Finishing Bottoms
Collated from newsgroup postings.
I am making a white wine goblet out of pear and am having a problem. I put the piece between centres, made it round, shaped the outside of the bowl, put the foot in a vicmark chuck, shaped the inside of the bowl, shaped the stem and foot, finished the piece, except for the underside of the foot. Now I am ready to cut the foot off the waste. Do I just sand the underside of the foot by hand? Am I out of sequence? Is there an easier way?
With a sharp thin parting tool part the goblet off, by cutting in toward the stem to make the bottom concave (it will set flat this way). If the tool is sharp you should not have to much sanding to do, also make sure that the cut is wide enough so that you do not burn the wood.
After cutting off, you could reverse mount the piece in a wooden jam chuck to finish off the bottom. Either turn a stub for the goblet to fit on, or a socket for it to fit into, using tailstock support as much as possible.
If you leave enough waste at the chuck end you can widen the parting cut and use a skew to make a cut down the bottom that will require no sanding. Gently cradle the cup in your hand while parting and you should be able to cut completely through and let the cup fall into your hand.
It sort of depends on how thin you made the stem. If it is solid and substantial, a jam chuck might be fine, but if it is thin & delicate, it might be better to try to part it in place.....if the foot is long enough and is flat on the bottom, it might be possible to shim it out using a flat disk of wood near the same size as the base.and use a thin parting tool or hacksaw. If you decide you do need to reverse it, a jam chuck with a gentle tailstock pressure can work. Either way, you'll need to do some final hand sanding.
Start parting the base off a little concave with a narrow parting tool. Stop while there is still about 1/4" supporting the goblet. Switch to a 1/4" spindle gouge sharpen to a very long bevel. Take a careful light shear cut making a graceful curve on the bottom. If you are careful you can completely part it off with one hand while catching in the other. (You will need a groove about 1/2" wide to swing the gouge.) Very little sanding if any will be needed. Or, part it almost off, cut it loose and sand off the nib.
If the stem has been turned to 1/8 or less, attempting to use a jam fit chuck on the bowl will probably shear off the stem no matter how careful you are.
I use the 1/16" Sorby parting tool, the one with the flute ground on the short face so the spurs do the cutting. On end grain you can part to 3/8" or so if you're not supporting the other end. Less if you've got the tailstock in play. On face grain, I'd never part to less than 3/4" for fear of losing it. From that point a dovetail saw and a curved knife clean things up safely. For final sanding, though you could also reverse and chuck the lip of the goblet to finish off. Sometimes I do that, but the other method does so well it hardly seems worthwhile.
Whichever of the methods for parting off you use and at least one should work for you, I find that for the final sanding of the bottom using a 2" power sanding disc gets the job done with hardly any effort and also tends to accentuate the concave profile of the base making for a stable goblet
I recently used one of those flexible flush-cut saws to get close when I cut off the nib. I've picked up some carving tools lately, so I'll try the curved knife. To make the final paring, I used a bench chisel with a low-angle grind, about 15 degrees (long bevel). It did a nice job cutting that end grain; better than the standard grind of 30 degrees.
"parting to" refers to the diameter of the nib. Since the wood likes to split along the grain, I've found it impractical to try and reduce my knife work by turning too small.
Curved knife is great, because you can hold the piece in one hand and trim with the other. Every way I've tried with a gouge has put one of my hands in jeopardy or put the piece in jeopardy of denting as I braced it against something.
Of course the power sander is the easiest, and I use it most of the time, though you can overheat and crack the wood if you're not careful.
Part off the goblet, take the 2" or 3" disk you use for power sanding and mount it in the drill press or for that matter in your lathe chuck. Sand off the bottom. It only takes a minute. After which, you can stick some nice green baize on the bottom, so no-one is worried about it scratching their nice polished tables (some people are paranoid about this - I lost a couple of sales a few years ago because of this, and since then, I try to baize everything)
For those that haven't heard it before, the best tip for getting a neat finish when using baize is to cut it to rough shape, but oversize, glue it on (I use a self-adhesive type), and then use abrasive paper (240 grit) to sand round the edge, working from the bottom side towards the top. The paper cuts the baize really cleanly to the exact profile of the work - hey presto, one neat finish!
Everyone looks at bottoms, so make sure yours is nice looking!
I have observed gallery and show customers (including myself and including instant galleries at symposiums and club meetings) pick something up and turn it over (dropping the test tube, light etc on the floor) with frightening regularity! I don't put the price on the bottom so that's not the reason.
I think it's the same thing acting when someone sees a box and first thing they do is open it. The hidden part intrigues us. In my turnings, I tool the bottom whenever possible, and add some v-grooves or beads, sand and finish like the rest of the bowl. Then I sign the piece and write on what type of wood it's made of. This gives them something to discover when they turn it over.
Is it worth the effort? (always the question for those of us trying to make a living with turning)..I believe it is. And another reason for that is that the detail on the bottom and my style of signing gives me a way to make my work distinctly mine. I think the customers notice the difference.
When I pick something up and notice the evidence of a chucking point still visible, It doesn't offend me if the bottom is finished nicely. I object to unplugged screw holes. Often when a chucking point is left on the piece, it means that the size of the chuck has determined the size of the foot or base of the piece, and that the base or foot is not in good proportion to the piece. For a well-proportioned piece to have evidence of the holding method doesn't detract from the quality of the piece.
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