Talk:Scarf joint

incomplete

You have illustrated only the unstopped splay scarf, the weakest and least used of scarfs. It depends entirely on pins, bolts or glue for strength and the thin ends are easily damaged during and after assembly.

The bladed scarf and stopped splay scarf with wedges are infinitely better.

Here are some scarf diagrams:

http://www.arlingtontimberframes.com/images/scarf2.gif
http://www.timberbestpractice.org.uk/tbpp/ATR/images/scarf3.gif

There are many, many scarfs; the half-lap and stopped splay scarf are probably the most widely used.

I have no cites, and thus I can no longer contribute outside of talk pages. Sorry, it was not my decision to exclude experts.

--C —Preceding unsigned comment added by 204.27.178.252 (talk) 20:28, 24 February 2009 (UTC)

guitar?

the headstock on guitar neck with an angled headstock is usually connected with a scarf joint 89.142.41.231 21:04, 18 June 2007 (UTC)

The right trade

This has been put into the category of Joinery. It should be pointed out that this is not a joiner's joint. It belongs to carpenters and particularly to shipwrights. (RJP 07:33, 4 August 2005 (UTC))

You're absolutely right. The problem is that both the Joinery article and the Category:Joinery are misnomers. They should be renamed "Woodworking joints" or something similar. I don't need to tell you that joinery properly refers to what is now called "finish carpentry" or "millwork" in North America, i.e. making and installing wooden fittings in buildings, which needs its own article. If you want to do the renaming please go ahead, otherwise, I will get around to it in the next few days. Luigizanasi 15:31, 5 August 2005 (UTC)

Use of glues and finger-jointing

The article appears to me to be one-sided with regards to boat building methods in the 16th to early 20th century, restricting its validity and usefulness to building practices outdated by nearly a century. It does not take into account modern advances in glueing wood, nor does it consider the availability, today, of machines that allow to create more accurate joints faster than what was possible when these methods were invented.

Consider just this:

When choosing a particular method of joining two planks of wood, a compromise is being made balancing the forces that act on the joint, in the longitudinal and both transverse directions, and the properties of the wood to bear them without failure. Visualize any wooden plank as being a composite material, a foam of essential lignine (the cell walls of the original tree), re-enforced with cellulose fibres running in the longitudinal direction. This view captures all essential properties of a wood, from its hardness (=thickness of lignin cell walls), absorption of water (porosity), dimensional changes with changing moisture content (via surface tension of water adsorbed inside cells), etc. Knots, in this picture, are just areas from which the fibre re-enforcing is missing (or mis-directed, if you like this view better).

The simplest joint between two pieces of wood, the butt joint, is the preferred joint if there are only compression forces acting longitudinally. But as the butt joint has zero strength for tensile forces, and highly variable resistance to lateral movements, it is a no-no choice in boat building for joining pieces of outer planking. If we want to increase the strength of a joint, we need to allow for sizable overlap of the cellulose fibres, as they supply the bulk of the plank's strength. Here the scarf joints show their mettle, each one having preference for a specific combination of forces, simply because they distribute the forces acting on the joint over a wider area and preferentially in the direction of the cellulose fibres. All of them have been developed, though, starting at the end of the middle ages, allowing structures, including ships, to be built in wood longer than the length of a single tree.

This happened during times when no suitable wood glue was available, freeing the keel from one of its original duties, to ensure stiffness for the vessel, and transferring that task to its planking. When doing so, the joined plank exhibits much of the stiffness a plank of the same length from a single tree would have, but not all. There remains some movement inside the joint because of manufacturing tolerances. Wedges, pegs, bolts, fishplates are some of the countermeasures used to (partially) compensate for these tolerances. For maximum stiffness of the joint, in particular when the load is not constant (wave and wind action!), the cellulose fibres must take up the load, not the lignin foam, i.e. the joint must be made by glueing, not by bolts or wedges. If a glue equivalent in wet and impact resistance to resorcinol had been available at that time, it would have allowed wood workers to create what we today call laminated timbers (e.g. glulam) and marine ply, and use it where it would have saved a lot of money, building large, lightweight sailing ships and wide-span roofs for houses, barns, etc. With resorcinol available, the simple scarf joint is the strongest joint possible to be made with hand tools, for any kind of loading, fully adequate for heavily loaded structures like e.g. the masts of sailing vessels. The more complex joints serve no purpose any more and are no longer needed.

The primary disadvantage of a scarf joint today is the amount of planking it consumes in building the joint: 8-10 times the plank's thickness for the simple scarf, others may be even longer to achieve sufficient overlap and thus stiffness. A finger joint supplies the same strength independent of the plank's thickness, consuming only 10-20mm, but requires a dedicated router to do it. Thus, for commercially supplied timber joints, that is what is used today. Scarfing as a method of joining pieces of wood is therefore, by and large, of historical interest only.W-o-f-o-w (talk) 08:22, 16 March 2014 (UTC)