OK. I'm a pretty savy wood worker here. Entertaining the thought of a big slab live edge dining room table.
Once I find a log big enough to harvest my table from, I am wondering about the thing cupping as it dries.
Assuming I do all the right things about stickering, keep it level, & keeping it out of the rain & sun & wind, is cupping something that can be controlled by weighting or clamping the thing in it's current flat position, or will it just creep/spring to its untensioned shape once the clamps are released ?
Can cupping while drying be controlled & stay flat, or just let it go, and machine it flat, else it'll come back to haunt me?
What kind of wood? I have a Woodmizer and have cut and air dried slabs from a variety of trees. (I haven't made a natural edged slab table though.) I find some like walnut and eastern red cedar are easy to dry flat and stay flat. Others, like oak and persimmon and sometimes cherry - not so much if at all.
I assume you will try to cut through the widest part of the log to get a wide slab, avoiding the pith. This should help some since it will be nearly quartersawn. How far to get away from the pith is a good question which also may depend on the wood itself. I understand some people would cut through the pith, rip down the middle to remove the pith, then glue the halves together. If the grain is straight in the center the seam might be invisible.
That said, if I wanted to make a slab table I would consider slabbing it thicker than needed (anchor seal the ends), sticker and air dry to EMC, bring into a conditioned space for additional drying, then flatten before use. (Seal both sides equally, of course!) This even works for persimmon!
What's large? A 3" thick x 42" wide x 8' long? Yeah, that will cup. It will also crack, AND, it will take years to dry. Maybe a year air drying and then into a kiln, depending where you live. With some species, you could park a truck on it and it will still cup.
I know a local saw mill that has dozens of slabs ready to go. I bet you could buy one for $1000+/-. They are in Virginia. If you have any interest let me know and I will send you their name. I have no interest either way but keep thinking I might make such a table.
Here are a few things that you can do. First, if you can get your slabs a little ways out from the pith / juvenile wood where the rings are small arcs when viewed from the end-gran. Cupping is a caused by the 2-1 ratio between tangental and radial shrinkage around an arc. So, if you could rip right through the pith, the slabs on either side would be mostly QS and stay flat, until near the pith, where the arcs are about the size of a tennis ball, then there will be more of a kink than a cup. As you move on out, the cup will become less.
I believe the kiln experts can manage to get a flat set in the process, but I don't think it would be permanent air drying.
One thing I do with wide slabs is to incorporate some of the under-structure into the top, by routing a big T slot into the underside, which bridges between legs or apron parts. The wings of the T are waxed to allow seasonal movement, and support for a seam, which may or may not be a glueline. The slot doesn't go all the way to the edges, unless it was a single board, then the slot would only be open for assembly, then filled on the side where it slid in from.
If you started with a slab too thick to clamp and hold the cup out, you can kerf the underside with a series of kerf that allow the remainder to be thin enough that the T can hold it flat. Choosing a good strong tight grain T member is good, but even that can be improved by running long screws down from the top, about every 6" apart to resist splitting can help.
I've never had this fail, and it WILL keep it flat as it was when constructed.
Odds are that a slab will always twist and/or cup in the drying, so plan on cutting heavy and flattening after it's dry. Also, watch out for internal stresses that can blow it apart if it's cut into. I've been there with a slab of maple.
Johnson's Lumber in Charlotte has a bunch of native and exotic wood slabs. They look to be kiln-dried and are of a wide range of sizes. They are about 2 hours from you since M-5 is closed. Their prices seem more reasonable than those I see online.
Yea, not sure if I'll be going down this path or not, but was just wondering if cupping was something that could be prevented with some degree of clamping during drying.
Plank size? Go big or go home. It'd be a dining room table for sure.
