Campaign Table

My friend Calvin has been carrying around an old fold-up table for as long as I've known him (which is a very long time). He had it when we were students together at LSU, and he'd dragged it with him to North Carolina and back in the thirty years since. But the old table had become so worn that it been banished to the back porch when he asked me to take a look at it. It was a simple pine table, painted olive drab, probably World War II military issue. It was so old the paint had become chalky. A bit of trim had broken off, and the screws that held the whole thing together were beginning to work loose. I wish I had taken some "before" pictures, but I didn't.

The photo gallery shows how the original table looks like now.



I suspect Calvin's "fold-up" table is actually a modern member (probably World War II era) of a family of furniture known as "campaign furniture." Campaign furniture was designed to be easily packed up and moved from place to place, as in a military campaign or scientific expedition. The British, in particular, turned campaign furniture into a higher art form during the glory days of the empire from the late 18th century to the beginning of the Great War. (Interestingly, there is a surprising lack of literature on the style. The one authoritative reference, British Campaign Furniture: Elegance Under Canvas, is a relatively recent publication (2001) and has been out of print almost since it was published.) The most common pieces are tables, desks, and chests (dressers) and while some of it can be quite crudely constructed, there are many examples that have been finely crafted from nice hardwoods like mahogany, trimmed in brass with recessed pulls.

As I folded Calvin's table to carry it home, I knew that reproducing it would make a perfect weekend project. But little did I realize what an interesting challenge it would turn out to be.




Building My Own Campaign Table

When I finally found the time to build the table, I found a nice supply of very wide cypress boards at a very good price. Perfect! I'd always wanted to work with cypress. The initial cuts were all very straight-forward--no fancy joinery. I did half-lap the aprons on to the leg pairs, but like the original I used screws to attach them. After I had assembled both leg pairs, I simulated folding up the legs and immediately discovered a problem.

Apparently I had decided to "improve" upon the original table when I drew up my Sketchup model. My "improvement" was to modify the inside/outside arrangement of the leg pairs and interweave them instead. I thought it made for a more symmetrical design. By interweaving the folded legs, the leg pair assemblies could be identical--except for the location of the slot in the apron used to tie-in the center support. It looked great on paper (or in this case Sketchup), however in practice it made for an Escher-like impossibility.

In the animated Sketchup drawing below, watch the red leg closely. In order for the legs to fold up, the red one has to magically pass through the apron of the opposing side. Oops!



Fortunately, I discovered the problem before the glue had dried on the leg pairs. I took them apart, made new aprons, and glued and screwed the leg pairs back together.

The next step was to install the strap hinges that attach the leg pairs to the table. The hinges turned out to be an interesting project by themselves. Calvin's campaign table had brushed steel hinges, and the only ones I could find at the hardware store were galvanized. However I thought black hinges would look better against the blonde cypress.

My brother-in-law Pete is a chemical engineer and the resident family scientist. I knew he'd have a clever solution, and he did not disappoint. He suggested that I dip the galvanized hinges in a bath of muriatic acid to remove the zinc, then paint them with black grill paint. Pete even provided me with the chemical equation for the process:

Zn (s) + 2HCl (aq) --> ZnCl2 (aq) + H2 (g)

I started by vigorously rubbing down the hinges with acetone to remove any oils and the adhesive from the price tags. I used acetone because it drives off water and evaporates very quickly. Next, I created a shallow bath of muriatic acid and laid a hinge down in it. I left it in about 3 minutes, watching it fizz while the zinc reacted with the acid. Using a pair of pliers, I removed the hinge from the acid bath and dipped it in a tub of water to stop the reaction. After drying it with a towel, I rinsed the hinge with acetone again to drive off the remaining moisture. I repeated this sequence for each hinge before spraying them with a flat black grill paint. Grill paint dries very quickly, so I was able to cover the hinges with several light coats over several hours. Finally, I baked on the paint by "cooking" the hinges in a hot grill for about 30 minutes.

The Center Support

After attaching the leg pairs with the strap hinges, I was left with what turned out to be the biggest challenge: the center support. In the end, it revealed just how cleverly designed the original table was. When the legs are unfolded, the center support acts as a wedge to hold the aprons apart. In Calvin's original there are two brackets that straddle the ends of the center support. Each bracket has a bolt protruding from the end of it that slips into a slot on the apron. A wing nut tightens the apron against the bracket, eliminating any wobble in the table. To fold up the table, you loosen the wing nuts and swing the bolts up and out of the slots as the brackets pivot on the pins that attach them to the center support. The center support then folds down flat against the table top and the legs fold down over it.

That specially-made bracket looked to be a key part of the original table, but I knew finding hardware like that was going to be impossible. Instead, I embraced the challenge of engineering my own solution. I started by drilling a 1" diameter hole through the center support using a forstner bit on the drill press. Then I cut a 1/4" slot in the end of the center support that intersected the 1" hole using a dado stack on my table saw.

Next, I drilled a hole that was large enough to accommodate a threaded insert into the side of a 1" dowel. Then I cut the dowel to length, making sure that the stub was exactly the thickness of the center support and the hole was centered in it. Finally, slipped the dowel into the hole in the center support and threaded a long bolt through the slot and into the threaded insert to hold it in place. The dowel would provide the mechanism for the bolt and the knob affixed to the end of it to pivot out of the way. With one end finished, I repeated the process on the other.
But I had overlooked something critical! What I had missed was the fact that the bracket bridged the gap between the center support and the apron, providing something for the wing nut to tighten against. I assumed that the gap was only there to accommodate the bracket, but I was wrong. The gap is there to provide just enough room for the apron to fold over the end of the center support! If the center support fits too tightly against the apron when it is folded down, it will pin the apron in place in the upright (unfolded) position anyway.

I solved the problem by marking the midpoint of the center support and marking the table at the midpoint between the aprons. This allowed me to quickly align center support between the aprons after I nibbled a little off each end on the table saw. After each cut, I laid the center support on its side between the aprons and aligned the center mark on it with the mark on the table, then attempted to fold down the leg assembly on either side. It took several passes before the gap on each was wide enough to allow the aprons to clear the center support and fold down.

But now there was a gap between the center support and the apron and nothing to tighten the apron against. I solved this last problem by glueing a thin block of wood--just slightly thinner than the gap--to the inside of the apron. Not beautiful, but it worked.

The simple campaign table presented a series of unexpected challenges, but I'm pleased with the results. And now that I've solved the problems it presented, I look forward to building this project with one of my sons.