three places.  This felt pretty solid.

This next shot shows all the clamps in place squeezing the 1/4" ply, the rubber caul, and the veneer against the substrate.  Before I got to this point, I had masked the area of the substrate adjacent to the beginning of the veneer panel using packing tape.  That way, when I removed the clamps I could simply peel the packing tape, leaving glue-free substrate for the next panel.  I worked my way around the perimeter of both aprons this way until they were completely veneered.

Next, I scored along the back side of the veneer along the edge of the apron with my Exacto knive.  I then bent the veneer towards me, breaking its fibers.  A quick snap away from me, and the excess veneer broke off. After a light sanding with 120 grit sandpaper along the edges, my veneering was complete.

If any of this is unclear and you'd like more detail, just leave a comment, and I'll be sure to respond!

1 comment:

neil said...

Tim.........that's an excellent explanation...Thank you!!!! As I was reading, I kept thinking ahead as to how is he going to handle this or that.

Just a wonderful explanation and fully visualized on my part.


PS - I see a picture above on the finishing...COOL!!!!!