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• Friday, June 30th, 2017

sensing wood moisture content

Can you really sense, with any practical utility, the moisture content of wood simply by touching it? Yes. Let’s take a look.

An object feels hot or cool to the touch of your hand because of the flow of heat between your hand and the object. For example, an object feels relatively cool because it is drawing heat from your hand.

Remember how mom or dad could tell if you had even a bit of a fever just by touching your forehead?

Consider wood. The heat flow depends on several factors. The variable that we want to isolate is the moisture content (MC) of the wood. Wetter wood will draw heat from your hand faster and thus feel slightly cooler.

We want to keep these other factors constant:

  • The wood species – density is the key. Denser wood will transfer heat faster.
  • Surface texture. The greater contact of a smooth surface will transfer heat faster than a roughsawn surface. To a lesser extent, a diffuse porous wood such as cherry transfers heat faster than a ring porous wood such as oak.
  • The temperature of the wood, especially relative to your skin temperature, of course, affects heat flow. Heat energy flows from the warmer object, usually your hand, to the cooler object, usually the wood.
  • The surrounding temperature and moisture conditions will likely affect your perception of hot and cool.

Those four other factors are constant in the typical situation of sorting through boards at the lumber dealer – a particular species, roughsawn, at the temperature and surrounding conditions on that day.

So, can you sense differences in MC based on how cool or warm the wood feels to the touch of your hand? I think I can. No, I cannot tell the difference between 8% and 10%, but with the aid of a pinless moisture meter, I have shown myself that I can tell the difference between, say, 8% and 14%, and even closer than that. Every time? No, but reliably enough that I can use my sense of touch to quickly sort through boards of one species at the lumber dealer and help me make choices. Larger differences are more apparent. This also can alert me to certain situations, such as a poorly stored 10/4 board that is much wetter on one side than the other.

The differences I am sensing are relative, not absolute, but that is what I am concerned with as I sort through the piles. It is even possible to “calibrate” my hand for absolute measurements for a particular pile of wood by taking a couple of readings with a pinless moisture meter, and correlating that with what I feel, but I wouldn’t rely on that and it is not what I need.

I am not suggesting you discard your moisture meter. I also understand that the “measurement” is shallow. And I’m not going to put my lips on the wood; that’s weird. Yet, with some awareness and very little practice, you can get a pretty good sense of the relative moisture content of boards just with your hands.

What’s your sense of this?

Category: Wood  | 4 Comments
Author:
• Thursday, June 29th, 2017

router mortise jig

Now let’s work through the elements of the jig. The top photo again shows an overall view with a leg blank in place.

Basic construction:

The jig is built on a piece of plywood about 5″ wide and 39″ long. Screwed down along one edge is a double-width T track with the groove placed up at the outer edge. The wide T-track allows the sliding stops to be far enough away from the leg blank to make room for the router fence. (See previous post.)

Workpiece registration:

The side of the leg blank registers against the track, and the end registers against the moveable tab stop that you can see sticking out sideways from the track in the photo below. (It is dark wood – wenge – with a brass knob.)

router mortise jig

Clamping the workpiece:

Two toggle clamps are mounted on 1 7/8″ square x 5″ moveable blocks, which are secured in the track with T bolts. These clamps provide lots of holding power and can be positioned away from the routing action.

For use in addition to, or instead of, the toggle clamps, there is a wedge system, seen in the photo below. This consists of three 5/8″ square x 1″ blocks, distributed along the length of the plywood, that are bolted to the plywood but free to rotate. Wedges, 5/8″-thick x 8″-long with a 1:7 slope, secure the workpiece.

router mortise jig

Stops for limiting the length of the mortise/haunch:

These are 3/4″ x 2 1/2″ x 2 1/2″ blocks that position in the T track and lock down with T bolts and star knobs. You can see them at the sides of the photo below.

router mortise jig

At the right of the photo below, the router fence jig meets the stop to define the bottom of the mortise.

router mortise jig

At the left of the photo below, the router plate jig meets the stop to define the bottom of the haunch (the limit of the full-depth mortise).

router mortise jig

In the photo below, the left-side stop has been moved out of the way create the haunch all the way to the end of the leg. In practice, you would rout this first. Then you would move the left-side stop into place to define the top of the full-depth mortise, as seen just above. That location is “remembered” by the little maple stop with the brass knob.

router mortise jig

In summary:

  • Understood in its separate elements, the jig is not difficult to make.
  • In practice, the whole thing is very intuitive to set up from mortises marked out in the traditional manner on one leg only.
  • The mortising work moves along quickly.
  • The jig can handle most common leg blank sizes that you will use to prepare the joinery before cutting the shape of the leg.
  • It can also be used with rail and stile work but workpieces thinner than about 1 1/4″ will need to be paired with thicker wood to better support the router. The jig was designed mainly for mortising table legs.

[Skip this paragraph if you want; it will be apparent when you work with the jig. Depending on the circumstances and personal preferences, you can rout four corresponding mortises with the leg registered at one end of the jig, retain the router fence setting, and then reset the mortise jig to register the legs at the opposite end of the jig to make the other four mortises. Alternatively, you can retain the mortise jig settings and reset the router fence.]

Author:
• Thursday, June 29th, 2017

router mortise jig

Here is a very direct approach to mortising with a router that works especially well for mortising legs.

The system starts with an auxiliary router base plate that rests on top of the squared leg blank and has two adjustable fences that hug the sides of the blank to eliminate side play. I have been using the one shown here, made from acrylic, since I bought it from Woodhaven more than 25 years ago.

router mortise jig

Though it is no longer available from Woodhaven, it does not seem difficult to make a similar version from plywood, perhaps lining the fences with adhesive UHMW plastic. The base is about 10″ wide and 8″ deep. Each fence is an L-shaped construction. The long arm of the L has two slots, in which slide bolts that pierce the base and are tightened to fix the fence position. The short (1″) arm of the L rides along the side of the leg blank.

It probably would be good enough to substitute the L fence with just a flat piece of plywood, though the height of the fence is added insurance against tipping. Alternatively, you could slot the base and use simple hardwood strips for the fences. I trimmed the fences to ensure that no part of them extends beyond the base plate, so it is only the base plate that will meet the stops that define the mortise length, as you will see later.

The idea is nothing more than a double-sided router fence.

router mortise jig

So, that’s simple enough. Now we need two more elements. First, is a way to reliably register the workpiece in place, and then clamp it there. Second, we need stops to define the ends of the mortise (and a haunch, if required). To make the jig adjustable for different layouts, these stops must adjust independently from the workpiece-registration element and clamps.

Below is an overall view. It is really simpler than it might look at first. Trust me, I hate complicated jigs – I’ll break down this one for you in upcoming posts.

router mortise jig

By the way, the plunge router is an Elu 3338, vintage about 1990 and still mortising strong. It is very similar to the current DeWalt DW625, though the Elu was made in Switzerland.

Author:
• Saturday, June 24th, 2017

edge joint failure

Many of us woodworkers have a habit of casting our judgmental eyes on woodwork we encounter anywhere, at anytime. Imagine if we were hair stylists. Recently, I noticed the condition of the tables in a certain non-chain pizza shop, which happens to serve the best pizza I have ever tasted. Great pizza joint, bad edge joints.

Only a year old, the joint in the tables are failing. Because we do not want this to happen in our work, we ought to ask why. It is not enough to point out that the exposed end grain produces more and faster moisture content cycling at the ends of the tabletop than toward the middle, which produces greater stress at the ends during the dry months.

bad edge joint

The situation requires more explanation. If the joint lines were truly as strong as the wood itself, the failures would not occur almost exclusively at the joint lines. Those joints are, in fact, weak spots – they were not made well. Furthermore, even if they were intact, they do not look good.

There are many reasons to consider. Because I do not want this to happen to your work, or mine, I direct your attention to a series of three full-length articles I have written for Furniture and Cabinetmaking magazine. They really constitute a book chapter on the subject, and I think you will find they cover the topic thoroughly. The first is in the current issue, July 2017 (issue #259). The second and third will be in F&C August (#260), available any day now, and October (#262).

Much of it is from the series on this blog but I have refined everything and added more useful material, along with all new photos. I think you will find the photos supporting the explanation of the all-important matter of wood selection to be particularly useful.

If you are not familiar with Furniture and Cabinetmaking magazine, I suggest give it a look. Produced in the UK, it is full of high quality content, beautifully presented. A single copy off the newsstand here in the US is pricey but the digital version is a good value at $36.99 for one year of 13 issues from PocketMags. You can also get small bundles of any selection of back issues.

And then put aside any fear that anything you make will end up like those tables in the pizza joint.

Category: Techniques  | Leave a Comment
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• Wednesday, May 31st, 2017

Tormek SE-77

For those not familiar with the Tormek grinder, the SE-77 jig, an upgrade over the older SVH-60, holds the blade and slides onto the guide bar, where it rotates to present the blade edge to the grindstone in a very consistent manner. The niftiest features of the SE-77 are its ability to reliably put a controlled amount of camber on a plane blade, and to microadjust the lateral angle of the blade edge to the stone.

The SE-77 has a sturdy build. The left clamp screw slides to adjust the width between the two clamp screws. This more securely holds a wide range of blade widths. There is an end stop on the right side that squarely registers the right side of the blade into the jig, which is useful for blades with parallel sides.

The pair of small thumbscrews, shown in the foreground of the photo below, controls the two special functions of the jig.

Tormek SE-77

To microadjust the lateral angle of the blade edge against the stone, you back off one of the screws and advance the other the same amount. This is much more reliable than shifting and reclamping the blade in the jig.

To camber the blade edge, you loosen both microadjust screws. This creates a pendulum motion about the small stem. (See the photo: the small stem has a brass washer and external snap ring on its end.) With this pendulum motion, you can guide a controlled amount of camber onto the blade edge. The system works very well, though you do have to blend a gradual arc. A too-heavy touch can create a shallow V-point edge instead of a nice smooth camber.

Another welcome feature of the SE-77 is the design of the lower jaw of the blade clamp, which gives a good grip on Japanese chisels (hallelujah!), even onto the shank.

At $66, the SE-77 is not cheap. Having used the Tormek for a many years for grinding – very little on the leather honing wheel – this new jig has been a worthwhile upgrade.

Dear readers, I hope this series on blade camber has been helpful. As always, what I write is born of “the sawdust and shavings of my shop.” These are the techniques and approaches that work for me as I make things. I welcome your ideas and comments.

Rob

Category: Techniques | Tags:  | 4 Comments
Author:
• Wednesday, May 31st, 2017

skewing effect

Creating the camber

There doesn’t have to be high art in producing the camber. On a coarse diamond stone, I start by leaning the blade to the left and slightly raising the right side. It is important not to overdo this. I then gradually reduce the lean, keeping aware of the approximate number of strokes, and blend the camber through the middle. Then I repeat this on the opposite side.

On the Tormek grinder with the older SVH-60 blade holder, I would lean on the slightly flexible guide bar to create some camber. The newer SE-77, which I will cover in the next post, is more controlled. The camber can be refined on a medium stone. Mild camber, such as in a high-angle, bevel-down smoother, can also be refined when honing the secondary bevel.

It is easy to underestimate the amount of camber by just looking at it without a straightedge reference, so I check the camber by holding a small, wide aluminum square (straightedge) against the edge and observe it against mild backlighting. Eventually, one can reliably relate the appearance to the performance on wood. Again, I do not measure it, nor recommend that as a habit.

cambered plane iron

If you overdo the camber, the nose of the blade will dull first, so when you go back to the stones to clean up the secondary bevel, some of the camber will automatically be reduced.

Skewing the plane

Skewing the plane at a typical angle used routinely has no significant effect on the camber function. However, an extreme skew angle, such as the 45° shown in the top photo, or even 60°, can occasionally be used to advantage to get the plane to pull a shaving from an isolated area, such as to correct a bit of tearout.

This is really just playing with how the plane sole bears on the surface contour of the board. The full camber depth is retained but is effectively spread over a shorter length of blade. (The plane stroke is still about parallel to the length of the board.) With some trial and error, you may be able to get the blade to “reach down” into a localized area.

Camber the chipbreaker too?

Very small differences, on the order of .1mm/.004″, in the setback of the chipbreaker may affect planing performance, at least according to this Japanese experiment. Should the chipbreaker therefore have a camber that matches the blade to create a consistent setback? With a straight-edged chipbreaker on a cambered blade, is there a difference in the shaving characteristic or wood surface across the width of the blade that cannot be explained by the difference in shaving thickness?

In theory, maybe so, but I have only rarely encountered advice to camber the chipbreaker. It also seems like too much trouble, so I don’t do it. Maybe it would help for a highly tuned smoothing plane. Any ideas, readers?

chip breaker setting

Next: the Tormek SE-77 jig

Category: Techniques | Tags:  | 2 Comments
Author:
• Wednesday, May 31st, 2017

plane iron camber

To master handplanes, a woodworker must master the matter of blade camber. To introduce the bevel-up/bevel-down/frog angle issue, please refer to my 2009 post. Here I want to present a more intuitive approach to guide you at the sharpening bench.

The issue

When checking the blade after grinding, you naturally hold it up and observe the camber, sighting at 90° to the face of the blade, like this. But when the blade sits on the frog at an angle, the effective amount of camber is reduced. Think of it this way: if the cambered blade were laid flat, there would be effectively no camber at all.

So, you have to create what looks like more camber than you need, and just how much more depends on the bed angle.

Please note that I am not suggesting that you take out a leaf gauge and measure the camber! I took measurements for these posts and other writing but that is not my method in the shop. I suggest use the guidelines set out in part one of this series, work intuitively, using a bit of trial and error, and get a sense of how the camber that you see performs on the wood.

As an example, in the photo at the top, with the blades standing vertically, the blade on the left shows about .004″ camber, and the one on the right about .14″. In the photo below, the blade on the left is set at 45° and the blade on the right is set at 12°. This results in an effective camber of about .003″ for both of them.

plane iron camber

So, to get the same effective camber, we had to grind an additional approximately 1/3 more (observed) camber for the blade bedded at 45°, but for the blade bedded at 12°, we had to grind almost five times more (observed) camber.

Here is a handy table to help absorb a general sense of the differences.

Bed angle       Grind this multiple more camber than what the plane needs

12°                 4.81 [whoa, must grind lots more to get what you want]

20°                 2.92

22°                 2.66

45°                 1.41 [grind just a little more than what you want]

50°                 1.31

55°                 1.22

60°                 1.15 [what you see is just about what you get]

And another thing

Camber is somewhat of a nuisance to grind into the blade edge. It slows down grinding and, especially, honing. Unfortunately, and, I contend, for little or no good reason, almost all bevel-up planes made today have a 12° bed. That requires you grind a lot more camber than in a bevel-down plane. If the bevel-up plane had a 22° bed, this problem would be greatly reduced.

This is yet another reason why I continue to advocate that bevel-up planes should be made at about 22°. I explored the matter several years ago in this post and elsewhere.

Skip this part if you want

For those who like this sort of thing (as I do), here is the derivation of the chart above. The key point is that it is a non-linear function because of the sine curve. So, there is a big difference between 12° and 22°, and much less difference between 50° and 60°.

Please refer to the diagram in the 2009 post, which shows how the camber that you observe when your line of sight is 90° to the face of the plane blade is reduced by the sine of the bed angle when the blade is placed in the plane.

f = functional camber with blade in plane

c = observed camber normal to blade

A = bed angle of blade

 

f = c · sin A

c = f/sin A

 

c/f = (f/sin A)/f

= 1/sin A

=sin-1 A

The ratio c/f means how many times greater must the observed camber be to produce a given functional camber. c/f is just the inverse of the sine of the bed angle.

Author:
• Sunday, April 30th, 2017

plane iron camber

Revisiting this matter, there need be no confusion as long as you keep in mind that the amount of camber that belongs in a plane blade is a function of how the plane will be used, and particularly, the kind of shavings the plane will take. Without getting hung up on numerical absolutes, here are three reliable guidelines that I use, which I hope readers will find helpful.

I wrote about camber in 2009 but I think some of it bears restating, and there are a few things I would like to add.

For a smoothing plane blade: Make a very small camber to allow the plane to produce very thin shavings, perhaps .001″, that are thickest in the middle and feather out to nothing at barely less than the full width of the blade. This produces only imperceptible scallops on the wood surface. The finer the shavings you intend to take, the shallower the camber should be.

For a jack plane blade: Use more camber to take thicker shavings without producing stepped-edge “gutters.” Vary the camber according to how aggressively you want to remove wood with the plane. The camber also makes it easier to direct the cut to take down the high spots on the surface of the board.

For a jointer plane blade: Make a very small camber to make the plane capable of correcting an out-of-square edge by laterally shifting the plane without tilting it. Position the deeper part of the camber over the high side of the edge to bring it down, and thus incrementally work toward a square edge. The camber also creates a miniscule concavity across the width of the edge of the board, which ensures there is never any convexity there, which would produce an inferior joint.

So, there’s the essentials. Coming up, I’ll revisit the bevel-down/bevel-up issue (that I brought up in 2009) in a quantifiable but intuitive way, look at the effects of skewing the plane, present a thought on chipbreakers, and maybe another thing or two that popped into my head while I was in the shop but forgot to mention so far. Then, we’ll take a look at the Tormek SE-77 jig, which I’m liking a lot.

Category: Techniques | Tags:  | 4 Comments
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• Sunday, April 30th, 2017

woodworking hardware

When installing hardware, it is important to have precise control of the location of the pilot holes for the screws. The options are to start with a mark made by a scribing point or awl, then use that to locate the drill bit, or drill the hole directly without a preceding mark. Here is my approach.

I mark first, and most of the time, I try to center the mark in the countersunk hole of the hardware. Sometimes, however, I will intentionally very slightly decenter the mark to laterally “pull” the hardware tightly into the mortise, or to one side of a mortise that was made a bit too large. In any case, I do not want a mark that will result in the screw pulling the hardware in the wrong direction.

The key is that you want that control. It’s that one-sided tolerance thing again. I love that concept.

Here is my low-tech, reliable method.

I use a scriber point or pyramidal awl to prick a starting mark for the drill bit. It is surprisingly easy and accurate to judge just by eye if the mark is centered in the hole in the hardware. Good lighting is essential, as in the first photo below. A crescentic shadow on the side of the hole will cause you to misjudge the center of it.

locating hardware screws

The mark in the photo below is actually centered but the shadow interferes with judging it.

Sometimes I use a fine point scribe (the two tools to the left in the photo below) to make a tiny mark to seat the point of a brad point bit. Other times I use my wonderful Czeck Edge awl (at right in photo) to start and enlarge a hole suitable to seat a twist bit. Twist bits are commonly available in more sizes than brad point bits, which is particularly helpful for using tapped holes and machine screws to mount hardware in wood.

marking awls

This simple approach makes it easy to reliably make a deliberately off-centered mark. Just as important, it is also easy to move a mark made with a scriber or awl. Just stab the sharp point into the sidewall of the original mark and push or swish the tool to make a slightly bigger mark with a new center location.

woodworking awls

How about self-centering bits (one brand is Vix bits)? In all the brands I have tried, there is always a bit of wobble of the drill bit within its housing. Even though I would drill squarely to the work surface, there is some random error in the location of the hole. The errantly drilled hole is then nearly impossible to “move.” Furthermore, there is no reliably controlled way to produce a deliberately off centered pilot hole. Depth control is also difficult or the depth is inadequate. Such bits have been banished from my shop for some time.

How about center punches – those that you tap and those that are spring-loaded in various ways? They avoid some of the disadvantages of self-centering drill bits, but all of the ones I have tried, even Starrett’s, also have some wobble of the scriber within its housing. They are faster than the low-tech approach I use but less consistent and, again, there is no good way to make deliberately off-center marks. Such tools also have been banished from my shop.

In summary, to accurately locate pilot holes for hardware screws, go low tech, use your skills, keep in mind the one-sided tolerance concept, and use the skillful adjustability of craftsmanship.

Category: Techniques  | 9 Comments
Author:
• Friday, April 21st, 2017

perfection?

Perfection. We might think we want it in our woodworking, yet it does not exist. But for the craftsperson, concern with perfection, far from being a benign wish, has a dark side – it can distract you from understanding excellence.

Consider the example of a simple straight line, such as the straight edge on a board. You may think you are at least trying to plane that edge “perfectly” straight. Upon inevitably failing, you say, “OK, I’ll try again,” this time harder and more carefully.

But where is the end point? It certainly is not perfection. You have failed in that pursuit, and you always will. The perfect becomes the enemy of even the good as hesitancy, frustration, or obsessiveness creep in. Continuing this way will retard your growth in the craft.

There is a better way. It is to understand and pursue excellence. There is a range of excellence, and you ought to recognize when you achieving within it. It is also important to accept when you have fallen short – of excellence, not perfection – and then take realistic corrective action.

So, that straight edge is not, in fact, ever perfectly straight but instead has a trace of concavity along its length because you know any convexity would result, for example, in an inferior edge joint. Excellence in this case is understanding an appropriate range of camber, and being able to reliably produce and assess it.

The same principle can be applied to nearly every critical process in woodworking.

One of the worst manifestations of the perfection delusion is the “perfect every time” come-on used by tool marketers and, particularly regrettably, in some instructional materials. A woodworker who then inevitably achieves something less than perfect is apt to incorrectly suppose that he did something wrong, or doubt his capability.

Awaiting perfection, your work is never finished, or maybe never again attempted. Better to work toward excellence. Certainly, distinguish it from mediocre. That is the realistic and hard work required in the real world of craft.

Category: Ideas  | 2 Comments