Oval(ovoid) Cone

[Peter Blair]

I do very little multi centre turnings and am hopeful someone can point me in the correct direction.
I want to make a Cone that is oval about 4" high and 4" wide at the wide part of the oval but am not sure of the process or math. I think I would like one centre on the pointed end. When finished I am hoping to cut the bottom and top on about a 10 to 15 degree angle to get the cone to sit at an angle and to be able to mount my sphere slightly off set as well.
Am I making any sense? I tried to draw it but for some reason I just can't get it on paper . . .
Any help would be wonderful.

[Roger Chandler]

Just off the top of my head, I think you should make the cone on center with the correct size blank and turn it to your dimensions. Then move the tailstock live center to a new center to one side about 3/4" [experiment with that as it may be 1/2" or 3/8"] from your original center point. when it turns, you will take off light cuts on one side, check your progress frequently, when you get the narrowed side about where you think it needs to be, then move to the other side of your original center mark, the same as you did the first time you moved to the other side, then cut away about the same amount as you did on the first side.

You need to experiment with this on scrap, then you might have to sand away some , but can shape it to an oval cone. Try this and see if it works, if it does not, you used scrap wood, and are only out of the time you experimented and you gained some knowledge to boot.

I have turned oval handles this way on some tools for hand comfort, and it did fine..........YMMV, however! :confused: Good luck!

[Brice Rogers]

Some thoughts to add to Roger's good advice.

To help you visualize or draw what you are planning try the following:

1. Use a compass or something round to trace with and draw a circle of the same diameter that you plan to turn. This would represent your first cut to make it round.
2. Draw another circle but move the center over (like Roger said - perhaps 3/8", 1/2" or 3/4 inch). This would represent your second cut when you moved the tailstock live center over. The shape of the wood remaining would be the portion of the two circles that overlap. If you are familiar with a "Venn diagram" it will jump out at you. Here is a Venn Diagram where the center is moved over probably further than you are planning. But it'll give you some ideas.
https://upload.wikimedia.org/wikipedia/commons/thumb/9/99/Venn0001.svg/180px-Venn0001.svg.png
If you are only moving one end, like the center at the tailstock, at the other end (headstock) the shape will be very nearly a circle. It would be possible to continue the oval approximation to both ends by moving both the headstock center and the tailstock center. But keep in mind that if you are planning on having a cone (taper) that you will want less offset at the smaller end.

The transition between the two circles may need sanding to blend the two circles.

I am attaching a picture of an experiment that I did with off center turning. I offset the centers on both ends at three different locations. At each end I placed the center along a circle and spaced the center points at 120 degrees apart. But the 120 degrees for the top and bottom was different and was also rotated by either 60 or 120 degrees. So I ended up with a swirl. I did the finish cut in the dead center. So, I had four different center locations and four separate cutting operations. The piece isn't overly pretty from a design point, but I enjoyed seeing what could be done as an experiment. It is a chunk of eucalyptus. I drilled the end (on the central axis of the piece) and stuck in a test tube to hold water for a flower. It turned out well enough that I didn't want to throw it in the fireplace.





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[Peter Blair]

Thanks guys. It appears that the best way to tackle this project is through experimentation. Brice, I am not familiar with 'Venn Diagrams" thanks for the lead.

[Jim Underwood]

Or you could build one of the Springett Oval Turning jigs:

https://www.youtube.com/watch?v=LX12OFJHQlg

[Peter Blair]

Jim, was that tongue in cheek? Watched the video and am non the wiser. Think that MAY be out of my 'pay grade'. Thanks anyway!!

[Jim Underwood]

Jim, was that tongue in cheek? Watched the video and am non the wiser. Think that MAY be out of my 'pay grade'. Thanks anyway!!

Not tongue in cheek. Springett actually has plans for this thing in one of his books. I bought a copy of that book and have always intended to build one. It's not that hard if you have any woodworking/fabrication skills at all.

Let's see if I can dig up the name of the book...

[Robert Henrickson]

Adventures in Woodturning

[Jim Underwood]

Looks like the book in question is "Adventures in Woodturning". (https://www.amazon.com/Adventures-Woodturning-Techniques-David-Springett/dp/0946819572/ref=sr_1_6?s=books&ie=UTF8&qid=1470406061&sr=1-6)
One can also buy a Springetts DVD strictly about oval turning. (https://www.amazon.com/Elliptical-Turning-Introduction-Springett-Publishing/dp/B009O19L0G/ref=sr_1_1?s=books&ie=UTF8&qid=1470410616&sr=1-1&keywords=springett+dvd)

[Peter Blair]

Thanks guys. I see that if I was interested in doing a bunch of ovals it would be wise to invest time and a little cash but for a one off, I think I'll just go ahead and make it by trial and error with heavy emphasis on the error!