Scalloped segmented layer question.

[Bill Stevener]

I know how it's done, really quit simple.
You get the other one finished first.

[Malcolm Tibbetts]

Quinn (and others),

Don't waste your time trying to fit two curved surfaces together. As Bill and others have said, this is a relatively simple process of laminating flat layers together and then orienting them so that when you shape the surface, the curves magically appear - what I refer to as lamination trickery. I have a whole chapter dedicated to this method in my book. In the piece that you displayed, I would guess that the segments were cut from laminated material with the glue line positioned approximately 45 degrees from vertical. Have Fun!

[joe greiner]

Quinn (and others),

Don't waste your time trying to fit two curved surfaces together. As Bill and others have said, this is a relatively simple process of laminating flat layers together and then orienting them so that when you shape the surface, the curves magically appear - what I refer to as lamination trickery. I have a whole chapter dedicated to this method in my book. In the piece that you displayed, I would guess that the segments were cut from laminated material with the glue line positioned approximately 45 degrees from vertical. Have Fun!

Maybe. Maybe not. Although the significance of the 45-degree lamination escapes me.

The piece in the link of the original inquiry has very little vertical curvature in the region of interest, so it'd be hard to get a circular projection as shown. And the angle off vertical is only about 15 degrees. I reckon I'd need to be very accurate, and very lucky, to get such uniformity among the separate scallops. Also, the inside scallops are almost exactly in line with the outside.

It looks more like matched cuts of two separate woods. The attached pic 1 shows some test cuts of 2x4 fragments on a bandsaw with the table tilted at a few degrees, so that the inside pieces nestle in the outside pieces at various depths of overlap. The cuts are made with the blade tangent to the curve.The smaller test sample was done on plywood a year or two ago with a scroll saw. This technique is used for relief assemblies in marquetry (or is it intarsia? I can never keep them straight), and also for spiral baskets cut from a single piece of wood - like the old telescoping camping cups.

Pic 2 shows a more elaborate insert made from two pieces of 2x6 after cutting them while sandwiched with carpet tape. The bandsaw table was set at 2.5 degrees. In pic 3, I've put the inside of the top piece into the outside of the bottom piece. Pic 4 shows the quality of the fit, even when done in a hurry. With slight refinement of the angle for the table saw, the planar misalignment could be improved, but with thick enough material the extra can just be planed off. For best results (which this is definitely not), the bandsaw should be well tuned with the blade tension set accurately; also, feed the work gently to avoid side loading on the blade which can produce barrel-shaped surfaces and an imperfect fit.

Joe

[Bill Wyko]

I would think tilt your band saw to 7 degrees and cut the same shape out of both pieces then push one into the other until it's tight. Then sand it down flush and cut your segment. Similar to marquetry. The post I made earlier would make a similar effect as well. Looks like the last post is a similar technique too.

[Alex Elias]

I'm positive it's done at an angle. If you get a block let's say 3" x 3" 2" thick and cut the top corner at an angle (whatever you choose I'd say 45 deg) you end up with 3" x 3" x 2" at the bottom and the top would be like a wedge about haft the thikness of the wood if you make a circle like that for the upper ring is going to turn into the scallops.
I have seen pens done like this. Chop the top corner at 45 glue a piece of contrastong wood to replace the cut off and when you turn it you have a scallop. If you cut a piece of wood in 2 at an angle and insert a lamination in the center and reglue when turned you have the countour of a scallop.
I'm sure the cut is at an angle.
Hope this helps

[Alex Elias]

Here is what I meant. I know it is not a scallop but you can get the idea of the concept.
http://www.flickr.com/photos/1703840...7602824997774/

[Bill Stevener]

How do you get it to come out the same on the other side?

[Alex Elias]

How do you get it to come out the same on the other side?

The thickness of that bowl does not appear to be more than 1/4" may be even less. So when it is that thin it can be that they are so similiar your eyes are compensating to making it look the same.

[joe greiner]

How do you get it to come out the same on the other side?

The size of the bowl in the original post isn't stated. But assuming "normal" proportions, the stock would likely be about an inch or so thick to accommodate the final turning. Suppose the stock was prepared by the sandwich technique I described; let's further assume that the optimum angle (found by testing) was 2 degrees. Then rip a bevel on each side of the stock strip of 2 degrees also. Prepare the segments with compound miters so they form a ring with its faces 2 degrees off vertical. Glue 'er up and turn to the final side angle of 15 degrees as shown. This would put the inside and outside faces of the scallops exactly in line, although there'd be extra material to be turned away at the outside bottom and the inside top of the feature strip.

Alternatively, a blade with a wider kerf might produce an optimum cutting angle closer to 15 degrees so there'd be less material to turn away; OR, a 15-degree cutting angle might produce a planar mismatch with an acceptable amount to be planed off prior to cutting the segments. It all depends on how much "extra" material you have available.

This isn't the sort of thing done repeatedly. The optimum cutting angle will vary with the amount of wear on the blade, as well as the characteristics of the woods, so it needs to be established for each project.

Joe

[Steve Ott]

Quinn

Try it this way. Use a router with an inlay bushing to rout the holes (circles) in a board of the white wood. Then rout the inlay (circles of dark wood). Glue the dark circles into the white holes. Make your segmented ring using full circles, and part into half. You'll then have two of these to use.

Hope that helps.

[Malcolm Tibbetts]

In Quinn's pictured bowl, the equal border of white wood on both the inside and outside convinces me that the curves were probably done by fitting two curved surfaces together. That's doing it the hard way. I'll attach a photo of the same type of cuves. In this cup and saucer, all the curves were exposed by shaping flat laminations - no curved pieces were glued together. This type of work does require precise centering, etc, inorder to create consistent designs.

[Bob Way]

These are some really creative ideas, and I always enjoy the inspiration they give me to try some new techniques.

As to the original scalloped bowl on Kevin's site that Quinn linked us to, Bob Pritchard has a tutorial of sorts on one of his sites for doing these kinds of feature rings. Basically his approach uses a router, templates, and bushings. It can be found at http://www.outofcontrol-woodturning.com/ by following the link under the articles section on the right side of the page.

Enjoy your turning.

[Jerry Gilman]

For the light color wood , I would use a large forstner bit to cut out holes in a long board, then cut it in half resulting in semi circular holes. They then can be cut into the segments. For the lower dark wood, I would make a circle cutting jig for a disk sander to swing an arc for the matching curve. It would take several trial and error set-up cuts to get the proper matching arc. Many years back, Bill Giese explained to me how he used this method to make the bowl in this link.
http://www.woodguild.com/giese/gallery.htm

Hope this helps

[joe greiner]

The technique I described is derived from an old trick for getting perfect miters on picture frames (for example); shown by Nawm (Abrams, NYW) several years ago, when the miter cuts are imperfect. Clamp the frame pieces in rectangular array as best you can. Run a back saw along the imperfect miter line so that the blade straddles both pieces. The kerf produces exactly parallel edges so that the pieces fit together properly. You need to do this at all four corners, and if the original cuts are way off you may need to repeat it. Some miter clamps have a slot on the diagonal to accommodate the saw blade.

The router technique requires a substantially perfect relationship among the router bit, the bushing, and two templates.

The beauty of the sandwich-cut method is that it produces mating pieces, as long as the blade doesn't flex transversely. By this means, the insert can be any shape desired. The only restriction is a need for entry and exit points for the cut. Even that restriction could be relaxed with a scroll saw instead of a band saw, except it'd be more difficult to keep the blade from flexing; also, the total thickness of the sandwich should be less than the stroke of the scroll saw to allow the gullets to clear. The access hole for blade insertion could be filled with a dowel of a third material for an interesting effect, but to preserve the mystery some additional dowels could be placed as "design features."

No question, Malcolm's lamination trickery is a lot less busy work. But precise centering has not yet joined my skill set.

Joe

[Quinn McCarthy]

Wow I can't believe all of the suggestions I have had. I was able to sell my first bowl and it will have the scalloped ring in it.

Thanks for all of your suggestion. Obviously there is more than one way to skin a cat.

Quinn