Loose fitting lids on hollow forms that lock.
One of the many requests I receive during showings of my work is for lidded containers that have a locking lid. I cannot afford to make speculative one-off pieces out of stable exotic timber so wood movement is a given when turning thin walled hollow forms from native Texas woods that could receive a lid. I thought that there must be some kind of latch that could work with a fitted wooden lid that must have been used in man’s history from native timber that is functional even after reaching an equilibrium moisture content.
As a child in Japan, I remember seeing “honey bucket” style containers that used a rod to keep a flat lid on the round bucket. The prototype needed to have a large mouth to let a hand reach into the container. This requirement robs the top of the expected rigidity of most common hollow forms seen today. With this dim vision in mind, I began making sketches and selecting local timbers for prototypes.
Mesquite, pecan, sycamore, hackberry, elm, chinaberry and walnut are good candidates for prototypes in my local area. My first attempt produced a fit that was “snug” in the morning, but too tight to remove by the afternoon heat of the summer. The next morning the same lid was loose / snug again in the cooler morning temperatures. Trial and error showed that a lid fit as loose and 1/32” to 1/16” was functional and allowed the application of sanding sealer and finish coats to be applied without making the fit too tight.
The tools in my studio are geared toward one-of-a-kind pieces. As a result, I confess to being a tool nut. If I can’t find a tool that provides a solution to a problem, I will make it. For this project, here are some of the basic “tools of the trade” used in measuring and repeating the locking mechanism of lids and rods. A compass, engineer’s square, caliper and ruler are handy for measuring the lid, locating the side wall holes and the locking rod. A few jigs were created to help in locating the holes through the sides walls and marking the groove in the knob on top of the lid for the locking rod to pass over.
These prototypes are 6” in diameter or larger and 6” to 14” in depth. These sizes allow out of round movement that requires the loose fit of the lid. The following procedure is for a container large enough for a hand to reach into, but the same technique can be used for smaller ornamental forms like a small “keep sake” box.
Step 1: The shape of the rough turned hollow form needs interior vertical space for the lid of more than 1-1/4” below to top rim. This reserved space is for the lid to nest onto a 1/8” inside ledge once the piece has reached EMC.
Note: I use the denatured alcohol drying method for native timber since most gathered wood comes from tree trimming services that cut year round when sap may be on the rise in the cut wood. This drying method seems to let green rough turned wood reach EMC within eight weeks by weight and leave the timber less prone to drastic movement once finish turned.
Step 2: After finish turning the hollow form and establishing the interior ledge for the lid, measure the interior diameter for the lid. I usually select a contrasting color species of wood for the lid that is more than one inch in thickness to provide enough wood for the knob and a reverse turned mortise in the base of the lid for a small expanding chuck. I cut the blank for the lid about 1/4” inch oversize in diameter to give room for the rough turning and reverse turning. Using large inside / outside calipers may help in sizing the lid, but I always make test fits of the lid before I am satisfied that there is enough “play” in the fit. Don’t forget we are making a lid for a hollow form that we know will “relax” out of round slightly.
Step 3: Once the lid is in place with a turned knob, time to measure for the length of locking rod that will pass through both walls of the form and over the top of the lid. I give the finish turned rod about an inch outside of the form with a 3/8” diameter. The diameter is dictated by the size of a Forstner bit to cut the side wall holes. There is a slight increase in diameter of the rod at the finial to make the rod stay snug in the hole. Esthetics will determine the final length once a decorative finial is turned on one end of the rod.
Step 4: Determine the location for the holes through the side walls at a minimum of 3/8” below the rim. Mark center of each hole on the outside and use a Forstner bit chucked in a slow speed hand drill. Masking tape over the inside hole position with a backing block will prevent tear out as the bit clears the inside wall.
Step 5: Using a 3/8” wide clear plastic jig cut to 8” long, place the jig through the holes and across the lid and knob aligned with the center of the knob. Mark where the jig passes over the knob for a groove to be cut across the knob that will let the rod pass through the holes and through the groove to “lock” the lid in place.
Step 6: I use a power carver fitted with a coarse typhoon roto saw bit to make the rough cut-out for the groove across the top of the knob. Trial fits with the rod running though one wall across the groove in the lid help determine how much wood to remove from the knob. Various carving bits and smoothing stones are used to finish the groove once a satisfactory fit is established for the rod as it runs across the groove and through both sides of the form.
