Wooden Screw Clamp (Possible Used in France in 19 th Century)

 

The idea for making these came during a cycling trip to Denmark when passing through Odense on the island of Funen. Since then, I have found similar designs for sale as "antique screw clamps" on the internet and mainly labelled as "French".

Carpenter screw clamp exibited in the museum in Odense, Denmark.

They are generally of similar design as the ones I saw on Funen. The arms are connected to a cross-piece by "Box Pin Joints" also called "Finger Joints" or "Lock Joints" and are made of hardwood (I am using beech because of it's hardness). Also beech is amenable for threading as used previously on screw clamps of a different design, see Blog contents. Also, some of the designs strengthen the arms with a metal rod either near the cross-bar or inside the cross-bar. The ones I saw in Denmark used a metal rod just below the cross-bar that attached to the two arms to help prevent movement or splaying of the arms under tension.  The arms and cross-bar are all large pieces of wood, typically two inches (about 50 mm) in cross-section. The size of the box joints adds some complexity to the project if hand-tools are used.

The design I came up with copies the antique design with a metal rod across the top of the arms and the box joints strengthened using two oak dowels in each joint. 

The first step was to cut the "fingers" of the joint on the cross-bar. These were marked-out with a tenon marking gauge to give three "fingers" per joint (about 8 mm in width). A marking knife was used to deepen the cuts on the end-grain and then extend the lines down the sides to the depth of the arms. The lines were then deepened using a wide chisel to cut along the gauge lines and followed by a guiding edge for the saw. I found that my normal tenon saw was hard to use on the wide and deep tenons so I started each cut with a large tenon saw and then used a fine-toothed cross-cut saw to finish the cut. The waste wood was removed using a fret saw and finished with a 5 mm chisel.

The first joint cut to size.

The corresponding joint was marked and cut being careful to saw on the correct side of the waste line to enable a close fit. Final adjustements to the finger joint were made using wood file and chisel as appropriate.

One of the joints complete ready for glueing. The beech threaded-screw and hazel handle is also shown.

Before making the joint on the other arm, I decided to make sure the tapped hole and screw-thread were alright. I made the screw-thread out of oven dried beech that had been soaked in butcher oil for three days. The first pass left the thread too tight so I had to deepen the thread a fraction to get a close fit into the arm. The handle of the threaded-screw was made from some dried waste hazel and glued on and then strengthened using a oak dowel. 

The joint on the other arm was then made and fitted ready for shaping and glueing. The holes for the steel cross-bar were also drilled.

Checking the alignment before finally shaping and glueing.

Oak dowels (9.5 mm) were inserted into the corners by drilling holes with a auger drill.

The clamp assembled with steel cross-bar in place.

The finished clamp after treating with linseed oil and ready for use.