How do I calculate the planing allowance for my slab before milling?

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Asked By WoodWorker123 On

I have two sections of trunk from short-leaf southern yellow pine, and I've got access to a local sawmill. I'm working on creating the Anarchist's Workbench entirely out of solid wood instead of laminating thinner pieces. I want two flattened slabs for the benchtop, each measuring about 13cm (5 ¹⁄₈") thick. After checking the shrinkage figures from woodbin.com, I determined that I'll need to mill them to about 14.085cm (5 ³⁵⁄₆₄"). Chris Schwarz mentions in his workbench book that while laminated tops need little leveling, solid slab tops require more flattening because they can have uneven corners. I want to factor in the planing allowance for these slabs when milling them, considering they're currently semi-green but have been properly dried off the ground for a few months. The widest pith-avoiding sections I have are roughly 49cm (19 ¹⁄₄"), which might shrink to around 45cm (17 ³⁴"). One trunk is 170cm (67") long and the other is 193cm (76"). How should I go about calculating the right planing allowance to ensure the dried slabs can be leveled correctly? Thanks in advance for your advice, as I'm a bit of an ambitious rookie in this!

1 Answer

Answered By SawdustSam On

It really depends on the specific boards you have. In my experience, larger slabs don’t usually twist too much, especially if they don't show any signs of spiral grain in the bark. If your log has a noticeable twist, then milling it a bit thicker might be wise. I wouldn't stress too much if you're off by 1/4"; your bench will still perform great! As for drying, a common guideline is one year of air drying for each inch of thickness, so your idea to air dry and then kiln-dry sounds solid.

RookieRebel -

Great point on the twisting! Thanks for sharing your experience with these thicker slabs. I've heard the drying rule too, but some pros say it's just a myth. Still, I totally agree that starting with proper air drying is way better than just tossing wet wood into the kiln.

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