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Large Scale Drying12/13
We have a need for large square molding blanks, 17/4 or thereabouts later to be milled to 4" square S4S. We believe we can find sawyers who will cut this for us - presumably out of soft maple - and we propose to purchase a small DH kiln. But we are wondering about drying schedules for these humongous pieces. We need, as much as possible, to avoid splits and checking.
The wood will shrink about 1/4" in drying. Then add for twist, cup, bow and crook, especially if the squares are much over 12" long. Splits and cracks can be controlled about 99%. As a sawyer, I would have an issue if you want the squares to be all white wood...my yield will be poor unless I have large logs and then you will have warp issues. You really need to have a test run to study performance and costs.
We are not very concerned about color. Doesn't have to be white. We are already able to buy this material from a couple of sources - at a hefty price. But around here there is a great deal of available soft maple left from many years ago housing development and we know a couple of outfits with small mills. After we dry the material, it will be sent out to our primary millwork. If we can avoid the cracks, I believe that they can mold it into 16/4 squares without too much difficulty.
So I'm thinking from what you say that we'd want to be thinking about 18/4 wet to start. How about schedules? Are there peculiarities about drying such huge pieces - aside from the typical temperature and humidity checks? I'm thinking a small Nyle dehumidifier and a relatively small box.
I can't think of anyone drying large Soft Maple squares but we have several customers drying Oak that size. And dozens drying Pine. But if you are buying it from several suppliers now and you are happy with what you get, then it must be doable. Are any of your suppliers using Vacuum? If they are and you are not using vacuum, doing some testing makes sense. Ask someone near you that has a dehumidification or conventional kiln to dry some and take a look. If there is defect, figure out why and how to saw to prevent it
Thanks. We hadn't thought of vacuum drying but that would be interesting. Rather than speeding it up, we have been thinking "slow it down" thinking that an annealing stage might relieve stresses. I built a classic solar kiln about 15 years back and it worked extremely well with 8/4 Soft Maple.
There are obviously numerous outfits drying 12/4 Oak and Ash for baseball bats and some drying other woods for large table legs, though many of the latter are laminated up. The problem with Oak is the roughness and pores, We need something fine grained, heavier than Basswood, and easy to dry. Pine would be good except our market just doesn't like the word, "pine." Poplar might work except a lot of the color of off-putting.
As I said earlier, forty or fifty years ago, local builders used a great deal of Silver maple for plantings around housing and construction projects and these mature trees are the bread and butter for tree cutters around here so there are lots of free logs.
Defecting is not a problem as we are mostly making short lengths; long splits or checking on the other hand are a distinct problem. Nothing for it but to give it a try, I guess.
Your main source of material is going to be yard trees? Good luck with that, you're likely to see a lot of metal! Around here you get a really short straight log too. 17/4 is a lot different animal to dry than 8/4. Look for a custom vacuum kiln service. A lot less degrade than other kilns. If you trash a couple loads of timber while you learn how to dry the blanks, a custom service charge doesn't seem that bad.
Yard trees are known to have excessive stress, called growth stress, that will result in warp during drying, even vacuum. The majority of the pieces will bow, crook and twist. As you get near the center of the log, warp will increase, due to natural shrinkage differences around the center of the log. The risk of a major crack also increases when the piece includes the pith. Pith pieces need the pith centered.
Air drying prior to kiln drying will reduce warp. For well air dried stock, kiln drying times will be over three weeks. Getting the moisture fairly uniform, she'll to core will be a challenge.
Again, I encourage you to cut a thousand pieces as a test run so you can see what will happen as far as warp, drying times, and so on. You can also determine if there are any special quality issues from the ultimate customer. My experience says that this has a number of critical areas that could cause failure.
Thanks for the advice. We'll see. As for the cutting and sawing, nails and whatnot - not our problem. I may even be wrong about why there's so much SilMap here. Anybody with a gutter can explain the proliferation. But we do know sawyers with logs and we know a couple of tree trimmers that sell them to the former - I just may be off base about the logistics here. Unfortunately, the one outfit with a real, commercial kiln around this area apparently went out of business.
But the notion of air drying first is great - that we can do. We only need about 1000 ln. ft. a year for the 4", so I think we'll just buy the little Nyle and take it from there.
I know a guy that does large, well massive actually, slabs of 3" thick stuff and he is successful by doing a few things. He stickers 1.5" for more airflow. If he stickers narrower, he gets mold. He air dries a minimum of 2 years, but likes 3. He ratchet straps every stack every 18" (he has a router groove in every sticker he uses (just ran all his stickers that way). He keeps his ratchets accessible and in the same area in each stack and actually has a record of when the piles are ratcheted and he reratchets on a schedule. I can't tell you the schedule, but it is more rapid early. And he coats every slab face and ends with a magical clear concoction, someone here probably knows a recipe (something similar to endsealer that slows down the MC loss, but doesn't stop it). And he tried weight on the pile, but the logs would lift any amount of weight. They don't seem to lift their own weight. He also piles the stack in exactly the order cut, but that is done for bookmatching. I don't know how that would affect drying and warping if you got away from that, but by preserving the log in its precut form, any delineation in the sawing is maintained in the stack and not a variable in drying. And any warping stresses seem to be manageable together better than all over which is counter intuitive, but works for him. As Mr. Wengert says, the shrinkage will be great, so you'll need to ratchet the stacks if you want your plan to work. As a word of caution, if you get the wrong ratchet straps they will rust quickly, so he even has a preferred strap(might be aluminum or something with rustproofing). And the stacks must be perfectly level to start. His stacks are all well protected from rain as each slab is worth several hundred or thousand dollars even.
I should add that the selection of the trees used and the sawing is not done blindly. The trees are selected by him and sawn by him. He saws every log to the best pith center possible and he readily rejects any tree with too much lean or any questionable problem. If you just lay a log on the saw and don't even raise the narrower end for even pith, you will have trouble succeeding. And of course if you do this, the outside parts of the slabs end up unused for flat drying...
Thanks, Fallguy. However, I can tell you for sure that up to 12/4 the lumber is relatively available as squares. There's a big industry of baseball bat manufacture around here in Hard maple and Ash and though I don't know too much about the details they are getting lathe billets from somewhere. These are rounded to 2-3/4. I buy a good deal of material from some of these bat makers and I assume that they must start with 12/4. or thereabouts.