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How can I turn a convex arc in wood? I want the arc to be perfectly symmetrical.

I have looked at various turning tutorials and they do not explain how to do this kind of operation.

  • A picture would help, since I'm not sure what you mean by "a convex arc" is what I'm visualizing. If you mean the whole workpiece is bent from end to end, like a bow, then turning is probably not the right way to produce it. If you mean a convex swelling in a straight turned piece, that's done by starting at the maximum diameter and cutting curves inward at each end ; "perfect" symmetry is unlikely but with practice you can get something good enough for most purposes. – keshlam Oct 14 '16 at 17:17
  • @keshlam I have watched woodworkers turning balusters and they just eyeball it. In my case I want a fairly exact symmetry that would be difficult to just eyeball or use witness marks. – Treow Wyrhta Oct 14 '16 at 17:25
  • Pattern turning, or some other guided cutter, could do that. Depending on how precise you need to be, making a set of cuts to specific depths at specific spacings and then fairing the curve might be close enough; you haven't told us how much error is acceptable, over what scale of work. Remember that a lot of large-scale machinery used to be made by cutting wooden patterns, casting molds from those, casting the metal in the mold and then finishing the surfaces by more turning or by handwork. – keshlam Oct 14 '16 at 17:31
  • This is one of the mainstays of spindle turning, I presume you don't need a primer on the tools and techniques to physically create the shape, so the answer is mainly (and rather frustratingly) practice. You just get good at both the mechanics involved and eyeballing the evenness of the results the more you do it. If you need absolute repeatability though you need to use a template, which can either be bandsaw cut from a piece of plywood or MDF, or a first turned original is cut down the centre (usually on the bandsaw so you don't lose too much to the kerf). – Graphus Oct 15 '16 at 8:10
  • I guess you don't have a problem achieving the symmetry as the process of turning will create perfect symmetry. – null Oct 15 '16 at 22:36

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