Monday, October 24, 2011

Simple Example of Vector Clamping

I was just looking at the photos I posted of the chair with all the clamps. Unless you go through a sequence of applying the clamps it is difficult to fully understand why each clamp is placed where it is. After dozens of clamps are in place it just looks like a mess.

I may be accused of using more clamps then necessary in my repairs. That may be simply because I have collected more clamps then a single person should have over the years. However, it is also because I study each repair carefully to fully understand where all the forces need to be applied.

If the part is shattered or previously repaired badly, it is necessary to take apart all the fragments and clean the glue off of each using small chisels or a small toothing plane iron I keep for that job. I use an Optivisor to see more closely what I am doing and I am extremely careful to not remove any wood.

Then it is important to begin the repair by gluing several small parts together, wait overnight, and continue adding fragments day by day until the repair is complete. Sometimes with chairs I have more than a dozen fragments to assemble just for one joint.

In other cases, the repair is simple and easy. Just remove the modern glue, clean up the wood surface and add protein glue.

In the case of this American Empire center table, pictured above, the two rear legs had come loose. Since the top of this table is marble, there was a lot of force on the joint, which was originally held by three dowels. The owner had had some person try to glue it with the "strongest glue on planet Earth" with horrible results. Part of his problem was the glue and part of the problem was the failure to understand clamping pressure on this joint.

Note the central axis of the joint, perpendicular to the face of the plinth, extends above the toe of the foot, out in space. There is no way to put a clamp there, unless you add a block. That illustrates very clearly what I intend to show about vector clamping. Just by adding a pine block of wood on the foot I was able to create a purchase for the primary clamp. The red clamp is the primary clamp. Since gravity also creates a force downward on the clamp in this position, I added a second, orange, clamp to compensate. These two clamps are all that are required to achieve a correct vector force on the face of the joint.

The entire operation took 15 minutes and made me a profit and the owner of the table happy. I have always guaranteed my repairs for life. Sometimes the project will return for more repair but never in the place where I repaired it. I can say, with some satisfaction, that I have never had a repair failure in my career of restoring antiques. Do it right and forget it.


Anonymous said...

If in your opinion the original joint, and let's use the Empire table pictured here as an example, wasn't quite done in the best manner would you consider redoing in a stronger method?


W. Patrick Edwards said...

There are several reasons not to alter or modify antique furniture. I respect the tradition and appreciate the evolution of the methods used as style changed and technology emerged.

It is true that different methods of construction in different periods created problems or actual failures which led to improvements over time. For example, when ebony was introduced in the 17th century as a new wood to the European craftsmen, they tried to carve solid cabinets from the stuff. They quickly realized that the solid ebony dried out and cracked soon after it was carved. The desire to use this wood was so strong that a new method of making and using veneer was created, so that the ebony would remain more stable as a surface material.

Those early workers were called "ebenistes."

If I make a clock from 1680, I use methods from that time. If I make an Empire table from 1810, same argument. I change nothing; as a student and historian of furniture evolution, I make every effort not to impose my modern knowledge on the work.

Much of the damage I work on in the antique furniture business is not the result of bad construction. It is the result of accident, improper use or bad repairs.