The glue line of a properly constructed mortise and tenon joint will almost never break from external load. Other things might break but not that.

To get a good sense of this, let’s think about what’s going on in just a small joint with a tenon 3″ wide by 1″ long. There are 6 square inches of glue surface, which is equal to that in an 8″-long edge joint between ¾”-thick boards. Now imagine trying to break that edge joint, not in tension as in hammering down on the unsupported joint line, but in shear! The wood will break, the glue line will not.

The mortise and tenon joint is strong because even in a fairly small joint there is plenty of glue line and it is stressed in shear. So if you’ve fit that decently, don’t worry; it is very unlikely to break. The tenon shoulders transfer much of the stress to that glue line. (By the way, the glue line of a half-lap joint can be stressed in tension if, for example, a frame undergoes severe twisting forces.)

The tenon itself is stressed mostly in tension and compression along the grain, which are also quite strong. So don’t worry there either, because a reasonably sized tenon is also very unlikely to break.

Furthermore, for the purpose of strength, there is no point in fitting the tenon tight to both ends of the mortise. That does not make the joint strong.

If something is going to break, it is most likely to be the wood of the stile or leg, which can succumb to stress in tension across the grain. This is especially so if the joint is designed with injudicious distribution of wood among the components.

Thus, make sure the stile or leg will be strong around the joint. In general, the walls of the mortise ought to be at least as strong as the tenon. And though it seems less popular lately, a haunch is a good idea when joining an apron at the top of a leg.

Also, hygroscopic cycle changes in the wood will stress every mortise and tenon but don’t let this be any more than it must. Don’t let a tenon and excess glue bottom out in the mortise and don’t jam a tenon to each end of the mortise (see above). Placing a peg too far from the shoulder will tend to make hygroscopic movement eventually produce a gap at the shoulder, though placing it too close to the shoulder will make the mortise wall more liable to break.

Inspecting old broken or cracked furniture and other wood structures, wherever you can find them, and thinking about why the failures occurred, is one of the most useful habits a woodworker can have. I’ve been doing this for several decades – I suppose because I would rather not have the same things happen to anything I make.

There are the good reasons for using a diamond stone as a nagura. This is not a novel idea – the intent here is to present a clear rationale for it. However, there’s also a significant practical problem involved.

All of this applies to synthetic finishing waterstones. I think most or all of this probably also applies to Japanese natural finishing stones but I defer to those with more knowledge about those.

The reasons for a diamond nagura:

1. It’s fast. The slurry is raised faster and the surface of the stone is refreshed faster than with any other type of nagura that I have tried. Whatever you perceive to be the benefits of these effects, as discussed in the previous post, they arrive faster with a diamond nagura.

2. The slurry consists of grit solely from the finishing stone; no new grit is added. This removes the uncertainty of introducing another grit, often unknown, from a stone nagura, along with the uncertainty of the amount of it that gets into the slurry based on the relative hardness of the bond in the main stone versus the nagura.

3. It is very capable of crushing the grit in the slurry. I first learned about this several years ago from So Yamoshito, a Japanese tool vendor in Australia and expert on Japanese natural stones. I wrote about it then. The rationale for specifying 1200 grit diamond is that it is fine enough to readily crush the loose fine grit in the slurry yet coarse enough to raise the slurry quickly. The latter effect is apparent.

I can’t directly prove the crushing theory. Furthermore, for it to be of value, the crushed particles would have to retain good cutting ability as finer particles. After working with this for years at the sharpening bench, it does seem borne out by the blade edges it produces.

By the way, what about just using the slurry created by flattening the finishing stone with a coarse diamond stone, say 220 grit? Yes, that’s pretty good but the crushing effect is better with the 1200 diamond. Also, a lot of water is used in flattening and the process tends to swipe the slurry off the finishing stone.

Now for the problem. When you rub a 1200 grit diamond stone, even an Atoma with its surface made of tiny dots of grit clusters, on the wet finishing stone, it sticks like crazy. This is very annoying and then it tends to carry away much of the slurry when you remove it.

I tried using smaller continuous surface diamond stones but they were no better. Then I tried a DMT 6″ x 2″ inch 1200 diamond stone with the “polka dot interrupted surface.” This reduced the sticking but still not well enough. It needed to be smaller.

The little DMT polka-dotted pocket stones were too thin to grip in my fingers. So I hacksawed a 2″ x 2″ section off the 6″ x 2″ stone, which you can see above. It works pretty well. The small size and the perforations eliminate most of the sticking.

Note that I do not consider flattening to be a function of the nagura. In fact, a reasonably evenly-distributed rub of the small diamond nagura should not significantly change the flatness that has already been established well by a coarse diamond flattening plate. I flatten stones at the end of a session when they are fully wet and so they are ready to go for the next use.

The best solution, I believe, would be a 1200 grit diamond nagura, about 2″ x 2″, with narrow channels extending to the edges that would reduce sticking and allow the slurry to flow away from the nagura and remain on the finishing stone. I am working on prototypes using 1″-thick ABS plastic for the base and various applied diamond surfaces. I’m hoping this results in a nagura that is the bee’s knees, but in any case I will report on this soon.

Several reasons are usually given for using a nagura on fine grit waterstones. These include: to raise a slurry, to remove unwanted deposits in natural Japanese stones, to refresh the cutting surface of the stone, and to flatten areas of the stone.

Let’s think about what’s going on when a nagura is used, recalling what we can directly sense at the sharpening bench.

The slurry

When the little nagura stone is rubbed on the finishing stone, a paste, or slurry, is generated. It is sometimes claimed that the slurry actually does the sharpening, but it seems questionable whether loose abrasive particles in the slurry are really cutting steel. There are microscopic photographs of blade edges and stone surfaces, but to my knowledge, no direct visual recording of the actual cutting action at a microscopic level. We can observe the effects but not the actions that produced them.

The thin edge of steel plows most of the slurry but perhaps some loose particles are held by the stone’s surface texture, enabling them to cut. Maybe it burnishes the steel. Maybe it creates a variable grit surface on a synthetic stone somewhat like in a natural stone.

In any case, we can sense that the slurry improves the feel and ride of the blade on the stone and reduces sticking, all helpful effects. So, whatever it is actually doing, the slurry at least feels good.

The next issues are what composes the slurry and what happens to it.

Are there particles of the finishing stone, the nagura stone, or both in there? Particles of the softer (more loosely bound) of the two stones will presumably predominate. This should be considered when the two differ in grit size. For example, a nagura that is softer and coarser than the synthetic waterstone with which it is paired will be probably be counterproductive.

With fine natural Japanese waterstones, nagura selection is an art unto itself. Consult a knowledgeable purveyor of these stones. The nagura also is used to remove defects in natural stones that can damage the blade edge. This function is, of course, not relevant for synthetic stones.

So, what happens to the particles in the slurry? Are they left intact or crushed to some degree? If the nagura could crush loose grit to a finer size, that would seem to be an advantage assuming these crushed particles retained their cutting ability.

The surface of the stone

We can see and feel that a nagura refreshes the surface of the stone by removing metal and glazing. Much like dressing a grinding wheel, cutting particles are better exposed at the surface, ready to cut steel.

As for flattening, there are better ways to do this accurately than with a nagura, though with natural stones a nagura might be helpful for some local flattening as it is used intermittently for its other benefits in the course of sharpening.

A solution

There may be more questions than answers here and you may be thinking that this is all a little bit interesting but enough already. I agree, I’d rather get back to woodworking. However, at least restricting the matter to synthetic waterstones, which most woodworkers use, there is a simple solution to all of this, to be discussed in the next post. The background discussion of this post will support why I think the solution makes so much sense.

Woodworking instruction and practice usually make use of easily worked woods such as poplar or pine. This is practical – it makes learning easier and fosters confidence.

However, when moving on to more cantankerous woods, the techniques may not be fully applicable. Not only quantitative changes but also qualitative alterations in technique may be necessary. This may surprise and confound the learning woodworker and, as I often say, that includes all of us.

For example, the adjustment in cutting dovetails in red oak after practice in poplar is not just that you have to swing the mallet harder. The tolerances for sawing and fitting that work for the more compressible poplar won’t produce good results in oak. Chopping to the baseline is also different in oak. It helps more to clear the bulk of the waste with a coping saw, yet once done, there is actually less tendency for the chisel to push back beyond the baseline when chopping if it is done in appropriate increments.

The point is that however you like to do it, it pays to reconsider techniques based on the wood at hand.

Hand tool enthusiasts seem to like chopping mortises with a chisel and making tapered sliding dovetails entirely by hand. Fine in pine, poplar, mahogany, and so forth, but how about bubinga? Similarly, I like to hand plane to the final surface whenever practical but for blister maple, hey, it’s time to reach for scrapers or the random orbit sander.

Likewise, someone working almost exclusively in mahogany will surely have accommodated his techniques to that wood and the design style in which he works. That’s good, but it’s not likely that you can transfer all of those techniques and habits to a substantially different wood or style, and certainly you cannot do so unthinkingly.

Woodworkers work in wood, and wood is a very diverse product of nature. We’ve got all sorts of tools – planes with different angles, saws with different teeth, machines with different cutters, and so on. As for anyone good at any skill, a good woodworker ought to have a range of techniques to thoughtfully employ as needed when building in different woods. Further, it pays to be open to expanding that range when encountering unfamiliar woods.

A good fit of the tenon to the mortise can be described as a comfortable swish fit. You should not need to pound the joint together, nor should the tenon simply drop into the mortise, nor should the tenon wobble in the mortise.

This matters because a mortise and tenon joint derives its strength from the restraining effect of the shoulders transferring stress to the bond between the tenon cheeks and the walls of the mortise. Against this shear stress, a well-made bond has great resistance, stronger than the wood itself.

To create a square assembly, M&T joints must also be true – the tenon cheeks should be in planes parallel to the reference face of the rail. Also, ideally, the tenon should have a good fit over the entire surface area of the cheeks, though perfection is not necessary because the glue does permit some leeway.

Whether the tenon is made by hand or machine, it is very helpful to have reliable ways to adjust the fit using hand tools. Test the corners of tenon into the mortise and feel for tight areas, then check the cheeks for burnishing. Look for bumps and steps from inaccurate sawing.

A rabbet block plane is one of my two favorite tools for trimming tenon cheeks. It starts easily, works right up to the shoulder, and automatically makes a flat surface. Pictured next to it is Lie-Nielsen’s big 1 1/4″ shoulder plane, which also can be used. Though it’s a great plane for other tasks, it and other shoulder planes are a bit tippy for this work.

My other favorite is the Iwasaki 10″ coarse float. One might expect a file or rasp to round over the surface but this tool has such a decisive bite it can be controlled very well. What’s more, it leaves an incredibly clean surface, without tearing, for a tool with such big teeth. The safe edges prevent damage to the shoulder. I use three fingers on top of the tool for feel and control. I like this tool a lot.

A wide paring chisel is another good option, especially for localized clean up. The length of a paring chisel offers considerably more control than a bench chisel. Pressure with left hand fingers on top coordinates with the right hand, which transmits depth of cut via the handle. Still, for a thin shave down of the whole tenon, the rabbet plane works better.

Yet another option is the router plane. I only use this if I think I’ve messed up the trueness of the tenon and need to establish a cheek into a plane parallel with the face of the rail.

Press the sole of the plane onto the face of the rail and start by setting a light cut at the most prominent part of the cheek, then work down from there. Mostly swing the plane, pivoting on the rail face, more than push it, to maintain steady contact and thus depth control. The tool is acting as a gauge to make the cheek face parallel to the rail face.

I generally hand saw tenons because setting up machines is usually not worth it for me for one-of-a-kind pieces. Even with several good options for fine tuning the tenon cheeks, I strive for a good fit directly from the saw, maintaining a one-sided tolerance to avoid having to patch up a tenon.

Shooting is a gateway technique that produces reliable accuracy and control unattainable with machines. Here are three simple tips to improve your results with shooting.

1- Put a grippy glove on your left (non-dominant) hand

An inexpensive, widely available glove with a rubbery grippy palm adds remarkable strength to your hand. The work piece must be controlled with the left hand in two respects. First, it must not slide or pivot during the cutting stroke of the plane. The torque can be considerable with a wide work piece of dense wood. The glove gives you control with much less effort than a bare hand.

Second, in preparation for the cut when shooting end grain, the work must be advanced a tiny amount along the fence toward the plane. Without this, the blade edge will simply clear the work piece because it has already cut away the previously projecting thickness.

Practically, the work piece is advanced just to meet the toe of the plane sole, as in the photo below. This is done almost without thinking but it is a precise move made more controllable by the gloved hand.

2- Simple microadjustability

Everything is not square in woodworking, even when we intend it to be so. For example, when fitting a drawer front to its opening, the sides of the front piece should be made to match the opening, even if it is a bit out of perfectly square.

To minutely adjust the shooting angle away from 90°, just place a piece of blue tape at the appropriate end of the shooting board fence. Realize too, that the angle can be adjusted with phenomenal precision by slightly altering the position of the tape.

Of course, this is done empirically, but for some mathematical fun, note that a .003″ thick tape placed at the end of a 7″ fence will change the angle .025° from 90°, and moving it to the 6″ position will adjust that new angle, in turn, by .004°. Using a .001″ plane shaving would create an initial adjustment of .008° from 90°. Shims are magic!

3- Hold the plane like you mean it

Whether you have a dedicated shooting plane like the #9 I use, or use a nice heavy bevel-up bench plane, or, yes, a bevel-down bench plane, grip that righteous beast over the blade. Get the big muscles at the base of your thumb firmly down on the sidewall of the plane, wrap your fingers around into the throat of the plane, and plant the ends of the fingers on the lower part of the lever cap. That way, you can control the ride of the plane on the horizontal track while keeping the sole tight sideways against the vertical runner.

Furthermore, you get a good tactile sense of the blade’s cutting action. In concert, all of this promotes accuracy by preventing the plane from tipping in any direction as it takes a firm, uninterrupted stroke.

I like the “hot dog” attachment from Lie-Nielsen on the #9. This is something I imagine could also be readily made by the user.

This is so easy. Shooting is a fast and accurate method for making a straight and square long grain edge on small boards, generally less than about two feet in length. This is far easier, especially for thin stock, than planing the edge while the board is held vertically in a vise.

Though shooting is mostly associated with truing end grain, I really don’t know why long grain shooting is not commonly discussed in instructional materials. True, it’s not absent but I think it should be included among routine methods.

A long shooting board is helpful for this work. The long grain edge of the work piece should overhang the edge of the platform by a half-inch or so (see below), while the end is butted against the fence. For narrow pieces, especially a series of them such as drawer parts, I clamp an auxiliary bracing piece of plywood or MDF onto the shooting board platform, as in the top photo, to help my left hand steady the work piece.

The plane does not contact the vertical running edge of the shooting board platform that is used for end grain shooting. You simply control the plane to produce a straight edge much as you would when planing with the sole down – initially emphasize pressure on the toe of the plane, transition to balanced pressure, and finish with pressure on the rear portion of the plane.

I like my Lie-Nielsen #9 for most of this work, but really any bench plane, bevel-up or bevel-down, with a length appropriate for the work, will do. The “hot dog” handle on the #9 is very helpful to control the plane in all directions. Placing my fingers on the lever cap gives a good feel of the blade’s cutting action. When using a regular bench plane, I like to grip the arch in the sidewall of the plane and place my fingers over the lever cap. The contour of the Veritas bevel-up jack plane makes it especially effective to place the heel of the hand on the rear of the sidewall arch.

Medium to larger work is more easily and accurately managed by clamping it to the work surface. This prevents the work piece from yawing as you push the plane, which would make it difficult to produce a straight edge.

It is also possible to accurately set the auxiliary bracing piece, referred to above, to produce a parallel-sided work piece. This can also be accomplished by planing to a gauged line. No table saw is needed here.

A nice way to combine machine and hand work to make small to medium pieces with accurate and smooth edges, such as drawer parts, is to refine and smooth the machine-jointed edge by shooting. Then rip to width on the table saw with the planed edge against the fence. The ripped edge can be smoothed with one or two passes of a hand plane, usually later in the building process.

You can even eliminate the shooting board and still do this work. Just take a piece of 3/4″ MDF, clamp the work piece on top with its edge overhanging the MDF, and run the plane on the workbench top. If you don’t trust the trueness of your workbench, temporarily cover it with another piece of 3/4″ MDF.

This is also an easy, effective method to edge joint a pair of thin or small boards, such as drawer bottom stock (see below). Decide on the mating edges, “close the book” on the joint, clamp the pieces to the platform, and shoot both edges at once. It’s hard to miss.

Shooting is also a sensible way to work with very small pieces (see below).

These are effective methods that require minimal infrastructure and can be used regularly on a wide range of projects.

Finer pitch saws generally produce more precise cuts than coarser pitch saws. Well, of course they do. The finer teeth make a cleaner kerf with which to track a line. They also advance the kerf more slowly and thus presumably more controllably since each stroke is a relatively smaller commitment that can be adjusted as needed.

The finer pitch, all else being equal, also produces a smoother sawn surface. Also, the thickness of the wood must be taken into account. At least several teeth should ride in the kerf to maintain control and prevent the saw from grabbing and tearing.

So, OK, we don’t use a 5 1/2 ppi rip saw to cut dovetails in 1/2″ stock, obviously.

But what may not be so obvious are the practical limits to fine pitch saws. In other words, finer and finer is not more and more accurate.

If each commitment – each stroke of the saw – is too small to judge whether accuracy is being maintained, then you have to wait for a few of them to really make a judgment. In other words, the feedback is delayed and you can be going off course without knowing it for a while. Similarly, the corrective action is harder to judge.

The object is to use a tool that is palpably controllable, not too coarse, of course, but also not too fine. Among novice woodworkers there is a tendency to think that using the finest saw available will be the most accurate way as long as one is patient enough, but for a saw, and probably for just about any tool, it might be too fine to function accurately. Note also that the stroke speed of a coarser pitch saw can be slowed to some extent.

As an analogy, a good car steering wheel should be responsive, not mushy. The result of an input action – such as a saw stroke – should give a sufficiently sensible and prompt result so that the feedback loop is closed clearly and quickly. This is much of what hand tool woodworking is about. In other words, if you go too slowly, you can’t tell what you’re really doing!

In summary, consider balancing factors when choosing the pitch of a saw. And don’t be charmed by superfine saws (e.g. superfine dozuki saws) or see them as a substitute for skill; they may be too fine.