Joining Wood #1: On Edge - Don't Be Scared!

Posted by Tobias Lochner on

This week I thought that I would begin to delve into the mysteries of joining bits of wood together. Joinery is something, we as woodworkers all do, from the very simple to the delightfully complicated!

           

In this blog I will concentrate on joining narrow boards together to make a wider board.

The days of sourcing wonderful wide boards are unfortunately now part of history and when you do come across a board of 400mm or wider, you need to sell a kidney to afford one, let alone afford enough lumber for an entire project!

   

Cutting a Giant Redwood (Sequoia Semperverens)

There are many ways to join solid boards together side by side to make a wider board, from simple Butt Joints, Tongue & Groove Joints and Spline Joints all the way to Biscuit Joints & Domino Joints.

If we reduce things to their most simplistic form, the basic concept of all furniture is the "Box". Whether the box is a drawer, TV cabinet, wardrobe, chest, sideboard, kitchen unit, jewellery chest, cutlery chest, or tool chest.....it is still a box! Even the basic design of a chair is based on a box.

This wonderfully humerous cabinet above made by Paul Miller who is my marquetry mentor!
The entire cabinet is made from solid wood and veneers, including the hinges, tin of varnish and its spilled contents!
Don't show this one to your wife!

To make any solid board construction, there are a few basic important rules to observe:

  • Wood is hydroscopic. It will expand and contract, predominantly over it's width, continuously, and in reaction to environmental humidity. For those who believe that the wood is still living, sorry to disappoint you, it has been cut, it has no roots, it has been dried, you are not going to water it, it is dead!  If you look at a piece of wood end-grain under magnification, it looks basically like a bunch of drinking straws. Moisture enters and exits these capillaries due to environmental humidity changes and this is what makes the wood expand and contract. That's all!
  • The wider the solid board, the more obvious the visible seasonal expansion and contraction will be and the more it will affect your construction!
  • A simple four sided solid wood box is inherently weak, until you add at least one more panel to it (a fifth side).
  • Do not try to trap wood across it's grain, it will expand or contract at some stage and something will fail & go bang! (usually in the dead of night!) 

Let us look at Solid Board machine based joinery first. Using machines and their Floating Tenon counterparts, there are a variety of Biscuit Joiners at your disposal and then of course, there is the Festool Domino Joiner. They both do their job well, although the Festool machine, due to the various lengths and thicknesses of loose tenons that the machine is capable of using, it is definitely a better option than standard biscuit joinery from a strength perspective.

                             

Wooden biscuits on the other hand, are made from compressed Beech wood and are available in three sizes only. They are all made to the same thickness.  Biscuits are great for assisting to line up two boards that are to be glued along their edges to form a solid board panel and they add a fair amount of strength to the joint, which is effectively a "Butt Joint" of two boards. The same goes for the Domino system, but with a lot more strength.

       

The Domino system has a further added advantage of you being able to create your own Floating Tenons from the same wood stock that you are joining together. The reason for doing this might not be immediately apparent, but will serve you well, usually a few seasons after you have finished the project, as these Floating Tenons exhibit exactly the same tensile strength, porosity & glue adherence, as well as the same reaction to humidity as the joined boards, and this then reduces the chance of the boards cracking on the glue line due to atmospheric influence. (Sometime this negative influence is not natural, as is the case in modern air-conditioned rooms, room with heaters & fireplaces).

Exquisite Circular Table with Sunburst Crotch Flame Mahogany Veneer

Even though the grain of a Floating Tenon is at right angle to the grain of both of the boards being joined, their small size, as well as the fact that they are completely enclosed by the host timber. Being fairly well sealed from the environment by this timber as well as the fully dried & dried bonded adhesive, means that humidity is very unlikely to have any effect upon them and generally speaking, these joints will remain firm.

Taking a look at the historical accounts of 17th and 18th Cabinetmakers, timber to be used for a specific item of furniture was rough sawn, air dried and then placed in the actual room destined to be the chosen place for the finished item, for a few months to fully acclimatise to the room, before the timber was turned into a fine furniture piece! (Climate controlled rooms did not exist in those days!)

Both the Biscuit and Domino machine joinery systems are based on the eons old system of joining two boards together with a third piece of wood.

Another example of this is the variation of the  "Tongue & Groove Joint", where each board has a groove and the separate tongue fits into both board grooves. This is called a "Longitudinal Spline Joint" or sometimes a "Tongue & Double Groove Joint", utilising a single long Floating Tenon. Why one would bother to cut two grooves and then make a long spline, is lost on me.....Why not simple cut a "Tongue & Groove Joint" and be done!

To achieve this joint entirely by hand is really quite easy and logical. You need to cut a groove (channel) of a specific width in each of the boards that you are joining together.

This can be done with a table saw, freehand router, router mounted in a table, spindle moulder or a hand plane designed for the purpose such as a Plough Plane, Router Plane, dedicated Tongue & Groove Matched Set of Planes or a Combination Plane.

All of these hand planes will accomplish this task admirably and they make use of an adjustable fence on the plane to control the cut parallel to the board.

                  

 

You then make a "Stick" that fits snugly into both of the grooves and allows the boards to butt up against each other. Simple, straightforward and easy. You also don't have the perennial problem of discovering that you don't have enough Biscuits or Dominos at 3pm on a Saturday to accomplish the task at hand!

Another very overlooked method of joining boards along the grain is the "Butt Joint". This has got to be the quickest and easiest way to make the two or more boards become one.

Working with a stationary jointer or a hand plane, you surface the two edges in question and then glue them together. Working with hand planes, you use your longest plane (#6, #7, #8 or a low angle #7-1/2) and plane each board's edge at 90º true to it's face. This is where the name "Try" as in Try Plane (Trueing Plane became Trying Plane and then Try Plane) originates.

    

Should you wish to plane each board individually with your hand plane, Veritas make an excellent right angle aluminium fence, that quickly attaches to most bench planes via built-in rare earth magnets, and gives you a 90º fence to plane bed angle, making edge planing dead easy.

Here's a tip for those of you who are new to edge planing boards: Take both boards and clamp them face to face to each other, making sure that the edge grain is running in the same direction in both boards. You then plane the two boards, as if they were simply a single board. This is definitely the easiest and most failsafe method for getting the two boards to mate, true to each other. The reason for this is that any small discrepancy in your planing angle on board one will be automatically compensated for by the equal and opposite angle on board two. It doesn't matter if you are a degree or a bit more out, your boards will mate so that the two face surfaces are parallel. Try it!

Another very good reason (other than simply making a board wider) for joining two boards over their length is to be able to "Bookmatch" them. If you find a really beautifully spalted, burled or patterned board, get it onto your bandsaw and split it, opening it up like a pair of exquisite butterfly wings and glue it back together along two of the long grain edges.

    

      Bookmatched Black Walnut                  Bookmatched Claro Walnut

Back in history, joining two board on edge (Butt Joint) was achieved by the use of the "Rubbed Joint method". The reason behind the terminology is that once the glue was applied to both surfaces, you "rubbed" them against each other over the length of the edge. As you apply pressure during the "rub" the excess glue will ease out of the joint, the glue film becomes even and very thin, and then surface tension takes over and becomes immensely strong.

Once you cannot move the boards by hand anymore, its time to clamp them. This was a very common way of joining boards over many centuries using Hide Glue, as it has a much quicker and higher initial tack (grip) than modern adhesives and does not exhibit the "Creep" of modern adhesives (which is basically the boards moving/sliding out of position as you clamp them).

Even with modern adhesives, "Rubbing" a Butt Joint along the grain of the two boards is still an extremely effective way to set them up before applying your clamps. Personally, I "rub" all of my long grain Butt Joints, as well as my Tongue & Groove and Spline Joints in my workshop. I do this, no matter whether I am using Hide Glue or AlcoIin Professional and Alcolin Ultra PVA adhesives.

Interestingly, a well "rubbed out" long grain joint will require less clamping pressure (therefore no dreaded clamp head impressions on the wood) as well as a shorter productive clamping time.

 

Another way of joining boards on edge over their long grain is the "Sprung Joint". This is basically a standard Butt Joint, but you curve one of the board's edges fractionally, over the length of the board. This is especially useful if you don't have enough clamps available.

The diagram below shows the correct way to make a "Spung Joint". Note that the curvature is somewhat emphasised for illustration purposes and the curve should be less than 1mm or so over the length of the board. With this method, by clamping in the centre first, you are bringing the boards together along the glue line at the outer areas first and effectively no clamps are required towards the ends of the boards.

So much for joining boards on edge to each other to make wider boards for solid board joinery. Whether you choose to plane your edges by hand or use machines, Dominos, biscuits, your own splines or "rub" your joints, the most important factor to always bear in mind is accuracy and flatness of all surfaces. Get this right from the beginning and you will thank yourself over and over again. 

Until next time, let's make shavings, not dust!

 

 

 


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6 comments

  • If the butt joint is well prepared, well glued and well clamped the joint is stronger than the wood itself. The point about Festool domino’s being stronger than biscuits is academic: you don’t need more strength. Both options simplify line-up during assembly and clamping. Biscuits are a cheaper solution.

    Denis Lock on
  • Hentie, you are 100% correct. I didn’t mention it in the post, but I use a proper glue brush for all of my glue-ups, whether I am using Hide Glue, Alcolin Professional (TiteBond II) or Alcolin Ultra (TiteBond III). I will ask Alison and Brian to get stock of these particular brushes.

    Tobias Lochner on
  • The way you explained the rubbed joint, it actually makes sense to still use it, even with modern glues. and the glue is spread better than with a brush (or finger if you didn’t think and prepare, prior to starting to glue up)

    Hentie on
  • Thanks for explaining this Tobias. I have been making rubbed glue joints for decades and agree its the best way to control the glue along the joint. I sometimes don’t even clamp after rubbing a joint on a small piece.

    Brandon Winks on
  • Thanks Johan. Appreciate the comment.

    Tobias Lochner on

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