Sphere-Cuttingjig

Shopbuilt Sphere-Cutting Jig

Eugene Lee ’ve been turning for a few years object. I wanted to spend more time (Above, l to r) Juniper spherical hollow form with and have honed my skills so that exploring surface enhancements a tilted band, 4¾" (12 cm)—band produced by I I can turn a sphere-shaped object, rather than turning the sphere itself, multiaxis turning. Walnut, 4¼" (11 cm); Avocado, either as a solid or hollow form. They so I decided to build a sphere-cut- with John Jordan-inspired carving, 4½". Spheres are always sphere-shaped rather than ting jig. were turned with the jig described. near perfect because when I rotated The jig’s cutter has to be mounted them in my hands, I felt some bulges at the lathe’s center height, on an arm and depressions—they were not as that pivots around a point directly spherical as I wanted. under the intersection of the lathe designed a jig that can be built with When turning a spherical object axis and the equator of the sphere- hardwood, phenolic-faced plywood, without the use of a jig, I am to-be. Swinging the arm through a and metal hardware. mindful that at any time I can cut semicircle sweeps the cutter across too much and go inside the target the surface of the sphere. There are a Make the jig radius. When that happens, I either number of metal sphere-cutting jigs There are two parts to this jig (Photo recut the sphere to a smaller radius on the market (see page 46), but I have 1): a platform mounted on the lathe or leave it alone as a sphere-shaped no experience with machining, so I ways, and a pivoting turret that

42 American Woodturner October 2012

42_SphereCuttingJig.indd 42 9/11/12 10:43 AM Feature

carries the tool. The turret pivots (73 mm) thick. The bottom view of not right on, you will get a football on a vertical pin embedded in the the platform (Photo 3) shows ¾" × shape. I fastened the top of the plat- platform directly below the lathe ⅜" (20 mm × 10 mm) T-track dadoed form to the sides with #8 sheet-metal axis. For tooling I am using the Easy into a guide bar of ¾" hardwood. For screws and washers in oversized Wood Tool’s Ci1 Easy Rougher and my lathe, the guide bar fastens 2¾" counterbored holes to permit a little the Ci0 Easy Finisher. For flatness, (70 mm) from the back edge of the play for final adjustment. The dis- stability, and low friction I made the plywood. Photo 3 includes two blocks tance from the top of the pivot to platform and turret base using ¾" of wood with ¼" (6 mm) T-bolts and a the lathe axis determines the biggest (20 mm) phenolic-faced plywood, plastic knob for locking the platform sphere, in this case a radius about for which you can find suppliers on onto the lathe. 4¼" (110 mm). the Internet. Photo 4 shows the underside of To locate the hole for the pivot, The jig dimensions are not critical the platform top plate with the ¾" place the top onto the platform so and can be tailored to your own lathe plywood block that carries the pivot, that the tip of a revolving center is and tools. The parts described here a 2½" × ¼" (63 mm × 6 mm) bolt with above the middle of the platform. apply to my JET 16-42 lathe. Photo 2 washer. A ¼"-20 threaded steel insert Use a square to mark the platform shows only the platform, a flat box secures the bolt to the platform directly under the tip. Use Forstner that slides along the lathe bed with about 1" (25 mm) protruding bits to counterbore the hole for a and houses the pivot. My platform from the top as the pivot. The pivot steel threaded insert, then complete measures 10" (25 cm) wide, 12⅜" needs to be directly under the lathe the hole with a ¼" bit. Run the bolt (31 cm) front-to-back, and 2⅞" axis in order to turn a sphere. If it is into the threaded insert to help

1 2 3 Sphere-cutting jig consists of a base The jig platform is made of ¾" phenolic-faced Underside of jig platform shows the platform mounted on the lathe ways with a plywood, which is flat, stable, and smooth. T-track, blocks, and knob that lock it onto pivot directly under the lathe axis. Pivoting Note the bolt as pivot. the lathe ways. the turret assembly and its carbide-tipped tool cuts the surface of the sphere.

4 5 6 The pivot is threaded through an internal The pivot mounts directly under the lathe axis. The jig turret consists of a housing for the plywood plate to keep it in place. cutter (parts A and B), a spacer block (part C), and a mounting block (part D) that connects the turret to the bottom plate (part E).

woodturner.org 43

42_SphereCuttingJig.indd 43 9/11/12 10:43 AM dado about ⅜" deep into the bottom plate, part E, and glue the connecting spline into it, then carefully fit part D onto the spline and screw the assembly together. With the completed turret in place, fit a ¼" nut onto the pivot and tighten it to barely touch the plywood. The sphere-cutting jig is complete. 7 8 To use this jig, first turn a cylinder Brass connector bolts and cross dowels, You may need to notch the turret’s that is longer than the diameter of the parts F and G, hold the turret assembly bottom plate so it can clear the headstock. sphere. Center the jig on the cylinder together. The bottom block, part D, fits over a hardwood spline glued onto the and start cutting from side to side bottom plate E. The nuts and bolts at right while you move the cutter toward the hold parts A, B, and C together. desired radius. Videos are available for viewing online with instructions on how to use a similar jig, so I will limit my discussion to a few advisories. you screw it into the hard plywood not critical, so long as the cutter is When turning larger spheres, I have without any misalignment. Recheck secure and ends up exactly on the found it best to rough out the shape with a square to make sure the pin is lathe axis. I used seasoned hard- using a bowl gouge before bringing directly under the tip of the revolv- wood blocks measuring 4" (100 the jig into play. I start with the Easy ing center (Photo 5). Clamp the top mm) long by 15⁄16" (30 mm) wide, for Rougher and, as I get close to the down, drill pilot holes, and screw a total height of 5⅛" (130 mm), which final shape, I switch over to the Easy the top onto the platform. for safety’s sake I shaped and cut from Finisher. This speeds up the process The turret’s bottom plate, part E in a larger board. and puts less wear on the carbide tips. Photo 6, has several holes for the pivot, Photo 7 also shows the ¼" brass to cut spheres of various diameters connector bolts and cross dowels, Cup centers without the cutter overhanging too parts F and G, that hold the blocks The last step in turning a solid far. To reduce wear on the holes in the assembly together. Cut a ¾" dado sphere is to part off the ends and bottom plate, I epoxied ¾" long by ¼" about ⅜" deep into the bottom mount the workpiece between cup steel spacers into it. Since the nominal of part D for attaching it to the centers to turn away the stubs. I ¾" phenolic plywood is actually a bottom plate with a ¾" square use shopmade cup centers like the little thin, I had to grind the spacers spline and screws. Make part A ones in “Spherical Thinking” by to match. last and install the ¼" × 20 steel Frederick Hill (AW, vol 25, no 4). threaded insert for the locking However, instead of fitting the cup Adjust the cutter height knob, part H in the photos. Fasten center over the Oneway-type revolv- The greatest challenge in the design part A atop part B using #6 sheet- ing center, I screw it onto the cen- of this jig was how to adjust cutter metal screws and washers. With the ter’s threads by epoxying a ¾" × 10 height without using metal parts. I turret assembled, trim the length to nylon insert lock nut into the wood ended up with the four-block turret 4" and set it aside. (Photo 9). The tip of the revolving shown in Photos 6 and 7. From the The bottom plate, part E, is 10" center juts out a fraction of an inch, top, block A and knob H clamp the (25 cm) long by 6" (15 cm) wide so if you epoxy a couple of washers cutter in place. Block B has a ½" × with a series of five holes 1" apart and a coin to the lock nut, it will ½" (13 mm) dado sized to house the for the pivot. The turret mounts completely cover up the threaded cutter. Block C is a shim that can be 1" from the last hole. This enables end of the revolving center. swapped out for height adjustments. making spheres up to a little more To build a tailstock cup center for Block D connects the turret to the than 8" (20 cm) in diameter. You use on spheres larger than 4" (10 cm) bottom plate E by way of screws into may need to notch out the left side in diameter, I turned a 3¾"- (9.5 cm-) a square spline that’s dadoed into of the bottom plate (Photo 8) to clear diameter cylinder out of three pieces both parts. The size of the blocks is the headstock. Cut a ¾" half-blind of glued up wood. I cut a 2⅜" (6 cm)

44 American Woodturner October 2012

42_SphereCuttingJig.indd 44 9/11/12 10:43 AM Feature

9 10 11 The tip of the revolving center extends Glue up the blank for the cup center, then drill Teflon tape on the threads of the beyond a lock nut with a nylon insert. a hole for the lock nut. The nut should sit flush revolving center will help control the with the wood face. wet epoxy.

tenon about ⅜" (10 mm) thick with the revolving center for use on spheres start inside the hole and take very fine a hole for the lock nut. Make this greater than 4" in diameter. cuts to match the surface already cut. hole just deep enough so that the nut Although it is possible to remove At this point you can continue swing- sits flush with the wood surface the stubs from a sphere using the ing the jig in either direction, so long (Photo 10). Remove the nut and rough sphere-cutting jig, I get better results as you take very fine cuts. When you up the inside of the hole with a Dremel by scraping with a sharp straight-edge have finished hollowing out the sphere, bit to provide an irregular surface for skew chisel resting horizontally on reverse-turn the bottom using the jig the epoxy to grip. Screw the nut into the toolrest and moving tangentially (Photo 13) as close as the jig will allow. the revolving center tightly and then, to the surface of the sphere. Finish the rest of the bottom freehand to help manage the epoxy, wrap the When turning hollow spheres there using a spindle gouge, then turn a metal with Teflon tape (Photo 11). is no need for cup centers. Instead, use shallow concave foot and part it off. Apply just enough five-minute epoxy a chuck to hold one end of the blank, into the deep part of the hole and to with the revolving center supporting Eugene Lee was a semi-retired engineer who the front part of the nut so that when the tail. After using the jig to shape lived in Palos Verdes Estates, CA, and was a member of the El Camino Woodturning you insert the nut there will not be most of the sphere, remove the tailstock Guild. Eugene died in July, but he did see his excess epoxy leaking out of the hole. center and drill a hole for hollowing. article in final layout. We are thankful to Don’t worry that most of the space Since the jig cutter is prone to catches Eugene for sharing his knowledge. between the nut and wood will not as it nears the stub, reverse the swing to —Betty Scarpino have any epoxy in it yet. Rotate the wood cylinder and nut once to distribute the epoxy. After it has dried, unscrew the tailstock center from the nut and remove the wood. Trim off the Teflon tape, then cover the nut with masking tape. Use a sharp knife to cut out a ring in the masking tape between the wood and the nut so that slow- setting epoxy can be put into the gap to completely fill out the space. After this epoxy has dried, remove the masking 12 13 tape and clean up the excess glue. Now Use a cardboard template to turn a hollow The jig helps remove the chucking grip the tenon in the scroll chuck so in the cup chuck. tenon that was used to mount this sphere for hollowing. The sphere’s you can hollow out a cup with a 2" (5 opening is hidden inside the cup chuck cm) radius (Photo 12). The completed in the headstock. cup chuck can now be threaded into

woodturner.org 45

42_SphereCuttingJig.indd 45 9/13/12 8:52 AM Spheres: A classic turning challenge Creating a good sphere is a classic turning chal- exploration, the most interesting being Andy lenge that can be approached by hand, or with Whyman’s prototype gadget, which can also hol- jigs. In early turning literature, such as Holtzapffel’s low a hemisphere simply by projecting the cutter 1881 treatise Hand or Simple Turning, the discus- beyond the sphere center. sions on spheres follow methods familiar to us All the sphere-cutting jigs that I have seen today. His detailed description of hand scraping an operate on this same fundamental geometry: The Christian Burchard, Spheres, 1994, White oak burl, walnut, olive burl, yew, manzanita, black locust, 4" to 12" (10 cm ivory billiard ball by repeatedly reorienting it in a cutter is mounted right on center height, on an to 30 cm) dia cup chuck is, well, fascinating. arm that pivots around a point directly under the Practical approaches to hand-tool procedures lathe axis and the equator of the sphere-to-be. Christian Burchard works with the cracks and checks that typically afflict wood spheres. are well documented in back issues of American Swinging the arm through a semicircle sweeps Woodturner, available for online viewing in the the cutter across the surface of the sphere. Aside Members’ Area at woodturner.org. Christian Bur- from Darlow’s chapter, however, not much chard offers the most engaging and easy-to-follow has appeared in print about making and using account (AW, vol 10, no 2). Starting with a log of sphere-cutting jigs like Eugene Lee’s. Not so on green wood or a sawn billet, the basic technique the Internet, where a search will turn up a number is to rough out the sphere between centers, then of informative videos on various approaches to part it off and remount it between shopmade cup the problem, a number of other plans for jigs, chucks to finish-turn on at least three axes. With the and two commercial jigs that well-heeled turners near-sphere spinning, you can see the ghost image might like to buy. of what is to be pared away and what is to remain. Whether they are working by hand or with Christian’s delightfully idiosyncratic presenta- jigs, turners can make good use of an interest- Holtzapffel’s geometric approach to the sphere tion includes his realization that no matter how ing geometric property of spheres: Any circular uses the ring gauge (last drawing) to check it. carefully you select and dry the wood, spheres ring laid onto any sphere will touch at all points. usually crack. He therefore decided to rough the Conversely, the ring will not touch everywhere sphere and then put the wood through wet-heat- if the workpiece is not (yet) a sphere, as you can dry cycles so it would finish cracking before final see in the photo. Brian Simmons wrote about turning. A few years later, John Brewer presented a using a plastic ring as a sphere gauge (AW vol sequential procedure solidly based in geometry as 16, no 3), forming the ring from PVC pipe and taught to him by Myron Curtis (AW, vol 16, no 2), attributing the technique to Soren Berger of New Fred Lindsay makes hollowing systems and and very similar to what you find in Holtzapffel. Zealand. Simmons says a good ring-to-sphere size sphere-turning jigs tailored to popular lathes, Jumping off from Christian’s article, Bob Rosand ratio is 1:2 to 1:4, and it is important to start at about $300, lindsaylathetools.com. Fred has video tutorials on his website and on YouTube. shows step-by-step the hand-turning procedure the equator of the sphere then work toward the (AW, vol 18, no 2). Cliff Hill in the same issue details poles. Well, if a ring works, what about a circular exactly how to cook and dry the wood to make scraping tool? Wouldn’t that help achieve the it crack and check. Frederick C. Hill reviews all of perfectly spherical surface? F. Robert Brueckmann these techniques and adds a number of sanding writes that indeed it will—he made such a scraper and finishing refinements (AW, vol 25, no 4). by carefully grinding the teeth off a oleh saw Mike Darlow’s book Woodturning Methods mounted on a handle (AW vol 15, no 1). I’m look- includes a comprehensive chapter on sphere ing forward to giving this clever trick a try. turning with many illustrations of various tools, jigs, and techniques. As usual in Darlow’s Enzo Verrecchia of Brisbane, Australia, makes books, there are lots and lots of ideas for further John Kelsey sphere-cutting jigs and many other turning tools under his Vermec brand. The photo shows the Vermec device, about $350, being demonstrated at the AAW 2012 Symposium in the booth of the U.S. importer, Woodworkers’ Emporium, woodworkersemporium.com.

As Mike Darlow shows with these photos of Andy Whyman’s jig, how far the cutter projects determines whether it cuts the outside of a sphere (l), or the inside of a hemisphere (r). Ring gauge

46 American Woodturner October 2012

42_SphereCuttingJig.indd 46 9/11/12 10:44 AM