staved bowl calculations?

[redfishsc]

I have never made a staved bowl, and will be making one (sorta) here soon using mahogany with maple dividers between the mahogany segments.


It's going to be actually a half-bowl (shaped like a D when viewed from above). Won't ever actually be turned on a lathe but rather finished like "flatwork".

It will be mounted to the wall with a very bright LED array installed in it (4 Cree XML driven at 1 amp). This will be mounted to the wall over my recliner, in between the two aquariums I have in my living room. My "man cave" if you will :biggrin:


The top of this "valence/sconce light" will be the same as the "bottom" of a bowl, and open for venting heat off of the LED's heatsink.


Anyhow, here is what I'm looking for, and this is by NO means a rigid design, it can change a little.

I just can't figure out the angles.

Number of staves (as if it were a whole bowl)-- 12 (will only be cutting 6)
Diameter of top of bowl--- 8"
Diameter of bottom of bowl-- 3"
Height of bowl-- 5"

Any help with the angles will be appreciated! Thanks!

 

[Steve Busey]

Does this help?

http://www.fisherwoodcraft.com/tips.php?TIP=calc

 

[redfishsc]

I saw that link Steve and I suppose I could use it in some way. The thing it doesn't tell me is what angle to cut the compound miter (the angle that I need to taper the pieces from wide to narrow).


That calculator shows how to cut the pieces for rings on a segmented bowl. I might still be able to make that work though--- thanks!

 

[jking]

I think you'd have more success if you glued up a stave barrel & glued a piece on for the bottom. What it sounds like you're trying to glue up will be extremely difficult to do.

How thick of staves are you planning to use?

 

[tommyd]

try these
Compound Miter Saw Calculator
Woodworkers Guild of Georgia, Miter Calculator

 

[workinforwood]

360 divide by twelve is angle. You can spin full circle and then cut in half. What u really really need is to buy segmented turning by malcolm tibbets. All u ever need know is in that mind blowing book! He will blow your mind

 

[workinforwood]

Just in case segments are new to you here's an important tip. In general woodworking all wood is edge glued. End grain glue up is a week joint. In segmenting 99% of the time all wood is joined end grain. If u join edge wise you will have expansion problems. A normal circle would be at least two layers thick so each layer is end grain joints and they overlap when two circles are glued together like bricks on a house. That makes the strength

 

[workinforwood]

Ah I read more carefully and see its a half bowl not half circle. You be best still make entire bowl cut it in half. Tough math but it is covered in tibbets book including how to clamp it

If it was me I'd keep it simple and basically make a pen blank like the pinstripe ones only supersized. Then you have no compoun cuts and easy to strap clamp. Easy to calculate too. Angle is 360/12 make pieces 6 long for mounting and trimming on lathe, width is 4.5 giving you a 9 inch blank diameter so u spin off 1" from top and more from bottom like a cone

So 12 boards 4.5x4.5x6 and 30 degree angle for rough blank then spin cone like bowl and. Cut in half

 

[redfishsc]

360 divide by twelve is angle. You can spin full circle and then cut in half. What u really really need is to buy segmented turning by malcolm tibbets. All u ever need know is in that mind blowing book! He will blow your mind

I have that and forgot he has a chart in the book, DUH! Great book too.

 

[jking]

360 divide by twelve is angle. You can spin full circle and then cut in half. What u really really need is to buy segmented turning by malcolm tibbets. All u ever need know is in that mind blowing book! He will blow your mind

360 divided by 12 will give you angle between the radial joint lines. You have to cut the edge of each piece at an angle that is half of that.

Cut angle = 360/number of pieces/2

This will give you 15 degrees which is the angle you need to cut the pieces.

 

[workinforwood]

Yep, thanks for correction John

 

[redfishsc]

Thanks guys, I got them cut today. I modified it and made it 12" tall. I decided 6" was too short.

Anyhow, I ended up cutting at a 5 degree angle (the "wedge" cut), and a 15 degree miter (the glue joint). Top is 1" wide, bottom is 3" wide. Will be a touch bigger than I originally intended but this is a "make it as you go" fun thingy.

I'll post pics when it's done, thanks all!