Archive for the Category ◊ Techniques ◊

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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Norton’s new ProSand Multi-Air Cyclonic hook-and-loop discs (above, left and right) have superseded their 3X discs (center).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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• Friday, April 22nd, 2016

glue up clamps

Clamp setups

The most important step in a trouble-free clamping regimen for edge joints is to get a set of parallel-head clamps, such as those made by Jet and by Bessey. These invaluable tools eliminate most problems.

It is best to do the glue up on a flat base such as a workbench with a sheet of 3/4″ MDF on top or a dedicated assembly table. You then want to transfer that flatness to the panel to be glued.

The best and most versatile method, especially useful for gluing up long boards, is to rip two thick boards to the same width and set them on the work surface parallel to the clamp bars where they will act as bearing strips. The top photo shows the bearing strips with the lower gang of clamps. One panel board is mocked up in place.

Make the height of the bearing strips sufficient for the boards to slightly clear the clamp bars, and cover their top surfaces with packing tape because glue will squeeze out on to them. You can make corrections for imperfections in the work surface by simply shimming the bearing strips.

[Tip: To make adjustments for creating a flat, untwisted bed for the panel, think of the bearing strips as winding sticks. View them directly as such or place actual winding sticks on top of them. Shim as needed.]

If the work surface is flat and the clamps uniformly sized, a quick method would be to put the boards directly on the clamp bars. However, glue will squeeze on to the bars, which is messy even if they are covered with plastic, an additional nuisance. Alternatively, pieces of 1/2″ MDF can be placed across the clamp bars and away from the glue lines, as shown below. This works well for small scale work and will keep glue off the bars unless it drips.

glue up option

These setups keep the boards close to the underlying clamp bars and thus minimize forces that would tend to bow the bars. A possible problem with the second method, where there is no air space between the underlying clamp bars and the work pieces, is the transference of bow in the tensioned clamp bars to the glued up panel, though in practice and testing, I have not found significant bowing using heavy clamp pressure.

I almost always alternate clamps above and below the panel because this seems more reliable and safer, especially when later moving the assembly around the shop. Further, it affords an opportunity to tweak the pressure balance if things are amiss. After experimenting with light panels, observing for distortion, I think one could get away there without alternating, but I have found no practical disadvantage to alternating in any case.

The bars of the fewer upper gang of clamps will be further from the panel boards, so in theory, this produces asymmetric bowing forces. In practice, this is little or no problem but if there is any upward bowing of the panel, you can slant the clamp heads or use the short sides of the heads to bring the bar closer to the work piece.

Again, I have never found the need to use over-under cauls or those specialized clamps that produce a similar effect.

One more thing: Parallel-head clamps also obviate the need for the pyramidal pressure blocks described by David Charlesworth in the article “Accident Prevention” in Volume 2 of his excellent Furniture Making Techniques series. The blocks (or similarly, rounding over the outer edges of the panel) make good sense to neutralize the effects of the bowing that seems to occur with the sash clamps he is using.

Next: clamp pressure and how many clamps do you need?

Author:
• Sunday, April 17th, 2016

biscuit alignment

When gluing up edge joints, you want to maintain proper alignment of the boards to produce a flat panel. Especially for small shop woodworkers, it takes a lot of work to flatten glued up panels, which accounts for the proliferation of specialized clamps and devices designed to keep the boards aligned during glue up.

Maintaining alignment

The simplest reliably effective answer is a tool you probably already own: the biscuit joiner. Start with flat boards and good edge joints. Place #20, #10, or #0 biscuits typically 8-12″ apart and just a couple of inches or so from the ends. Remember to account for the trim allowance so you do not leave an exposed biscuit in a tabletop.

The most consistent results come by pressing the joiner’s fence against the reference face of the board, which is secured slightly overhanging the edge of the workbench. Even for “standard” 3/4″ stock, this is easier and more reliable than trying to register the board itself against the bench and using the sole of the joiner as a reference.

Make sure the fence is flat and exactly square to the joiner’s face. Test to make sure the fence is also parallel to the blade/slot and if necessary, shim the fence with tape to achieve this. You can even use a 5/32″ slotting bit in a router to make the slots if you don’t have a dedicated joiner.

The biscuits are not necessary for strength. A well-made edge joint is strong enough without them, though they can’t hurt and offer some insurance against imperfections especially near the ends of the joint. The goal is minimize the work of flattening the glued up panel.

Some authors recommend hammering the boards into alignment during glue up. With the partial exception noted below I do not like that method. Time is very limited once the edges are brought together. Using a hit or miss process while playing with clamp pressure, rushing, and hoping are not my style of woodworking, particularly when a very fast and reliable alternative is available.

At glue up, squeeze glue in the slots before spreading it on the joint edges. If you reverse the order, the coat of glue on the edge has time to start skinning over while you are fiddling with the slots. Another option is to forgo gluing the slots, but why?

Later, when you are ready to plane or sand the panel, remember to avoid sunken areas above the biscuits by giving the extra moisture and consequent wood swelling time to dissipate. Use a pinless moisture meter or just check for remaining swelling with a small rule. Anyway, before working the surface of the panel, you have to wait for the immediate area of the glue line itself to loose its swelling but this small added delay for the biscuit areas is about the only real disadvantage of using biscuits.

I do not use any of the following: special over-under clamps, cauls, pinch dogs, dowels, Dominos, splines, or incorrigibly distorted wood that does not belong in a panel.

Thin panels

What about thin panels such as drawer bottoms that will not accommodate a biscuit? Here is a straightforward method using simple shop-made blocks to control the boards near their ends that will cover most of those situations. Depending on the length of the panel, a bit of tapping in the interior of the joint is usually necessary to align the boards but this is usually easy because it is a small panel with relatively light clamp pressure.

 

For shops that need to make lots of panels efficiently, such as dining tables and large frame and panel doors, the Plano Glue Press is one specialized tool that looks worthwhile.

The other major aspect of reliable alignment is clamp set up, which we’ll look at next.

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