Surgeons employ a technique which woodworkers would do well do borrow.

Immediately prior to starting an operation, all action stops and the entire surgical team participates in a “time out.” Everyone takes a fresh look  – a figurative step back – and makes sure all details have been attended to. This includes technical matters such as physiologic indices and medications, but also seemingly obvious things such as patient identity, the procedure to be performed, consent, laterality, and operation site.

In other words, there is a deliberate break in the workflow to ground the situation – to stop and create clarity. No removing the wrong kidney from the wrong person.

A woodworker with a stack of boards ready to mill, or a set of mortises or dovetails to cut, is in a similar situation, ready to move into the next phase of a project. At the outset of the procedure, you must make plainly clear to yourself:

• What you are trying to accomplish relative to the requirements of the project.
• The critical steps that will determine success, and the critical things to avoid.
• Are the basics all set?

If all of this seems just too obvious, let each of us recall his last forehead slap after a costly mistake performing a no-brainer procedure . . . let’s see . . .oh yea, that one . . . I’m done. OK, now we can talk.

Here’s an example. Imagine you are at the jointer and planer with a stack of boards. Stop. Time out. Name the task. Be more precise than just intending to dress the boards to 3/4″. Think, for example, that it is OK to be 1/64+” fat, but not OK to go under 3/4″, and minimizing tearout would save a lot of hand planing later. Since this is curly maple, the passes need to be thinner than usual. And oh yea, one piece needs to stop at 7/8″, so that one is marked and separated.

Is the machinery ready: jointer depth, guard in place, outfeed plan, and dust collection hooked up? Are all the boards oriented and properly marked as to face and end? Is this safe – what is my hand and pushing device procedure all the way through?

The point is that the while the content of the time-out thoughts or verbalizations are very simple, it is highly valuable to take a minute to do the time out. Most woodworking mistakes, and usually the biggest ones, happen because of a failure to heed what should have been apparent.

It takes just a quick time out to recognize that.

Happy woodworking.

Sanding blocks with a curved face can be very effective for smoothing and, with coarse grits in the right circumstances, even shaping curved surfaces in furniture making. I use spokeshaves, specialty planes, rasps, and scrapers to shape and smooth curved surfaces, but not to the exclusion of the humble sanding block.

They can be made quickly and easily with the bandsaw or bowsaw. For working concave surfaces, the curve of the block should be slightly steeper than the steepest part of the curve of the work piece. For convex work, a flat block is adequate for working shallow curves. For working steeper convex curves, the block’s curve should be slightly shallower than that of the work.

The top of the block should be shaped friendly to the hand using saws and rasps. I like to steeply cut down the corner of the block near the base of my right thumb, as well as the diagonally opposite corner.

The backing surface for the sandpaper should be have some type of firm cushioning, similar to a random orbit sander. For most broad surfaces, I like the high-friction cushion material available in with a pressure-sensitive adhesive backing from Lee Valley. PSA-backed 1/16″-thick sheet cork is firmer and thus good for narrower, smaller scale, or more detailed work.

Cutting regular sandpaper sheets and wrapping them around these sanding blocks is particularly annoying because of the curved surface. I much prefer using PSA-backed sandpaper that comes in large rolls, such as that available from Klingspor. It is quick, effective, and wastes less sandpaper, especially if the block is made to the width of the sandpaper roll. It is also reduces hand fatigue because there is no need to grip the paper to the block.

A gum rubber block is usually associated with cleaning retained sanding dust from the sandpaper on power sanders, but it also works quite well on these sanding blocks, especially when doing heavy work.

As with any sanding, it is important to remember that only the coarsest grit – the first one in the sequence – should do any required  shaping. (Though most or all of the shaping will have already been done with other tools.) All the subsequent grits simply remove the scratches made by the previous grit until the surface is smoothed to your satisfaction.

In time, one accumulates a small collection of these curved sanding blocks, so some will coincidentally be just right for future projects. This is simple, effective woodworking – one more tool for working with curves.

The American flag hangs at the top of my shop to remind me that creativity depends on freedom, which begets opportunity. And the best place for that is right here, supported by core American values. For this, I feel blessed.

May God bless America.

Happy woodworking.

Take a look at the end grain of this live-edge board. Without causing undue stress and tension, do you notice anything?

OK, enough goofy hints.

You probably notice that the board is from a tree with an off-center pith. The wider growth rings on the far right side, compared with the corresponding years on the left side, represent tension wood.

When a tree trunk leans due to environmental stresses such as gravity, snow, or light availability, it wants to redirect its growth upward and thus bows. To accomplish this, it forms aberrant wood known as reaction wood on one side of the tree, often recognized by its wider growth rings with the pith located off center.

In softwoods, the reaction wood, called compression wood, is usually on the underside of the bow, while in hardwoods it known as tension wood and is usually found on the upper side of the bow. The growth ring width asymmetry and consequent decentration of the pith can be dramatic in softwoods, but mild to absent in hardwoods. Reaction wood differs from normal wood in cellulose content and structure.

There are visual and behavioral clues to the presence of reaction wood.

It may be difficult to recognize in roughsawn boards at the lumberyard. Look for growth ring asymmetry in flatsawn boards. This is easy to notice in a live edge board but possibly not in a board with sawn edges. An unexplained lengthwise split or a pronounced crook (a curve in the width plane of the board)  may be caused by the abnormally high longitudinal shrinkage of reaction wood.

After the wood is in your shop, take note of behavioral clues such as persistent and unexplained distortion after milling. Another possible clue that most woodworkers have encountered is a stubbornly persistent fuzzy surface on an area of wood despite repeated attempts at smoothing it – you sand it and the fuzz never goes away. More confusing may be an unexpected excessively blotchy look that shows up after finish is applied.

This wood does not want to play nice; avoid it. I have read, however, of wooden bow makers taking advantage of the abnormally greater strength of tension wood.

There are exceptions, of course. This is wood – every tree, every board is an exception!

Being very cautious, I’ve monitored this walnut board with suspicion for a long time now, through partial milling and changes in moisture content. There are only some old shallow surface checks and a little distortion that has settled. I think it is safe to use in a project.

It pays to watch the wood.

4. Interpret the information and use it.

“Yes, I am asking you to fuss with wood.”

-James Krenov, from The Fine Art of Cabinetmaking

In this final installment on the topic of moisture meters, I will broaden the discussion to the management of wood that has been dried and brought into the shop, from wherever you have obtained it, because it still needs attention before it is ready to be used in a project. A moisture meter can help here.

When a new board comes into the shop, I write the date and moisture content (MC) on it. I refer to the back of the Lee Valley Wood Movement Reference Guide to know the equilibrium MC for the ambient relative humidity (RH) indicated on my shop hygrometer. (Temperature is a negligible factor for practical purposes.) The FPL Wood Handbook has the same information. I try to keep the RH within about 40 – 65%, winter to summer, with the use of a humidifier and dehumidifier, as needed.

Unless I am lucky, the wood has some adjusting to do. Therefore, I store it so air can circulate on all sides of each board by storing it horizontally on a rack and stickering it, or leaning it vertically against something. Sometimes I will do an initial light skim planing to get a peek past the rough surface, and to facilitate measurements with the pinless meter.

Then I keep an eye on the wood, checking the MC in a few days to see if it is moving. Depending on the initial MC, species, and thickness, I look for the MC to level off over the next few weeks. The wood is then ready for the first dressing.

Another approach is to look for when the MC of the new wood matches that of wood of the same species that has been in the shop for a long time. Beware, however, of the density issue with pinless meters that was discussed in the previous post. Also beware of the possibility of a moisture gradient through the thickness of the wood, especially in thick stock.

I usually use the pinless meter for this because it is faster and doesn’t make holes in the wood. However, if surface or density issues seem to be confusing, or if the stock is thick and I want to look for a moisture gradient, I will turn to the pin meter for additional information. If I could own only one? Pinless, probably. No holes.

Could this be done without a moisture meter? Sure. Patience and experience will work. Even quick monitoring with a straight edge on flatsawn boards will be informative. I like the convenience and greater reliability offered by the meters to help avert disappointments.

Unless it is very tame straight-grained wood and the final thickness is only slightly reduced from the initial state, I usually dress rough stock in two stages, even after it has reached uniform equilibrium MC. For example, to get a finished 5/8″ from a rough 4/4, I will first joint and thickness down to 3/4″, taking approximately equal thicknesses off each side of the board.

I watch the wood. Did the initial jointing stay flat and true? Did new a twist arise, or maybe a slight bow? These surprises can come about from internal tension releasing when some thickness is removed. Odd grain and case hardening are among the possible causes. These issues will usually manifest their effects quickly, sometimes immediately.

Then I take the wood down to final thickness, removing any slight distortions. If the distortions are large, or reappear, I usually find another board.

Resawing is another matter, discussed here, but requires knowledgeable observation and understanding casehardening to avoid disappointments.

Understand the wood. Watch the wood. A moisture meter can help.

3. Important factors that affect the readings

This is the third of four keys to making effective use of a moisture meter. Even properly taken readings are subject to factors inherent in the design of the meter.

Pin meters are affected by temperature. They will overestimate the moisture content (MC) in a hot environment (wood temperature), and underestimate it in the cold. This will probably only be significant in a cold lumberyard where the meter will read perhaps 1-3 points less than the actual MC. Consult the table that comes with the meter.

The species of wood also affects pin meters but, in the MC ranges we are typically measuring in the wood shop, there is little difference among most species, in the range of one or two points.

Measuring boards of one species in a consistent environment will cancel any significance of these two factors.

Surprisingly, wood density is an unimportant factor. Measuring with the grain, versus across it, is a slight, but generally insignificant factor. Of course, wet spots on the wood (such as melted snow) will greatly distort the readings.

In summary, for pin meters, there are not too many factors to be greatly concerned about. The main issue is to be aware of the depth into the thickness of the board at which the meter is measuring, and be aware of the possibility of a moisture gradient, especially in thick stock.

Remember too, the meter measures the wettest layer between the probes. This is usually the deepest point of penetration by the probes if the wood is still in the initial drying process, though not if it is rapidly gaining moisture.

And, of course, they make holes in your wood!

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Pinless meters are significantly affected by wood species, density, and, as addressed in the previous post, surface quality.

The “species” is really just a proxy for density, and this can be confusing. The tables or programmable functions that accompany the meter are necessarily based on average density values for a given species. However, because each tree is unique, the densities of different samples of a species can vary greatly.

The manufacturer supplies a formula to calculate your own correction factor, but it requires an accurate measurement of the specific gravity (density) of the sample of wood in question, which is usually rather impractical, especially when you do not already know how much of the measured weight is water.

Furthermore, when assessing newly acquired wood, referencing boards of same species on the racks in your shop, fully equilibrated, is not necessarily helpful since they may be quite different in density.

I recently bought some white ash which measured 13-15% MC with the Wagner pinless meter using the correction table. This seemed oddly high for wood that was kiln dried and stored indoors. I brought the wood to my shop, stickered it, and after a couple of weeks, the apparent MC decreased very little. After over two months, it was reading only 12%. Other ash that had been in my shop for a long time was reading about 9%, about what I would expect in the ambient humidity.

So, what’s going on? As I suspected, the recently acquired ash is just denser than the average value for ash used for the Wagner tables. How do I know? Well, two months ought to be plenty of time for the wood to equilibrate and it did not change much over that time. Furthermore, the pin meter, which is unaffected by wood density, verified that this wood was now about the same MC as the other wood in my shop, and there was no gradient through the thickness of a fresh crosscut.

Thus, we have two easy ways of dealing with the density issue affecting pinless meters: time and a pin meter.

Next: We’ll distill all of these technicalities into practical options for wood management.

2. Taking the readings

Whether a moisture meter or your blood pressure, if you don’t take the readings properly, they won’t mean much. So let’s take a look.

Pin meters:

The pins must be inserted and held in without backing off, which will create a small air gap, or cause the spring-loaded activation button to release. This can take considerable force, especially if using longer pins. Though longer pins are available, even big hammer-in probes for some meters, I almost always use the default pins on my miniLigno that penetrate about 1/8″.

The pins at the left in the photo penetrate about 1/4″, and even those are difficult to push into dense woods, and I find they tend to break.

One of the advantages of a pin meter is its ability to check precisely for a moisture gradient through the thickness of a board that has not reached uniform equilibrium moisture content. In the photo at the top, my pinless meter, which has a measuring depth of 1/2″, could evaluate just about the full thickness of the 1 1/8″ Claro walnut board. Remember however, those would be readings of the average moisture content in the measured volume of wood. By crosscutting the wood, then promptly comparing pin readings taken in the end grain near the surface and near the center of the board, a moisture gradient can be detected. The same can be done, sometimes with dramatic results, in a stick like the 16/4 Doug fir in the photo.

I have found little or no difference in pin readings taken along versus across the grain. Furthermore, there is usually little or no difference in the readings for most species whether the meter is set on “wood group” 2 or 3 on the miniLigno meter.

Pinless meters:

Readings are best taken on a smooth, flat wood surface with the length of the sensor aligned along the grain. In the photos of the cherry board, below, my Wagner L609 meter is reading 9% with the sensor along the grain of smooth wood, but 7% on the immediately adjacent rough surface. It read 11% with the sensor placed across the grain of the smooth, flat wood. These relationships are typical. Note also that if the wood surface is not flat in any case, the readings are likely to be relatively underestimated.

At the lumberyard, you probably won’t have the luxury of reading off a smooth surface, but at least you can make comparisons between similarly rough boards.

Pinless meter readings must be corrected for the density of the species. Some meters allow this to be programmed in before taking a set of readings, but with my meter I must hassle with having to add or subtract an amount based on tables in a little booklet that comes with the meter.

By the way, do not measure thin wood in the manner as shown below, unless you want to average it with the moisture content of your workbench!

Next: In part 3 of the series, we’ll look at important factors that affect the readings, especially for pinless meters.

Woodworking In America, the annual extravaganza hosted by Popular Woodworking magazine, will be held Friday through Sunday, October 18-20, 2013 in Cincinnati, Ohio (Covington, Kentucky, to be exact).

I’ll be there, and I’m stoked. Here’s why:

Most of all, I will meet many of my fellow woodworkers, including readers of this blog. Some I have communicated with for years and will finally meet in person.

I plan to do a lot of learning (and drooling) at the booths of the toolmakers in the Marketplace section of the conference. This will be a great chance to pick the brains of the small-scale, ultra quality toolmakers that I so greatly admire. I might even have a suggestion or two to offer.

The classes have first-rate presenters and useful topics. Among the many offerings, I have my eye on a carving class with Mary May, Sketch Up sessions with Bob Lang, the historical perspectives of Don Williams, and gleaning what I can from the brilliance of Silas Kopf.

As if all of that is not enough, I plan to take up saw maker extraordinaire Mark Harrell of Bad Axe Toolworks on his claim that he can transform any key on my keyring into a serviceable dovetail saw in five minutes with nothing more than a 5″ extra slim saw file.

Of course, Mark has said nothing of the sort, but I do know that WIA is going to be a great time, and I will gain knowledge and skills. I hope to see you there. Go to this link to register.