when is it ok to plain?

[kenfrommaine]

Wondering how dry rough cut 1" pine boards have to be to plain them and not have to worry about shrinkage.  Is 12% dry enough? Thanks

[Ianab]

What's the end use, as in, how critical will a little movement be?

In my part of the world, equilibrium moisture is 12-14%, even inside. So that would be perfect MC for me. In most of the US you want interior wood more like 8%, so if you plane them now, there will be some small amount of shrinkage as the wood continues to dry.  But it wont be much, ss maybe 90% of it's movement has already occurred. 

If you are making T&G wall panelling for example, it's probably close enough. The method allows for a little movement (either way). A more critical use? Dunno. 

Also, if the wood is air dried (outside), that's about as dry as it's ever going to get. It would need a kiln or drying inside with climate control to get any drier.  

[Brad_bb]

Something that is used outside in non-conditioned space, 12% is fine. In winter it may shrink a little if very dry air.

But for something in a conditioned space, Have it kiln dried down from 12% down to 6-8%.  It can also go through a sterilization cycle too to kill any beetle larvae inside the wood.  Also, if it's paneling or flooring or whatever, let the boards acclimate in the house for a few weeks before installation. 

Forgive me if I don't get this 100% correct but others here on the forum can correct the details....There's something about kiln drying down to 6-8% that reduces the amount of free moisture the board can reabsorb.  Something about collapsing the cell walls.  

I build a bedside table from air dried (probably around 12%) Walnut.  The first season the width of the top shrank probably 1/4", and then the next summer re expanded 3/16", then next winter shrunk a little more than 1/8", then reexpanded in the summer, etc... After about 3 seasons the expansion and contraction stabilized to about 1/16" or slightly less from season to season.  What kiln drying does is get it stabilized like that in the kiln instead of 3-4 years.

Our ancestors built some fine furniture 100-200+ years ago, but they didn't have kilns, They built with air dried wood and built with movement in mind. I wonder if they stored wood for several years before using it to try to get the movement out of it?

[scsmith42]

The short answer to your question is that it is ok to plane lumber when it is at equilibrium moisture content (EMC) with the environment that it will be used in.

For interior furniture use, that's typically 6% - 8%.  For external use, 12% - 15%.

Pine has some rules all of it's own because unless your tooling is very sharp you can get tearout if the lumber is dried below 12%.

[GeneWengert-WoodDoc]

A lot of softwood lumber including boards are planed at 12% MC.  In fact, under 10% MC, chip out increases.

For hardwoods, this high MC will likely result in a lot of fuzzing.

Appreciate that if the wood will dry some more after planing, warping, especially twist and cup, can occur.