Replies

1. 
   MBerger | Mar 12, 2006 05:31pm | #1

   Hi PAP.

   I thought I'd chime in here. FineWoodworkingNetwork.com has a few articles that will assist you in the construction of a rule joint for a drop leaf table.

   To see all related articles, search for "rule joint" in the Network Search bar. Here's a direct link to one helpful article.

   Harvest Table
   by Christian Becksvoort
   http://www.taunton.com/FWN/ProjectsAndDesign/ProjectsAndDesignPDF.aspx?id=2813

   Matt Berger
   Fine Woodworking

2. 
   pellaz | Mar 13, 2006 09:42pm | #2

   Hi, I did extensive research on this, and have found David Charlesworth's discussion of the rule joint illuminating. (Vol II of his books).  The hinges I have used are extrusion brass, and very similar ones seem to be available from both White Chapel and Lee Valley, although the LV hinges are already polished to remove the extrusion marks.  Note, for whatever reason, the thickness of the hinge tapers!!!!  If you cut a mortise of constant depth, the hinge will not be flush with the surface.  David's book is the only one that discusses this.

3. 
   ErnieConover | Mar 15, 2006 04:00pm | #3

   The only instruction in installing drop leaf hinges that I previously knew of was in Ernest Joyce’s Encyclopedia of Cabinet Making. I will be interested to look at the references listed by other readers in this thread. For many hears I have run a drop leaf table class and the inletting of the hinges is sufficiently complicated that I finally made a series of sketches for my students. The following is annotated with those sketches which are attached as a pfd file. They were originally done on large 11” by 17” sheets of art board and I had to cut them up for scanning.

   The hallmark of a fine drop leaf table is a good fit in the rule joints between the main table and the leafs, as well as, properly functioning hinges. The rule joint gets its name from the folding boxwood rulers that every woodworker kept in their apron pocket years ago. These wonderful rulers were swept aside after WW II by cheaper zigzag rules and steel tapes. Rule joints are best made with a router; however thy can be made with a set of matched molding planes for that purpose. I have a set made by Todd Hurley a modern day plane maker in Indiana. Although sets of router bits (and shaper cutters) are sold for this purpose all you really need is a cove and a round over bit of the same radius. Drawing 1 shows a well milled rule joint. Although milling the joint is straight forward, installing the hinges is not a self evident process.

   Since both the folding halves of a hinge and the folding parts of the table are properly called leafs, this discussion could get confusing so bear with me. The hinges for drop leaf tables have narrow leafs of unequal length as show in drawing 2. The shorter leaf is inlet into the underside of the main table while the longer is inlet into the underside of the drop leaf. Uncommon to other types of hinges the knuckle of a drop leaf table hinge is inlet into the underside of the main table top. The center of the knuckle has to be on the exact center of the radius cut by the round over bit used to cut the profile in the main top.

   Proper layout is the key to a properly articulating leaf. The remainder of the drawings walks you through my methods. I find a 6” machinist’s combination square, a marking gauge and a scriber are invaluable for laying out. A well sharpened scriber (awl) gives a much more precise line than a pencil. If I chisel precisely to my scribed layout I get a fit like the tree grew around the hinge.

   The first step is to measure the radius of the round over which is distance “A” in drawing 1. This is added to the distance from the center of the knuckle to the end of the hinge’s short leaf (distance “B” in drawing 2). I use a marking gauge to transfer the combined distances to the underside of the main top as shown in drawing 3. I now place the hinge at the desired location, with the knuckle against the edge and scribe along the sides as shown in drawing 4. I extend this layout to the gauge line with my 6” machinist’s square.

   The next step is to carefully chisel around the layout as shown in drawing 5. I do this with a very sharp bench chisel. To clean out the rest of the mortise I mount a mortising bit in a laminate trim router and set it to the depth of the hinge leafs. I use a CMT mortising bit which is ½” in diameter but with a ¼” shank. It is now an easy matter to use the router free hand, using my chiseled profile as a guide, as shown in drawing 6. The router gives an absolutely uniform depth to the mortise which is the secret of good drop leaf hinges. It is usually necessary to clean up the corners where the bit does not reach with my bench chisel.

   Now lay the hinge in the mortise upside-down. Mark out the knuckle area with four pencil ticks as shown in drawing 7. Remove the hinge and connect the pencil ticks with the aid of a ruler. Now chisel out a trough for the knuckle. I chisel the ends of the trough with a 1/8” bench chisel then cut a V with a larger chisel that is the width of the mortise. I now enlarge this V with hand pushed scooping strokes. The trough should allow sufficient room for the hinge to fold freely but not be overly large or the round over edge is weakened in this critical hinge area. For a tricky fit smoking the knuckle with a candle and pressing it down in the mortise will leave soot where the wood needs to be chiseled away. Drawing 8 shows a finished mortise.

   Lay the hinge in the mortise right side up and drill with a self centering bit). Now screw the hinge in place and just bring the screws tight—no more. If the hinge still works smoothly go on to the next step, if not you will have to enlarge the knuckle trough in the area where the knuckle rubs. Now place the leaf in its correct position against the table but with some cardboard shims to provide clearance in the finished joint as shown in drawing 9. I find a matchbook cover works well. Now transfer the hinge layout to the leaf. I just put tick marks with my scriber at the edges of the hinge. I transfer the total length of the hinge from my gauge line on the main top to the leaf with a steel ruler. I now remove the leaf and extend the tick marks to the ruler line with my scriber. Mortise the leaf in the same way as the top, but there is no knuckle to bury. Put the leaf back in place, drill with the self centering bit and install the screws just tight.

   I often remove the leafs at this point for final sanding and finishing. On the very final installation of the hinges I bring all of the screws just tight as before then give them a final tightening until they align with the axis of the top as in drawing 9 You now have a world class drop leaf hinge installation.

   I install all of the hinges in the top then transfer the layout to the leafs in mass. If using brass screws drill carefully matched holes and wax the screws with paraffin. When working in cherry or maple it is easy to snap a screw in an undersize hole. While brass hinges are beautiful, they are expensive. Steel hinges can often be had at about 1/3 of the price and steel screws are easier to work with. Since a drop leaf hinge is not exposed (except for miniscule amount when the leaf is down) steel can be a good choice.

   Ernie Conover