Thread: wood expansion question.

Originally Posted by AlanS

I want to accomplish two projects. Both involve the same problem: wood expansion. I want to set in a 1/4" panel into a 1/8" dado, thus having a 1/8" rabbet along the edges. I don't want any space between the panel and the box sides. Is this impossible? I also want to inlay a metal (silver) band between a panel and the sides, thus taking up the space that would normally be there for expansion. Trouble again? Here's a pic of what I'm speaking about...

Hello AlanS,

Hobbyist wood worker here, AlanS, not a cabinet maker................

Fitting a lid as you describe is not impossible. (I think I'd have some trouble fitting a lid without gaps in the manner you describe.) If the box was small enough expansion and contraction of the wood might not be an issue. However, box makers do not usually build in that manner because they know wood moves and there may be issues with the box in the future. I think rather than expansion, contraction of the panel resulting in cracks and splits in the lid and cupping of the lid panel yielding a poorly fitting lid would be the issues.

Wood movement in the lid can be lessened by veneering the feature wood onto a plywood or MDF substrate. Is this a possibility? I know cutting your own veneers easily means you'll need a bandsaw and a drum sander........

If you do manage to make a veneered lid, accurately sizing it to eliminate gaps is your next challenge. If you look at examples of boxes with flat lids (as opposed to a raised panel and frame style) you'll notice the lids have a decorative inlay or stringing 3 to 6 mm in from the edge. This inlay or stringing is there to hide the join between the lid and the box sides. This box, below, has solid wood sides and a veneered plywood lid. The join between the box and lid is hidden by the inlay.

Box lid.jpg

I have never inlaid metal into wood but can't see it being a problem especially if you veneer some plywood or MDF to make the lid.

I hope this helps. I'm keen to see the views of other box makers.

Homesy has described the problem and the solution perfectly. Remember though, if you're going to veneer the top of the panel, you should put a similar thickness veneer on the underside.
It's possible to get the top of the panel the right size. Cut it a little over size, the use a rabbeting plane to shave it down to the correct size. Inlaying metal shouldn't be a problem - I've seen both silver and brass used.

Alan,

Two excellent replies above so not much to add.

if your top panel is solid wood you can get a feel for it’s potential expansion/contraction by looking at the Wood Shrinkage Calculator here: Timber and Lumber Calculators at WOODWEB

Although I too conform to the established wisdom when fitting tops, it’s worth mentioning that I’ve restored a few 18th and 19th century boxes and in every case the timber tops were glues to the carcass - no allowance for movement. I’m not sure what that says but I’m still hoping to find out

To hide any expansion/contraction you could have your top fit like this. Apologies for the poor diagram - finger painted in a spreadsheet on an iPad!

54294132-0978-40E7-82CF-008E66E006A8.png


Best regards,

Brian

Brian,

Were the lids glued onto the box sides or glued, captured within the box sides?

Both the antique boxes I've restored have had the lids glued onto the sides, not captured within the sides. The veneer on this box helped to hold that cracked pine lid together.


DSCN8235.jpegDSCN8237.jpg

Paul

I have been glueing lids to sides for years and have never had a box come apart or lid crack from expansion or contraction. I have however had the odd lid bow a little when there is a quick and major change in humidity. After an event like this the lid does not go back to how it was so needs a few shavings off here and there to get the gap right again.

The wood shrinkage chart is in American timbers so i chose the Sassafras which i use and at 160mm wide there was zero movement. So AlanS i would not worry to much about it.

The amount of shrinkage calculated is: 0.00 millimeters The information you entered was: 16 centimeters Initial Moisture Content: 0.12 (decimal percentage value) Final Moisture Content: 0.12 (decimal percentage value) The type of lumber you chose was: Flat Sawn The Shrinkage Percentage Value used for the species you chose (Sassafras) was: 6.2%

Hi Paul,

The top in each case was glued onto the top of the sides then veneered over. In fairness I have seen old boxes like this that have had the top come adrift, just not the ones that have come my way. The fact that I don’t know where these boxes have lived, or in what conditions makes me reluctant to draw any conclusions from this, but it is interesting anyway.

double.d - your calcs show you’ve used the same value for initial and final moisture content so perhaps no surprise there is zero change in the timber. If you use 0.12 as the initial vale and 0.2 as the final value, the shrinkage is around 2.3mm.

The amount of shrinkage calculated is: 0.1063 inches or: 0 3/32 inches (rounded to nearest 1/32 inch) The information you entered was: 6 inches Initial Moisture Content: 0.12 (decimal percentage value) Final Moisture Content: 0.2 (decimal percentage value) The type of lumber you chose was: Flat Sawn The Shrinkage Percentage Value used for the species you chose (Sassafras) was: 6.2%

That said, I don’t know where the OP lives so I’ve no real idea how much change there’d be in moisture content so this is no better than a guess really.

Best regards,

Brian