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Bottom of stave bowl (Read 1,177 times)
 
Bruce Kamp
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Bottom of stave bowl
Nov 28th, 2016 at 1:34pm
 
I am making a staved sided salad bowl out of mahogany. It has 16 sides, simple miter not compound, and is 12" diameter. My question revolves around how to do the bottom. I want to mortise the bottom in so that the sides of the bowl just turn down to the surface without a foot.
I have read Malcom Tibbits discussion on using a floating bottom but even he says that this will not work for salad bowls because of the potential of food getting into the crack between the floating bottom and the sides. He suggests using a quarter sawn piece for the bottom.
I am wondering if I can safely use glued up strips of mahogany to make a solid bottom. Of course I cannot follow grain orientation with the sides so I am worried about cracking.
What do you think?
Thank you
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Ed Weber
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Re: Bottom of stave bowl
Reply #1 - Nov 28th, 2016 at 1:56pm
 
I think it is less likely for there to be an issue with the base on a stave constructed piece than a standard brick-lay piece
With a stave construction, when moisture (relative humidity) changes, the entire circumference of the vessel will increase, this doesn't happen in basic brick-lay construction. In Brick-lay orientation the sides remain stable while the base piece tries to expand and can potentially cause a failure of some kind.
Barrels have hoops to hold them together, you used wood glue.
I've done it both ways and there is always a risk but at least with staved sides, they will move with the bottom, where as standard construction wont move at all.
After you construct your base piece, you can seal the end grain to minimize or at least potentially slow the transfer of moisture that can lead to problems

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Bruce Kamp
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Re: Bottom of stave bowl
Reply #2 - Nov 30th, 2016 at 1:36pm
 
Thanks Ed.
I am now thinking of trying to build a segmented  bottom for the bowl. One big problem is it will require segments that are around 6" wide if I attempt to have them meet perfectly in the center. This is difficult, even with much smaller width segments. So, my thought is that maybe I can build a disk/ring but using narrower segments so that I can easily cut them on a wedgie sled. This would give me a ring that I could then insert a solid "plug" into giving me a solid disk.
I have done the "plug" thing before and it has worked well. However, in this case I want to try to have the plug much larger than I have used in the past. I am thinking maybe 4" to 6" in diameter. Remember the bowl is 12" in diameter. 
I would visualize building the ring, hot gluing it to a piece of MDF, maybe using a cole jaw,  then turning the interior to the desired size. Then turn the plug to fit the interior hole in the ring. Glue those together.
Then turn a mortise in the bottom of the bowl. Once I have that set I would turn the completed disk to fit in that mortise.
Lots could go wrong, I know, but generally, what do  you think?
Has anyone done anything like this?
Thanks for your thoughts.

Bruce
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Ed Weber
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Re: Bottom of stave bowl
Reply #3 - Nov 30th, 2016 at 8:52pm
 
Bruce Kamp wrote on Nov 30th, 2016 at 1:36pm:
One big problem is it will require segments that are around 6" wide if I attempt to have them meet perfectly in the center. This is difficult, even with much smaller width segments.


Don't try to glue them all at once.
I'll repeat that,
Don't try to glue them all at once.
Glue them up into pairs and sand (keeping the proper angle) until the points on each pair are even. Dry fit and check again, then glue.
It's much easier to glue up three 120 degee segments than it is to try and align 6 points to meet in the center with no gap.
You don't get a prize for gluing a ring up all at once and there are times like this when you don't want to.
Don't just take my word for it, try a test piece first.
Good Luck
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Bruce Kamp
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Re: Bottom of stave bowl
Reply #4 - Dec 1st, 2016 at 11:48am
 
Thanks Ed.
I am going to give that a try. I have successfully merged the pieces in the past on rings up to 5" or 6" but I think it has been mostly a case of good luck. It would be nice to have a technique that I can count on.
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Ed Weber
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Re: Bottom of stave bowl
Reply #5 - Dec 1st, 2016 at 12:38pm
 
By gluing in pairs initially, you can sand the edges to 'fine adjust" the point until it's perfectly even. Once that's done, join the pairs or sub-assemblies into halves, then align and glue the two halves.
Getting a perfect (gap free) center point isn't easy, don't try to make it harder.  Smiley
There are many ways to accomplish this, you'll figure out what works best for you.
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Bruce Kamp
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Re: Bottom of stave bowl
Reply #6 - Dec 8th, 2016 at 12:23pm
 
I decided that for this project I would not chance the process that Ed describes. I am not doubting that it will work. I just need to do a test run at it with some less expensive wood to make sure I am doing it correctly.
I chose, instead, for this project to go ahead with the "plug" procedure. I have attached an image of the result. The center has a different grain because I had to cut it from a different board. It is all mahogany though.
I am fairly satisfied with the design. Although I do think the full segments meeting at the middle would have looked more interesting.
Thank you
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Ed Weber
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Re: Bottom of stave bowl
Reply #7 - Dec 8th, 2016 at 12:59pm
 
Judging only from your photo, I would have to have to point out that this does not appear to be stave construction, these are just tall segments.
It looks as if the grain is running horizontally, (glued end-grain to end-grain) the grain needs to run vertically for this to be considered a stave piece.
Could you please confirm this.
While I stand by my previous posts, they may not apply to this piece.
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Ron Sardo
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Re: Bottom of stave bowl
Reply #8 - Dec 8th, 2016 at 3:35pm
 
I think it is Ed.
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Ed Weber
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Re: Bottom of stave bowl
Reply #9 - Dec 8th, 2016 at 7:13pm
 
Ron Sardo wrote on Dec 8th, 2016 at 3:35pm:
I think it is Ed.


You think it's what, I have two choices Huh
Staved or standard, I honestly can't tell from the photo. I'm guessing the grain pattern and grain direction are different.
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Bruce Kamp
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Re: Bottom of stave bowl
Reply #10 - Dec 8th, 2016 at 10:00pm
 
I'm not sure my original question was dependent on whether it was a true staved bowl or not. Maybe it would if the end grain gluing would affect the stability of the bottom and therefore affect what design was better for the bottom.
As you can see from the currently attached photo the grain is actually running at an angle but it probably would be considered end grain to end grain. If so would this be considered more stable than pure side grain to side grain?
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« Last Edit: Dec 8th, 2016 at 10:01pm by Bruce Kamp »  
 
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Ron Sardo
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Re: Bottom of stave bowl
Reply #11 - Dec 9th, 2016 at 8:39am
 
I would have laid out the staves so the grain runs top to bottom. Also if I had that thick of a segment I would have cut a slope from top to bottom and avoided the squarish look. But then maybe that was what you intended?
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Ed Weber
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Re: Bottom of stave bowl
Reply #12 - Dec 9th, 2016 at 9:14am
 
Thanks for clearing that up Bruce.
I thought it was running at an angle and therefore is not a staved vessel.
Bruce Kamp wrote on Dec 8th, 2016 at 10:00pm:
I'm not sure my original question was dependent on whether it was a true staved bowl or not.

It does make a difference.
Staved vessels (like barrels) are more prone to change size (circumference) be shrinking and swelling. Standard (brick-lay) segmented vessels are quite stable when it comes to changes in circumference, this is why the bottom makes a difference.
If either the bottom or the sides moves while the other is stable, then it is more prone to failure. The piece and the bottom either need to move together, be able to move independently or be joined well enough to withstand wood movement.

The piece looks good with the angled segments, one word of caution though.
Many times pieces like this (long end-grain joint) tend to want to separate at the top of the joint (the rim) where there is no adjacent ring to hold them stable. This is one reason why many times you see a thin ring at the rim, not just for aesthetics but for support.
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Re: Bottom of stave bowl
Reply #13 - Feb 19th, 2017 at 12:02pm
 
Hi Ed. Do you have a preferred method of putting a bottom on a stave sided vessel? I've read a discussion with M Tibbets and others debating the options and he has settled on a floating base with a keeper ring. I find that a little tough to make on a thin sided bowl. Could you comment on an inset end grain base? That would at least be simpler to construct and allow side to side grain gluing. I appreciate the comments you've made above wrt wood movement. I have read that a wedge constructed bottom is also likely to have glue joint failure in time because of wood movement. Thanks.
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Ed Weber
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Re: Bottom of stave bowl
Reply #14 - Feb 19th, 2017 at 2:14pm
 
An end-grain is simple to do, you just need to make sure it's a good stable wood and thick enough not to blow out. You can use a solid piece although a pie slice glue-up will be more stable (more uniform in movement)
I haven't done an end-grain bottom on a large bowl, mostly on vessels where the outside aesthetic is more important.
Multimedia File Viewing and Clickable Links are available for Registered Members only!!  You need to Login or Register is a slideshow of a staved vessel, at 3:05, it shows an end-grain base being sized and attached.

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