Working With Natural Defects in Wood, Part 2
This month we will finish up with our discussion of working with natural defects in wood. Last month we covered ideas for planning your project in the best manner to reduce the chances of finding/producing unwanted defects. Here we are going to discuss how to recover pieces that might otherwise be lost when a defect occurs in a partially finished project.
Dealing with checks and cracks -
For anyone who has turned green wood for any length of time, checks and cracks sometimes become a part of the process. Carefully monitoring a piece as it is drying will allow you to reduce these problems, but sometimes they are unavoidable. Most minor checks can be turned away when a piece is being trued up, but what can be done about larger cracks? Don't throw that cracked piece away! Instead try some ways to handle these big cracks - by adding material...or removing it. Let's look at both.
Adding material - When cracks become too large to remove, consider filling them. Simple wood filler can be used. A mixture of CA glue (super glue) and sawdust created from your turning can be mixed and placed in smaller cracks to effectively hide them. Epoxy resins can be mixed with a variety of colored dyes, metal powders and/or stone powders to create a wide variety of attractive effects in pieces which have developed large cracks. Don't be afraid to get creative either! Some turners will cut pieces of other materials, such as metal, leather, glass or plastic and use them as inserts/inlays to fill cracks.
Removing material - Sometimes, a simple adjustment to the shape of a roughed out turning may be all that is required to remove a check or crack. Other times, a crack is located in a place which inevitably means it cannot be removed. If filling the gap doesn't seem the best choice, consider doing some carving. Power carving (or hand carving) can be a difficult task to master, but hey...the piece might have been about to go into the fire pile already, so why not practice? A small rotary tool (such as a Dremel tool or Rotozip) with a carving burr installed can be used to carve the area out around a crack. A little bit of careful planning may be required to lay out a pattern that will remove your defect, but sometimes you can create a finished piece that will be even more stunning than the one you originally had planned.
Dealing with knots -
Typically, we try to remove all knots from most of the woods that we carry in our inventory. Some woods, however, will almost always contain knots (eastern red cedar, for example), or may contain hidden knots not visible on the outside surface. If you encounter an unwanted knot, consider either removing it or hiding it.
Removing knots - Initially, a drill may be used to bore through the knot to remove it. Consider using Forstner type bits, which typically will leave the cleanest hole while drilling. Once the knot is removed, it can be dealt with much like a check or crack, as described above. Additionally, if you have access to plug cutting bits, you can cut a plug from wood, plastic, or other materials, then fill the drilled hole with a small plug which can be turned down to match the shape of your project.
Hiding knots - If for any reason you don't feel comfortable removing a knot from your piece, consider hiding it. A small, simple pattern can be painted onto the wood surface to hide the knot, or a larger, more intricate one if you choose. Oil or acrylic artist's paints work very well in these situations, as they are relatively thick and do a good job of hiding the surface beneath.
Dealing with stained wood -
Some woods, such as oak and cherry, can develop dark stains while being worked in their green/undried state. The tannins contained in these woods reacts with iron in tools, or the metal of a chuck used on your lathe, staining the wood a dark blue or black color. Most of these stains do not penetrate deeply, but severe staining can occur if wood is improperly handled. To remove these stains, a treatment of oxalic acid is recommended. This acid comes in powder form at many hardware stores, and is mixed with water per the included instructions. Using a Q-tip, apply a light coat of the mixture to the stained area of the wood. After several minutes, wipe the surface with a cloth dampened in white vinegar to stop the acid's bleaching reaction. If necessary, repeat this process until the stain is removed. Also...remember that oxalic acid is strong stuff. Wear protective gear while handling this mixture.
Dealing with excessive warping -
Excessively warped wood can sometimes occur, and can make a roughed out shape so out of round that it can be impossible to true up without cutting through a side wall. Unfortunately, In most cases, there's not much that can be done for a piece like this cost effectively. If it was an inexpensive or free piece of wood, its best to use this as a learning experience for future endeavors. Perhaps the grain of the wood could have been lined up more properly when planning the piece, or the roughed out wall thickness should have been greater. For expensive pieces that may be worth salvaging, though, there is a product available called PEG (polyethylene glycol). Wood soaked in PEG will absorb the waxy chemical compound, and expel any water within the wood. After treatment, the wood usually will return more closely to its original shape...but there are no guarantees as to how individual woods will react. We have not worked directly with PEG ourselves, but have heard some success stories. Please only attempt using PEG after doing a little bit of research and speaking with persons who have used the compound prior to using it. This information is only meant to point you in the right direction, not to suggest that there is a definitive solution to this issue.
Just remember, wood is a natural product, and can behave quite unpredictably at times. Try not to get frustrated when things don't work out as planned! Any good wood crafter will tell you that the sign of a true expert is not the ability to never make a mistake, it is the ability of that person to cover up their mistakes so no one else ever knew that they were made.