Turning spheres part 1: Preface

[Dave Mount]

In response to periodic requests for information on how to turn spheres, last night I sat down and wrote a bunch of text describing how I do it and why. It got really long. A video would probably be a better medium but I'm not set up to do that, so writing will have to do. Because it's so long, I'll put it out in pieces over the course of a few days, so there will be more to follow.

So. . .here goes:

I started turning spheres shortly before my 30^th wedding anniversary. For old schoolers, the 30^th is the “pearl anniversary”, but SWMBO is not much for pearls as jewelry, and they’re too expensive to buy just because. I got the idea to turn her a pearl, in the form of a wood sphere. Initially I was going to paint it with pearlescent paint, then I got the idea to make it out of a wood that naturally had pearl-like characteristics, so I made one out of a piece of curly silver maple. Actually, that's not quite true, I did do a practice one out of a piece of maple firewood. Here is that first "non-practice" sphere:

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I had no idea what a rabbit hole I was headed down. Suddenly, every piece of gnarly wood looked like a possible sphere, then I started buying exotic (to North America) woods and, without meaning to, started kind of a “life list” of sphere woods, looking to turn one out of every kind of wood I could get my hands on. I’ve since turned a lot of spheres.

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Turning spheres is nothing new, and little, if anything, that I’ll write about here is actually new. I’ve watched a number of videos and read articles on turning spheres. I’ve learned something from most, yet none of them seem to combine what to me seems like all the best tips and techniques. Another thing I found is that some sources say “what” to do, but not necessarily “why”, and they’re often short of tips on what to watch out for or to troubleshoot if you’re not getting where you want to. If the description of the process I’m going to offer has value, I expect it is in collating tips from many sources, and offering a little more on why I do things the way I do.

From my survey of things, there are three main categories of sphere-making approaches: 1) sphere-making jigs; 2) the jam chuck method; and 3) 3-axis turning by compression chucking between centers. I’ve never used a jig because I don’t know anyone that owns one, and I kind of backed into this as a one-off project so it never crossed my mind to spend a lot of money on a jig. Then after having early success with the 3-axis method, I never saw a reason to buy a jig. There are a few different types, but the ones I’ve seen are usually a scraper-type cutter mounted in a fixture that rotates in an arc to remove the wood down to spherical. I read about people that use jigs and love them, so they apparently are a good option for some. I will say that it’s hard for me to imagine using a scraper as a cutter that you could get as good a finish as you can with a shearing cut with a gouge, so I’d have to think there’s more sanding involved with a jig, but I don't know that to be true.

I’ve never done the jam chuck method – this is where you get a piece of wood to nearly spherical spindle turning between centers, finish one “pole” of the sphere by putting the other in a chuck so you can access it, then turn a hemispherical recess in a waste block that you can jam the sphere into and it will be held by friction while you round the exposed part. This seems hard because there’s little to guide you toward spherical, and you have to make a new jam chuck to fit each individual sphere. People have made nice spheres with this method so it clearly works, but I didn’t find it intuitively appealing compared to 3-axis turning.

To me, a great strength of the 3-axis method that I’ll go through in detail is that it involves a geometric trick to provide you with landmarks to indicate where you need to cut and where you don’t. If I had to completely freehand a sphere without these landmarks, I’d have a bunch of round-ish wood objects but few if any true spheres. Another feature of the 3-axis method is that it is iterative; if you make a mistake, you can just continue until you work it out. For me, the 3-axis method works extremely well, and I’ll try to explain why, but I don’t say that to imply that anyone preferring another method isn’t justified in doing so. To each his/her own, and I really mean that.

More to come,

Dave

[David Walser]

Dave -- This is a great series. Perhaps one of the moderators could enshrine it into a 'sticky post'. I'm sure many of us would like access to it in the future.