Thread: turning oval shapes

here is a pic may make it clearer what i mean. bob

How deep are they? or are they thin like a picture frame? If thin, I would use a router with an ellipse jig. If it needs to be turned! I watched a very expensive jig being demonstrated at the T&WWWS.

Page 10 of this PDF has a review.

http://www.fholder.com/Woodturning/sample.pdf

Sorry, just posted and saw your sketch.

There's a couple of ways of turning "true" ovals... but they tend to be expensive unless you build your own setup.

• using a special faceplate that contains a mechanism to move the blank's centre-point from an arbitrary point on the rim of the faceplate to the opposite edge and back once every revolution
• building a rose engine where the headtsock "rocks" back and forth, twice every revolution.

For the size you're talking about, they'd need to be very, very robustly built. That's a LOT of weight being thrown around off centre! The advantage of these methods is that you can hollow them in exactly the same way as a bowl... ie. they'd have a constant wall thickness.

Personally, I'd just use a bit of string and two nails to draw the oval onto a blank and then cut it out with a bandsaw.

However, if you insist on turning and are feeling daring, you can also go the path of a "pseudo-oval." (There's probably a technical term for this, but I couldn't be bothered googling. )

On a scrap of ply, a large sheet of paper, or whatever, mark out the dimensions you want and draw in both axis. Grab a compass and mark out smallish circles at each end (at equal distances from the centre-point) and larger circles to the side. (Again, at equal distances from...) Repeat the process until you get something that's as close to the shape you want that you're going to manage. The four centre-points of each circle will be the centres that you'll need to mount your blank at. You'll see that the arcs don't quite meet perfectly, leaving 4 small "points" that you'll need to remove by hand after turning, to get the arcs to merge smoothly.

I heartily recommend mounting a large disk (larger than the blank you're turning!) to a faceplate and then mounting the blank to the disk offset to turn one of the large arcs. Then securely mount weights to the disk to counterbalance the blank and turn to size. Change the offset to that of the second large arc, rebalance the load by shifting the weights, turn that and finally repeat the process for the small "end" arcs. The comes the fun of merging all four arcs by hand.

Warning: I've done this for oval plaques some 16" x 10" x 1"thick and it scared the living crap outta me! Doing it with a piece the size (and mass) you're talking about you're looking at really, really serious damage if anything goes wrong. ie. It can be done, but don't ask me to do it.

(Oh... and this method can't be used for hollowing out on the lathe!)

all you have managed to do is scare me, think i,ll syick to the bandsaw. bob

Well, Skew beat me to it, but here 'tis anyway:

The Old Schwamb Mill has been turning oval frames for over 100 years:

http://www.oldschwambmill.org/main.html

Boink "The oval frames"
Then boink "How the lathes work"

Also presented in "Lathes and Turning Techniques; The Best of Fine Woodworking," Taunton Press, 1991 - 1997; ISBN 1-56158-021-X. The article originally appeared in Fine Woodworking magazine (May 1986).

Google ["elliptical chuck"] for some more modern equipment. I think one of the biggies (Vicmark? Oneway? Teknatool?) sells one with a slightly different mechanism.

For the 6" depth desired, a Rose Engine with an oval cam would likely be the simplest. Have a look in the Woodturning - Ornamental Turning forum for some links to DIY equipment.

21 1/2" circumference (average diameter 6.8") is an incomplete specification. Need major and minor diameters and/or aspect ratio.

Joe

Originally Posted by robyn2839

all you have managed to do is scare me, think i,ll syick to the bandsaw. bob

My apologies, but frankly the whole idea (behind the method I described) scares the bejeezus outta me too!

Don't get me wrong... it is perfectly do-able provided you understand the method and it's perils, as well as having the appropriate equipment.
I don't think it's in the realm of a hobby turner though.

vicmarc have a oval turning machine thingo for a nice little ( ) sum.
http://www.carbatec.com.au/store/ind...1&keyword=oval

Originally Posted by Skew ChiDAMN!!

I don't think it's in the realm of a hobby turner though.

It would be if I could just get around to building the damn thing (Rose Engine, that is).

Joe

I built a chuck as described in one of David Springetts books. Since then I have re-designed and built four chucks all out of wood. For this to be successful, you need to be able to control the speed of the lathe accurately. The speed needs to less than 500 rpm. There was a cast metal oval turning chuck designed and built by John Ross in NSW.
I am sure if you do a Google for woodturning clubs in the Brisbane area you will get some help.
Jim