This section is from the book "Spons' Mechanics' Own Book: A Manual For Handicraftsmen And Amateurs", by Edward Spon. Also available from Amazon: Spons' Mechanics' Own Book.
This implement, Fig. 268, is for the purpose of securing a true surface and straight edge on wood when planing. It is generally made by fastening one board on another in such a way as to form a step between them; shooting-boards made by gluing 2 pieces of board together, are very apt to twist and cast through the action of the air, and once out of square, are very hard to set right, generally requiring to be pulled apart, and made again. The following plan renders this unnecessary: - Take 2 boards (of the length you require the board, allowing at least 1 ft. extra for the plane to run; thus, to plane up 5-ft. stuff, make the board at least 6 ft.) of thoroughly dry pine, 1 in. thick and 11 in. wide, and plane them perfectly true; cut 4 in. off one the whole length of the board; these 2 pieces are for the bottom board, and across these glue about 8 pieces of 1/2.-in. pine 11/2 in. wide by 10 in. in length and one piece 5 in. in width by 10 in. in length to build up or strengthen the upper board where the groove will come, leaving a gap 4 in. wide between the 2 bottom boards, thus making it 15 in. wide; now glue on the upper board, allowing it to lap 1 in. over the cross-pieces (as in cross section), and screw together with 2 1-in. screws from the bottom.
This will allow the top to be planed if it should cast, as the screws do not come through, and the edge being raised and lapping over the cross-pieces, allows the edge to be squared, without parting the boards, while the air having free play all round the boards they are not so likely to cast, and, in shooting an edge, the shavings and dust work away under the top board, so as not to throw the plane out of square. The blocks are generally screwed across the board, but it is better to cut a groove across, wedge-shape, 6 in. from the end, and cut wedges of various thicknesses for planing wood of any substance, so that the plane may run over the block, as in section. The measurements are a-b, 4 in.; b-c, 4 in.; c-d, 7 in.; d-e, 6 ft.; f-g, 10 in.; g-h, 5 in.; h-k; 4 in.; and in the section of the boards, a-b, 11 in.; c-d, 15 in.