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cone shape angles

S

Stanley Keenum

Joined
Dec 27, 2008
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Trinity, Alabama
I am a fairly new turner. I want to cut, glue up, and then turn a cone shape made from staves for a birdhouse roof.
I am thinking the cone should be about 4" tall, 4" in diameter at the bottom (widest dimension) and 2" in diameter at the top (narrowest dimension). From reading that I have done I know that the stave angles will be determined by the total number of staves in the cone and that I will have to size the individual staves to achieve the dimensions above.
How do I hold the staves for cutting the angles. I have a table saw, a chop saw and a band saw. Best jigs and/or tips, or other help on making this staved cone/birdhouse top would be appreciated.

Thanks in advance,

Stan
 
Ah compound cuts. I will be watching this question because I too want to do something like that. The key is the pieces are small and photos would be of great help. Thanks.
 
Stan, I just posted this response on the Sawmill Creek site to your question, so I'm doing a "copy/paste" to put the same answer here.

You've asked for a pretty complete lesson on compound-mitered staves. First step is to choose the slope angle. If the cone is "small end down", this is the angle between the horizontal and the side of the cone. Again, you choose this angle. For your cone, let’s assume 45-degrees. Next, you choose the number of staves (8, 10, 12, 14, 16. Etc – your choice). Let’s choose 12. Now you need to determine the two cutting angles – the blade angle and the miter angle. This can be done using high school trig, but it’s much easier to just look them up in a chart or you can use a website such as: http://jansson.us/jcompound.html

In this case the angles are: blade tilt =10.55 and miter = 10.73 These angles will dramatically change if you decide upon a different number of staves or a different slope angle.

Now that you know those cutting angles, it’s a matter of setting up a table saw sled and blade tilt to conform. Before cutting the staves, you’ll need to create some short boards (the dimension from end to end of the staves). That dimension can be estimated by simply drawing a sketch of your cone and measuring. The exact sled set up is kind of difficult to describe, but it involves a stop block and at least one hold-down clamp. Once set up, it’s a matter of making a cut, flipping the board, butting the first cut against the stop block, and making another cut, then flipping again for the next cut.

Regarding the width of the staves (the big end), that can be estimated by multiplying the desired diameter by pi (3.14) and then dividing by the number of staves. This is not exact, but close enough for this type of work. The position of the stop block determines the stave widths.

Hope this helps. For what it’s worth, my Volume Three DVD includes a complete lesson on compound-mitered staves.
 
Malcolm,

Thanks for your help. I didn't realize how complex this subject might be. I knew I couldn't get my brain oriented to how to make the cuts. I think I am starting to get some understanding from your post. I now understand that I will have to tilt the blade to make a certain degree bevel cut while orienting the piece to be cut at a different complementary angle. I think I understand the concept of setting up a sled with a stop to make the cuts.
I can begin to comprehend the process now thanks to your reply.
I did visit the link you mentioned and that will help greatly. I also visited your web site. Your web site is great (you do great work!).

Thanks again for the reply and thanks to any others that may have other insight.

Stan
 
You can get a preliminary visualization of what the pieces look like with graph paper and some minimal drafting instruments. NOTE: the Miter Angle I show isn't exactly right; it needs another projected view.

The left side of the sketch, through the faces, establishes the minimum piece dimensions for your final diameter. I chose 8 staves for simplicity.

Full size drawing, or larger, is better, and CAD is even better. But this method works when you lose access to the internet, or your computer gets sick.

Google [descriptive geometry] for more, unless your computer is sick.
 

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Stan,

I've made birdhouse roofs using stacked rings. I learned from a demo by Susan Schuaer.

About 5 minutes to get rings ready to glue up. no math required.

The roof is generally conical. The process basically is to pin a wooden disc against a backing board with the tail stock. cut rings with a parting tool at about 45 degree angle to the face of the stock. stack the rings and glue them. when dry turn the outside.
I never bothered to turn the inside figuring the birds didn't care.

Now that all the journals are on line see Turned Birdhouses by Susan Schuaer page 14 ,March 97, .
There are photos and diagrams for cutting the rings

Not nearly as elegant as compound staves.
Happy turning,
Al
 
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Ok, I'll plug Malcolm's book one more time. Get "The Art of Segmented Woodturning", available on Amazon or from himself at tahoeturner.com. No connection, just a satisfied customer. It will teach you to make this (looking for picture).
 

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