This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
This is the most simple of all the joints, and is made by merely placing the two pieces together with the end of one piece against the side of the other and nailing them firmly to each other, after both have been trimmed square and true. Such a joint is shown in Fig. 38. The two pieces are perpendicular to each other and neither piece is cut. The nails are driven diagonally through both pieces, an operation which is known as "toe-nailing" and are driven home, if necessary, with a nail set. This is called a "square" butt joint. Fig. 39 shows two pieces which are not perpendicular to each other. They are trimmed to fit closely together, and are then nailed in place. Such a joint is called an "oblique" butt joint. The butt joint does not make a strong connection between the pieces, and should not be used if much strength is required. It depends entirely upon the nails for its strength, and these are very likely to pull out.
Fig. 37. Example of Plain Joint.
Fig. 38. Square Butt Joint.
SUMMER HOME IN MICHIGAN, OF W. CARBYS ZIMMERMAN, ARCHITECT, CHICAGO, ILL.
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This form of joint is sometimes modified by cutting away a part of one of the pieces, so that the other may set down into it as shown in Fig. 40, the square joint at A, and the oblique joint at B.
Fig. 39. Oblique Butt Joint.
Fig. 40. Special Types of Square and Oblique Butt Joints.
This gives much additional strength to the joint, especially in the case shown at B, where there may be a tendency for one piece to slide along the other.