Wood Movement

[Simon Reznick]

Hello,

I have a built a table out of solid maple thinking that I allowed for a lot of movement between the top and apron.

It was built in a garage and then transported to my sisters apartment for finishing to take place. Where there is an definately a difference in humidity levels.

Before she had a chance to apply a finish, the boards shrunk quite dramatically. This proved to mess up the alignment of the top to the apron (which was supposed to be relatively flush.)

I was wondering if this could have been prevented at all by finishing first while the furniture was in the garage, and then transporting? Also, are there specific finishes that are better a reducing wood movement?

Thanks for your replies!

Simon.

[Jim Becker]

Welcome to the 'Creek, Simon.

Maple moves a LOT seasonally across the width of a board...and finishing it makes no difference. In fact, depending on the grain orientation of the boards, a 30" wide surface made of hard maple can move nearly 1/4" or more seasonally! Finishes do not change the properties of the material in that respect since with very few exceptions, they pass moisture. How you build the piece is what you need to pay attention to. How the top is fastened to the aprons is a good example of that. You need to accomplish the task of holding the surface to the rest of the assembly so it remains flat while at the same time making sure that the top can expand contract width-wise. Usually that means minimal fasteners and using them in such a way that they don't constrict the movement.

For example, lets say you choose to use screws to fasten your top to the aprons and for this illustration, you have a rectangular table...you have two short aprons on the "ends" and two long aprons on the "sides" (front and back). Let's say you are going to use three screws through the end aprons, either vertically or in pockets and they are located with one in the middle of the apron and one toward the front and one toward the back of each apron. (No fasteners on the long aprons for this example) The screws in the middle of each aprons would be installed "normally" and directly into the bottom of the top. The other two screws would require you to have slots in the aprons that allowed the metal fasteners to move as the top shrinks and expands seasonally. Other methods for fastening the top can be used, such as "figure 8s" or wooden clips in slots, etc., but in all cases, there is a need to insure that the top can still move independently of the rest of the table assembly. Glue is pretty much never used for this particular assembly need.

[lou sansone]

simon

Jim gave some good answers, but here are a couple more questions that might result in some additional answers.
1.Do you know the moisture content of the wood you were working with while it was in the garage?
2. Do you know the moisture content of the wood now that it is in your sisters apartment?
3. Based upon those values one can provide further guidance.
4. Some wood movement is goning to happen no matter what. Part of the furniture design should take this into account. Having the apron flush with the edge of the table is almost impossible to correct for, unless you are using mdf and veneering the whole top.

regards
lou

[Steve Cox]

And, since I notice you're just north of the border, if you used our local maple (bigleaf maple) you will get more movement than if you were using hard maple.

[Kelly C. Hanna]

This topic has meandered right into the slot I needed to hear about. I have a Curly Big Leaf Maple piece about 9"x18" and I want it to be centered in a table top containing both Bloodwood and Walnut (framing the CBLM). How would you guys attach the two to CBLM and account for the movement? The CBLM piece is now 1/2" thick and the others will be 13/16" or so.

[Steve Cox]

If that bloodwood and walnut are going to go cross-grain, I'd resaw it down to 1/8" veneer and glue it to a plywood substrate.

[Simon Reznick]

Thanks for the suggestions/info!

I don't know the moisture content of the wood in either places yet... I may have to get a moisture meter in the near future.

It is good to know that finishes won't really change anything!

I'm pretty sure that wood is eastern maple. Most of it is from a previous table that I have refurbished/redone.

Simon.

[Kelly C. Hanna]

Thanks Steve...is there a solid wood I could use for substrate? I really don't want any ply or MDF etc. on this one.

[Richard Wolf]

Lots of good advice here. I would like to add that being in the North East (wet & humid) I always plan on the first wood movement on my projects to be shrinking. Its almost impossible to bring wood from outside or in a shop to inside a house and not expect it to shrink. After this first move it will than move with the seasons.

Richard

[Alan Turner]

I plan on wood movement to be whatever happens between 6% and 13%, and do calculations via the shrinkulator, which is a spreadsheet already outfitted with the correct formula and the shrinkage rates, tangential and radial, of a pretty good list of species. It is on Woodbin.com. I don't think I have done one of these calculations longhand since learning of that site.

Kelly, if you are wanting to use solid wood, and it is not crossgrain, just check the math to see if the species are relatively the same in terms of shrinkage rates.

[Tim Sproul]

Before she had a chance to apply a finish, the boards shrunk quite dramatically. This proved to mess up the alignment of the top to the apron (which was supposed to be relatively flush.)

Simon,

Depending on the table......flush fitting the top to the apron is really only done with solid wood tops on tables that are typically directional. Hall tables...the back side is almost always up against a wall. In this instance, you'd fix the front and let the back overhang (it must overhang or you run the risk of exposing the innards) vary with seasonal movement.

There is more than one reason why traditional designs of dining tables DON'T have flush fitted tops.....

The other go around that has been mentioned is to employ a sheetgood for the top.

[Howard Acheson]

Kelly, there is no practical way to have a cross grain walnut or bloodwood to your maple. The maple will want to expand/contract quite a bit do to seasonal changes in relative humidity. A cross grain attachment will inhibit this movement which will lead to warping or cracking. The only way to use the maple is to build the item like a raised panel door. In other words create slots for the maple to expand/contract into.

Really though, the best way to use the wood is to cut it into a veneer less than 1/8" thick and glue it to a composition material substrate. Not only will you end up with a nicer looking project, but you will get a lot more mileage from your pretty maple.