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Need advice on unusual glue up

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Forum topic by jaybird72 posted 12-04-2018 01:49 PM 438 views 0 times favorited 9 replies Add to Favorites Watch
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jaybird72

2 posts in 232 days


12-04-2018 01:49 PM

Topic tags/keywords: glue up wood movement expansion contraction

Hello everyone. I’ve been coming here for 10 years off and on, but this is my first actual post. I can usually find the advice I need from previous posts or googling around, but this one has me stumped. As I try to get more creative and break out of the box, I find my references more limited, so here I am, seeking your thoughts and advice about my latest idea.

I’ve been asked by my office to make a new coffee table for our new space. Long story short, I’ve decided I’d like the top to be in the shape of an abstract butterfly. I’m including a pic because instead of just gluing up the boards lengthwise like I would normally do, I thought it would be much more interesting and unique to have the boards tapered, so when glued up (short-wise), they fan out to give the feel of a butterfly spreading it’s wings. I’m including both a rough drawing and one with wood in place to help clarify this.

My question pertains to wood movement. Because the panels are shorter at the bottom and wider at the top, should I be concerned about the wood expanding more at the top and less and the bottom, and possibly eventually compromising the glue up? I could take an easier way out and either glue up the panels lengthwise or vertically and straight, but I really love this idea of tapering them to make it extra special and unique. As long as I don’t sacrifice the quality down the road when the wood begins to expand and contract with seasonal changes (I’m in Chicago).

And I still need to figure out a way to glue them because the tapers will make it more challenging.

Any thoughts our suggestions are appreciated. Thank you!


9 replies so far

View HokieKen's profile

HokieKen

9979 posts in 1561 days


#1 posted 12-04-2018 02:24 PM

I don’t think there will be any issues with movement as long as the top is attached to your base in some way that allows for expansion/contraction. I think within the top itself that while the total expansion at the wider side will be more than at the other side, the difference will be linear throughout the width so the glue joints should withstand it without complaint.

As far as the glue up goes, I think I would use some dowels to maintain alignment during the glue up. I’d leave it oversized until after glue up then cut to final shape.

-- Kenny, SW VA, Go Hokies!!!

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Aj2

2321 posts in 2220 days


#2 posted 12-04-2018 02:38 PM

I also don’t see any problem with wood movement. As long as you allow for the expansion esp along the top since it’s wider.
It’s a cool idea very interesting
Good luck I also like the taper idea I think it’s worth a try

-- Aj

View Underdog's profile

Underdog

1357 posts in 2458 days


#3 posted 12-04-2018 03:09 PM

Allow for expansion and contraction, and you’ll be ok. What are the dimensions?
If I remember correctly the general rule of thumb is to allow an 1/8” per each foot of width. This is assuming that the boards are flat sawn. And each species varies. So look up the specification for your wood and calculate how much you’ll need to allow for.

-- Jim, Georgia, USA

View Steve's profile

Steve

1360 posts in 1005 days


#4 posted 12-04-2018 03:11 PM

I would try to keep it as square’ish as possible for the glue up. Then cut it to final shape afterwards.

View MikeDilday's profile

MikeDilday

258 posts in 882 days


#5 posted 12-04-2018 03:18 PM

Cut an angled board with a dado or rabbet that you can clamp to the edge. Then just use clamps across to clamp it.

-- Michael Dilday, Suffolk, Va.

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TWegs

60 posts in 1038 days


#6 posted 12-04-2018 03:26 PM

Regarding the wood movement, a few thoughts… When the table takes on moisture from humidity, it will expand width-wise and will do so proportionally across the length, which shouldn’t create a problem. Because it’s tapered down the length, that just means that you’ve severed the length of the wood fibers on the tapered ends, so they won’t be there to expand or contracts and won’t be there to cause pinching into the adjacent boards. It also appears you are using the same species across the top, so you won’t have to worry about disproportionate movement. The bigger issue will be the grain direction from how the lumber was sawn. If it’s flat-sawn or rift-sawn and you don’t alternate the grain direction, you could have some undesirable cupping of the top when it starts expanding from humidity or starts contracting as it dries out.

A good practice is to start taking your project in the house and keeping it at a normal room temperature when you’re not working on it. No point in building it and storing it in a climate that is much different than where it will be used. Regarding the glue up, use some scrap boards to make a jig so you can glue it up square. I think you just need two right triangles with the 90 degree angle at the outside bottom. Use the triangle jigs to brace against the sides when you do the glue-up. Before gluing, do a test clamp up with two bar clamps stretched across the width, then ensure your measurement corner to corner is consistent so you know it’s square. Use shims to get it where you want, then go for it. Be careful not to over-tighten the clamps so as not to starve the joints. Good luck.

View oldnovice's profile

oldnovice

7488 posts in 3790 days


#7 posted 12-04-2018 06:44 PM

You can make a gluing jig to hold part/all of it together, as TWegs suggested.
And, I agree, glue it up then cut to shape.

-- "I never met a board I didn't like!"

View jaybird72's profile

jaybird72

2 posts in 232 days


#8 posted 12-04-2018 08:37 PM

Thanks very much for the thoughts and advice everyone. Very much appreciated. Happy Holidays!

View shipwright's profile

shipwright

8320 posts in 3220 days


#9 posted 12-05-2018 12:36 AM

Personally, I’m a veneer guy.
If you made the top out of B.B. plywood you would have no wood movement problems at all. The big plus is that you would have a spectacular variety of choices of amazing exotics, burls, and figures to “paint your butterfly”. You could buy sequenced veneers and have radial / book matches that could look really beautiful.
The edges could be solid or veneer.

-- Paul M ..............the early bird may get the worm but it’s the second mouse that gets the cheese! http://thecanadianschooloffrenchmarquetry.com/

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