Milling Damaged Wood


Split Oak LogLife out in the woods is brutal, even for a tree. During its lifetime, a tree can sustain damage from fire, insects, lightning, drought, floods, freezing weather, wind and whatever else Mother Nature decides she wants to throw at it. Add man-made damage from careless logging, grazing and the consequences of recreational use (deer blinds, target practice and off-road vehicles) and it’s amazing there are any quality trees left to put on a portable sawmill. There are some milling techniques, which allow you to get quality lumber from damaged trees and, in some cases, produce lumber of greater value than if the log had been perfect to begin with.

Your first choice is whether you wish to cut around the damaged area to minimize its impact or, conversely, accentuate the damage and produce unique character wood sought after by some custom woodworkers. Either choice will present challenges that will test your skill as a sawyer. Let’s look at some options for different kinds of wood damage.

Cutting-a-Hollow-Oak-LogHollow logs are the most common. Most are just left in the woods to rot or are cut up for firewood. Any making it to the mill are generally rejected because of the amount of work it takes to get any usable wood out of them. This gives the custom sawyer a unique opportunity to obtain free logs, if he or she has the imagination and skill to use them. The cut-offs from hollow logs are often short, since the logger doesn’t want to leave more in the woods than necessary, so it may take some creative clamping to hold it down on your mill.

Depending on the amount of rot in the log, you may get some good lumber by using a technique called full-taper sawing. This involves simply leveling the top of the log to the mill so that as you mill, you cut around the hollow area. You can use shims or toe boards to lift the narrow end of the log and keep it level. Big production sawmills generally cannot afford to take the time to do this, but there may be walnut or other valuable lumber worth your while to mill.

A second technique for hollow logs is to quarter them and to mill each quarter using the quarter-sawing technique of turning the log after each cut to maintain as much vertical grain as possible. This can produce exceptional grain in oak and sycamore trees. However, the parallel grain pattern is attractive in any species and often in demand because quarter-sawn wood is more stable than standard flat sawn lumber.

Blue stain is the result of a fungus, which attacks pine trees. Beetles, which have bored their way into standing dead timber, allow the fungus a pathway in the trees. Sawn lumber, which has not been properly stickered or air-dried, is susceptible to fungus attacking the surface of the boards. Many sawmills reject blue-stained pine because of its appearance. Others label it as “denim pine” and charge more. You can certainly do the same. However, it is important to remember the fungal attack is actually an early stage of decay and if the wood is left too long it will lose much of its strength. It will still be all right for non-structural purposes, such as paneling and tabletops, but should not bear any significant weight. The use of blue stain pine is purely a matter of marketing the wood as having character instead of defects.

Boring insects, such as the Asian Pine Beetle or Emerald Ash Borer, not only introduce fungus, but also leave holes in the wood, ranging in size from pinholes to pencil-sized, depending on the type of beetle. These are especially common in salvaged dead trees, since the insects, sensing the tree’s weakened condition, often infest the tree, ultimately contributing to its demise. Most holes from boring insects are not evident in rough-sawn lumber and woodworkers generally take them in stride, using color wood filler to match the wood.

Most of the damage caused by an insect will be in the sapwood, so heavy edging to produce mostly heartwood will help minimize boring insect damage, but there may well be holes in the heartwood as well, from beetle attacks when the tree was younger and smaller.

Another very serious pest is the Powder Post Beetle, which can even infest wood while it is air-drying. If wood containing these insects is brought indoors, they may very well bore into wood in the house, as well. The best protection from the Powder Post Beetle is kiln drying, which requires heating the wood to at least 135° F.

Mulberry Log on a MillSplit logs can be the result of lightning strikes, frost cracks or damage from tree felling. If the tree has a straight grain, it’s pretty easy to mill the wood parallel to the crack. If you are careful, you can get all of the cracked wood in one or two boards, which you can edge to remove the damaged bits. Many species, such as sycamore, have spiral grains with cracks winding around the tree. If you have use for short boards or turning stock, you can salvage the log by simply cutting short pieces on your mobile sawmill. It is also possible to fill in cracks with epoxy or use bowtie connectors to hold boards together. Wood with spiral cracks is often a good candidate for firewood, since there is no way to cut full-length logs without including a crack in every board.

Ring shake is the term used for cracking along the growth rings of a tree and is also caused by a fungus. It may be possible to get some narrow boards from logs with ring shake, but avoid the common assumption that it only goes a little way up in the tree. It is not unusual to see the same ring shake in both ends of a 16’ log.

Storm damage can naturally put a lot of stress on logs. Stressed out logs can still be milled.  They may be split when they fall, with no sign of damage, until you start milling your lumber. The biggest issue is usually around the actual salvaging of blow-down trees. There can be a lot of residual stress, which causes a log or tree top to move in unexpected ways. The most dangerous part of salvaging blown-down trees is when cutting the log off the root ball. The remaining roots can pull the root ball back into the hole in the ground with amazing—and sometimes lethal speed. The effects of wood stress may happen with a 16’ log attached to your sawmill or ¾ of the way through the last cut, splitting and ruining the log in the process.

Safety is always a major issue, but especially so when working with damaged wood. Of course, you want to maximize the value of the lumber, but any log can be rolled off the mill, if it is not worthwhile to cut. With practice, planning and clever marketing, you may well find salvaging damaged logs provides a lucrative niche market for your portable sawmill. As the old saying goes, “One man’s trash, is another man’s treasure.”

Happy milling!

Milling a Mulberry Log


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