Sunday, 13 September 2015

Troll Bridge

Back in June of 2006, I bought that month's issue of Fine Woodworking because of a cover that promised "Razor sharp in two minutes."  I was just beginning to learn to sharpen at the time and, having spent long hours flattening the backs of my chisels and plane blades and giving them fresh bevels I was intrigued.  Although I never adopted any of the methods described in that article, one other article magazine has stuck with me to this day.

That article was "An Exercise in Design" by Mark Schofield.  In it, he was building a hall table inspired by a bridge like the one in the picture above.  Because of copyright I can't show you the actual picture, so this is the Broadway bridge here in Saskatoon.  Its close enough so you get the idea.
Schofield was using steam bent arches for the legs and he was worried that under load the arches would spread and the table top would sink down.  Looking for ideas, he sent the picture, along with the dimensions of his table and an explanation of his problem, to three other furniture makers.

These gentlemen (Jere Osgood, Wayne Marcoux, and Garrett Hack) all came back with different solutions to the problem.  Although there were similarities all of designs were quite distinct, solving the problem in very different ways.  In the end, Scofield ignored all of their designs and did his own thing.  If it proves anything, it proves that if you ask 4 different woodworkers how to do something, you will get 6 different answers.

Of course, I had my own idea for the table.  Did I rush to the shop to build it?  No.  I sat on it for almost nine years.  And, really, I still haven't built it (This is not an unusual process for me.  I think it might make a good blog post some day) but at least I have built a prototype.  Half size.

Instead of having the arches go vertical, I put them on angles so they crossed.  Then, to keep them from spreading, I ran a stretcher between and through them.

The impetus to build this prototype came from the Guild's annual 2 x 4 challenge.  Here is the 2 x 4 in original condition.

The legs are each made up of  eight 1" x 1/8" x 40"  strips.

These were then bent around a form and then all glued together except for the inside strip.  This will make sense soon, I promise.

If you're looking at that picture and thinking "That's not enough clamps" or "He should have used something to spread out the pressure" you're right.  It was pretty obvious when I took it off the form where the clamps had been.  It's just the prototype though so I didn't get too bent out of shape (Pun intended),  On the next leg I did use some cauls and it looked a lot better.

The next move was to taper the legs from the centre to the ends.  I wanted the legs to end up 1/2" thick at the ends so, because there was still one strip to glue on, I marked them at 3/8" from the outside edge and tapered to the centre.  Then I cut the curve on the bandsaw.

Now I could put the leg back on the bending form and glue the last strip to the inside.  This gave me an unbroken surface on both the inside and the outside of the leg.  Probably not necessary on a prototype but it just looks better, and maybe a little stronger too.  My plan for the actual table is to taper each strip from 1/4" to 1/8" before gluing them together.

I built this jig to hold the leg arches in place so I could line up, mark, and cut the 2 joints where the legs intersected.  It was long enough to offset them a bit and work my way in.

To me this joint is the heart and soul of this table, the thing that makes it unique.  And it did not turn out at all like I expected.  In my mind's eye, before I built this prototype, the surfaces of the two arches would cross in basically the same plane.

Please ignore the terrible joinery.

As you can see that is not the way it actually worked. The surfaces were not even close to being co-planar.  In fact, it is hard to imagine that they could be any further out than they were.  It kind of threw me for a loop.

I pressed on anyway, mostly because I needed a project for the Guild's 2 x 4 challenge.  I didn't quite get it finished in time but it was close enough.  When I showed it to the Guild everyone seemed more intrigued by the lattice top than the legs, which kind of surprised me.

If this blog entry seems to end rather suddenly it is because I have been trying to write it for six months now.  It has happened in bits and pieces here and there and none of it really feels right.  There is something I want to say about this table but I can't figure out what it is.  Anyway, it has held me up long enough.  Time to move on.