Hollow Box Ball

1. I started out by making a hollow box, mitering all the edges. The thickness of the material is proportional to the size of the finished ball, too thin and you will cut through the glue joints. For a given size box, this affects how large the triangular openings will be.

2. The teak box was glued together with epoxy but for subsequent balls I used Titebond III. If the triangular holes end up fairly large, you can see inside the ball easily so pre-finishing the inside and waxing will make it easier to remove any glue squeeze out in the final part of the process. I also sign the ball on the inside before gluing together.

3. In the picture below, the Hickory ball had greater thickness for its diameter and shows the smaller openings. In a post coming up I will show the geometry and math for sizing the material for a given box/ball size or vice versa.

4. I picked the axis that I wanted to turn on and located the centers, drawing the circle and the material thickness. . See figure 1 for the way I orientate the grain of the wood. With the axis as shown, the first turning will be standard spindle turning. It is important to locate your turning centers because if you are off center, the diameter of the cylinder will be less than its length, making the holes bigger and glue joints smaller.

5. I rough cut the box to a cylinder and then turned and glued on mounting points for attachment to the lathe using CA glue.

6. Mounted on the lathe and ready to turn.

7. I turned to a true cylinder, the goal being to make the diameter the same as the length. I am usually within 1/16”. The more you lose in diameter at this point, the larger your openings become and less final glue joint size. I figure that the final ball will be about 1/8” smaller in diameter then the original box, assuming that everything goes according to plan during the turning.

8. I located the centerline with a solid line and shaded on either side, an area to stay away from when rough shaping into ball form. Thank you Richard Raffan for this and much of the following method.

9. I made hardboard templates for checking the progress while turning. It is easy to see where the material needs to come off. If you orient your pieces as per figure 1, the turning techniques will go between parallel and face grain as you round the corner during this second stage of turning. I go between a spindle gouge and a bowl gouge for doing this part of the turning.

10. The first end is rounded and the openings are showing.

11. Close enough at this stage although the closer to true round at this point, without overturning, the easier it is to remount in its next orientation and keeping it there for the next turning stage.

12. I turned the ends at the attachment points before parting off. In subsequent balls I shear scraped more of the nub left under the mounting point to get it truer to round. This makes it easier to get the ball to round in the next stage. The ball is ready to be mounted in its new orientation.

13. I turned cup centers, which are padded, to hold the ball for turning. It is important to make sure that the old centerline is now parallel to the new axis. After much trial and error, I found that gluing 80 grit sandpaper into the cup for the next stage, gripped the ball well for turning to truer round. Because the ball is hollow and the glues joint are fairly small, care has to be taken to not break it with too much pressure from the tailstock. I glued a leather pad into the tailstock cup.

14. After initial remounting, I use a dial indicator to make sure that the ball is also centered front to back. I try for + or – .005” to keep the ball as close to round as possible.

15. My goal is to turn away the ghost, getting down to round in its new orientation. This shows that I am close, a little overturned at the center, but close enough for this stage. The ball can be rotated 90 degrees on the pencil line axis, re-centered and turned once more to get it ready for sanding.

16. I make a custom hard felted block to do the rough sanding to bring it into truer round. I started with 80 grit, being very careful not to get the ball too hot, which would soften the glue joint. After a couple of passes. I stop the lathe and rotate the ball in a different direction, doing this as many times as needed to get the to smooth round. It is not as important to get it to true center when rotating as some off center wobbling can be tolerated. After this initial rough sanding, I change to a drive center using a cupped drive with a piece of rubber shelf or toolbox liner glued in the cup. As I tighten up the tailstock, I grab and try to rotate the ball, allowing me to feel when there is just enough pressure to hold the ball for sanding. You can skip the felted block for the rest of the grits unless you start to get a wavy surface from the difference in grain hardness in early and late wood. Douglas fir would be an example of where you would continue using the felted block.

17. After sanding I cleaned and trued up the openings and carefully removed the excess glue on the inside. Now to make a stand.

In a following post I will show the geometry and math for sizing the box /ball for a given thickness of material.

hellllllllo2

2 Responses

03.23.11

Very nice article, easy to follow. I’m going to give it a try. Keep up the good work, I’ll let you know how my first hollow ball TURNS out

you have really made an art of the hollow ball, I am proud of you.

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