Without delving into the artistic issues, from a manufacturing standpoint it costs me a lot more to produce wide slabs as compared with standard lumber.
For starters, frequently each slab weighs several hundred pounds (the one in the photo below is over 1000 lbs). This means that you're not offbearing them with a person or two. Instead you have to shut down the mill and use a combination of muscle and heavy equipment to remove them one by one from the log. Then you have to sticker them (without crunching your fingers). Production rate when milling and stickering large slabs is very slow.
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Second, the production rate when sawing through a ultra wide log (48", give or take) is much slower than slicing up an 18" log into lumber. Sometimes it takes us 20-30 minutes or more to mill a single slab. Some of you may recognize this photo from the current issue of FWW Tools and Shops (photo used with permission of The Taunton Press). It took us almost 25 minutes per slab on this log, and another 10 -15 minutes to off-bear and stack it. In that same amount of time we can produce several hundred board feet of typical flat sawn 4/4 lumber with our hydraulic band mill.
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Third, big old trees are usually yard trees, and they almost always have metal in them. So your yield is lower and your costs are higher ($150 loss per destroyed chain in my instance).
Fourth is the drying costs. I just pulled several very large oak slabs out of the kiln that have been air drying in a shelter for over 4 years. Even then they required over a month in the kiln to finish off and sterilize. So maybe this year I'll see a partial return on investment for significant costs that I incurred back in 2015 to acquire, mill and transport slabs.
Fifth is the drying losses. Long, wide slabs are going to move as they dry, and there isn't a whole lot that you can do to prevent it. I've had slabs distort that had over 20,000 lbs of weight on them. So if you've got a 70" wide, long gnarly log that you want to net a 2" S2S kiln dried slab out of, you'd better be milling it around 4" green in order to have enough room to flatten it after drying and still net 2". So you're yield drops almost in half, and your costs are significantly greater. It takes us about half a day to S2S ultra large slabs.
Sixth is loading and transportation costs. The log in the photo below weighs almost 35,000 lbs. That requires very expensive cranes on each end for loading and unloading, not to mention setting up to mill.
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These factors don't apply as much to narrower slabs (less than 20"), or green slabs, but if you're buying well dried, very large slabs there are a lot of costs associated with milling, drying and surfacing them.
Originally Posted by John Makar
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