LEVELLING THE SLABSTOCK OR FRAME
Levelling a harness, or rather levelling the mails of the harness, is the most important part of the mounting, as, if the mails are not levelled as true as a straight-edge, good work need not be expected from the loom. The position in which they are levelled, in relation to the breast beam and back rail, will depend upon the nature of the cloth to be made, to a certain extent; but as a general rule, for ordinary work, the eyes of the mails should be half the depth of the shed required to be drawn below the level of the breast beam for hand loom work, and a little more than that for power-loom work. This is to have the top and bottom portions of the shed of an even tension, and to make both sides of the cloth equally good. The position of the back roll can be altered a little afterwards, if it is required to slacken either the top or bottom portions of the shed. Raising the back roll throws up the weft pattern to the under side of the cloth, and sinking the back roll gives the upper surface of the cloth a finer appearance, by tightening the top portion of the shed. A 3-1/2-in. draw of the harness is sufficient for power-loom work, and perhaps less would sometimes be preferable. Levelling the harness mails 1-3/4 in. for light work, and 2 in. for heavy work, below the breast beam should be a good average standard for a 3-1/2 in. draft of harness. The levelling frame or slabstock is levelled to this height by means of a spirit level and straight-edge, making allowance for whatever spring there may be in the harness after it is tied, and the wires drawn out of the mails. This can only be ascertained by experience, and depends principally on the tension the mounter puts on the twines when tying them; it will also depend upon whether the harness twines have any spring in them or not, but they should be well stretched before being used, to avoid this. A mounter who ties slackly will generally make a more level harness than one who ties tightly. About 1/8 in. may be allowed for the mails to rise if the cords are slackly tied, and if tightly tied 1/4 in. may have to be allowed, and sometimes more than this.
Sometimes the level is taken by placing a straight-edge on the race of the lay, when the cranks are at the back centre; then the under edge of the straight-edge should give the position for the tops of the mails on the slabstock, when it is fixed in its position in the loom. In levelling by this method the race must first be set at the proper height, and it must also be properly bevelled. From 1/2 in. to 3/4 in. below the breast beam is a good level at which to have the race, when the cranks are at the top centre, the latter for a low harness. The angle, or bevel, of the race may not at all times suit for levelling in this way. If not, the race should be made correct when possible; if it cannot be corrected, the harness must be levelled a little lower and the back rail kept down for working. A loom with the race bevelled for plain work is not suited for damask; the angle between the race and reed should, for damask, be about 93°, whereas for plain 87° would be more suitable.