This section is from the book "A Practical Treatise On The Joints Made And Used By Builders", by Wyvill J. Christy. Also available from Amazon: Practical treatise on the joints made and used by builders.
The use of the wedge in securing joints is very commonly met with. Cottered joints owe their adjustability to wedges. Columns are wedged up plumb before running their bed joints. Overhead columns are thus tightened up in the sockets or caps of piles, and in many cases iron piles are secured to holes bored in rock with wrought iron wedges, with or without concrete. Small solid wrought iron bars, forming the legs of piers, etc, have been made fast to foundation holes cut in the rock to the proper size and tapered at bottom by bringing the bars first to a white heat, then splitting their feet and inserting wedges therein. Thus prepared, the bars were immediately dropped into place and driven home before the ends became too hard to assume the requisite enlargement.
In theory the welded joint is unsurpassed in strength and thoroughness. It results from cohesion between the two surfaces coming into play, the white heat enabling compression or a single vigorous blow to bring the opposite particles within a sufficiently insensible distance to cause the law of cohesion to at once operate, whereby the joint is, as it were, lost in the entirety of the metal. Every smith cannot make a good weld, hence the utmost firmness should be shown in rejecting iron fastenings suspected of any treacherous flaw, or of being badly forged. Before being raised to the welding heat, which is just above whiteness, the two pieces to be united are roughly shaped and scarfed at a bright red heat so as to overlap and approximately fit, and when both are white hot sand must be sprinkled over the surfaces about to be brought into contact, for by fusing and spreading it prevents oxidation and retards the combustion of the metal. If the joint is too long to be completed at one blow the work must be returned to be reheated, and after the union is thus quite effected further blows will tend to consolidate the joint and bring the work to the desired shape. Although the process appears tolerably simple, perhaps it is no exaggeration to say that a sound weld between two plates is unobtainable, and between bars, rods, etc, owing to the imperfection of workmanship, always uncertain, therefore the more important the work the more it is avoided, but there are occasions, nevertheless, when the welded joint if skilfully executed proves both useful and safe.
This is a term applied in riveting when the rivets in each parallel row, or file, or pitch line, are spaced so as not to stand immediately behind one another in the line of stress, but so that each rivet is opposite the centre of a space between the rivets of any adjacent line, as in Fig. 94. Consequently a line joining their centres would run from right to left in zigzag fashion. To obtain the strongest lap joint with two rows of rivets thus arranged the distance between the pitch lines ought to be about two-thirds the pitch, which may be made equal to 4½ or 5 diameters.