Archive for the Category ◊ Techniques ◊

Author:
• Thursday, March 31st, 2022
glue squeeze-out

The real problem with glue squeeze-out is not taking the matter seriously. If you pretend that when it appears, squeeze-out is really a surprise, you are likely to waste time and get poor results. It is more efficient to anticipate and manage it as a legitimate part of your joinery and glue up plan.

In many cases, such as edge-to-edge joinery (above), squeeze-out is functional. Consider that too little glue and just the right amount of glue look about the same when the joint is assembled. A modest squeeze-out ensures that you have not used too little glue. (It’s that one-sided tolerance thing again.)

Edge joints are easy to manage. I wait until the squeeze-out is rubbery, and then gently scrape away most of it. The remainder is removed when surfacing the panel after the glue is cured. I never use a wet cloth to wipe away excess glue in careful work. That spreads the glue and helps it soak into the wood. Unless the glue is very diluted by this process, it can interfere with finishing.

It is important to think through how and where the glue will be pushed as the joint goes together, and then how you will deal with the excess. Each situation is different. Where there is good access on the outside surfaces of a joint, such as carcase dovetails, I let the glue go where it wants, knowing that I will later scrape away the glue and create a wood surface that is unadulterated by the glue.  

The inside surfaces are a different matter. Removing glue from the inside corners could be a pain, or a big pain if there is excessive glue that has soaked down into the wood fibers, and maybe even a royal pain if the wood is cherry, for example, and will be getting an oil finish. 

My favorite solution is to simply line the inside surfaces adjacent to the joint with 3M #2080EL blue tape. This takes little time. I set the tape very close to the joint line but make sure to avoid putting the tape where it would prevent the joint from fully closing – it only takes a bit to mess up the glue up. 

What about the outside of a dovetailed drawer joint? If you plan to plane or scrape away a substantial amount of excess glue, especially if it has seeped into the end grain or the side grain of a coarsely textured wood, that may change the fit of the drawer, depending on your drawer fitting technique. Consider that clamps may thwart access to the squeeze-out when it is in its rubbery stage and easy to remove. 

I do not have a universal approach to this, but it usually is fine to gauge the glue to minimize squeeze-out, plane down the sides, and just barely touch the end-grain of the pins. I find Lee Valley 2002GF glue to be a big help here because it does not seep into the grain if it is not pressed upon. And, all of this depends on the wood species and finish. 

For mortise-and-tenon work, I try to avoid external squeeze-out all together. I am generous with the glue in the mortise. I do think the best practice is to put glue on the tenons, just enough to ensure the glue wets the surface. I use a very thin coat, but because this can quickly skin over, I work fast and it is the last step before bringing the joints together. I usually leave about 1/8 inch extra at the bottom of the mortise for the excess glue inside the joint. 

In frame and panel work, I pay attention to the corners to anticipate where the glue might squeeze out. This is part of planning the joinery. I don’t want to make a mess there and inadvertently seize the panel at the corners in its groove. Sometimes I wax the corners of the panel if there is little room for error.

Another approach to squeeze-out in general is described in detail by Michael Fortune in Fine Woodworking, issue #232, April 2013. He uses a non-silicone wax applied sparingly around the joint where squeeze-out is anticipated. Glue will not stick to it and so is easily removed. Later, the wax is removed with alcohol. This works for sure but it does take work. I think it is best for awkward areas and especially with shellac or oil finishes for which a little remaining wax will not interfere with adhesion. 

The point is to think it through – squeeze-out is part of woodworking. 

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Author:
• Wednesday, January 05th, 2022
glue flexibility

Wood, and thus wooden joints, moves with moisture changes, and since we put pieces of wood together with glue, it is worthwhile to consider if the glue itself flexes. In other words, how elastic, or stiff and brittle, is the glue itself? 

Here, I want to look at differences among PVA glues, which in almost all discussions get lumped together without attention to significant differences among them in the property of flexibility. Here is a nice simple demonstration.

As background, we know that at one extreme, urea formaldehyde glue such as Unibond 800 forms a rock-hard, extremely strong, rigid glue line making it the best choice for bent laminations. Hide glue also forms a quite hard, rigid glue line. PVAs are, in general, more flexible.

I spread four different glues into approximately one-inch discs on a birch plywood scrap, and then let them dry thoroughly for several days (photo above). From left to right:

Titebond Liquid Hide Glue

Titebond Original PVA

Titebond III PVA

Lee Valley 2002 GF PVA

The Lee Valley glue is a PVA that is claimed to have gap filling properties. I have had good results over many years with this product. Titebond III is touted for its water resistance and as a good all-round wood glue. 

Working on the discs on the plywood, I could not dig my thumbnail into the surface of the hide glue. Even pushing as hard as I could, I could not make a mark. The surface also cracked as it dried. 

The Titebond Original was the second hardest, taking a lot of pressure to make just a trace of marks. Titebond III was clearly the softest of the four; it was easy to dent with my thumbnail. The Lee Valley 2002 GF was intermediate between the other two PVAs.

I also spread discs on a piece of silicone “tape” (non-adhesive wrapping). After they dried for several days, I gently lifted the discs away, which had almost no adhesion to the silicone. I then curled and snapped them (photo below).

glue flexibility

The results were consistent with the thumbnail test. The hide glue was the most brittle but Titebond Original was a pretty close second place. 2002 GF was intermediate; it could snap or curl depending on how I deformed it. Most interesting, Titebond III did not snap at all. No matter how I deformed it, it was quite flexible and only curled.

The simple point here is to show that there are distinct differences in flexibility among PVA glues. How you use that information is another matter. Depending on the type of joint, its dimensions, the wood properties, and the intended use of the piece, you may want more or less glue flexibility. 

Also, this is a separate issue from the strength of the glue bond. There are also several other properties of glue to take into account when choosing among them. 

Now this is obviously not a scientific test. However, I trust my observations in the shop and watching how pieces fare over the years as much as I trust some of the elaborate tests in woodworking magazines. My personal take away is this confirms what I noticed about Titebond III, which is that it is quite flexible, and so I’ve learned to avoid it in certain situations. Titebond Original is a better choice when you want a more rigid glue line and water resistance is not important. 

Category: Techniques  | 3 Comments
Author:
• Tuesday, August 31st, 2021
carcase doweling jigs

For designing this joint, I suggest 3/8″ diameter dowels for most work with boards about 3/4″ thick. For components 5/8″ thick, 5/16″ dowels are a better choice. The larger diameter dowels create more glue surface area but you do want to have some minimum meat around the dowel in the long grain workpiece. 

I usually space 3/8″ or 5/16″ dowels about 3/4″ to 1″ apart, on center, as you can see from the jigs, above. Generally, the dowels are closer toward the outer parts of the joint, and spaced wider at the middle of the joint. This is what Krenov taught though I think I am a bit more generous with the number of dowels. You can think of the dowels as individual dovetails. 

I suggest the longest dowel penetration into the side grain workpiece that is possible without getting too close to the outside surface. The hole should not go closer than 1/8″ from the outside surface, and actually more clearance is better. Don’t forget the penetration of the brad point of the drill bit, and the soaking of glue, especially in less dense woods. Many of the dowel joints in my pieces take advantage of an increase in thickness of the side grain piece at the joint as part of the design, which works with the structural needs. 

The penetration into the long grain piece is less critical because it is long grain-to-long grain gluing. It is not going to fail. 3/4″ is probably sufficient in all cases. 

dowels

The best dowels ever were Laurier dowels (above). They were made with great precision and consistency. The compressed flutes expand when water-based glue is used in the joint, making for a tight, strong fit. The spiral configuration of the flutes serves to work the glue up and fully around the dowel as it descends into its hole. 

Unfortunately, these are no longer available. My stash is getting depleted. Here are some options, though I cannot vouch for any because I have not used these brands yet. None of these have spiral flutes, and the available dowels with spiral flutes are not compressed flutes, as far as I can tell.

Dowelmax

JessEm

Bear Woods

Lee Valley

When it’s time to for glue up, it’s worth rechecking the hole depths with a go/no-go setting on a calipers or just a stick. You really do not want to be caught in the middle of a glue up with a surprise dowel projection longer than all the others that prevents the joint from closing. If that happens anyway, grab a coping saw quickly.  

depth setting gauge

As for glue (PVA), avoid being too generous. Don’t ask me how I know this, but it is very easy to overload the holes and make a squeezed-out mess all over your carefully prepared components as you draw the joint together. A simple depth gauge with a hole helps to seat the dowels reliably.

I clamp the joint strongly, having prepared whatever pads and cauls are necessary for a true carcase. 

You can trust a well-planned and executed carcase dowel joint used in appropriate situations. It is not a difficult or complicated joint to make but precision and care are needed. And no, doweling is not cheating. The key is that it opens up design possibilities with practical construction. 

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Author:
• Saturday, July 31st, 2021
dowel jig alignment

Continuing with the carcase dowel joint, shown above is the reference face of the jig being squared to the inside of the carcase. This is the same reference face of the jig to which the side piece was attached as the jig was screwed into place on the end grain workpiece. (See the photo in the previous post.) 

The jig’s end cleat references the placement to correspond with the end grain workpiece. Note that the end cleat should be a bit narrower than the jig itself to avoid interfering with the placement of the square, as seen above. I usually prefer to clamp the jig to the side grain workpiece and recheck it for square before screwing it down. 

Keep track of your references. You can see why I label the jig so much. In this build, the reference face of the jig corresponds to the inside faces of both workpieces. 

I drill all the holes with a portable power drill. I find no need to use a drill press or, if I had one, a horizontal boring machine. The carefully made jig ensures accuracy.

Below, left, the brad point bit is for the cross grain holes but it is slow and tends to burn when drilling along the grain. For that, the DeWalt Pilot Point (middle) bit is my favorite. The standard twist bit on the right works well enough too. Check the actual diameters of the bits to keep the holes consistent.

I have never seen an oversized good quality bit in these categories; they all seem to be made with a one-sided tolerance toward the small side. I suppose this is because all drilling systems have at least some runout, and you can make small holes bigger but not big holes smaller. 

drill bits for doweling

Please don’t use masking tape as a depth stop when drilling these joints. One slip of the tape can ruin a lot of work. And it will happen. So, is there a good drill stop out there? Yes, but you have to make it. But it’s easy. Please see this post

Add chamfers to all the holes – long grain and end grain. This will help with excess glue, and to prevent raised loose chips, which can prevent the joint from closing fully.

dowel holes on side grain
dowel hole chamfers

Next, we’ll look at dowels, gluing, and some joint design considerations.

Category: Techniques  | Tags:  | 4 Comments
Author:
• Wednesday, June 30th, 2021
shopmade dowel jig

It is reasonable to be skeptical of dowel joinery. After all, half the joint involves gluing the long grain of the dowel into a hole where the glue surface is partly end grain with limited true side-grain glue surface. However, the carcase dowel joint, used in the right circumstances and made properly, works and lasts without doubt. Joints in pieces that I have constructed as long as 20 years ago and have been able to observe since are still cleanly tight.  

We associate this joinery with the late James Krenov who wrote about it in detail in The Fine Art of Cabinetmaking. Here my attempt is to humbly add tips and refinements, particularly toward ensuring accuracy.

Making the jig is more than half the job for this joint. Use a very hard, fine-grained wood that will hold clean, sturdy holes to last through repeated use, including inevitably repurposing the jig for future projects. I have long used bubinga, though its availability is now limited. Your shopmade jig will be at least as accurate as manufactured jigs of this type, and it will be customized to your project. 

dowel jig

I usually make the block about 1 1/8″ thick (in the direction of the length of the holes) and about 1″ wide. The width does not need to match the width of either workpiece but will, in fact, be a little wider than the end grain workpiece to ensure good seating on the side-grain workpiece. The length will usually be a little longer than the width of the workpieces.

Employ every effort to make the block with two absolutely flat surfaces that are dead parallel to each other. This is critical because the jig will be used to drill from both directions. Any error in parallelism will be doubled when making the joint. 

A third face, the reference face, should be flat and dead square to the two faces with holes. The fourth face, which I mark with a big “X”, is not critical.

The holes should be drilled with a well-tuned drill press. This is cross-grain drilling, so a good brad point bit is the best choice. 

dowel jig references

A small, removable cleat on the end of the block serves as a physical reference against the workpieces. This can be augmented depending on whether the workpieces meet flush at their edges. 

Krenov’s description shows the block being nailed to the end grain workpiece, using the tablesaw top as a flat reference. I do not like this method. Instead, I use a removable side piece to reference the jig on the end grain workpiece. The jig is attached with two #8 screws going through countersunk clearance holes and penetrating the workpiece only about 3/8″. The jig is attached to the side-grain workpiece without using the side piece but instead squared and clamped to the workpiece, and then screwed in place. 

Below, the jig is placed on the endgrain workpiece using the back cleat and side piece to ensure solid referencing. (I have not screwed it in place for the photo.) Note that both the end cleat and the side piece extend beyond both hole-faces of the jig. This allows the jig to be used at both ends of the workpiece.

dowel jig in place

I mark up the jig all over: “back,” “Reference” face, “X” for the non-reference face, the size of screws to use, the drill bits to use, etc. 

Now, more than half done, next we’ll look at designing the joint, dowels, drill bits, etc.

Category: Techniques  | Tags:  | 11 Comments