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

 

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Monday the 19th. Thanks for visiting Woodturners Unlimited.