Joinery - Sighting for Winding
The easiest way to describe the process of sighting for winding is by taking an example. Suppose, then, that it is proposed to sight the top of a small table, about 3 ft long and 1 foot 9 inches wide. By kneeling down in front of the table with the eye level with the top and about 3 feet from the front, in such a way that the head being kept perfectly still, and only the eye moved in its socket, the edge of the end appears level with the edge of the front, and the corner is neither above nor below the front, but touches it, then by keeping the head steady and only moving the eye in its socket, it will be observed whether the end ed in like manner appears level with the front, and the corner touches the front.
If this should be the case, the table is flat, and “out of winding”; but if, as is more probable the table is not flat, but in winding, one of two things will be observed; namely, first, that either the corner d will be visible, and a small triangle and will be apparent, and the corner will look too high; or, secondly, the corner, as well as the edges of the side ad, and of the end dc, will be quite invisible; in the former case, if a straight-edge be placed diagonally across the table, resting upon the corners b and d, it will be found that it does not touch the centre of the table at h; also that when the straight-edge is placed across the corners a and c, that it rests upon the center of the table, level by raising the leg, as might be necessary.
When this has been done, if the level be placed across the other end, it will show whether the corner d is too high, too low, or level; if level, the table is without winding; if it is too low, a straight-edge laid diagonally would touch the table, and not at the two corners; but if it is too high, the straight-edge would rest upon the corner, but would not touch at it. When using a spirit level, care must always be taken to see that the under side of the level, as well as the object to be tested, arc clean and free from dust, etc. also, after noting the position of the bubble, the level should always be turned end for end and the testing repeated in the same place. Spirit levels are seldom absolutely correct, but by reversing the level an average for the error can easily be taken, and a true level obtained for the piece of work.
To return to the box. The amateur, having tested his board with his straightedge and also by sighting, and having planed the high places till the surface is true and without winding, he must plane one edge straight, and at right angles or “square” to the side he has finished. He will test it for being straight in the same manner as when he made his straight-edge out of his ruler; but, in order to be able to plane it at right angles to the flat side, he will require a square. As he does not possess this tool he will proceed to make one for himself, sufficient to answer his purpose. To make a small square, a piece of an old cigar box will answer the purpose admirably. The amateur will take a thin piece of wood about inch or inch thick, 2 inches long and 1 inch wide, 6 plane the sides smooth, marking one side for the “face,” then plane the edges straight, and draw a pencil line across the middle. It is evident that the surface is in winding; but if should not be visible above, a fresh line of sight must be taken through, and the eye turned towards, in order to see if that point be too high.
If, after sighting, the surface appears to be quite true, one of the straight-edges should be turned end for end, or upside down, and the operation repeated. If great exactitude be required, several sights should be taken, the position of the straight-edges being changed each time, and their edges, as also the surfaces where they rest, being constantly examined, lest a small particle of dirt should accidentally get between the straight-edge and the surface, and thus render the sighting incorrect; after some practice, an error not exceeding the thickness of a piece of thin tissue paper is easily detected. The amateur must learn how to sight accurately. If he turns a candlestick with a square base, and part of the pillar is also square, the two parts must be put together without winding; he places a small straight-edge upon the side of the pillar, and sights it, using a side of the square base, instead of a second straight-edge, as in the case of the side of the long post.
An extraordinary degree of accuracy can be obtained by this system of sighting, but the eye requires training, and constant practice is indispensable; but, if the amateur always tries to do his work as well as he can, and does not rest satisfied with “good enough,” he will imperceptibly train his eyes to see straight, and to detect slight errors, which are quite invisible to an ordinary observer. His time is not wasted when he does his work “unnecessarily vell,” as it is termed, because he has been training his hands and his eyes to obey his will.