I can't see why going through all this trouble. Why not use a piano hinge from underneath and install it while the boards are snugged up tight on horizontal?
On Fri, 21 Dec 2007, Boyce, Ray wrote: > Installing a Drop Leaf Table Hinge > > Drop leaf table hinge in the dropped position > > Drop leaf table hinge in the raised position > > Drop Leaf Rule Joint > > While at first glance the rule joint seems simple, the realities of this > joint can be frustratingly troublesome. A first attempt will often result in a > joint that scrapes and binds or leaves unsightly gaps. To get it right the > first time requires both an understanding and application of the geometry at > work. > > These days the majority of us will cut the rule joint profiles with a router. > Though this tool can quickly produce a very accurate pair of matching cuts, > it can just as easily cut a good looking but unworkable joint. > > Because different hinges will require different settings for your router, > hinge selection must be your starting point. A rule joint hinge is specially > manufactured > with an extra wide leaf to span the joint. Because it is screwed into the > underside of the table with the barrel facing up it is countersunk on the > reverse > side. > > Start by opening the hinge and laying it barrel upward on a flat surface. > Accurately measure up from this surface to the center of the hinge pin. In the > case of our standard drop leaf hinges this measurement will be 1/8" > (Alternatively, and assuming the hinge is a traditional flat back style you > can simply > measure the hinge barrel and divide by two). When this hinge is mortised into > the underside of the tabletop the center of rotation of the table leaf will > be 1/8" up from the bottom. > > Most tabletops are built of 3/4" thick material and so it seems reasonable to > select a 1/2" radius cutter for the joint. Many woodworkers cutting a rule > joint for the first time will fail to take into account the center of > rotation described above and will assume a 1/2" radius cutter will leave a > 1/4" fillet > in 3/4" stock. If a 1/2" radius cutter is set correctly, with the center of > its described circle raised 1/8" above the underside of the table, the fillet > will actually be only 1/8" not 1/4". An 1/8" fillet is a workable minimum > because, while the fillet is cut into the tabletop, the table leaf must match > its profile with perhaps 1/32" clearance. With a full 3/4" material > thickness, that will leave an edge of 3/32" which should be regarded as the > absolute > minimum. If the tabletop is thinner due to planing or sanding, then a 1/2" > radius cutter will be too large and must be abandoned in favor of a 7/16" or > smaller pair of bits. > > After having established the center of rotation as defined by the hinge > choice and having selected the cutter, you can run the profile on the table > top. > If you are using a 1/2" radius cutter you will need to set the base of your > router to cut a fillet of a thickness that is the result of the following > formula: > > Tabletop thickness (3/4") minus 1/2 hinge barrel diameter (1/8") minus cutter > radius (1/2") > > With this profile cut you can run the mating profile in the table leaf. > Ideally you would select a cutter with a 1/32" larger radius to provide a > little > clearance at the joint. Such cutters are not generally available, so in order > to create the needed clearance, you will separate the leaves by this much > when installing the hinges. > > The hinges can now be mortised. The first cut will be in the table top and > will accommodate the hinge barrel. This is best cut with a ΒΌ" straight cutter. > The center of this cut should be a 1/64" outboard of a line drawn down from > the vertical cut left by your radius cutter. With the table top upside down > and with its leaf nesting in place but separated by 1/32", lay the hinge > barrel in it's mortise and with a sharp knife scribe its outline. Finally > route > a mortise to set the hinge flush with the table underside and screw into > place. Make sure the table leaf remains firmly in place during this operation. > > ********************************************************************** > This message and its attachments may contain legally > privileged or confidential information. If you are not the > intended recipient, you must not disclose or use the > information contained in it. If you have received this e-mail > in error, please notify the sender immediately by return > e-mail and delete the e-mail. > > Any content of this message and its attachments which > does not relate to the official business of Eraring Energy > must be taken not to have been sent or endorsed by > Eraring Energy. 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