Friday, January 13, 2017

Carpenters, Electricians or Plumbers?

I have quite a few clients who are doctors.  Now that I think of it I also have had quite a few doctors as students.  Years ago (many years ago) I taught a series of classes on Decorative Arts at my alma mater, U.C.S.D.  In one of these classes I had a distinguished looking gentleman who always sat in the front row, directly in front of me, and asked very intelligent questions.  After several lectures, I asked him who he was and he responded, "I'm Dr. U".  It impressed me, since he confirmed that his last name was the singular letter "U".  I asked him what kind of doctor he was and he replied "brain surgeon."

As my degree was in High Energy Particle Physics, I thought this was interesting.  I can see the headlines now: "Rocket Scientist teaches Brain Surgeon."

In conversation after class, I asked him why he would take the time to sit through my lectures, as he must be rather busy with his profession.  He complimented me very much when he simply replied, "You are a good teacher."

Some years later I noted in the news that a difficult medical case had been treated at UCSD Medical Center, where a tumor was removed from a patient's brain in a 23 hour procedure.  The doctor who stood in one position for 23 hours and patiently cut away the tumor, stitching each vessel with 10 microscopic stitches was Dr. U.

When I taught my first class at Marc Adams School of Woodworking I had the school make 8 chevalets, and I thought they would be in different sizes.  However, they made them all the same size, 61cm tall, which would be perfect if the student was 6'2".    Naturally all the students were different heights, so I had to make risers for the seats.  In that first class I had a very enthusiastic woman who was 4' 11" tall.  Her name was Pepper and she was a medical doctor.  Doctor Pepper.  She was an exceptional worker and impressed me with her attitude.  Out of the 8 students 3 were medical doctors and one was a medical nurse.

At some point (I can't remember who or where) I had a client who was a doctor tell me that "We're all either carpenters, electricians or plumbers."  I thought that was a rather humble description of one of the most important professions on earth.  "Carpenters" fix broken bones, "Electricians" repair damaged nerves and "plumbers" solve leaky pipes.  (I don't want to be more specific...)

If I had entered the medical profession I would be a good doctor.  I would be a "Carpenter" since I understand how to repair structural damage, with the least invasive methods.  When I fix something it is fixed.  I spend a lot of my work repairing the damage caused not only by the accident but also (and much worse) the damage caused by amateur attempts to repair it, before it was brought to me.

I have posted before about Vector Clamping.  It is my way of teaching about proper methods of applying pressure on a glue joint.  When the joint is straight and even and the clamping surface is parallel to the joint, it is obvious where to clamp.  However, when the repair involves complicated curves and many different breaks it becomes more difficult to visualize where to apply the clamps.

This is where amateur woodworkers get in trouble.  Either they don't have enough clamps or the proper clamps, or the proper glue, or they try to just flood the break with glue, thinking it will fill all the gaps.  In any case, the repair is usually horrible.  By understanding Vector Clamping theory the repair will be easy, and the minimum number of clamps will be needed.

Vector Clamping means that a single clamp must be applied in the center of the joint and perpendicular to its surface.  On curves this means an additional scrap piece of material must be attached temporarily to properly provide a place for the main clamp to do its work.

Repairing a curved leg on a tripod table is a good example.  This nice early table came in last week with a broken leg.  An effort to repair it involved a large dowel going sideways, lots of yellow glue and a lot of missing wood.  The person who had attempted to repair it had damaged much of the surface of the joint so that it was no longer useable.

I used a toothing plane to clean up the glue residue.  You must glue to clean wood.  You cannot glue to dirt, old glue (unless it is a protein glue), or any other contaminant.  The success of the repair depends on the wood to wood surface contact.  This is why dowels are not as good as tenons.  Dowels present a circular surface which contacts as much end grain as side grain.  Tenons contact a larger area of side grain than end grain, so are stronger.

To begin the repair I fashioned pine clamping jigs, which are attached to the leg and foot.  If you study the photo you will see only two of the clamps do the actual work on the repair.  The vertical center clamp holds the piece in position while the diagonal clamp (on the back of the leg, difficult to see) is pulling the foot towards the leg. The rest of the clamps are used to hold the jigs.

Wood Elements Added for Vector Clamping 

I used a pattern to determine the shape of the new piece.  In this case I used a piece of recycled Cuban mahogany, as the table was made in that wood.  Note the tenon extension I provided which fit into the foot element, as there was not enough end grain on the foot piece to guarantee strength.

Foot on Left Photo, Leg on Right Side, Pattern for Repair

This shows the repair after the clamps were removed:

Cuban Mahogany Element Before Shaping 
Looking at the leg from the end to be sure it was straight:

Looks Straight To Me
A second piece of mahogany was added to the bottom of the leg for extra strength across the weakest part of the repair:

Second Piece of Mahogany Added to Bottom of Leg
This is the repair before finishing:
Note The Curve Is Continuous and Smooth
I actually don't like the term "Carpenter".  I am not a "Carpenter".  Carpenters build houses and use nails to fasten wood together.  For the purposes of this post I will not complain.  It is a metaphor.

I am a Problem Solver.

1 comment:

António said...

Thank you very much for this 'tutorial' :)