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This article was published in the December 2016 edition of More Woodturning
I usually start the introduction to an article with where I got the idea. In this case, I don’t remember. My sketch book wasn’t much help as all it had was a sketch that was pretty much fully formed. So I’ll just tell you about it. I call it a cap ornament because it’s a sphere with a cap sitting on top. Not a cap like an acorn, but one with vertically square sides which produces a scalloped look when viewed from the side. I think the dramatic scallops and the sharp points really make the look of the ornament. As mortal woodturners couldn’t preserve the sharp points through turning and sanding square stock temporary joints and waste wood are used to make the blank round. To further help, the outside is turned using a mandrel that supports the entire inside to try and cut down on vibration.
The cap ornament concept turns out to be quite versatile as you can put a cap on any sphere, such as a turned ball, foam balls, or commercial ornaments. Our own tree, with mostly wooden ornaments, is sadly lacking in bling according to my wife—and the latter option can correct that. Furthermore, you can add any number of treatments to a basic foam or commercial ball. You could collaborate with a fiber artist and put a cap on a quilted ball. Or you could collaborate with your grandkids by giving them a foam ball and some glitter glue. Have a look at my cap ornament online gallery listed in References for some of the possibilities.
Briefly, first the cap blank is made by wrapping waste wood around square stock using blue tape and wood glue to make temporary joints. One or more (depending on the method chosen to turn the top of the cap) templates are made. The blank is cut to length and pinned to the chuck face with a tailstock center so it can be turned round and a chucking tenon formed. The blank is then mounted in a 4-jawed chuck and the inside (or bottom) hollowed to a hemisphere with the aid of a template. Then the blank is mounted on a hemispherical mandrel to turn the outside (top) with the aid of the shadow sphere jig or another template. Three different ways of attaching the cap are shown, and a simple way to cover the ball with fabric.
Creating the Cap Blank
Start by creating a square blank for the cap. You’ll get the most dramatic scallops if the cross corner diagonal of the square equals the diameter of the ball. On the other hand, if you’re going to obsess over the lengths of the points of the scallops being exactly the same length, you could give yourself a break and use a slightly smaller square, as with tangent lines a tiny error in centering is multiplied (see drawing in Jigs and Templates in References). The “3 inch” foam balls I’ve seen are closer to 2.9”, for which the square sides should be 2.05”. “3 inch” shatterproof ornaments tend to be just about 3”, for which the square sides should be 2.12”. If you’re using a different sized ball, the side length of the square should be 0.707 times the diameter. It is, by the way, a good idea to obtain the balls and actually measure them first before going to the trouble of making blanks and templates. You can sand the sides of the square core now to avoid dubbing over the edges and points later.
Once you’ve made the square primary wood for the blank, cut the waste wood pieces. Just because it’s waste wood doesn’t mean it should be trashy wood—I had much better survival rate of the temporary joints with Radiata Pine than with lesser quality pine (100% versus maybe 50%). 3/4” thick wood will work well. Cut it the same length as your square core and 3/4” wider than the width of a side of the square. You need 4 pieces.
Cover the square core with blue tape and sand the tape lightly with 150 grit (or so) to remove the coating and promote better glue adhesion. Figure #1 shows the tape covered square core and the waste wood pieces. Temporary joints made with blue tape are stronger than most people think, but at the end you’ll be down to a joint width of around 1/8” so tight fitting joint are a must. This means that the edge of the first waste piece must line up precisely with the corner of the square core. To ensure this, cover a conveniently sized piece of sheet goods with waxed paper so glue won’t stick to it. Apply a thin even coat of wood glue to one side of the square core. Clamp the square core to the sheet goods at each end so that the side of the core with glue is about 3/4” from the edge of the sheet good piece. Clamp a waste wood piece lightly to the core. Then use clamps at each end of the waste wood to clamp it to the sheet goods and ensure the edge of the waste lines up with the corner of the core. Then tighten up the clamps holding the waste wood to the core. The top image of Figure #2 shows the blank to this point.
Figure #1: The taped square core and waste wood pieces.
Figure #2: Clamping waste wood to the square core.
Wait until the glue has a chance to set—at least a half hour. Then remove the clamps. Apply blue tape to the exposed inside edge of the first waste piece. Then spread a thin, even coat of wood glue over the taped waste piece and the adjacent side of the square core. Lightly clamp another waste wood piece to the square core, and then clamp the two waste wood pieces together. Then tighten the clamps holding the waste piece to the core as in the bottom image of Figure #2. Repeat this step for the third and fourth waste pieces and let the glue cure overnight.
Templates and Mandrel
Download the templates you need (see References) and print them out. You’ll need the hollowing template for the correct size ball, and a cap template for the correct size cap if you aren’t using the shadow sphere jig, and a shadow sphere pattern if you are. Print the templates out and use spray adhesive to fasten them to a suitable substrate as in Figure #3. The hollowing template needs to be on something thin, such as sheet metal (you could use 1/8” plywood if you carefully beveled the bottom edge, otherwise you’ll get oversize results). The cap template should be on something thick enough to set calipers on, such as 1/8” plywood. Poster board, or cereal box cardboard will suffice to stiffen up the shadow sphere pattern.
Figure #3: Fasten the needed templates to suitable substrates.
Cut out the templates. I used a scroll saw. If you don’t have one you could use tin snips on the sheet metal and a coping saw, or a bandsaw followed by sanding or filing of the plywood. There are two nested diamonds in the hollowing template. One is 1/2” on each side, the other 5/8” on each side. Use the size that corresponds to the diameter of your tailstock cup center.
Now make a cap drive which will both drive the hollowed cap for turning the top and support it to minimize vibration at the same time. The cap drive is shown in Figure #4. I made mine as a wooden face plate (see references) to mount directly on the lathe spindle, but a simple tenon to fit in a 4-jawed chuck will also work. Glue up suitable stock (I used 3 layers of 5/4 x4 Radiata Pine). After the glue cures, pin the center of the blank to the closed 4-jawed chuck with a tailstock cup center. Turn the blank round and about 1/4” greater in diameter than the sphere size. Form a tenon that will fit in the 4-jawed chuck and mount it. If you want to make the drive with a spindle mount, drill tap holes and form a recess for the spindle flange with another drill or by turning. Then tap the spindle threads.
Figure #4: The completed cap drive.
If you will be using the shadow method, measure back a little more than half the sphere diameter. Drill a 7mm hole for a pen tube, or a 1/4” hole for a piece of dowel to help center your light. Mount the blank on the spindle or chuck. Turn the nose to a hemisphere using the method you prefer. If you are using the shadow method the base of the hemisphere should bisect the hole for the dowel.
Hollow the Cap
Determine how long to cut the cap blank. You need half the ball diameter, plus 1/8” for the cap thickness, plus the length of the finial you want. If you allow extra you can erase hollowing mistakes by trimming off some of the length. For a 3” or so ball 2-1/4” is a good place to start.
It’s important that the cuts at each end be perpendicular to the axis of the cap core and parallel to one another. The blank is too thick to cut on one pass on most table saws, but if you use a face piece on your miter gauge with the blade at full height you can cut all but 1/2” or so and then cut the remainder on a bandsaw. This method has enough of the cut done on the table saw to align it properly. You can also cut the blank to size on a bandsaw if you lay out cutting lines with a square and follow the lines very carefully. It’s the perpendicularity to the core that matters, not the surface quality. If you have a chop saw it will probably cut through the entire blank in one pass and will cut perpendicular to the core if you clamp the blank in place before each cut.
Use a freshly sharpened pencil and a straight edge to draw cross diagonal lines from the corners of the square core as in the left image of Figure #5. Carefully align the hollowing template so that the diagonal lines on the core match up with the corners of the diamond on the hollowing template. Trace the diamond and the hemisphere of the template on to the core. Turn the template 180°, line it up again, and trace the hemisphere again as in the right image of Figure #5. The circle you’ve made tracing the hemisphere twice should intersect all four corners of the core.
Figure #5: Layout centering marks on the square core.
Knock the center pin out of your cup tailstock center. Fully close the #2 jaws on your 4-jawed chuck and lightly pin the blank to the chuck jaw face with the cup center. Tap the blank to center the diamond on the cup center as in Figure #6. Rotate the blank by hand 90° a couple of times to make sure it’s centered. Tighten the tailstock center a little and turn the lathe on and make sure that the circle drawn on the blank doesn’t appear blurry as in Figure #7. Then stop the lathe and fully tighten the tailstock.
Figure #6: Center the blank.
Figure #7: Check the centering of the blank.
Gently cut the blank to round with a spindle roughing gouge. Then use a parting tool to cut a tenon about 3” in diameter and less than 1/2” deep on the blank as in Figure #8.
Figure #8: Turn a mounting tenon on the blank.
Mount a combined drill and countersink with a 1/2” body diameter in your tailstock and drill a true starter hole as in Figure #9. Use the drill depth indicator on the hollowing template to set the drill depth on a 1/2” drill bit as in the top image of Figure #10. Then drill to that depth with the 1/2” drill bit as in the bottom. In the photo I’m using a #2 Morse taper drill bit which is convenient, but of course mounting an ordinary drill bit in a drill chuck will suffice.
Figure #9: Drill a true starter hole with a combined drill and countersink.
Figure #10: Set drill depth and drill the blank to depth with a 1/2” drill bit.
Use a medium sized bowl gouge to roughly hollow the cap. Since the cap is mounted in spindle orientation, cuts from the middle outwards will yield the best surface. I found that keeping the flute pointing to the side for the entirety of all cuts was most stable. I also found that pinning the gouge to the tool rest with my hand and swinging the handle away made the tool cut in an arc. Continue this process as in Figure #11, being mindful of not cutting deeper than the drill depth nor outside the circle until the hollow is roughed out as in Figure #12. Hollowing with a template is an inherently fussy process, so the closer you are to the final shape before you start using the template the better. If it turns out you over hollow, then trim the blank a little shorter. You can turn a finial separately if you didn’t allow enough blank length.
Figure #11: Rough hollow the cap blank using the drill depth and circle as a guide.
Figure #12: After rough hollowing the cap blank.
I found that it was easier to tell where more wood needed to be removed if I split the template up into three parts so that I was only working on a narrow zone at a time. Start with the shortest template and insert it into the hollow with the lathe off as in Figure #13. It should be on a diametrical line—the blue lines of the temporary joints will conveniently indicate this. If the template won’t insert all the way, wiggle it up and down and the pivot point will indicate the high point where more wood must be removed. Mark the zone where wood must be removed with a pencil as in Figure #14. This keeps you from forgetting where to cut, and removing all the pencil marks keeps you from making obsessively light cuts. At least it helped for me.
Figure #13: Test the fit with the shortest part of the template.
Figure #14: Mark where to cut with pencil.
Continue in this fashion until the shortest part of the template fits. Then switch to the middle template until it fits, and finally fit the hollow to the full hemisphere as in Figure #15.
Figure #15: Fit the full template.
Decide how the cap will be mounted to the ball. If you’re gluing the cap directly to the ball or holding it on with a through wire and finial, then select a drill bit that matches the diameter of your hook. If you’re using a bamboo skew as a dowel to glue the cap onto a foam ball, then select a 1/8” drill bit. Use a centering drill to start a true hole and then use the selected drill bit to drill through the center of the cap as in Figure #16. This lets you use the hole to align the cap blank when turning the top of the cap.
Figure #16: Drill though the center of the cap to help align the cap when turning the top.
Turning the Outside of the Cap with the Shadow Sphere Jig
Mount the cap drive on your lathe spindle or chuck. Then align the light and pattern before mounting the cap blank as in Figure #17. Align the light so that a vertical post inserted in a hole at the base of the hemisphere doesn’t cast a shadow. The pattern has two semi-circles. Adjust the height of the light and/or platform so that the shadow cast by the cap drive aligns with the smaller semi-circle. You may notice that the my platform looks a little different. I attached steel sheet metal to the platform with spray adhesive so that I could use a couple of magnets to hold the pattern in place. I like this because the magnets don’t get in the way like the clips I was using do, plus they hold the pattern more securely and flatter.
Figure #17: Align the pattern and light to the cap drive.
Mount the cap blank on the mandrel using a cone tailstock center as in Figure #18. Gently turn the cap blank to the correct diameter with a spindle roughing gouge. Then use a spindle gouge to turn the cap to match the outline of the larger semi-circle of the pattern as in Figure #19. You may wish to use a pyramid point shear scraper to refine the surface.
Figure #18: Mount the cap blank on the cap drive.
Figure #19: Turn the cap blank so that it’s shadow matches the pattern.
Turn a finial as in Figure #20. There is no need to sand or polish the base of the cap where only waste wood is visible. So, you can hold the cap on the cap drive with blue tape as in Figure #21 so that you have full access to the top of the finial. Sand and optionally polish the cap.
Figure #20: Turn the finial.
Figure #21: Hold the cap on the drive with blue tape for full access for sanding and polishing.
Turning the Outside of the Cap with a Template
The template uses a procedure modified somewhat from the system pioneered by Myron Curtis for turning a sphere using the side lengths of polygons that contain the circle to approach the ball shape. The Berger calipers work similarly, using proportional arm lengths from a pivot instead of math. My template, however, indicates the diameter of parting tool cuts to cut to rather than measuring from the corners of the previous polygon. I find this easier to measure. Its liability is that different sizes require different templates. On the other hand, there’s no math, no table reading, and no trying to measure accurately where you can hardly see.
When right side up the text on the template would be read from the right side. The only straight edged side is on top. Across the top are notches for tracing lines indicating the corners of from the base of the hemisphere of a 16-sided polygon (I can never remember it’s a hexadecagon), an octagon, and the top of the hemisphere. On the right side of the template are three notches you can use to set your calipers for parting tool cuts to set the diameter of the hemisphere, the diameter of an octagon side, and the diameter of a hexadecagon side. On the bottom of the template is a notch with two indicators to layout cutting lines for hexadecagon sides on the oblique octagon side. On the left side of the template is a curve that can be used as a final check to make sure the hemisphere has been cut to a fair curve.
Use the biggest step on the right side of the template to set your calipers to the diameter of the hemisphere. Make a parting tool cut to this diameter on the blank and then gently bring the entire blank to this diameter with a roughing spindle gouge. Now hold the template so that the base line aligns with the base of the blank and put a pencil in the notches on the top edge to trace three layout lines as in Figure #22.
Figure #22: Use the template to trace three layout lines on the side of the blank.
Use the middle step on the right side of the template to set your calipers. Make a parting tool cut to this diameter so that the left edge of the parting tool aligns with the rightmost layout line traced in the previous step. Be sure to keep your parting tool at a right angle to the lathe axis when making this cut or the measurement of the depth of the hemisphere will be off. Use your spindle roughing gouge to reduce the entire nub to the diameter of the parting tool cut as in Figure #23.
Figure #23: Make a parting tool cut indicating an octagon side and the top of the hemisphere.
Now use a spindle gouge to make a straight cut from the middle line traced in Figure #22 to the left edge of the parting tool cut in Figure #23. Make the cut gradually by taking off the corner and then successive cuts. Pay attention to keeping the distance from the cut to the traced line on the left and the parting tool cut on the right equal. Figure #24 shows the finished cut.
Figure #24: After cutting the oblique octagon side.
You can use the top edge of the template to make sure the cut is straight as in the left image of Figure #25. Correct it if necessary, then set your calipers using the smallest step on the right side of the template and extend the parting tool cut to this diameter. Again, be sure to keep the parting tool at right angles to the lathe axis so as to keep a perpendicular cut. Use the notches on the bottom of the template to layout lines on the oblique side of the octagon as in the right image in Figure #25.
Figure #25: Check the straightness of the oblique octagon side and trace layout lines on it.
Use a spindle gouge to make a straight cut between the leftmost layout line on the original cylinder in Figure #22 and the leftmost layout line on the oblique octagon side made in Figure #25. Then make a straight cut between the rightmost layout line on the oblique octagon side made in Figure #25 and the parting tool cut made in Figure #25. You can mark the middle of each segment as in Figure #26 so you know where not to cut in the next step.
Figure #26: After cutting between layout lines mark the middle of each side with pencil to indicate where not to cut when rounding over.
Now use a spindle gouge to round over the corners as in Figure #27. Check your results with the curve on the left side of the template. You may wish to use a pyramid point tool as a shear scraper to refine the surface. You can tape the cap to the cap drive for full access to the end of the finial. Then turn the finial and then sand and optionally polish the cap.
Figure #27: Round over the cap.
Mounting the Cap
Remove the cap from the cap drive. Gently break the temporary joints. This may be easier if you first use a utility knife to cut the temporary joint between waste pieces below the points of the cap. You can use 220 grit abrasive to remove any stray fibers on the inside bottom of the scallops. Then optionally polish the edges of the cap with friction polish by hand.
If you turn a wooden sphere to go with the cap the easiest way to mount the cap would be to simply glue it on and then add the hanger of your choice. If you are using a foam ball glue 2” of bamboo skewer into the hole drilled in the cap in Figure #16. Take another piece of skewer and poke it slowly into the foam ball, checking as you go from two right angled directions so that the hole goes towards the center. Then apply hot melt glue or CA glue to the skewer in the cap and insert it into the hole poked into the foam ball and hold the cap tight against the ball until the glue has a chance to set. Figure #28 shows the set-up for gluing a cap onto a foam ball with a skewer. The ball in the photo was coated with white gesso and sprinkled with large glitter while the gesso was still wet.
Figure #28: A cap ready to glue onto a foam ball using a bamboo skewer.
If you want to cover a ball with fabric I suggest you use a shatterproof (plastic) ornament. It’s difficult to gather evenly when using a foam ball as the surface is rough and grabs the fabric. It also telegraphs through shear fabrics requiring two layers of fabric. Mount a shatterproof ornament in a sphere chuck (see references) using a tailstock cone center to center the ornament and blue tape to hold it in place as in the left image of Figure #29. Remove the tailstock and turn a hole in the end of the shatterproof ornament with a spindle gouge as in the right image of Figure #29. Make the hole big enough to contain the gathered material. Then mount a 3/16” drill bit in a tailstock mounted chuck and drill through the bottom of the ball as in Figure #30.
Figure #29: Center the shatterproof ornament in a sphere chuck and cut a hole in the top of it.
Figure #30: Drill a hole in the bottom of the shatterproof ornament.
Chuck up a piece of wood that hopefully matches the cap in a chuck and turn it to about 3/4” diameter. If you will be using 20 gauge brass wire for your hanger, mount a #50 drill bit in a tailstock mounted chuck and drill into the end of the blank as in Figure #31. If you are using a different size wire, or don’t twist it, experiment to find a size drill bit that makes a hole the wire will slide through. Replace the tailstock cone center for support and turn the end into a pleasing shape. Sand and optionally polish the shape.
Figure #31: Drill a hole for the wire in the end of the finial blank.
Back off the tailstock a little so the point is still in the wire hole, but not actually touching. Cut off the finial with a 1/16” parting tool at enough of an angle so that the rim of the finial can contact the ball as in Figure #32. By backing off the tailstock slightly before making the cut, hopefully you won’t have to chase the finial after cutting it off nor damage it by getting it trapped between the parting tool and the tailstock.
Figure #32: Cut off the finial.
Cut a 10” length of 20 gauge brass wire, double it over and clamp the ends in a vise. Bend a short length of steel wire into an L shape and chuck up the long arm of the L into the chuck of a drill. Insert the short arm of the L into the loop of wire and run the drill until the wire is twisted into a nice spiral. Remove the wire from the vise and cut off the untwisted wore ends that were in the vise. Slide the wire through the finial from the bottom.
Select a stretchy fabric. Wrap it around the ball to a moderate tension to determine the diameter of a circle to cut the fabric to. Make a paper pattern this diameter and pin the fabric to it, then cut the fabric to match the pattern. Select a sturdy thread such as button hole or upholstery thread and cut a piece long enough to go around the circle about one and a half times. Thread a needle with the thread and use it to do a simple running stitch (under/over with no back tracking) around the fabric circle. Try to space the stitches evenly but you don’t have to measure them. Leave the ends free. Mark the center of the fabric with the pattern and poke a hole with an awl at the center and insert the end of the twisted wire through the hole. Figure #33 shows the set-up for covering the ball.
Figure #33: Ready to cover the ball with fabric.
Insert the spiral wire through the ball, small hole first. Pull the ends of the thread to gather the fabric at the top of the ball as in the left image of Figure #34. I’m using a sphere chuck to hold the ball still for photographs. Tie the thread snugly and clip the ends. Adjust the gathers so that they’re even. Insert the end of the spiral wire through the cap from the bottom and push it down on the ball. Holding firmly, bend the wire over to hold it taut as in the right image of Figure #34. Put a drop of CA glue on the wire where it exits the cap and wait for the glue to set. Then bend the spiral wire to form a hanger and cut off the excess. If your cutter leaves sharp ends file or sand them straight across.
Figure #34: Gather the fabric and hold the cap on with spiral wire.
You can use the pointed end of a bamboo skewer to make any last-minute gather adjustments. Figure #35 shows the completed ornament.
Figure #35: The completed ornament.
You could put the cap on a contrasting wood ball. One approach would be to turn a sphere with a temporary joint, split the joint and hollow the hemispheres and then reassemble. See Sphere Ornaments in References for more on this technique. Another way would be to turn a ball on a 1-3/4” mandrel. If you use a lightweight wood such as Box Elder, you could probably get away without hollowing further. Or you could mount the ball in a sphere chuck (see References) and hollow it further. There’s a template for turning a 3” sphere on a mandrel in Jigs and Templates in the References.
You can put the cap on a commercial ornament. The shatterproof ones are easier and safer to work with. You can further treat the shatterproof ornaments with such things as Glitter Spray, Glitter Glue, 2mm Craft Foam, etc. It is possible (although perhaps not a good idea) to sand or break off most of the neck of a glass ornament (you can hollow a little extra under the cap for what’s left of the neck) if you want a mirror gloss. Assume a significant percentage will break, and wear gloves and eye protection.
You can use foam balls. The local Walmart only has the rough ones, but Michael’s et al. have smooth foam balls as well. I like white gesso and glitter on the rough balls—it looks like a disco snowball perhaps? The smooth ones are easier to cover with fabric. If fabric covered you can use either a bamboo skewer or a through wire (drilled BEFORE covering if possible). You could sculpt flutes in the ball with abrasives or files or carving tools before treating with gesso. I’m sure a search on Google (well, yes, 1,600,000 hits) or You Tube will turn up huge numbers of methods to decorate foam balls such as sequins, bric-a-brac, glass head pins…
If you’re feeling a bit obsessed about doing as much as possible yourself instead of gilding foam balls make your own out of Paper Mache (7.9M hits) using hemisphere templates…
Furthermore, only the top of what you put the cap on has to be a hemisphere?
Sphere Ornaments: http://davidreedsmith.com/Articles/SphereOrnament/SphereOrnament.htm
Jigs and Templates: http://davidreedsmith.com/Articles/CapOrnament/JigsAndTemplates.html
Shadow Sphere Jig: http://davidreedsmith.com/Articles/ShadowSphereJig/ShadowSphereJig.htm
Cap Ornament Gallery: http://davidreedsmith.com/Gallery/CapOrnaments/CapOrnaments.html