Dale Dallon: Turning Onion-top Lidded Boxes
Chris Stott's book, Turned Boxes—50 Designs, is the source for the basic design of the box demonstrated and contains a wealth of ideas for interesting designs and techniques.
The box demonstrated consists of a bottom bowl and a lid with a tapering stem topped with an onion-shaped bead. A tenon or spigot on the base of the lid fits snugly into a cylindrical recess in the top of the bowl. The basic design rule of 1/3 – 2/3 produces a pleasing shape and proportion for this piece with the separation line between the bowl and the lid occurring at about 1/3 the height of the piece and the narrow point of the stem appearing at about 2/3 the height of the piece. The total height of the piece should be about twice the diameter of the bowl. In this demonstration the bowl diameter was just over 2" and the total finished height was about 4½", but virtually any size piece could be created using these relative proportions.
The length of the cylindrical tenon on the lid that fits into the bowl recess should be long enough to provide a stable fit and short enough to allow good grain matching. About 1/8" – 3/16" is usually enough. The following diagrams provide a starting place, but the final dimensions are best determined by eye to ensure the finished form flows smoothly with pleasing proportions.
Preparing the blank
Before preparing the blank a decision must be made concerning whether the bottom surface of the lid is to be machine finished or merely sanded. If it is to be machine finished, e.g., to machine decoration into the surface, it will be necessary to create a chucking tenon on both ends of the blank. If the surface is only to be sanded, all the machining can be done from a single tenon at the bottom of the piece. That decision will also affect the choice of length for the blank. It is important to leave at least ½" of wood between the tenon and the bottom cut-off point of the bowl to allow creating a jam chuck for finishing the bottom surface of the bowl. If the bottom surface of the lid is also to be machined it is necessary to leave about ¼" of wood between the tenon and the upper cut-off point of the top of the lid. In this demonstration a 2-1/8" × 2-1/8" × 6" mahogany blank was used.
The blank is placed between centers and turned to a cylinder with a spindle roughing gouge, bowl gouge or spindle gouge. A dovetail chucking tenon is then cut on one or both ends. In this demo a single tenon was used in the interest of time. When cutting the tenon be aware of the closing diameter of the chuck you will be using. Most 2" jaws will not close on a tenon less than 1-7/8" in diameter so if you are using a 2" × 2" blank you cannot reduce the diameter much for the tenon. You can, however, just turn the corners off the square blank to leave the diameter large enough to fit the chuck rather than tuning the entire blank down to a true cylinder.
With the lathe turned off mark with a pencil the bottom cut-off, top cut-off lines and other critical positions. The preceding diagrams show locations for each of the major transition points, however, the demonstrator finds it convenient to mark only the 1/3 and 2/3 length positions, but adding ¼" to the section above the 1/3 mark to allow for the length of the parting cut and tenon on the bottom of the lid. Since most of the shaping is to be done by eye, the additional transition points are somewhat redundant.
With a parting tool make superficial cuts at the cut-off lines and the 1/3 and 2/3 positions to provide a visual reference for forming the basic shape. These parting cuts are not made to the finish diameter of the intended shape so the blank will remain sufficiently strong and rigid to support the shaping cuts to follow. Those cuts are illustrated in red in the second diagram above.
Turning the basic shape
Mount the blank in a four-jaw chuck using the tenon at the bottom of the piece. Bring the tailstock with a live cup center up for support. The basic profile of the box can be turned almost entirely with a 3/8" spindle gouge. The demonstrator prefers to develop the entire shape gradually rather than focusing entirely on one section at a time. It is important that the curve of the bowl flows smoothly into the curve at the base of the lid so the joint between them will be almost invisible. Hence the upper curve of the bowl and the lower curve of the lid should be developed together as parallel curves although separated by the length of the tenon (about ¼") on the lid. The original parting cuts can be deepened as needed to provide room to shape the curves. The upper curve of the bowl can be shaped first while deepening the cuts forming the lid tenon to its finished diameter and the curve of the lid second so it flows from the finished diameter of the tenon toward the narrow point of the stem. At this juncture it is appropriate to turn the upper part of the lid to a diameter of about ¾" to facilitate establishing the proper curve at the base of the lid while not weakening the wood too much.
Turning the Lid
If a double chucking is intended, i.e., the bottom surface of the lid is to be machined, this would be the appropriate time to part off the lid, mount the lid section in the four-jaw chuck using the chucking tenon on the upper end of the blank and machine, sand and finish the bottom surface of the lid. Using a thick pad of folded paper towel to protect the finished surface from the cup center, use the tail-stock to stabilize the piece and finish turning the lid to shape before parting it off from the upper tenon. This procedure was not used in the demonstration.
If the piece is being turned from a single chucking, i.e., no machining on the bottom surface of the lid, it will be necessary to completely finish the onion-top prior to parting off the lid. To avoid chatter this must be done before the stem is narrowed to finished diameter. The tail-stock can be removed to expose the end of the lid for final shaping. Since the intended shape of the top of the lid is essentially a bead sitting on a chamfered flare it is convenient to rough out an oval bead slightly larger than the desired finished diameter and slightly longer than the combined length of the onion top and the chamfered flare together. The top of the bead can be turned into the onion shaped curve and the flare can be turned by making a V-cut into the base of the bead to create the chamfer. The base of the bead can then be rounded into the V-cut to form the spherical curve at the bottom of the bead. A ½" skew or ¼" fluteless gouge might be useful in making these delicate cuts into the tight corner where the chamfer and the bead meet.
With the bead formed the stem can now be turned to finished diameter creating a smooth cove-like curve from the base of the lid to the tip of the chamfer. The minimum diameter of the stem should occur somewhere near the 2/3 point marked at the beginning, but can be adjusted to please the eye. The upper half of the lid is now complete and should be sanded and finished. The demonstrator sanded with 150, 220, 340, 400, and 600 grit paper and then applied EEE Ultrashine abrasive wax and buffed it with paper towel. He then applied thinned lacquer as a sealer and friction dried it with paper towel. Friction polish might have been equally useful rather than the lacquer.
The completed and finished lid should now be parted off from the piece using a thin parting tool. The width of the parting cut should be adjusted to leave the desired length of tenon on the base of the lid, bearing in mind that very light cuts might still be required to finalize the curve match between the bowl and the lid. These finishing cuts will have the effect of shortening the tenon a bit further. Be sure the parting tool is sharp to provide as clean a cut as possible to minimize subsequent sanding on the bottom surface of the lid. It is wise to make the parting cut into the base of the lid either dead flat or very slightly concave. Too much concavity will complicate the sanding process to follow.
Turning the Bowl
With the bowl section still mounted in the four-jaw chuck, begin hollowing the inside of the bowl. Do not attempt to hollow to finished dimensions at this point since the wood must not be weakened to the detriment of finishing cuts to follow. The intent at this point is to remove just enough internal wood to relieve most of whatever internal stresses might exist in the wood. In a piece this small those stresses are likely to be minor. The hollowing cuts are best made with a sharp 3/8" spindle gouge using the common pull scrape method. The tip of the gouge enters the center of the end grain with the flute essentially closed in the 9:00 position and the tool is pulled toward you so the bottom wing of the tool removes wood with a scraping cut. Be careful to leave sufficient wall thickness to create the shoulder on which the lid is to rest inside the opening. Be careful also not to go too deep with the hollowing cuts. You will want to leave enough wood in the interior bottom to allow some cleanup cuts and sanding without risking going through the bottom of the bowl.
Next comes the most critical step in the turning process: fitting the lid into the bowl. Form a cylindrical opening in the mouth of the bowl ending with a flat shoulder on which the bottom face of the lid will rest. This cut is best made with a box scraper but can be made with a bedan or skew used as a scraper. Measure the diameter of the lid tenon and mark the top of the bowl as a diameter reference. If the parting off of the lid was done carefully a residual ring might still be visible at the top of the bowl showing the diameter of the tenon. Avoid the temptation of using that reference as a starting point for cutting the cylindrical recess. Instead make the initial recess inside the reference diameter so you can sneak up on the final fit. It is also wise to create the initial recess only half the intended final depth. That will allow you to correct an error without sacrificing too much of the top of the bowl. Create the recess by carefully scraping into the end grain while keeping the wall of the recess perfectly cylindrical. Test the initial recess against the finished lid. If the recess is significantly narrower than the lid diameter, scrape a very small chamfer on the lip of the opening and test against the lid again. If the chamfered opening still does not engage the lid, make another cut out to the diameter of the chamfer and create a new chamfer. Continue this cut-and-try procedure until the lid just does engage the chamfer. Delicate adjustments to the fit can be made by laying the skew flat on the tool rest with the cutting edge exactly parallel to the recess cylinder wall and making extremely light scrapes to remove mere dust from the recess wall. At this time you are seeking a tight fit. When satisfied with the diameter of the recess, finish it by deepening the recess to match the length of the lid tenon being very careful not to change the diameter in the slightest.
With the lid fit completed, you are ready to finalize matching the exterior curves of the lid and bowl Insert the lid tightly into the recess ensuring that the bottom of the lid registers squarely on the shoulder of the recess. Bring the tailstock up against the tip of the lid using a pad of folded paper towel to protect the finished bead from the cup center. Apply just enough pressure on the tailstock to hold the lid securely against the bowl as if it were a jam chuck. With very light cuts with the spindle gouge, probably shear scraping cuts, finalize the shape of the upper bowl and lower lid to achieve a perfect joint between them with a naturally flowing curve. Sand the tooled area to 600 grit and finish with abrasive wax and lacquer (or friction polish) as before. The lid is now complete except for sanding the bottom face. Remove it from the bowl and set the lid aside.
It is now time to finish hollowing the interior of the bowl. This is best done with a small interior scraping tool such as the Dale Nish ornament scrapers. Carefully scrape out the interior of the bowl striving to match the exterior curve of the bowl with uniform wall thickness. Sand the interior of the bowl to 220 grit being careful not to damage the shoulder or lip of the recess.
Now adjust the tightness of fit of the lid into the bowl. Ideally the lid should be tight enough that the box can be lifted by the lid without the bowl falling off but not so tight that the lid is difficult to remove. This adjustment is made with the same very light scraping cuts that were used to establish the initial fit. When satisfied with the fit, touch the lip of the recess with 600 grit paper to remove the slight burr that probably formed there.
With the heavy tooling now complete it is safe to refine the exterior curve of the lower part of the bowl to achieve the spherical shape and create the conical foot on which the finished piece will rest. A combination of cuts with the spindle gouge, fluteless gouge and skew can be used to achieve clean edges and corners on the foot and the joint between the foot and the bowl. Use the thin parting tool to separate the bowl from the chuck leaving sufficient wood in the chuck to create a jam chuck.
Finishing the Base of the Box and the Bottom of the Lid
Create a jam chuck to fit into the recess of the bowl. This will consist of a short tenon matching the tenon on the lid in diameter and almost in length. The lip of the bowl should register against the perfectly flat shoulder at the root of the tenon. The end of the tenon should not bottom out on the shoulder of the bowl recess. The same cut-and-try approach used earlier should be used to fit the tenon to achieve a snug fit. Verify the jam fit allows the chucked bowl to spin true then secure the bowl in the jam chuck with a wrap of masking tape. You are now free to machine the bottom face of the piece to a slightly concave profile. Make any desired adjustments to the shape of the bowl and foot if needed. Sand the bottom half of the bowl and the foot to 600 grit and finish with abrasive wax and sealer as before. Remove the tape and remove the bowl section from the lathe. Avoid putting any solvent based finish on the inside of the bowl. The odors can be very persistent in such a closed area. The demonstrator applied lemon oil wax to the interior and the recess then wiped it out thoroughly with paper towel.
To finish the lower surface of the lid, the demonstrator mounted a 2" sanding disc holder in a Jacobs chuck and inserted it into the Morse taper of the headstock spindle thus converting the lathe to a miniature disk sander. Using the tool rest as an arm rest he was able to carefully sand the bottom surface of the lid to remove tool marks and torn grain. Be careful not to disturb the edges of this surface that register with the shoulder in the bowl recess. Such damage will harm the fit of the lid in the bowl. Grits of 180 and 220 should be sufficient for this finishing step. Lemon oil wax can be used to seal the surface as with the interior of the bowl.