It is awful hot & humid here so I'm sitting in my arm chair musing instead in my shop finding out for myself about making some oval picture frames on my trusty N3K. An elliptical chuck is not for me. I had thought the oval sections below the 'low points' of a cross grain natural edge bowl were illusionary; actually round and only appear to be oval. Like the way circles seen in perspective often appear to be oval. If I'm wrong and they really are oval, would it be possible (not necessarily practical) to devise a way to turn decorative oval frames in these sections and slice them off? BUT_ there is nothng new under the sun and if it worked, we all would be doing it. Leo, where are you when I need you. Help, someone, please. Arch
Arch wrote: (clip) I had thought the oval sections below the 'low points' of a cross grain natural edge bowl were illusionary; actually round and only appear to be oval. Like the way circles seen in perspective often appear to be oval(clip)Leo, where are you when I need you ^^^^^^^^^^^^^ Arch, wouldn't that be nice? Just turn a natural-edge bowl, and slice it up for a matched set of oval frames in graduated sizes. Unfortunately, that's not what will happen. As you correctly stated above, each cross-section of any bowl, above or below the "dips" is round*. The oval shape comes from the fact the the bowl continues to grow outward on the long axis, above the "dip" limits, while there is nothing but air on the short axis.
*Except the the effect of shrinkage.
This fact is easily overlooked, but is important to remember when you are vacuum chucking a natural edge bowl. The vacuum chuck must be ROUND, and small enough to contact the bowl below the "dips."
The reason circles appear as ovals when viewed at an angle, as in a photograph or drawing, comes from the fact that it is seen at its full diameter along one axis only (the one perpendicular to the line of sight.)
Arch: Just took a look at one of my (few) natural edge bowls. The ovals (ellipses?) that you see are real, at least as a projection, not optical illusions. However I think that the problem with your plan is that they don't lie in a plane. Without looking at it too critically it seems to me that there are two effects here.
The first is that the annual rings are curving down into the bowl (toward the outside and the bottom of the bowl) from the long axis of the oval. The second is that (at least in most bowls) the surface that the ring is following is curving toward the center of the bowl which would, I think, add to the already ovalizing effect of the ring curvature around the tree.
If you use a growth ring as a pattern to follow with a bandsaw,. you would surely get an oval but it would be one with a bowed surface. If you cut a secton at right angles to the turning axis, you would get two concentric circles with a surface between them that would essentially have the same figure as the same circles cut from a flatsawn board.
This is probably about as clear as mud but it's the best I can do without a drawing.
One further thought. Due to the tangential shrinkage of the log compared to the axial shrinkage, there would obviously be some real planar ovalization, but the effect would be relatively small.
If someone can make this clearer than this, please do it, because I now have myself thoroughly confused.
Well, sorta... You could make two circular frames (one large diameter and one small diameter) then cut arcs from each. With a little juggling of where you make the cuts, you can use about 3/8 of a circle of the smaller circle for top and bottom of the oval, and about 1/8 of a circle of the larger circle for the sides. It will approximate an oval, but will look really funny if you compare it to an actual circle....
A better way to make an oval frame if you really want one is to draw the oval using a loop of string and two nails. Put the nails about 2/3 of the long axis of the oval apart, with the string around both nails and long enough to create the oval shape you want. Use a pencil to stretch the string into a triangle, then just draw the oval. A longer string will make a bigger oval, and moving the nails to make the distance between them larger will make the oval taller relative to the width. (I forget the formula for making one to exact size, but you can get a real good idea of how it works if you just play around with the nails and string loop length). Once you've got an oval, increase the string size to draw the other side of the frame, and cut it out.
Use a router (blasphemy, I know, for a turner, but hey, you've got to learn to use other tools now and then, you know) to put a profile on the face, and a rabbet on the inside of the back, and you've got an oval frame.....
Ok, so it didn't use an elliptical turning attachment, but I don't have one and don't make enough oval frames to justify building or buying one...
After sending the last message about nails, string, jigsaw and router, It occurred to me that if you really want to make an "oval" frame and must use a lathe, you could turn a hollow tube, then just cut slices of the tube at an angle. They would be an oval (or elliptical) cross section. (However, the sides of the oval frame wouldn't be perpendicular to the mounting surface except at the middle of the sides. One could, of course, use the odd edge as a sanding guide to make perpendicular sides of the frame, but that sounds like a lot of extra work to me... (OK, go back to the string and nails method, unless you can sell the odd angles as "art")
Saw somweone making oval bowls on a 3000. Very smart it was. The whole "contraption" was made from Medium Density Fibre board (MDF), made a noise like a chaff cutter, but worked and worked very well. I believe it might have been a derivation of your dreaded eliptical chuck concept, but it turned (and allowed sanding) of an eliptical bowl, by holding the chisel in one place. (you had to be there)
The gentleman concerned's name is Fred Irvine. Fred is into Ornamental turning in a fairly big way. I am not sure if he is on the net but I can phone him and find out his email if he has one and set up a contact if you would like.
Interesting idea, if one were to take one of these ellipses and cut it in half on the short axis, flip one piece over, and glue together, then all the angles would be on the same side.
Turn a thick bowl from a sopping wet piece of sycamore and put whatever picture frame molding you want on the rim of the bowl. Part it off and press it in between two board that do not limit wood movement in the plane of the rim. I think you will end up with a nice oval frame.
I would conjecture that you can do this with most wet woods, but the amount of ovaling is variable for each species.
I have a picture of a sycamore hollow form that a fellow club member turned and it is amazing how it moved.
Joe Fleming - San Diego ================================
I make oval mirror frames, not much different from picture frames. I just make a segmented circle the size I want, whack it in half, and stick in a straight piece on each side. After that I just run it thru a dado bit on the router table, stick the mirror in and its over with.
Arch: How about this: Turn an eliptical hollowform with the major axis on the axis of the lathe spindle. Cut off slices parallel to the major axis of the elipse. Voila! eliptical frames. The process I envision would be something like this: Mount the workpiece between centers with the grain parallel to the spindle axis. Turn an eliptical shape with major axis on the spindle axis. Leave a large diameter short tenon on the headstock end to grasp with the chuck or to mount on a glue block later. Leave a longer tenon on the tailstock end. Remove the work from between centers and remount in the chuck or glue block. Part off the tenon from the tailstock end and set aside for reuse later. Make a small opening in the tailstock end. (Must be smaller than the tenon you parted off.) Hollow through the small opening. Do your best to make the inner wall parallel to the outer wall. Try to get the best finish you can. Recut the opening to a slight taper, larger at the tailstock end smaller toward the inside. Remove the workpiece from the lathe. Chuck the tenon you set aside earlier and turn a taper to match the opening in the hollowform. Glue it into the opening. Remount the work between centers and turn the tenons down to the smallest practical size. Remove from the lathe and finish the ends. Cut the hollowform in half along the major axis. Cut slices off each half to create eliptical frames. If the first slices are thicker than the radius of the plug it can be hidden on the back side of the frame. Brian Rosencrantz
InspirePoint website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.