Turning Large Diameters

dboo1As most of my woodturning is done to support either furniture building or architectural restoration projects, it tends to be between centers, in other words spindle  work.  Oh, occasionally I’ll turn a fairly large bowl for a gift.  But recently I turned a Doric column base, from walnut, that measured twenty inches in diameter and the blank weighed in at thirty-five pounds.  Clearly it was one of the largest I’ve done and it quickly reminded me that are some points to consider when you’re doing large face work that don’t come into play while turning the average table leg.tn1

The first consideration was a mounting method that would minimize deflection, as the large diameter of the work forced me to turn over the side of the lathe bed.  My lathe has a 1 1/4 x 8 spindle.  Oneway and several other highend lathe builders provide excellent faceplates with super reinforced webs.  Unfortunately, I did not have one.  However I did have a five inch face ring which mounts on the 100 mm jaws on my Nova chuck.  This provided a secure method of holding the work.  Further I mounted the workpiece to a piece of 3/4″ particle board which was substantially stiffer than any other material that I had available.  I was still concerned about deflection created while working the surface perpendicular to the axis so I placed a heavy steady-rest  opposite of the tool-rest.

The second consideration was tool selection.  The diagram below shows the difference in tool positioning while turning a small (2″) diameter and a large (20″) diameter.  Sheer cuts that would be the norm on a small diameter become more difficult to accomplish on the larger.  Heavy scraping tools may be a better choice.diameter comparison

The third consideration has to do with speed.  I tend to do most spindle work at about 1440 rpm.  At that speed a 2″ workpiece is presenting approximately 9050 surface inches per minute.  At 200 rpm, a 20″ diameter workpiece is presenting approximately 12566 surface inches per minute.  (dia x 3.1417 = sipm)

There are a number of calculations that can be used to determine safe operating speed ranges, but the goal is to find a speed range that eliminates vibration while allowing for clean cutting and control.

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2 Comments on “Turning Large Diameters”

  1. When I initially commented I clicked the “Notify me when new comments are added” checkbox and now each time a comment
    is added I get several emails with the same comment.
    Is there any way you can remove people from that service?

    • D.B. Laney Says:

      Wow! I’m not sure how you turn it off. But there must be a way. If you figure it out first, please let me know. I will do likewise.

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