Polygon

[Jiroma]

Hi all, I want to build a base for a table approx 24 inches tall and 10 inches in diameter in maybe octagon or decagon shape ..or whatever the number of individual slats turns out to be. I just wondered if anyone knew a way to work out the size of the slats and the angle they should be cut at to give the 8 or 10 sided shape I am after. Basically I am making a cylinder out of wood and need to calculate how many pieces, what width those pieces need to be and what angle they should be cut at to give me a 10 inch tube. I hope someone can help or point me in the right direction.

Jtroma

 

[CHJ]

http://www.quest42.co.uk/woodwork/Segment/Seg-Calc.htm

 

[Steve Maskery]

A little tip about making a segmented structure.
All your errors in angle will be cummulative. So no matter how carefully you set your blade for sawing, you will end up with 8x or 10x however much you are out.

But panic ye not.

Glue up two halves, using tape to hinge and clamp the joints, then, when all is set, pass each half over the P/T. You'll get it, just about, on a 10" planer; no problem on a 12". The two halves will then mate perfectly with no gaps.
HTH
Steve

 

[Jiroma]

Im sorry I dont understand how half of an octagon can go through a planer.

Jiroma

 

[Steve Maskery]

Ah. In the UK a planer is a surface planer. We don't put things through it, we pass things over it. If you are used to US terminology you would pass it over the jointer.

America and England. Two countries separated by a common language...

 

[Jiroma]

Thanks Steve, I am in the UK but sometimes my brain doesn't engage before typing. I understand now but I dont have a planer wide enough. I had hoped that if 1 cut was off on my saw table they would all be off and correct the problem but I see what you mean if they are off by .5 of a degree then after 8 cuts I will be 4 degrees out.


Jiroma

 

[CHJ]

With careful setup you should be able to get within .1 deg. on a decent table saw. The odd+ paired with the odd - evens things out.

Although these are somewhat smaller than your project they were cut on a bandsaw and needed very little adjustment for angle correction.

I never resort to half section glue ups, preferring complete cylinder clamping to get a tighter clamped glue line, although on your size structure and half cylinders you would only have to match up four mating surfaces with a decent plane.

 

[niagra]

This is how I make drums. You can use the make two halves and then glue together, or a bit of jiggery pokery with a table saw and/or plane will sort out the angles. You do have to get the angles dead right so there are no gaps for maximum strength, although this may not be too much of a problem if your staves are thick enough, however it matters when you're making a drum 8mm thick!

Have a good read of this site, which includes a stave calculator:

http://pdgood.us/drumshed/staves.html#figuring

Hope that helps,
Dario

 

[Jiroma]

Sorry to impose on your generous assistance but what would the minimum thickness of stock be to make the octagon. For example would 12 or 15mm ply be ok. I'm not concerned with the weight it has to support as that will be minimal but I am curious as to the mating surfaces for glue up.

JK

 

[Wildman]

Polygon ah yes here you are
https://www.youtube.com/watch?v=4vuW6tQ0218

 

[Jiroma]

LOL very good Wildman

Jiroma

 

[niagra]

The thickness you start with depends on the number of staves really. The more staves you use, the thinner your stock can be to start with.

Have a play around with the file called Stave Drum Calculator (Updated)2.xls.zip. It calculates the cross section of the stave for you so you'll know the minimum thickness you need. If you are going to round both the inside and outside of the polygon, you'll be surprised by the wastage, especially with fewer staves like 8 or 10. For my drums, the minimum number of staves I use for a 14 inch diameter drum is 20, but usually 24.

Feel free to ask, I'll do my best to answer,
Dario

 

[Jiroma]

Thanks Dario. I dont intend to round off the shape of the staves and i plan to use 8 so it will be a proper octagon shape when finished. where do I find the file you mention.

Jiroma

 

[woodbrains]

I never resort to half section glue ups, preferring complete cylinder clamping to get a tighter clamped glue line, although on your size structure and half cylinders you would only have to match up four mating surfaces with a decent plane.

Hello,

Half section glue ups are done as a complete cylinder, just omit the glue from the centre staves. Tight joints and the facility to true up a slight error. This is useful on large cylinders, for sure, where a bit of twist in the staves can be a pain.

Mike.

 

[CHJ]

I never resort to half section glue ups, preferring complete cylinder clamping to get a tighter clamped glue line, although on your size structure and half cylinders you would only have to match up four mating surfaces with a decent plane.

Hello,

Half section glue ups are done as a complete cylinder, just omit the glue from the centre staves. Tight joints and the facility to true up a slight error. This is useful on large cylinders, for sure, where a bit of twist in the staves can be a pain.

Mike.

Having tried that I found I got some wider joints than I would like due to the tipping of the glued sections to their natural lie. (no adequate clamping on minor diameter or gaping of outer edges)
Even if the outer edges are tight the joints become more obvious when turning a complex curved form.

 

[monkeybiter]

If you intend using ply then I don't think you should consider a construction of just edge glued staves, I reckon the joints would tend to fail. If you wanted to use ply the I think I would go for a number of internal frames to fix the staves/panels to.
IMHO a better solution would be solid wooden panels which would glue better, and the edges could be tweaked easier to ensure a decent joint.

 

[niagra]

Hmm, can't seem to attach an xls file.

In the link I posted earlier go down about a third of the way to the section, "The Stave Calculator Method". The link to the file is in there.

Hope that helps,
Dario