00 Chinese Balls

 with Jean-Claude Charpignon at the Escoulen School of Woodturning

 

Part I: Turning a sphere

 

The first step in making a Chinese Ball is to have a perfect sphere with which to work. Jean-Claude taught us a simple way of turning a very accurate ball by hand. It is the method taught by Plumier in the ‘Manual for Turners’ from 1749.

01 Manual for Turners thumb 02 Manual Illustrations thumb

 

We want to turn a sphere with a precise 65 mm diameter. The first step is to take your wood stock and turn it between centers into a cylinder with a precise 65 mm diameter. At this point you can leave this a little large, say 65.5 - 66 mm to allow for sanding. This cylinder is then cut to 67 mm long with nice precise square ends. A line is drawn around the cylinder in the precise center, or 33.5 mm from each end.

03 Center Line thumb

 

First chuck. You then need a simple wooden jam chuck, with a recess that is 90 mm in diameter and 30 mm deep. This recess is tapered a bit on the sides but must have a nice flat bottom.

04 Flat Bottom thumb

 

It is made to hold the cylinder you turned sideways. Jam it into the chuck so that the side of the cylinder hits the bottom of the recess.

05 Seated in Chuck thumb

 

Turn away everything down to the line you drew in the center. Be sure to use a sharp chisel and rub the bevel. I had at first tried to use a push cut that has served me well for doing bowls, where the flute is completely open/level and the handle horizontal. Even with bowls, this is a tough cut, as the slightest turn inside can cause a catch. With the uneven surface spinning around, I had my cylinders flying all across the workshop. Jean-Claude finally saw what I was trying and said the obvious - that was the wrong cut. Lower the handle way down, rub the bevel and cut with the leading edge of the gouge. With the correct cut, I had no more trouble.

06 Leading Edge thumb

 


 

 

 

So you begin cutting away down to the line in the center to create a half sphere. You have 3 different means to help you. First, there is the usual ‘ghost’ image. Turn away all that is not solid. Second, as your cuts approaches that center line, keep the ‘flat’ part parallel to each other.

07 Parallel Flat thumb

 

Thirdly, you have the middle line to carefully approach. When you are almost there, switch to a scraping cut. When you have cut/scraped away everything except just barely that line you have a perfect half sphere on a half cylinder.

08 Half Sphere Cylinder thumb

 

Then you need a second chuck with a tapered 64 mm hole, in which you jam the just turned spherical half of your ball, notice that it is not important to have it parallel or seated against the chuck, in fact having that space allows you blend the two halves together seamlessly and turn away the second half, again cutting down just to leave the line on the sphere. When you have reached that line your sphere is done. Sand to exact size.

09 Sphere in Chuck thumb

 

Of course, an alternative method is to use a sphere jig, and when great accuracy is needed, this is probably the way to go. We practiced with sycamore, and even turned our first Chinese ball with our hand turned sycamore spheres, but he then had some perfectly turned boxwood spheres for us to use also.

 

 

Part II: Turning the Chinese Ball

 

Now you want to mark the 12 points of a dodecahedron on your sphere.

10 Marking Sphere thumb

 


 

 

 

Excel Chart thumb

There is an Excel table that you can enter the diameter of your sphere, in this case 65 mm, and it will show the distances for the points of a polyhedron. Here you set your compass points 34.1705 mm apart, and plot your points. Starting at one of the endpoints, scribe a circle with the 34.1 mm radius; then anywhere on this circle set a point and not changing your compass, mark out 4 more points 34.1 mm apart, the last should meet up exactly with the first point. Then from every two adjacent points scribe intersecting arcs; these are the next 5 points. From each of these points, a 34.1 mm arc should meet up for your 12th point, exactly opposite the first. This last point should meet up exactly also, or else re-do your drawings. We found that marking the centers points with a little push of the compass point or even a push pin, left a small precise hole that was not sanded away. Then using your compass draw a circle around each dot marking what will be your 12 holes.

With your turned sphere, and 12 points marked out it is time to turn your Chinese Ball.

The real secret is having the right tools and setup. We were able to simply and quickly turn the jigs needed to turn a sphere, but the special tools needed for the Chinese Ball were provided by the school and Jean-Claude and we simply learned to use them.

First you need a sphere jig. Jean-Claude designed a sphere jig actually based on the old Plumier book, made out of plywood which is ideal as it is very stable and won’t move. Each size Chinese ball you want to make must have its own specifically made-for-it sphere jig. So these were designed for 65 mm spheres, and had a perfect 65 mm hemispheric cavity turned in it to hold the sphere without any play, yet easily turned. A flange is then employed with an inside curve matching the sphere which is tightened to hold the sphere in place. Many sphere jigs employ a flange with 4 bolts which are tightened to hold the sphere. Jean-Claude’s sphere jig has a threaded ring that tightened the flange with a simple twist. He threaded the plywood to screw on the lathe spindle, and for the ring to tighten the flange. He said it was no problem to turn threads on the plywood with a threading jig. This method works great to apply pressure evenly to your sphere.

11 Flange thumb 12 Secured Sphere thumb

 

Other special tools: the tool rest is replaced with a little steel table. The tool holder slides on this table perfectly level.

13 Steel Table thumb

 

Special cutters must be made to undercut each inner sphere you want to cut, each with the precise radius and depth of the inner sphere. Jean-Claude supplied cutters for a 5 sphere Chinese Ball, and a 7 sphere Chinese Ball.

14 Cutters thumb

 

The tool holder must allow for precise placement of each cutter each time. Jean-Claude’s tool holder is machined to hold the cutters at the exact place each time. Simply slide the cutter in the slot to the very bottom, tighten the grub screw, and go. Its leading edge is also machined with a 32.5 mm radius so that at the correct depth it rubs the outside of the sphere, allowing precise and repeatable placement of the cutters each time.

15 Tool Holder thumb

 


 

 

 

Finally, there is the all-important sphere ‘nudger’. You must align your little pin hole with the exact center of the lathe each time. So he has a large spike, flattened and with a crisp edge, that you use to gently nudge the sphere into alignment.

16 Sphere Nudger thumb

 

So with your specialized tools, you are ready to go. Put the first straight cutter into the tool holder, and before you put the sphere jig onto the lathe, set the height of your tool table so that the top of the cutter, when in the tool holder and resting on the tool table is at the exact center point of the lathe. Attach your sphere jig and put your sphere loosely into it. Do not change the height of the tool table for the rest of the project. Now you must align one of the points of your sphere with the tool.

17 Alignment thumb

 

You should start with the two end grain points first. The top of the cutter in the tool holder resting on the tool table marks the center. Spin your sphere by hand, if your pin hole is moving in a circle, stop at the high point, grab your ‘nudger’, set its edge on the sphere where it will be turned away, and tap it with a piece of wood, or your tool holder. Repeat until that little dot turns true.

The tool set consists of a straight cutter, and the undercutting tools. You begin with the straight cutter to turn a cone into the sphere. [see photo 14, the straight cutter on the far right] Push the cutter straight into your revolving sphere. Begin at the middle and slowly work your way out to the edge of the circle you drew around each point. [see photo 13] The cutter is designed to cut only with the leading edge, not the side, so the last cut must be straight in at the edge of your circle ending with the tool holder rubbing the edge of the sphere. Thus depth and angle are precise and repeatable.

Loosen the grub screw of the tool holder, set that straight cutter aside, slip in the cutter for the innermost sphere, being sure it is seated against the end of the tool holder slot, (the tool holder has a hole at the end of the slot to easily clear out any sawdust). With the tool holder always resting on the tool table slide it into the cone opening along the right edge of your hole until the tool holder rubs the outside of the sphere, move the tool holder to the left keeping the edge rubbing on the sphere as far as it will go, undercutting the innermost sphere, move back to the right and carefully remove from the sphere. Repeat for each of the other cutters.

18 Undercut 2nd Hole thumb 19 All 7 Undercut thumb

 

While this process can go pretty quick, obviously, you still must be deliberate and accurate, especially cutting the final sphere, you don’t want any chatter or catches at that point. For my final project, he had a beautiful piece of boxwood root burl for me, but the inconsistent texture gave me some trouble getting smooth cuts, and I juggled a few of them, necessitating some creative sanding.

You can now sand the inner edges of your 5 (or 7) spheres and should do as much as you can, as you will not be coming back to this hole again. The hole is then plugged with extruded polystyrene. The old books instructed one to make wooden plugs for each hole; the polystyrene greatly simplifies this whole process.

20 Polystyrene Plug thumb

 


 

 

 

Loosen your sphere jig, rotate your sphere to another point, align the center, and repeat. It was recommended that you rotate your sphere to the opposite side as much as possible, because as you complete each hole you are weakening your sphere, and you want to keep the pressure on it as even as possible as you work your way around each point.

21 Final Undercut thumb

 

When all 12 points are cut and sanded, you are done. Sand the outer sphere as needed, rotating it in the jig to remove all pencil markings and any rubbing marks from the tool holder. Remove the polystyrene plugs and pat yourself on the back.

22 Jean Claude Tool Demo thumb 23 My Final Project thumb 24 Projects from Week thumb

 

Jean-Claude was able to demonstrate for us the next step: to turn a Chinese Ball with a star in the center.

25 Chinese Ball with Star thumb

 

Basically, you turn each hole with a star spike in the center, he has then modified the cutters so that they are narrower, and able to fit alongside the spike and still able to do the undercutting. Unfortunately, there were not enough of these modified tool sets available, and we did not have enough time for everyone to try it for themselves. Instead several of us practiced turning star spikes in a round half-sphere artsy thingamajig.

26 16 Spike Thingamajig thumb

 

Fr. Dave Means

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Monday the 19th. Thanks for visiting Woodturners Unlimited.