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Bottom of stave bowl (Read 1,159 times)
 
Jeff Hankinson
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Re: Bottom of stave bowl
Reply #15 - Feb 20th, 2017 at 10:36pm
 
Thanks for the slide show. I am interested in making Beads of Courage type bowls and after having made many from solid wood I wanted to move on to segmented and staved since there is less waste, and I'm trying to add to my skill set. Straight staves are a lot less work than multiple segmented rings and the addition of a thin ring on top to overlap the joints is an idea but as with the bottom, the cross grain problem is there. I have seen people simply inset the sides into a solid base and get a little side grain alignment that way, or inset the base into the sides with a mortise. I suppose with a bowl bottom of 6" or less a guy could get away with it. I had planned to make a barrel shape tapering the sides top and bottom from 1" or more thick stock. I have joined the staves with the appropriate miter angle, or with a birdsmouth bit and the glue up seemed straightforward both ways. I was trying to decide how to do the base - as a crossgrain board, or as an endgrain glueup. Cheers
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Ed Weber
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Re: Bottom of stave bowl
Reply #16 - Feb 21st, 2017 at 8:55am
 
Jeff Hankinson wrote on Feb 20th, 2017 at 10:36pm:
I have seen people simply inset the sides into a solid base and get a little side grain alignment that way, or inset the base into the sides with a mortise.


A ring of staves will expand and contract evenly around the circumference.
A solid bottom will expand and contract across the grain but not along the length.
A segmented bottom can expand evenly, similar to the staves
but then
If you're planning on making the sides of you bowls from stave construction, no matter what orientation the base or rim are. You'll need to address the butt connection between end-grain (staves) and side or face grain (standard segments or solid base). This is a weak joint, It's almost necessary to use a mechanical connection like a mortise & tenon to reduce the potential for joint failure.
With stave construction, a captured base (like a barrel) or a floating base are typically considered the safest.

With a small bowl (like beads of courage) if the bottom is 3" or so, the wood movement of a solid base "probably" won't be a problem. I would perform an experiment.
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Jeff Hankinson
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Re: Bottom of stave bowl
Reply #17 - Feb 21st, 2017 at 7:21pm
 
Thanks Ed. Alas, I figured that would be your answer... Of course I could make 'fake staves' by making long segments from a crosscut board, and edge joining them stave fashion. Then a simple solid bottom, and a short ring overlapping the top edge and voila (waa laa) a stave type bowl! Seems like cheating but who wants a joint failure.
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Ed Weber
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Re: Bottom of stave bowl
Reply #18 - Feb 21st, 2017 at 7:42pm
 
Jeff Hankinson wrote on Feb 21st, 2017 at 7:21pm:
Seems like cheating but who wants a joint failure.


It's not cheating at all, just another construction technique.
It also gives you a chance to show off some grain patterns or do some grain following.
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Glenn Roberts
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Re: Bottom of stave bowl
Reply #19 - Feb 21st, 2017 at 9:26pm
 
Ed, You are a master at this.
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Jeff Hankinson
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Re: Bottom of stave bowl
Reply #20 - Feb 22nd, 2017 at 12:35am
 
Great examples. Imagination plus well thought out construction equals very attractive pieces. A good illustration of why it doesn't take a zillion pieces to make a pretty piece. Thanks.
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Jeff Hankinson
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Barrhead, Alberta, Canada
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Re: Bottom of stave bowl
Reply #21 - Feb 22nd, 2017 at 3:42pm
 
Since I don't like reinventing the wheel, has anyone used adhesives rather than glue for cross grain joints? I am thinking of hide glue or industrial adhesives a guy can find in the hardware store. Since the problem is wood movement, a more flexible joining medium might be a way to crack (sic) the problem. I don't know if they dry out in time and eventually let go, but someone might know... Glue gun glue is insufficiently adherent so a non starter sadly - so convenient. I know, the 'dog with a bone' thing - won't give up on the problem. Thanks again.
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Ed Weber
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Re: Bottom of stave bowl
Reply #22 - Feb 22nd, 2017 at 5:30pm
 
You can use three types of glue
1. Cheap glue that will either leave an unattractive line or have poor holding properties.
2. Standard PVA wood glue (titebond). This type of glue has some give, as well as good holding strength.
3. Other (polyurethanes and epoxies) not always easy to work with of clean up, although have great strength.

If you're really worried about holding together a butt joint between end grain and long grain, probably something in category 3.

I prefer to rely more on joinery than adhesives.
Part of the challenge of segmented construction is building attractive pieces, while not breaking too many grain alignment rules, which provide the strength.

The problem with a 90 degree grain alignment is that if wood wants to move, it will move. If the glue joint doesn't break, the wood will.
Unless the size is too big or stresses to great,  there really isn't too much to worry about with PVA glues. The bottom of a bowl shouldn't be an issue.
Try an experiment.
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