Tuesday, May 8, 2012

More Vector Clamping

I make a lot of my income from repairs. They are often quick and the simple methods I use guarantee results. I have always told customers that, if I fix it and it breaks where I fixed it, then I will repair it free. I can't recall a time in the past 43 years when I have had to fix something for free due to that guarantee.

 The reason I want to have the customer return it to me, if it breaks, is so I can learn from the failure and not repeat it in the future. Also, in the rare instance that I could not repair it properly, I don't want my work to end up in some other workshop. I value my reputation; it is all I have and it is good.

 Take chairs, for example. Nothing else comes close to making me money as broken chairs. There is no way I can even think of how many chairs I have fixed. Usually they come to me after other people have tried and failed. Therefore, I have also learned from other's mistakes. I have seen iron braces, iron rods, bolts, screws, epoxy, wire, staples, string, tape, "the strongest glue on planet Earth", and auto body filler, just to mention a few tricks, and all of them failed. At some point, the owner finds out about me and they end up on my bench. Always a challenge to undo the damage of previous repairs, which usually are worse than the original problem.

 Chairs take a beating. They are designed to be attractive, stylish and comfortable. They are not designed to support modern American bodies which are heavy and tend to force the structure in ways that it was not designed support. Add to that problem the fact that a majority of old chairs have suffered at least one repair in their life and you understand why I have so much work.

 Last week I was searching on the internet for Ming dynasty chairs, and I found a story about a visitor to a museum in China who felt tired and decided to sit down in a Ming chair which was on a pedestal behind a barrier rope. He broke the chair in three places, fortunately all places where there had been previous breaks. Like I said, antique chairs were not designed for the modern man. I think Frank Lloyd Wright had a point when he designed chairs so uncomfortable that no one wanted to sit in them.

 In any event, I repair chairs practically every day I work. Here are a few simple rules which I follow that make it pleasant. First of all, try to remove all other repairs. This means that, in the case where you have severely fractured wood, and lots of small fragments, you must do the repair over several days. Each day you glue two or three fragments together to form a larger piece. The next day this piece is glued to another, and so on, until you have a two large elements to assemble properly. Most workers try to put all the little pieces together at one time and it makes a mess, as they move around under clamping and the glue gets into the voids.

 Another rule is that it is always necessary to remove all traces of dirt and glue from the wood surface. Usually, with synthetic glues, this requires scraping and using a chisel to carefully remove the glue from the wood, without removing any wood. I prefer to use a toothing plane iron to scrape away, with the grain, the glue and dirt. You can use a small section of a hack saw blade (with larger teeth) to do the same thing, if you cannot find a toothing plane iron. Remember, you cannot glue dirt and expect it to work. Always consider the surface area of the wood in the repair to calculate the potential success of the job.

 End grain surfaces don't count. Long grain surfaces are the only areas where glue holds, and experience will tell you if there is sufficient surface area inside the joint to hold the stress. If not, you may need to add wood to the repair to make it work, either with an internal tenon or external "blister patch". Always use the most conservative repair that you can to protect the value of the object.

 I do not need to stress that the only glue to use is animal protein glue. Any reader of this blog knows where I stand on this question. As I've said for years, "I will use a synthetic glue only if it can be shown that my preferred animal glue won't work and the synthetic glue is better." Never gonna happen.

 The final advice is to understand vector forces when you apply your clamps. Most people do not have enough clamps or the proper variety of clamps to do the job professionally. I have many hundreds of clamps, of every imaginable type. I also have a large box of wood scraps to fit most common furniture shapes. You cannot clamp on curves or complex surfaces without adding wood blocks to provide a purchase for the clamps. The essential rule of vector clamping is that the primary clamp, which actually pulls the joint together, provides its force directly perpendicular to the center of the joint. With curves that means the clamp needs to be out in space, somewhere away from the actual furniture. Therefore, you need to provide a piece of wood shaped to fit the furniture, with a spot on that scrap of wood to hold the primary clamp in its proper position.

 I use a soft wood, like pine or tulip, so as to not damage the antique surface. I cut it to fit the shape of the curve. I provide enough surface area for the scrap to not slip and clamp it firmly to the chair part, before I use any glue. I use scraps of cork under the clamp blocks to protect the surface. I make a dry run after all the scraps are attached to see that it works properly. Then and only then do I reach for the glue.

 Old Brown Glue gives me the additional working time I need to assemble complicated repairs, and has amazing holding power. I apply the glue and then the primary clamp. If I have done my job properly, then I am rewarded with a nice bead of glue evenly squeezing out under pressure as I tighten the primary clamp. No slipping, no change in alignment, no panic. Just success.

 I am rewarded with a happy customer who can use his antique chair, and a quick paycheck. When i make $100 for a 15 minute repair, I am reminded that the 15 minutes took 43 years to learn.