Archive for the Category ◊ Techniques ◊

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• Tuesday, November 29th, 2016

handplaning thin wood

Handplaning thin boards, those less than about 1/2″ thick for most species, sometimes produces surprising frustration. The solution to many problems is to consider what is happening on the underside of the work piece.

I usually plane such wood, for example, a thin drawer bottom, on a very flat planing board with front and side stops only about 7/32″ high, or on a nice flat section of my workbench against a low-profile planing stop that inserts directly into the bench. This avoids distortion from the pressure of bench dogs and gives me a better feel for how the plane is meeting the wood.

planing stop board

The handplane sole acts somewhat like the feed rollers in a thickness planing machine. It presses on the flexible board and forces it downward to close gaps under the board. This effect varies, sometimes unpredictably, with the length of the plane and the skew angle of planing.

Suppose now we are trying to smooth plane the surface of a drawer bottom or panel and the underside is a bit concave. (Here I do not mean an even-thickness board that is simply cupped a bit.) A finely set plane will miss areas on the topside that are over the concavities underneath.

This is especially annoying if you are trying to clean up a few spots of tearout and the plane keeps missing them. The tolerances involved are quite small because in these situations the plane is trying to take a very thin shaving, say .001″.

shimming concave side

The solution is to be cognizant of the interaction of work piece and the work surface, and resort to good old shims. Sometimes I’ll use blue tape but more often just a few shavings stuffed under the board. or even some paper.

In fact, this little trick is handy even if the thin board is perfectly flat and you want to raise a small area to plane away a defect without having to plane down the whole surface just to hit the defect.

When using a shim, it usually is helpful to dog the board to keep the ends down and thus push up the shimmed area.

Note that if the work piece is of even thickness and just a bit cupped, this will usually not be an issue. The board will flatten against the bench as it is being planed, all areas will be hit with the plane, and the board will simply spring back to its cupped state when you are done planing. Within limits, that is not a problem because the panel will usually be easily coaxed into flatness by the frame or drawer grooves.

So, the real key in all of this is to not take your handplaning setup for granted but rather to be aware of the actual interaction between a finely set handplane blade, the plane sole, the work piece, and the work surface. With this awareness, it’s just a matter of common sense to diagnose and fix what otherwise could be vexing problems.

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• Sunday, October 23rd, 2016

woodworking library

Wendell Castle once commented that often not enough time is spent designing a piece. The same can be said of researching a piece.

Unless you have previously executed something very similar, neglecting adequate research can lead to a lot of wasted effort building a disappointment. The research phase of a project should be enjoyable as the possibilities unfold and your woodworking knowledge expands.

Here are four categories that require attention. To illustrate the breadth of research sometimes required, I have used the example of a wedding wine box that I recently completed. This piece had very special significance and I wanted to approach it fully prepared.

1. Function

Almost all woodwork is functional. You do not want the beauty of a piece to belie an inability to do its job. Think of it this way: making a bat requires more than understanding wood and turning; you have to understand baseball.

I researched all the dimensions of the wide variety of standard Bordeaux and burgundy bottles to design a versatile cradle that would accommodate a range of bottles. I also had to learn about how wine should be stored long term.

2. Materials

This is not an area for guessing or shortcuts. Processes that are routine in one wood can be fraught with surprises in another species. What’s more, nearly every project involves several non-wood materials that woodworkers have to understand.

A few boards of gorgeous curly ovangkol (shedua) caught my eye. I had not worked with this species before, so I needed to explore the range of figure it had to offer to be able to choose top quality stock. I looked at objective data on its physical properties and movement characteristics. Most important, I did some practice sawing, chiseling, and planing to appreciate its working properties. It was surprisingly incompressible and somewhat brittle so there was very little margin for error in the joinery.

I considered lots of options for secondary woods, settling on wenge and a billet of killer figured redheart big-leaf maple. I trialed finishes, tested glues for special situations, and also researched leathers.

Then there’s hardware. Ugh. There are always oodles of options here, though often I am not happy with any of them and end up modifying or at least fine-tuning the best available materials.

woodworking research

3. Constructions

Almost every piece I make involves at least one modified or non-standard construction technique. It really helps to consider solutions that other woodworkers have used, though it is important to use sound principles and experience to distinguish good information from bad.

If you never venture from the conventional, you miss out on a lot of fun in woodworking, but you must build right, so do your research.

In this project, I could not find a satisfactory solution for a cradle that would snugly hold a range of wine bottle sizes. What I worked out is no marvel of engineering but I did have to sit at the drawing board for a long time scratching my head, and make mock ups, before settling on a solution.

4. Techniques and Tools

Similarly, every project is an opportunity to develop as a woodworker by learning new techniques and reinforcing skills that you have used before. A good woodworker should never be too proud to practice even those skills that were acquired some time ago.

And yes, there is also the excuse – oops I mean perfectly valid reason – to buy a new tool, which, by the way, has to be studied and tuned. In this project, because I did not do enough research, I needed the excellent Lie-Nielsen drawer lock chisels to bail me out, as mentioned in an earlier post.

In summary, researching function, materials, constructions, and techniques/tools is smart woodworking. Note to self: don’t cheat on your homework.

Category: Techniques  | 3 Comments
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• Sunday, September 11th, 2016

Bosch random orbit sanders

Here is most of the power sanding gear in my shop. Once again, I hope you will find a useful tip or two in here.

The gentler Bosch ROS20VS (5″ disc, 2.2 amps, 3/32″ diameter orbit) random orbit sander gets much more use than the larger Bosch 3725DVS (5″ disc, 3.3 amps, 3/16″ diameter orbit) because I am mostly using these tools to smooth surfaces, not to form them. As mentioned in the first post of this series, there are much better options, with and without sanding, for the later task.

In any case, these Bosch sanders perform very well at reasonable cost. The 6″ size has 44% more area, helpful for bigger jobs, but the 5″ is handier and suits the scale of most of my work. I always use these sanders hooked up to my Fein shop vac with the auto-start feature.

A crepe rubber stick (above, left) is a must for cleaning power sanding discs but also works well on hand sandpaper. Get a big one.

Norton ProSand discs

Norton’s new ProSand Multi-Air Cyclonic hook-and-loop discs (above, left and right) have superseded their 3X discs (center). Amazingly, the 246 laser-cut holes (I read that; I didn’t count them) give better dust extraction than the big holes in 3X and other brand discs. The ProSand discs also have more sanding area, an efficient ceramic abrasive, and are easier to apply because you do not have to align holes – just put the big one in the center.

sanding disc rack

This storage tree keeps the discs organized. It is nothing more than dowels set at a slight angle into a wood strip.

Ridgid EB4424

The Ridgid EB4424 combination oscillating spindle-belt sander, shown above in belt mode and below in spindle mode, may be the best thing Home Depot sells in their “tool corrals.” The designers thought of just about everything. This certainly is a sanding tool for shaping wood.

The oscillating action, which runs true, makes shaping smoother and more controlled, as grabbing is minimized, and leaves a smoother surface on the wood. Changeover between modes is fast and convenient. Belt tracking is easy to adjust and the setting is retained very well.

The most significant downside of this machine is the cheap table but it is not a deal breaker. Though it adjusts from 0° (shown) to 45° and has a serviceable miter slot (3/4″? Yea, sure.), it should be flatter and firmer. Dust collection with the Fein vac is surprisingly good for this type of sander.

I highly recommend this machine.

Ridgid EB4424 belt/spindle sander

By the way, those purple 3M flexible mesh sanding sheets found their way into the two photos above, at the left edges. I forgot I had them since 3M’s much better Ultra Flexible Sanding Sheets became available. (See the previous post.)

sanding belts and sleeves

Norton’s blue Norzon belts are incredible wood eaters. Most of the extra sleeves and belts get stored in this boot box.

Singley, Robo drum sanders

The Singley drum (above, left) uses ordinary sandpaper, cut to size and easily wrapped around and tucked into the drum. With this tool, drum sanding can be done economically in a wide range of grits. Many sizes are available.

The Robo sander, chucked in the drill press, works like a flush trim/end-bearing router bit but more gently and without the risk of tearout.

Shown beneath the Robo is the Veritas Drum-Sander Support System bearing. It is essentially a live center that sits on the drill press table, and whose point engages a dimple in a retrofit modified drum shaft. This trues and stabilizes the rotation of the drum.

This concludes the four-part series on sanding. As always, there is more than one good way to do just about everything in woodworking, but I hope this material has been helpful to you.

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• Saturday, September 10th, 2016

This is just about all of the hand sanding gear I use in my shop. I present this in the hope that you will find a useful tip or two.

sanding blocks

A cork block, 1″ x 2″ x 3 7/8″, is the best tool I have found for hand sanding. It has just the right compressibility and resilience to produce a consistent and true sanded surface, and it feels comfortable in the hand. A piece of cork glued to a wooden block is a decent substitute but not as good. Almost all of the area of one-third of a standard 9″ x 11″ sandpaper sheet can be utilized by re-wrapping it just once.

The Norton pad gets less use but is handy for fine sanding large areas. It uses the same one-third sheet with little waste.

curved sanding blocks

Convex and concave rubber sanding grips are handy, though I more often use ad hoc blocks made from combinations of wood, cork or rubber sheet, and pink foam insulation. Some of these are worth preserving but some live for only a single fleeting employment.

sandpaper cutter

The sheet cutter makes it almost fun to size sandpaper. A hacksaw blade is screwed to a piece of plywood with enough slack to permit the sheet to easily fit under. A piece of thin plywood is glued to the blade to make it easy to press the blade firmly onto the back of the paper prior to tearing it. A slat is placed in one of the table-sawn kerfs that have been placed to yield the desired sizes of paper. By far most common are one-third sheets made by cutting across the narrow width of the full sheet to yield strips about 3 2/3″ wide.

sandpaper bucket

This little plastic bucket screwed to the wall is a good place to store partially used strips. Contrary to comments by some shop visitors, it is neither a garbage can nor a urinal.

Norton 3X sandpaper

I’ve used Norton 3X paper for years with excellent results. Norton has superseded it with ProSand, which they claim has more durable abrasive and backing paper, so I will gradually restock with that.

PSA sanding rolls

Once you get these 2 1/2″-wide, PSA-backed (sticky) rolls in the shop, all sorts of uses arise. They are great to quickly make impromptu sanding blocks and tools, such as those below. I also reload the Veritas shooting sander with them.

sanding sticks

These little shop-made sanding sticks solve vexing detail issues in almost every piece I make. Apply an oversized piece of PSA sandpaper to the squared end of a wooden tongue depressor, and then trim the excess with a utility knife. Of course, as needed, you can also create a V-point or other shape on the end. You’ll wonder how you ever managed without them.

sanding products

From left to right in the photo above:

The silicon carbide “wet-dry” paper is there for sanding between coats and sometimes for wet sanding of oil-varnish. I have 600, 1000, 1500, and 2000 in stock but rarely use the finer grits.

3M Ultra Flexible Sanding Sheets, available in 100, 150, 220, and 320 grits, really live up to their name. The grit stays on and the backing does not crease or tear. These are a far better option for contour work than sanding sponges, which I have always found to be useless. You can back up these sheets with whatever you want – contoured rubber or foam, a sponge, or just your hand.

3M has also recently introduced Sandblaster Pro sheets with a grippy back. So far, I have not found an advantage from them for woodworking but they are very handy to flatten tools when simply placed on a granite surface plate. They stay put without spray adhesive or water.

I use the MicroMesh set of 3″ x 6″ sheets for tool and hardware alterations, not on wood. The grit ranges from 1500 to 12,000! The sheets are cushioned and thus not a good choice for sharpening.

Next: power sanding gear.

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• Thursday, September 08th, 2016

plane vs sand

Let’s consider the finished surface qualities produced by sanding compared with handplaning. Here there will be no blanket declarations, including none extolling the superiority of handplaning, and no simple catalog of species with recommendations to sand or plane.

The real answer is to experiment as part of planning your project. In each case, consider the look you want and the practicalities of the building process.

You have to assess the surface of the wood (the particular boards at hand, not just as a species) in combination with the applied finish. Just as it pays off to plan the applied finish at the start of a project, so too should the method of finishing surfacing the wood be planned. Winging it is usually not smart.

Here are examples from the shavings and dust of my shop. YMMV. This discussion pertains to the final surfacing of wood that has already been trued or shaped; we’re only dealing with the last few thousandths of an inch of wood.

By the way, for exposed parts in fine woodwork, I never finish with the surface from a random orbit sander, no matter how fine the disc paper. When sanding, I always finish with hand sanding. In fact, most of the time, I don’t use the ROS at all.

For figured big leaf maple, one of my favorites, with satin gel varnish, I can see no difference in the final look whether the wood surface is finished off with hand planing or fine hand sanding. Therefore, I do whichever is easier and that is usually sanding.

The same goes for figured bubinga with oil-varnish mix. Bubinga responds exceptionally well to scraping, so little sanding is required thereafter.

Claro walnut, another favorite, with oil-varnish, seems to look more clear and lively when handplaned. With brush-on varnish however, I cannot tell the difference between planing and sanding. For highly figured Claro, its visual impact often seems to override subtle differences between planing and sanding.

Curly cherry with gel varnish, the finish I like best for it, is finicky. It looses some of its pizzazz when sanded. Pearwood similarly looks exquisite straight from the smoothing plane and can well be left unfinished, but after two coats of water-base acrylic, it is hard to tell if the wood was planed or sanded.

Oak, red or white, flatsawn or quartered, plain or figured, with wiping varnish and the grain unfilled, usually looks about the same to me, sanded or planed. Oil-varnish is different.

Again I emphasize that I always experiment at the outset of a project with the actual wood and finishes that I am using for that project, and try to anticipate the practical issues that I will encounter in building the piece.

We ought to be practical. A curvy table leg creates most of its visual impact from its form, while it is the surface and figure of a cabinet door panel that we appreciate. Again, choose planing or sanding based on the overall look that you are after and the practicalities of building. Maybe there are fine facets on the leg that sanding would obscure and a spokeshave is the right tool to use, or maybe there are gradual curves that look good sanded.

Work with a smoothing plane is usually more pleasant than with sandpaper, but sometimes planing is just awkward, such as when finishing off a dovetailed case. And let’s face it, sometimes we just don’t want to spend more time at the sharpening bench.

There are also some special situations. For example, when fitting a drawer, a hand plane is the only tool to use on the sides. Choose the wood for the sides to allow easy planing and usually leave it unfinished.

One more thing: when finish planing difficult wood, there are almost always a few spots of tearout that just seem unavoidable, or maybe the blade developed a nick (especially some A2 blades) and left a little row of raised wood. I touch up these areas with a 0.020″-thick sharp scraper rather than with sandpaper. Nothing is perfect.

Next: sanding tools

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• Saturday, September 03rd, 2016

sandpaper

Sanding does not get much respect among woodworkers. Hand planing uses more gratifying tools in a more pleasing process, and when suitably employed, leaves lively surfaces and is more efficient. This series of posts will attempt to put sanding in perspective in the world of fine woodworking and present practical information on tools and techniques.

James Krenov wrote in The Fine Art of Cabinetmaking, “To me, sanding is not a way to express sensitivity with wood, even less a sign of true skill,” yet he recognized a legitimate role for sanding, recommending, for example, scraping and sanding as the best way to finish rowed woods like padauk.

The first thing to clear up is whether you are sanding to shape wood or to produce a nice surface on wood. Are you forming a curve or smoothing the surface of an existing curve? Are you flattening a surface or just smoothing an already flat surface? Sanding is hardly ever the best way to shape or dimension wood unless you are using jigged machines such as a spindle sander or thicknessing sander.

True, sometimes you are both shaping and smoothing, such as when forming a light chamfer with a hand sanding block or running a figured panel through a drum sander. But generally speaking, it is important first to be clear about just what you are doing when sanding. In fact, most problems with sanding come from inadvertently mixing shaping and finishing.

For example, you have a fantastically figured board in the rough, or perhaps is flat from the planer but full of tearout. You are afraid to touch it with a handplane so you take out the random orbit sander, start with a 60-grit disc and work through to 320. Unfortunately, despite all efforts to evenly distribute the sanding, the final smooth surface is wavy, the outer edges are dipped, and there is no hope of using this as a reference surface for further work, such as for a drawer front.

There were lots of better options that would have produced and/or retained a true surface that would then require only fine sanding, which would not squander the flatness. Among them, for various stages, are: a spiral cutterhead on the planer, a thicknessing sander, a jack plane worked across the board, a toothed blade in the jack plane, a Veritas scraper plane, a micro-toothed blade in the scraper plane, and a hand scraper.

An equally unpromising plan is to take a curved table leg rough sawn off the bandsaw and hope to use a curved sanding block with coarse paper as the primary final shaping tool. You will not get the proper feedback to produce a true curve that comes instead from high quality rasps, spokeshaves, and curved planes. When the curves have been trued with some of those tools, then you can use the curved sanding block to just finish smooth.

The point is that sanding – by hand and with small and large machines – has its place but it pays to be mentally clear about exactly what you are trying to accomplish with it, and restrict it to that task.

In the next installment, let’s consider the finished surface qualities produced by sanding versus handplaning. Be prepared for some surprises.

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• Wednesday, August 31st, 2016

brass machine screws

When installing solid brass hardware in fine woodwork, matching solid brass screws are essential to complete the look. However, brass wood screws are weak compared to their steel counterparts and there often is limited depth with which to work, such as in a small box lid.

Lee Valley recommends the use of brass machine screws as having much better strength than brass wood screws in short holes. I have tried this with excellent results with 4-40 (above, left) and 6-32 (above, right) flat head brass machine screws. Here are the details.

The why

The machine screw has the advantage of a thicker, non-tapered body that is less likely to break than the wood screw as you torque it down. Furthermore, because the machine screw threads have already been cut by a tap, the screw goes in easily and only tightens as the head meets the countersunk hole in the hardware.

By contrast, a brass wood screw has to cut its own threads and the screw is stressed throughout the range of installation. Yes, you can use a steel screw to pre-cut the threads, but good luck trying to find a steel wood screw with threads that match the pitch of the same nominal size brass wood screw. They usually do not, which means you are simply breaking down some of the inter-thread wood that the brass screw’s holding power depends upon. A recent Brusso hinge set came with such a mismatched steel screw.

Tightening into a properly tapped hole, the brass machine screws feel very solid. I find I can now relax with this method for small hardware installation.

The how

The preparatory hole is drilled at the root or “minor” diameter of the machine screw (the diameter of the screw body without the threads), which yields 100% thread depth when the hole is tapped. Typical work in metal uses 75%, or less, thread depth by using a pilot hole somewhat greater than the root diameter of the screw.

For 4-40 machine screws, the minor diameter is .0813″. This is approximated with these drill bits: 2mm (.0787″), #46 (.0810″), and 5/64″ (.0781″). For 6-32, the minor diameter of .0997″ is approximated with these bits: 2.5mm (.0984″), #39 (.0995″), and maybe 3/32″ (.0938″).

Fortunately, those wonderful folks at Lee Valley sell inexpensive sets of drills in the metric sizes with imperial taps through 1/4-20. In cherry, maple, and shedua (ovangkol), all tight-grained hardwoods, the method worked very well in 4-40 and 6-32. Of course, it pays to experiment beforehand in the specific wood species.

tap wrench

Use a standard-point tap and ratcheting hand tap wrench for most situations, but consider a bottoming tap when you want to eke out every last bit of functional depth. Tap carefully, without wobbling the tool, especially for the smallest sizes whose wood threads are still fairly delicate while in the formation process. Even fine threads in wood are surprisingly sturdy once they are fully filled with the screw, but I like to harden the wood threads with a tiny bit of cyanoacrylate glue. Epoxy is not worth the hassle in my opinion.

I bought a supply of brass machine screws 4-40and 6-32 in longer lengths than required and easily cut them to length with an electrical multitool (shown), and then filed the cut edge clean.

Since we are often dealing with shallow depths and small tolerances, make sure the screw will actually tighten against the countersunk hole in the hardware and not just tighten against the taper left by the tap at the deep end of the hole.

I often prefer to enlarge the countersink and hole in brass hardware if there is room to accommodate the next larger screw size, e.g. 4-40 to 6-32, for more strength.

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• Monday, May 16th, 2016

glue joint test

When to remove the clamps

The instructions on the Titebond III bottle recommend “clamp for a minimum of 30 minutes (longer is better)” and “Do not stress joints for 24 hours,” which is how long PVA glues generally take to fully cure.

I leave the clamps on at least overnight. There really is no hurry to remove them unless they are needed for other work. Furthermore, I will not be working the board for at least 24 hours to allow time for the joint to condition and the board to reach a uniform moisture content as excess moisture exits the glue line area. This avoids producing a sunken joint line or depressions over the biscuits when surfacing the panel.

Also, it seems plausible that the joint could be stressed from changes in moisture and applied forces if the clamps are removed too early in the curing process.

For these reasons, I put the assembly aside and wait until the next day to remove the clamps, tending toward longer times for larger work, and up to 24 hours if there are any doubts about the behavior of the wood. Small, light panels such as a drawer bottom can be unclamped sooner.

Flattening the panel

Hopefully, this will be fairly easy and corrections will be well within the range of hand planing for small to medium panels if biscuits were used for alignment. The panel only needs to be flat enough for its function. Don’t worry about small imperfections that yield to light hand pressure and, for example, a table frame will easily flatten. On the other hand, don’t allow an errant panel to twist the frame of a light cabinet door that needs to fit and close precisely.

As needed, work diagonally with the jack plane to true the surface, then finish off with the smoother or scrape or sand to the final surface.

If you glued up a large panel in stages, you may be able to flatten the intermediate glue ups with a wide jointer-planer, minimizing the work required on the final panel. For a big table top that needs significant correction, consider using the services of a local commercial shop with a giant wide-belt sander.

It is reassuring to do some testing on the off-cuts, as in the photo at top. I grasp both ends of the off-cut and bash the joint line against a hard table edge. Though the force is directed on or very close to the joint line, only the surrounding wood will break while the joint line remains intact.

Summary

To confidently and efficiently produce sound edge-to-edge joints and beautiful glued-up panels, here is what to do:

  1. Select reliable wood to produce visual and structural harmony, especially along the joint line.
  2. Use straightforward methods, finishing with hand planes, to make good joint surfaces that fully meet. Use the slightest bit of camber as a one-sided tolerance.
  3. Use biscuits for alignment in boards thick enough to accommodate them and the special method for small, thin boards.
  4. Use parallel-head clamps with a simple tunable setup.
  5. Rehearse the glue up then work fast.
  6. Feel good about what you made – it’s going to last!

Closing thoughts

I hope this series on edge-to-edge joints will assist you in this essential aspect of woodworking. In writing this blog, I want to empower people to make things and experience the quiet – yet great – joy of it. I’m not an infallible guru – no one is. Nevertheless, I can assure you that these methods are carefully thought out, researched, have been used by me for many years, and actually work in my shop.

Of course, there is more than one good way to do almost everything in woodworking, so you will surely find those who disagree with some of what I have presented. No problem. Please do consider alternatives, try things in your shop, and ultimately use your judgment to find what works for you in your shop to give you the results you want.

NOTE: The entire 6000-word series on Edge-to-edge Joints and the many other series on this blog can be conveniently accessed via the Series page.

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• Sunday, April 24th, 2016

glue brush

This discussion primarily applies to PVA glue, which most woodworkers use for these joints. I prefer Titebond III for its relatively long open time, ease of use, and dependability. Alternative glues with longer open times include special slow-set PVAs or liquid hide glue.

The gluing process

Speed is paramount. It is absolutely imperative that the thin layer of glue not start to skin over or stiffen. This can result in a weakened joint and/or a glue line that is too thick. I suspect this is one of the main causes of failed edge joints and cosmetically poor joints.

A good glue up requires a rehearsal – it is worth the time. Dry clamp the boards, working out clamp placement and distribution, and examine the joint. When readying for the glue up, prepare the clamps open to the correct length. Rehearse how you will hold and move the boards for glue application. For example, the middle of a three-board panel needs glue on both edges. How will you support it for gluing the second edge?

Again, if the glue skins over at all, you lose, so when it’s game on, move fast! In the first photo below, the glue is good to go but the glue that is partially skinned over and stiffened in the next photo will produce a failed joint.

glued edge

glue skinning over

Applying glue to both sides of the joint ensures good wetting and equal penetration on both sides of the joint. Set up two edges side-by-side and work on both at once. First, put a modest amount of glue in the biscuit slots where its bulk will delay skinning over. To apply glue to the joint surfaces, I run a bead directly from the bottle and then spread it out to the edges with a brush or roller. Using my finger to spread the glue seems inevitably to transfer glue to somewhere I don’t want it.

I like the inexpensive hog-bristle brush available from Tools for Working Wood but I crop the 1 1/2″ bristles to about 7/8″ (see photo at top), which allows me to push the glue faster using it nearly upright. Flux brushes are a poor substitute as they cannot spread the glue as fast and shed bristles on the work.

Squeeze out

I aim for light squeeze out along the full length of the joint, trying to avoid dripping. In theory, one could apply the perfect amount of glue that is just short of producing any squeeze out but then when you assemble the joint and see no squeeze out, you would not be sure if there is just the right amount of glue inside the joint or too little. Thus, squeeze out is simply assurance that you have applied enough glue and as such, there is no point in making it excessive.

As for removing glue squeeze out, I prefer to wait until it is rubbery then lift most of it away with a sliver of wood cut to a chisel edge. Then I spot remove most of any remaining glue with a wet rag that is more than damp but less than drippy.

I recall reading somewhere that removing the squeeze out before it fully dries can cause the outside of the glue line to dry faster than the interior and thus produce a tiny gap on the outside. There may be some truth to this as I have infrequently observed a hint of gapping early on after clearing the squeeze out but it has never persisted in a well-made joint. Therefore, and also because removing substantial fully dried squeeze is a hassle and can chip the wood, I keep it practical and don’t worry about this issue.

Next: Finishing up, a summary, and a thought.

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• Friday, April 22nd, 2016

clamp pressure

Clamping capacity

Can small shop clamping methods generate enough pressure to make a good edge-to-edge joint? The short answer is yes. Let’s look at the details.

The US Forest Products Laboratory in their very useful Wood Handbook, chapter 10, page 16 (2010 edition), recommends pressures of 100 pounds per square inch for low-density wood and up to 247 psi for the highest density woods. The book also states: “Small areas of flat, well-planed surfaces can be bonded satisfactorily at lower pressures.”

Jet claims (I suspect rather conservatively) 1000 pounds of force can be generated by their parallel-head clamps while Bessey claims 1500 lbs. for their similar K Body Revo clamps. As an example, 1500 pounds of force produces 200 psi over a 10″ length of 3/4″-wide glue line (7.5 square inches area).

So yes, adequate pressures can be generated in the small woodshop. There’s no need to get out the calculator, just lean toward more clamps and more torque with denser species/thicker boards and less beef with less dense species/thinner boards. And, of course, make good joints.

Clamp spacing

How about spacing the clamps? This depends partly on the above issue but also on the mechanics of the force spread. Even a wanabe engineer like me can surmise that the board is acting as its own caul and thus the transmission of force to the glue line depends on the width and stiffness of the board. I long ago adopted, with consistent practical success, Ian Kirby’s rule that the clamp force can be assumed to spread in a 45° fan.

Thus, referring to the diagrammatic photos herein, the maximum distance between clamps (remember, there will be clamps above and below the panel) should be twice the width of the narrower of the two outer boards in the panel. Shown at top, the 5″-wide board requires fewer clamps (maximum 10″ apart), than the 2 1/2″-wide board below (maximum 5″ apart), if all else is equal.

clamp pressure

Assembly

Regarding assembly, I first moderately tighten the center clamp, and then work outward, avoiding heavy pressure. Then I add the upper gang of clamps, moderately tighten them, check with a straightedge for problems, and make any needed adjustments. Then I torque down everything, and check/adjust again. All of this is done very quickly!

Accordingly, I glue up any panel with more than three boards in separate sections, and usually prefer to limit the sections to only two boards, especially if the intermediate panel can fit in my jointer-planer. This is wood – nothing is perfect all the time. I’m usually working with very expensive stock and like to preserve the opportunity to reset any errors rather than let them accumulate.

Next: Glue issues.

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