The Forestry Forum

General Forestry => Drying and Processing => Topic started by: John Mc on November 24, 2017, 03:17:31 PM

Title: Air Drying Red Oak slabs?
Post by: John Mc on November 24, 2017, 03:17:31 PM
I had some nice oaks blow down in a wind storm (tipped up the root ball on most of them). I'm interested in cutting some of them up into slabs 3+" thick. (A couple of friends looking for mantle pieces and some other projects).

I'm doing a bit of reading here, and downloading some articles mentioned in this forum on drying. The only logs I've sawed myself are hemlock (for a non-critical application). I've also air dried some White Oak that a friend milled for me (that all went into 4/4 boards). I'm hoping for a few tips on sawing this: is it better to avoid the pith for a mantle piece? (most of the timbers in my timber frame house include it, but that's a different species and a different application). Quartersawn, flatsawn, or ??

Title: Re: Air Drying Red Oak slabs?
Post by: scsmith42 on November 24, 2017, 05:03:50 PM
John, for thick slabs I would suggest that you flitch cut the logs and leave them live edge.  We always center the pith on both ends of the log and mill so that the juvenile wood is captured in the center slab.

We use 3" thickness for slabs less than 54" wide.   Between 54 and 72" width we incrementally increase thickness up to 4" green.  These are specs for slabs 14'- 16' long.  Shorter slabs such as 8 footers can be milled a tad thinner if desired.  We mill thick so that we can be able to S2S the slab after drying and still net 1-3/4" or greater.

3" is a bit thin for our local mantle market.  Seems as if most folks want 5" or thereabouts.

Your looking at 3-4 years air drying under cover for them to drop down to 15%MC or thereabouts.

Title: Re: Air Drying Red Oak slabs?
Post by: John Mc on November 24, 2017, 05:54:04 PM
Thanks for the info. I don't have the actual dimensions yet 3"+ was their top-of-the-head guess as to desired finish dimension.

How much extra do you think I should allow, once I have the final dimensions?

I know it will take quite some time to air dry. The friends already have a mantle that they will be replacing, so they are not in a rush.
Title: Re: Air Drying Red Oak slabs?
Post by: scsmith42 on November 24, 2017, 07:57:56 PM
It depends upon the width of the slabs, and the quality of the log. 

You will lose around 6% - 12% in thickness due to drying related shrinkage.  So figure 1/8" shrinkage per inch of thickness.  Next, the slabs will distort somewhat as they dry, with wide slabs distorting more than narrow ones.  For instance, if a 24" wide slab cups around 2%, you might have a 1/4" gap in the middle when you lay a straight edge over it.  The same slab in 48" will have a 1/2" gap.  So that's a full 1" loss in thickness when you S2S.

If I look to my left as I type this I will see the end of a 40" wide, 3.5" thick red oak slab that a customer brought us to finish off in the kiln and to S2S.  It's been air drying for three years in a stack of similar slabs, so it had a few thousand pounds of slabs stacked on top of it.

A straight edge reveals that we will need to remove 7/8" from one side to flatten it (and this slab was milled at 4" thick).  So to fully S2S it we will lose 1-3/4" in thickness from the 3.5" slab.  If we assume that it will be installed with the cupped side up, we can plane 1" from the top and just skip plane the bottom to net out 2-1/4" or so finished thickness (with the slab being thinner in the middle when viewed from the end).

Low grade logs with lots of branches, forks, etc, will distort more as they dry. 

For netting a 1-3/4" - 2" thick KD S2S slab, my rule of thumb is to mill at 2-1/2" green for a 20" wide slab, and to add 1/2" of thickness per additional 10" of width.  So a 30" wide slab is milled at at least 3" and a 40" wide slab milled green at 3-1/2".  If the log is pretty gnarly, I'll add another 1/2" or more.  If the customer wants to net more than 2", then I'll add that dimension as well to the green thickness.

I have a stack of 4' -  6' wide, 14' long red oak slabs up in the drying barn right now (see photo below).  Each one of these slabs weighed up to 2000 lbs green, and the entire stack is around 30,000 lbs.  Even with that amount of weight on the lower slabs, they have still distorted somewhat during the drying process to the point where there are gaps between the slabs and some of the stickers. 

It is impressive the amount of weight that a thick slab can lift when it distorts as it dries.