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Failed design - where did I go wrong?

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Forum topic by TEK73 posted 12-22-2019 10:20 AM 768 views 0 times favorited 10 replies Add to Favorites Watch
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TEK73

289 posts in 436 days


12-22-2019 10:20 AM

Topic tags/keywords: question joining

Hi

Build this not to long ago:

Click for details

It’s all beech (except the
Two small Walnut stripes).
The design was as follow:
- the bottom was made from two flattened planks joined together (apprix 1cm thick)
- side planks on the long side mounted on the side, same wood direction as the bottom
- side planks for the ends made by endgrain wood, same direction as the bottom plank

So, everything should be in the same direction, however it seems like it is bending up on the sides.
So, I’m wondering about the following:
- what is wrong with the design that causes it to bend?
- if I flattend it now, will it stay straight or bend more or back as huminity changes?
- how should I have built it?

Some pictures if the current state:

-- It’s good to have an end to journey toward; but it is the journey that matters, in the end. - Ursula K. LeGuin


10 replies so far

View Tony_S's profile (online now)

Tony_S

1323 posts in 3812 days


#1 posted 12-22-2019 11:48 AM

Notice the end grain in the area that the corner has lifted. The whole thing changes quite rapidly, right to left, from Quartered(still flat) to Rift(still flat) to flat sawn(not flat) The corner has lifted or ‘cupped’ in the opposite direction of the growth rings in true flat sawn fashion.
Flat sawn lumber always cups in the opposite direction of the growth rings as it dries or acclimates. The 1/2” thick bottom would offer very little resistance.

-- “Wise men speak because they have something to say; fools because they have to say something.” – Plato

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Madmark2

1254 posts in 1317 days


#2 posted 12-22-2019 01:42 PM

Esthetically it reads heavy due to the what appears to be 3/4” stock on the edges. Thinner stock will build less internal stress. Also was you stock kiln dried? Wood moves as it attempts to reach a balance in moisture content, perhaps your stock wasn’t as dry as it should have been.

I don’t think the warp is caused by the bottom. More likely the side rails aren’t perfectly straight any more. If you are going to remake anyway gently bust it apart on the glue lines an see which piece is off. Ideally you can shave a hair off the glue sides and rebuild it slightly smaller.

It doesn’t look like a technique failure. We’ve all been let down by material failures.

M

-- The hump with the stump and the pump!

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Sylvain

1027 posts in 3228 days


#3 posted 12-22-2019 02:06 PM

I could understand the choice of end grain for aesthetic reasons, but…
A frame and panel is never made that way because the whole piece could split in the middle if it was to receive a heavy blow.
This (if it were not moving) might be good for a cutting board which is supported while in use but not for a laden tray.

As Tony_S says: “The 1/2” thick bottom would offer very little resistance.”
Indeed, in a frame and panel, it is the frame which constraint the panel. That is what you get.

-- Sylvain, Brussels, Belgium, Europe - The more I learn, the more there is to learn

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bondogaposis

5730 posts in 3080 days


#4 posted 12-22-2019 02:12 PM

I think the problem lies with the design, I would make he frame the conventional way with long grain boards and then inset the bottom panel in a groove with allowance for movement or use plywood for the bottom.

-- Bondo Gaposis

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Tony_S

1323 posts in 3812 days


#5 posted 12-22-2019 02:29 PM



I think the problem lies with the design, I would make he frame the conventional way with long grain boards and then inset the bottom panel in a groove with allowance for movement or use plywood for the bottom.

- bondogaposis

X2

-- “Wise men speak because they have something to say; fools because they have to say something.” – Plato

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stefang

17039 posts in 4063 days


#6 posted 12-22-2019 02:34 PM

It might work better if the inlay boards were on edge. That way if the warped a little they would bend sideways instead of upwards.

-- Mike, an American living in Norway.

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RCCinNC

108 posts in 1055 days


#7 posted 12-22-2019 03:44 PM

I agree with the need for a traditional floating outer frame with allowance for contraction and expansion of the center panel. It’s very likely that a panel of that width, made from two fairly wide boards, is going to cup a bit over time, especially with plain sawn material. Tony S. is spot on with the issues caused by the variation of grain in your panel. This is why alternating the grain of adjacent boards, and using narrower boards in the glue up, are important steps towards providing stability. Perhaps then you would have had better luck with your design, but as noted by Sylvain, overall integrity of the piece still suffers. Book matching wide boards, though aesthetically pleasing, can often be frustrating, especially when using plain sawn lumber. As Madmark2 states, kiln dried material is a must, and will help minimize the range of future wood movement, but wood will always and forever move in changing humidity…so design need accommodate for it.

I’ve often found that my wished for designs are counter to best practice though…and sometimes I break the rules… sometimes I win, sometimes not!

I really like your overall design Tek73. Don’t be frustrated by the “failure.” It’s no more than a successful lesson wrapped up in a tad bit of frustration. I’ve got more than a few of my own…to the point where I just laugh maniacally and move on!

-- Live to putter...putter to live!

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TEK73

289 posts in 436 days


#8 posted 12-22-2019 09:44 PM

Thanks for your good input.
It’s a learning path, so having to change or redo the design is no problem – but very happy that I did not make 10 of these as gifts to family and friends ;-)

I made the grain at the end of the frame go the same direction as the bottom it should move together and not tear eachother apart.
That kindof worked, but other issues raised their ugly head.

For now I will just reflatten it on the plainer and see if it has stabilized or will continue to move.
So, a frame that allows for movment would be the way to go.
And maybe also glue up the bottom from smaller piced wood.

-- It’s good to have an end to journey toward; but it is the journey that matters, in the end. - Ursula K. LeGuin

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iminmyshop

319 posts in 2723 days


#9 posted 12-22-2019 11:51 PM

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Woodknack

13247 posts in 3109 days


#10 posted 12-23-2019 03:54 AM

Panels cup because of uneven moisture exchange, but the most stable panel will be quartersawn strips.

-- Rick M, http://thewoodknack.blogspot.com/

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