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Why did this Crack!!!

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Forum topic by jcyphert posted 02-05-2018 02:35 PM 787 views 0 times favorited 22 replies Add to Favorites Watch
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jcyphert

29 posts in 898 days


02-05-2018 02:35 PM

Here is a link to the original project: http://lumberjocks.com/projects/356065

On the short wing which meets the wall, it developed a crack.

I’m fairly certain all of the cherry was at a uniform moisture. I glued and screwed it from the bottom to a piece of 3/4 plywood to (I thought) reduce the chance of this happening. Is the the ply what caused it?

Secondly, If I rip cut that crack out and piece it back together, will it happen again?


22 replies so far

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Aj2

1436 posts in 1823 days


#1 posted 02-05-2018 02:43 PM

Absolutely it was the plywood.

-- Aj

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jcyphert

29 posts in 898 days


#2 posted 02-05-2018 02:45 PM

Suggestions on fixing it? 3/4” deep relief cuts on the bottom?

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bbasiaga

1234 posts in 2020 days


#3 posted 02-05-2018 02:46 PM

As it tired to expand and contract with temperature and humidity, it could not due to being fastened to the plywood. Stress built and it cracked.

Brian

-- Part of engineering is to know when to put your calculator down and pick up your tools.

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Lazyman

2051 posts in 1413 days


#4 posted 02-05-2018 03:14 PM

Gluing it to the plywood probably caused it to crack rather than preventing it. The cherry will expand and contract across its width with changes in moisture. The PW will move almost none. The tangential shrinkage factor for cherry is about 7% which (I think) roughly equates to about .0023” movement for each 1% change in the moisture of the wood (if I am doing the math right). So if the wood was at say 15% moisture content when it was glued to the PW and when you brought inside and you turned on the heating and/or AC on it dropped to 12%, it wants shrink a little more than 1/16th of an inch for each 1 foot of width (there is very little movement in the length). So if you glue the cherry to an immovable surface, either the glue has to fail, which is unlikely if you glued and screwed it down well, or the wood has to split or buckle (depending upon which direction the moisture moves) to relieve the stress.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

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bonesbr549

1558 posts in 3092 days


#5 posted 02-05-2018 08:13 PM

Lazymand hit the nail on the head. You bound it to a material that would not move so it could not move and shrank and cracked.

As to the fix, tough you could remove screws and try to get that ply off and redo, by attaching to the bar with a non binding method i.e. crazy-eights or just chuck it to experience and redo the top.

Sometimes experience is painful. I had to redo a series of cabinet doors due to learning what happens when glue seeps into the grove of the rails and styles and you put the raised panels in. They cracked. I fiddled with a bunch of options to “save” and ended up chucking and doing over.

-- Sooner or later Liberals run out of other people's money.

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jcyphert

29 posts in 898 days


#6 posted 02-05-2018 08:25 PM

Thanks for the help. I’m going to give the relief cuts on the plywood back a try first. One every 6 inches or so. I’m hoping that will give it enough room. Otherwise, it will be a re-do. Hope I can at least save the bar rail…. I think it was just screwed on.

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Smitty_Cabinetshop

15369 posts in 2644 days


#7 posted 02-05-2018 08:25 PM

Ditto to Nathan and Bones, they’re right on the money. You simply cannot keep solid wood from moving by glueing/screwing to plywood. Wood’s gotta move, and that movement must be accommodated in some way.

-- Don't anthropomorphize your handplanes. They hate it when you do that. -- OldTools Archive --

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jcyphert

29 posts in 898 days


#8 posted 02-05-2018 09:12 PM

Any takers on thinking the cuts thru the plywood will work? After hearing from everyone, I certainly don’t know what I was thinking using the solid play base… It seemed like a good idea without thought applied.

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Smitty_Cabinetshop

15369 posts in 2644 days


#9 posted 02-05-2018 09:29 PM

Try to free it from the plywood altogether, and then glue the cherry back together and ‘mount’ the cherry to the ply using elongated holes in the ply. That way the cherry can move. Short of that, cutting through the plywood will get you to the point the piece can be glued, but it will happen again more likely than not. Next time it may be a buckle rather than a crack.

-- Don't anthropomorphize your handplanes. They hate it when you do that. -- OldTools Archive --

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Woodknack

11785 posts in 2405 days


#10 posted 02-05-2018 09:32 PM

Grab a good book on woodworking to learn the basics.

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

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jcyphert

29 posts in 898 days


#11 posted 02-05-2018 09:33 PM

Thanks for the backhanded slap Rick… Real Classy


Grab a good book on woodworking to learn the basics.

- Rick_M


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Lazyman

2051 posts in 1413 days


#12 posted 02-05-2018 09:37 PM

In theory, the relief cuts could relieve the stress and prevent more cracking. I’ve never tried that but if someone brought this to me and asked me to fix it, that is what I would try. Note that if you also glued the panels to the frame you could be in for problems where the panels’ grain is at right angles to the grain in the frames.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

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jcyphert

29 posts in 898 days


#13 posted 02-05-2018 10:52 PM

The panels are not glued. Thanks for your input!

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fivecodys

1019 posts in 1661 days


#14 posted 02-05-2018 11:46 PM



Any takers on thinking the cuts thru the plywood will work? After hearing from everyone, I certainly don t know what I was thinking using the solid play base… It seemed like a good idea without thought applied.

- jcyphert

We all make mistakes and hopefully we learn from them. I sure have had my share! :)
At this point I would try the cuts through the plywood.

Good luck!

-- There' are two theories to arguin' with a woman. Neither one works.

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JBrow

1361 posts in 945 days


#15 posted 02-06-2018 01:24 AM

jcyphert,

The relief cuts that extend all the way or nearly all the through the thickness of plywood underlayment would be my repair approach. Making a relief cut every 6” may be enough, but I would probably make relief cuts 2” to 3” apart since I would like to make sure I never had to revisit this repair. The relief cuts could be made using a table saw, circular saw, or a router with a straight bit.

Eliminating the plywood backer would be more effort but should also prevent reoccurrence of splits. If this option is selected, a handheld router with a straight bit or a bottom cleaning bit in multiple light passes may be the easiest method and would reduce chances of damaging the bar top.

If you can manage a relief cut under the crack, it may be possible to spread some glue into the crack and draw the bar top back together.

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