Basswood In Service Stability


From original questioner:

The shrinkage values for basswood from green to oven dry are pretty large. The word seems to suggest that "in service" shrinkage is actually pretty good. However "pretty good" can mean lots of things.

Is there any data regarding emc swings from 7%-10% of basswood radial and tangential. This as a means to quantify shrinkage in that emc range for poplar & mahog...(the small amounts of Mahogany I have and use these days is referred to as South American Mahog..not sure of the genus, but its probably not Sweitana)

From contributor Da

The Shrinkulator has all those answers and much more.

Save it in your favorites - you'll be surprised how much it comes in handy.

From contributor Ji


Though the Shrinkulator is using the green to oven dry shrikage #'s.

My understanding is, though I could be wrong, that basswood's dry in-service #'s are less than the green to oven dry would suggest.

From contributor Da

Yes, those values are filled in once you select a species.

Then go below that and select "Wood Moisture Content" or "Relative Humidity". Then fill in the next boxes as best as you can and hit "Compute".

Try it for several different values to get a feel for both how it works and what the species you are inquiring about is like.

Your specific question is easily answered using the Shrinkulator - 7% to 10% EMC, radial and tangential....

From contributor Ch

I noticed you are a piano guy. I do not know what the expansion coefficient is for dried basswood, but this may help:
We use basswood for special 5-ply lumber core. We got into this making lids for grand pianos for a well known piano manufacturer which you probably know. At any rate, we use 1-1/4" strips, RF glued and sanded flat with a 1/20" poplar x-band followed by what ever face veneer is ordered. Then we CNC to shape. Our customer will acclimate the tops by putting then in alternating rooms with high and low humidity and finally bringing the M/C down to about 5-6% as I recall. The product comes out flat and stable, but there will always be some movement, but theses guys have been building pianos for over 100 years. They have told us after trying many cores (poplar etc) and a bunch of vendors, this is the only product that gives them what hey want. In the 12 or so years we have been doing this, we have very few rejects.

From contributor Ji

Yes, this is for piano work, but a very different application than your lid cores. This is 1/2" wide x 1/4" by 3-ish" long "key buttons". There is a shy 1/4" slot mortise run on these, and then the mortise is bushed with felt bushing cloth.

The bushed mortise fits a .146 key pin. The key pin/mortise/bushing interface has to have minimal clearance, only a few thousandths, in order to keep the key traveling true but with minimal friction.

The usual technique is to bush the mortise a tad sloppy to avoid moisture cycling caused binding or increased friction.

Basswood is/has been commonly used by some companies, as has maple, and some poplar. Basswood...I think more out of an economizing mindset...but maybe not.

I tend to use quartersawn mahog so I can tighten up the tolerances safely, just a tad. My question regarding the basswood was how much more movement the basswood would have relative to mahog, genuine or SA.

Was wondering exactly what the in service expansion rates would differ.

I looked at the shrikulator, but I find all those #'s somewhat questionable for already dried, small EMC gradient applications. As the shrinkulator says, dried values are 1/3 to 1/4 the calculated green to oven dry 3's calculated.

So in your work Charles, stand alone basswood, rather than glued up panels, does the stuff behave itself for picky dimensioning?

From contributor Ch

No clue on that. The only thing I can think of is maybe use a 3-ply lamination. I will be stronger and possibly more stable. Qtr mahogany sounds like the best choice, but I have no data on that. Try contacting the Forest Products Research Lab in Wisconsin (I think).

From contributor Wi

Have you looked at aspen. the numbers look very good.