Tools: Just like there are many ways to turn a sphere, there are no hard and fast rules on what tools you need. I use four basic lathe tools to shape a sphere from square stock: 1) roughing gouge; 2) spindle gouge; 3) parting tool; and 4) bowl gouge. The size of the roughing gouge and parting tool don’t really matter. I turn spheres mostly in the 2-3 inch range, though I’ve turned them as small as 1.5” and as large as 5.5”. I do the vast majority of this work with a ½” (US scale) Thompson V-groove bowl gouge with a moderately swept-back grind (middle in pic). On small spheres I may switch to a 3/8” bowl gouge (same make and grind; second from right) if the bulk of the ½” is too much to get where I need to get; however, after the initial roughing out, almost all cuts you make are interrupted cuts, and I like the stiffer shaft of the ½” to have the mass and stiffness to resist bouncing. For the spindle gouge, I also use a Thompson gouge in the ½” (US) size, without a lot of sweep back on the wings (second from left). In sphere-making, you’re basically making a very large bead, so a wider tool that is less pointy is helpful to me. You’re not turning in tight spaces, so in my opinion there’s no need for a pointy grind like in a detail gouge. As for the bowl gouge, I’ll sometimes drop down to a 3/8” spindle gouge for smaller spheres for more maneuverability. The mass isn’t critical for the spindle gouge because most of the cuts I use a spindle gouge for are not interrupted, but a broader curve on the cutting edge is something I prefer.
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Beyond those, one other tool I use when I need to is a negative rake scraper (NRS). I try not to need one, as I think the finish I get with a shearing cut with the bowl gouge is generally better, but if I’m struggling a little, an NRS can sometimes get me over the hump easier. Other turners with skill far greater than mine swear by them, so I’d encourage you to experiment with them. My other minor gripe with NRS is that they lose sharpness faster, but if that’s a tool that works for you, by all means use it. Part of my opinion about short lived NRS edges may be because all my scrapers are bargain basement M2 scrapers; maybe if I spent some money on better steel I’d think differently.
Sharpening: There’s nothing special about sharpening so there’s no need for great detail. I use a 600 grit CBN for most routine sharpening. I used to use a 180 grit CBN and hone with a diamond paddle and diamond cone, but I decided that just using the 600 grit straight off the wheel with no honing gave me nearly as good an edge and was much faster. I can still hone if I want an extra fine edge. As in all turning, if you feel like you’re fighting your tool a little, sharpening will almost always help. Sphere-making (as I do it) is full of interrupted cuts, and that’s a type of cut that can really get hard to execute if the gouge isn’t sharp. If your tool is bouncing around instead of gliding through the wood, sharpen it. And, always a good idea to touch up your edge before final cuts, just to save on sanding time. Nobody enjoys sanding, do they? Plus, on a lot of woods, having to do too much sanding actually puts you at risk of sanding your sphere out of round because the resistance of the wood to sanding changes so much from flat grain to side grain to end grain. Best to cut the tearout away and do as little sanding as possible, at least with coarser grits.
Lathe accessories: There are lots of ways to hold work for sphere turning. I’ll explain how I do it, but that doesn’t mean you need to go out and buy everything I mention in order to do it. I acquired these tools over time as my technique evolved do this, but there are lots alternatives that don’t involve the accessories I use. When I started, all I used was a scroll chuck, a cone-shaped live center, and a couple of wood blocks I shaped on the lathe.
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For the first part of the turning, where you’re turning as you would any spindle (end grain facing headstock and tailstock), I prefer to use Steb centers. For those not familiar, these are centers with a spring loaded retractable point in the center surrounded by a circle of teeth, something like saw teeth but not meant to cut. You use the point to locate the marked center of the piece, then as you compress tension with the tailstock the point retracts and the saw teeth contact the wood and that’s what drives the piece. There are several advantages to this approach, but one that I value a lot is that you all you need to mark the center is a tiny pin-prick, and the teeth don’t sink in far. Especially if you’ve purchased an expensive exotic wood, you don’t want to have a bunch of extra wood on the end that you spoil driving a spur drive into it.
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For the tailstock, they are less common but you can buy live centers than have the same steb center design. The business end is the same as for the drive center, but it’s coupled with bearings so it turns freely. I like it for the same “non-invasive” properties as on the drive side. In addition, steb centers don’t exert any “wedging” action as you compress the wood between centers, so there’s no chance of them inducing a split. With steb centers on both sides, I generally turn a sphere out of a blank that’s just 1/8” (or 1/16” if I push it) longer than it is square. Steb centers are available in different diameters. Strictly for sphere making, the smaller diameters are better, especially if making smaller spheres – they get in the way less. However, mine are actually larger ones (one is 1” and one is ¾” I believe) and the inconvenience isn’t enough to motivate me to buy smaller ones.
Cup live centers are another option, but the one I have still has a point that goes a fair distance into the wood before the “cup” contacts the wood. Before I got the steb centers, I used a cup center but I turned a wood washer that I put over the cup to reduce how far the point drove into the wood before you got compression.
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If I could have only one non-standard lathe accessory for sphere making it would be a threaded live center. This is a live center that terminates in a thread, typically 1” x 8 tpi. With this fixture, you can screw a waste block to a faceplate and shape it any way you want to conform to the piece you’re holding. Or, you can buy a wood threading tap of the same thread size, and directly thread waste blocks so they can screw onto the threaded live center. Or you can thread a chuck on there. A wonderful tool. I bought it for sphere turning, but now I use it for chucking the tailstock side of all kinds of things. You can turn a dowel on the waste block and use it to center something with a bored center. Using a waste block, you can even make your terminal cuts going right into it. But I digress.
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The other accessory you need you can make – the cupped centers you use to hold the sphere in compression while you’re bringing it to spherical. These compression chucks can be any wood, but there’s some advantage in having your compression blocks be a wood that is softer than the wood you’re making the sphere out of, so if there’s enough squeeze to crush some grain, it’s your compression chuck that gives first. Mine are mostly paper birch or maple because, well, I have lots of both readily available. The bigger diameter ones are made from pine, as I used them to turn large spheres of Douglas fir and redwood -- softer chuck wood for softer sphere wood.
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I almost forgot dial calipers (or digital calipers). These are not essential, but very useful. I have both fractional (i.e., showing 1/8”, 1/16”, 1/32”, etc.) and decimal (reading thousandths of an inch) in the shop, but I prefer the decimal for spheres because the math is easier (more on this later). Metric would work great for the same reason.
Next installment will be prepping the blank and initial turning.
Best,
Dave
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Originally Posted by Dave Mount
