Question
What is the best way to dry rough sawn discs from a walnut log? I'm trying to make a clock face from a disc and it seems to split very easily.
Forum Responses
(Sawing and Drying Forum)
From contributor B:
The splitting is from the natural effects of drying. I have never run across any crosscut pieces of a log that did not eventually split. With most wood the end grain is not very pretty. Why don't you use the conventional grain orientation? If you are dead set on using this kind of cut then about the only sure way is to cut the "disc" into several wedge pieces, dry, fit back together and glue. The fitting back together will require the use of machine or hand woodworking tools.
Sap and heart wood dry differently and very quickly on thin cuts of wood. As soon as you get your piece home put it in a round container (may have to be a 50-gallon drum cut way down on the sides.) Thin cover the entire piece of wood with denatured alcohol (costs about $15.29 per gallon at the box stores). Let it sit in that for about 4-12 hours (the thicker the piece the longer - if soaked up to 12 hours it will not hurt it even if not needed that long.) The alcohol forces the water out of the piece and replaces it with alcohol.
Once the disc is removed drip-dry it on a screen for about 2-3 hours. Then cover one side of it completely with paper (such as from a brown grocery bag.) Let it sit for a couple of days with the paper down and the open side up. If you have the ability you could weigh the disc after the 2-3 hours of dripping. Then weigh it again every day. When it has stopped losing weight for a few days your wood is dried and you can then make your clock. This later procedure does not remedy the problem above. This is a woodturner’s trick for drying wood so that it does not split. There are other tricks woodturner’s use but this is the best and quickest in my opinion. The alcohol may be reused (strain it like paint). Replace the volume lost due to the process with fresh denatured alcohol.
Why does a disk want to crack? Consider a green, circular disk that is 24" in diameter. As this disk dries, the circumference will want to shrink about 8%. So, the original circumference of (24 x pi =) 75.4" wants to shrink 8% down to 69.4". Of course, this cannot happen unless the diameter is reduced to 22.1" (that is, 22.1 x pi = 69.4 circumference). But, the bad news is that the diameter will naturally shrink only about 4% during drying. (Technically speaking, the circumference shrinkage is called tangential shrinkage. The radius shrinkage is called radial shrinkage.) So, the radial shrinkage is not enough to prevent the development of some substantial stress.
To avoid stress development and cracking, we have several options:
A fairly large hole could be cut in the center to allow the radius to shrink more.
Several disks could be cut and then one used for repairing the others. See archives here for more info.
A salt paste could be applied to restrict shrinkage
For thin, porous wood, the disk can be dried in alcohol.
The porous wood can be treated with a chemical that restricts swelling; PEG (polyethylene glycol 300 to 1000) is one such chemical, but it is expensive.
1. On the back side you can make saw kerf cuts in an x pattern with the center of the tree in the center of the x. You do not have to cut the x kerfs to be revealed on the sides if you are careful on a tablesaw jig.
2. After soaking in PEG or Pentacryl allow to surface dry and use a thick epoxy finish to lock in the solution. I have not done this myself but have heard of sucess.
3. Allow to crack and simply put in a butterfly.
4. For the paper bag method on drying woodturnings, I highly recommend and prefer a plastic bag packed with the same woodchips from that exact green woodturning. Take the bag, fill it half way, place in the woodturning, and fill the rest of the bag carefully surrounding the woodturning. This allows less air around the turning itself, and the moisture is released more slowly thus not shocking the wood.
Back when I was just starting to turn wood I was working on a 16" diameter x 8" deep red oak bowl. I was using a friend’s one-way lathe with the large outboard, and I was very fortunate to know him. With only a few hours of time once a week I slowly turned the bowl over the course of a month, and the warpage was very minimal. The piece turned out to be a total success after a month of turning on 16" wide x 8" deep. This is an extreme that proved the method to me. If it was more of a tension wood like burls, crotch grain, or end grain slabs, working more quickly would greatly help.
I do have my doubts about #2, as locking water into the disk will not work well with epoxy. Eventually, if not when the coating is applied there will be an opening allowing a fungus to enter into the wood. I am not sure how a butterfly will close a gap that is wider than an inch in technique #3. Maybe I am missing something about this approach. Likewise, I do not understand how technique #1 is able to prevent the un-sawn surface from shrinking and cracking and the disk will still stay flat.
Common Lumber Name | A | B | C |
Hardwoods | |||
Alder, Red | 9.9 | 19.2 | 2506 |
Apple | 10.9 | 31.7 | 4132 |
Ash, Black | 9.3 | 23.4 | 4132 |
Ash, Green | 14.3 | 27.6 | 3590 |
Aspen, Bigtooth | 10.3 | 18.7 | 2439 |
Aspen, Quaking | 10.3 | 18.2 | 2373 |
Basswood | 6.2 | 16.6 | 2174 |
Beech, American | 8.9 | 29.1 | 3793 |
Birch, Paper | 8.8 | 25.0 | 3260 |
Birch, Sweet | 11.9 | 31.2 | 4065 |
Birch, Yellow | 9.2 | 28.6 | 3723 |
Buckeye | 8.9 | 17.2 | 2235 |
Butternut | 11.3 | 18.7 | 2440 |
Cherry | 13.8 | 24.4 | 3184 |
Chesnut, American | 11.6 | 20.8 | 2708 |
Cottonwood | 8.5 | 16.1 | 2102 |
Dogwood | 6.8 | 33.3 | 4331 |
Elm, American | 10.2 | 23.9 | 3116 |
Elm, Rock | 12.2 | 29.6 | 3860 |
Elm, slippery | 11.5 | 25.0 | 3251 |
Hackberry | 11.8 | 25.5 | 3319 |
Hickory, Bitternut (Pecan) | 14.7 | 31.2 | 4062 |
Hickory (True) | |||
Hickory, Mockernut | 9.1 | 33.3 | 4332 |
Hickory, Pignut | 9.3 | 34.3 | 4332 |
Hickory, Shagbark | 10.9 | 33.3 | 4333 |
Hickory, Shellbark | 6.6 | 32.2 | 4195 |
Holly, American | 8.3 | 26.0 | 3387 |
Hophornbeam, Eastern | 7.9 | 32.8 | 4266 |
Laurel, California | 15.1 | 26.5 | 3456 |
Locust, Black | 21.2 | 34.3 | 4470 |
Madrone, Pacific | 7.8 | 30.2 | 3925 |
Maple (Soft) | |||
Maple, Bigleaf | 12.8 | 22.9 | 2980 |
Maple, Red | 13.1 | 25.5 | 3318 |
Maple, Silver | 12.4 | 22.9 | 2981 |
Maple (Hard) | |||
Maple, Black | 12.3 | 27.0 | 3523 |
Maple, Sugar | 12.3 | 29.1 | 3793 |
Oak (Red) | |||
Oak, Black | 11.7 | 29.1 | 3792 |
Oak, California black | 16.4 | 26.5 | 3455 |
Oak, Laurel | 6.3 | 29.1 | 3791 |
Oak, Northern red | 13.6 | 29.1 | 3793 |
Oak, Pin | 13.0 | 30.2 | 3928 |
Oak, Scarlet | 13.2 | 31.2 | 4065 |
Oak, Southern red | 9.6 | 27.0 | 3520 |
Oak, Water | 10.4 | 29.1 | 3793 |
Oak, Willow | 6.4 | 29.1 | 3790 |
Oak (White) | |||
Oak, Bur | 15.4 | 30.2 | 3928 |
Oak, Chestnut | 10.1 | 29.6 | 3858 |
Oak, Live | 17.5 | 41.6 | 5417 |
Oak, Overcup | 10.7 | 29.6 | 3860 |
Oak, Post | 11.0 | 31.2 | 4063 |
Oak, Swamp chestnut | 10.7 | 31.2 | 4063 |
Oak, White | 10.8 | 31.2 | 4062 |
Persimmon | 7.0 | 33.3 | 4332 |
Sweetgum | 8.9 | 23.9 | 3115 |
Sycamore | 10.7 | 23.9 | 3115 |
Tanoak | 9.0 | 30.2 | 3926 |
Tupelo, Black | 10.4 | 23.9 | 3116 |
Tupelo, Water | 12.4 | 23.9 | 3115 |
Walnut | 13.4 | 26.5 | 3454 |
Willow, Black | 8.6 | 18.7 | 2438 |
Yellow-poplar | 10.6 | 20.8 | 2708 |
Common Lumber Name | A | B | C |
Softwoods | |||
Baldcypress | 13.2 | 21.9 | 2844 |
Cedar, Alaska | 14.4 | 21.9 | 2844 |
Cedar, Atlantic white | 10.9 | 16.1 | 2100 |
Cedar, eastern red | 16.4 | 22.9 | 2981 |
Cedar, Incense | 13.1 | 18.2 | 2371 |
Cedar, Northern white | 11.1 | 15.1 | 1964 |
Cedar, Port-Orford | 12.6 | 20.2 | 2641 |
Cedar, Western red | 12.2 | 16.1 | 2100 |
Douglas-fir, Coast type | 12.3 | 23.4 | 3049 |
Douglas-fir, Interior west | 13.2 | 23.9 | 3116 |
Douglas-fir, Interior north | 14.0 | 23.4 | 3048 |
Fir, Balsam | 9.9 | 17.2 | 2236 |
Fir, California red | 10.6 | 18.7 | 2437 |
Fir, Grand | 10.7 | 18.2 | 2371 |
Fir, Noble | 10.1 | 19.2 | 2507 |
Fir, Pacific silver | 10.4 | 20.8 | 2711 |
Fir, Subalpine | 10.5 | 16.1 | 2101 |
Fir, White | 12.2 | 19.2 | 2506 |
Hemlock, Eastern | 12.6 | 19.8 | 2573 |
Hemlock, Western | 11.5 | 21.8 | 2847 |
Larch, Western | 11.3 | 25.0 | 3251 |
Pine, Eastern white | 12.3 | 17.7 | 2303 |
Pine, Lodgepole | 11.5 | 19.8 | 2576 |
Pine, Ponderosa | 12.6 | 19.8 | 2573 |
Pine, Red | 12.2 | 21.3 | 2777 |
Southern yellow group | |||
Pine, Loblolly | 12.9 | 24.4 | 3183 |
Pine, Longleaf | 15.0 | 28.1 | 3658 |
Pine, Shortleaf | 12.9 | 24.4 | 3183 |
Pine, Sugar | 12.6 | 17.7 | 2302 |
Pine, Western white | 10.0 | 18.2 | 2370 |
Redwood, Old growth | 14.9 | 19.8 | 2573 |
Redwood, Second growth | 13.2 | 17.7 | 2302 |
Spruce, Black | 11.3 | 19.8 | 2575 |
Spruce, Engelmann | 10.0 | 17.2 | 2234 |
Spruce, Red | 10.6 | 19.2 | 2506 |
Spruce, Sitka | 10.8 | 19.2 | 2506 |
Tamarack | 12.0 | 25.5 | 3318 |