Printable View
After many years of building furniture, I am screwing around with turning bowls, which I have concluded is the world's Second Oldest Profession.
Last night I saw what appeared to be a turned oval bowl. For the life of me, I can't figure out how the heck a guy would do that without some fancy-dancy machine attachment gizmo. It even had the bark left on the edges.
If you want to make a bed lemme know, but in the meantime, what's up with the oval bowl deal?
Thanks in advance.
It's an optical illusion that occurs when you turn a natural edge bowl. The curve of the bark makes the turning look like an oval but if you extended the sides of the piece up it would be round or close to it at least.
The only other suggestion is that the piece was turned wet and the bowl shrunk more across the grain than it did with the length of the grain. If I remember correctly from my reading, you get about 4 times the movement across the grain than you do lengthwise depending on the species of wood and the moisture content so you'll get an oval after the bowl dries.
HI
Check out this site. http://www.volmer---ovaldrehen.de/englisch.htm
Vicmark now make and sell the chuck. http://www.vicmarc.com/default.asp?contentID=549
john
I got to see the Vicmark oval turning thing up in Portland, and it is very interesting, as well as expensive. If you turn wet wood to finish thickness, and let it dry, it will go oval, almost no shrinking long grain, but quite a bit cross grain, just like boards. Of course, some woods warp more than others, and if you harvest and turn when the sap is running, you will get more warping than you will get if you harvest when the sap is down. As said before, natural edge bowls are a bit of an illusion, but if turned green, they will warp also.
robo hippy
I suppose it comes down to exactly what you mean when you say "oval bowl": it is trivial (using standard lathe tools) to make a bowl that is oval from the top view. OTOH, making that same bowl so that the rim is a flat ellipse (i.e. it looks like a standard bowl from a side view) takes some serious hardware and ingenuity. (Or a big bandsaw, but that's cheating. :eek:)
Or just work with ceramics, but that's a different forum. :p
One way to do this is to turn a deep bowl then split it from top to bottom then glue what was the 2 top 1/2s together. This is popular with segmenting.
(scratches head) How do you put a foot on it? (Other than the obvious, "I don't.")Quote:
Originally Posted by Bill Wyko
Turn it with a thick band then chuck it to the now oval face and turn it sideways. Then the left over is trimmed down by hand.
What I saw was a bowl, if you look at it from the top, that was about 4" x 6" oval.
Sorry I didn't describe it well.
The method I was refering to is in Malcolm Tibbets book on segmented turning. Another way to add to your knowledge of the art. I do like that vicmarc chuck as well.
I've got that book...even read it :p. But the only things I remember from the "cut-and-paste" section were those ribbon pieces of his that make my head hurt to look at. :eek:Quote:
Originally Posted by Bill Wyko
There are several ways to skin that cat! :eek:
Now, if the bowl is a true oval and the rim is flat with bark on it (natural edge), the next question in my mind is "what shape is the foot?"
If it was turned on a chuck designed to do ovals and done at the same time as the bowl itself, the foot was probably done the same way and is oval. Green turned self-ovalling bowls won't react like that. Green bowls warp is overemphasized because of the empty middle of the bowl; it's not so apparent on the whole chunk of wood.
I agree with Ray's thoughts, but not his math. :) I don't think the ratio is 4 to 1. I think it's usually 5:4 or 6:4 (3:2). The 3:2 or 6:4 (same ratio) would produce the 4x6 oval someone was talking about. That ratio is easily found by researching "lumber shrinkage ratio" in Google. Since we all wear our safety eye protection, should we going to Goggle instead of Google??
Back to business here... If the foot is circular or really close to circular, and the bark is still on there, that says to me that it was turned as green. It was turned to the desired wall thickness and allowed or encouraged to oval to the shape you saw. The larger the diameter of the tree, the flatter the top edge of the bowl would be. If the trunk was 30" diameter, that would make a 90"+ circumference, and a 5" circle would be a really small portion of that 90" circumference, thus pretty darned flat!
For the REAL oval turning, and not the traditional optical effect of some natural edge bowls, you have to use a special "chuk"
This was already in use back in the 18th century.
Nowadays you can buy these devices (rather expensive)
From those I tried, the smoothest is the oval device produced by Vicmarc.
A Rose Engine with an elliptical cam can also do it; other shapes also possible. Not quite the same as "Oval Turning," and there'd be some hand or power sanding needed after the cutter(s) have done their duty.
Joe