FOREST PRODUCTS LABORATORY t FOREST SERVICE .U. S. DEPARTMENT OF AGRICULTURE
SMALL SAWMILL IMPROVEMENT
PRACTICAL POINTERS TO FIELD AGENCIES
S AW LE AD
considerable number of small mi I; er do not
maintain the correct lead in the saw. eto inaccurate adjusting for lead, skewing of th e belt
pull levered through the mandrel, creep of sills from rain or frost, etc. The result is a saw which dodges in the cut, heats, and performs very much like one in need of hammering.
Lead is put in a circular saw to counteract the tendency of the saw to cut out of the log in slabbing and to give clearance of the back of the saw on the gig back. Normally 1/8 inch in 20 feet is used, or a saw 4 feet in diameter has the front edge 1/40 inch closer to the track than the back edge. If this saw is run in a perfectly vertical position, the back edge will clip on the board side approximately 1/32 inch until the spreader is engaged. Additional lead increases the depth of this clipping. When the front edge is 1/10 inch closer to the log than the back edge, the board side contacts the saw about half way back and forces the blade against the log face at the extreme back of the saw, thus effecting a clamp which usually heats the rim and the midportion of the saw. spreader is engaged the pressure may be reli itial 4 feet of feed under this clamping a t enough to cause the saw to dodge even when narrow faces in cants. Apparently as the log passes th ugh the sa ore reaching the spreader, the side thrust at t e bactf[h1iNlade is accompanied by a tendency of the saw to ay over as it revolves out of the log, hence the cutting ed is turned slightly out of the log. As the spreader is en a e fjOrd
thrust is eliminated and the cutting edge ca bw ''k
is liable to dodge from a true cut if heatin occurred.
Of the several methods used to measure lead, the follow. Ing is recommended for simplicity and accuracy: Stretch a string or fine wire over the track to extend about 6 feet each side of the mandrel, being careful that it is exactly in line with the part of the guide rail that controls carriage alignment -- the top of the V in this type or the inside edge where flat-topped rails are used. Remove the saw, and clamp the end of an edging 5-1/2 feet in length between the collars. Use a short piece of the edging on the opposite side of the mandrel so that the collars have contact at opposite sides of the
Mimeo. No. R899-20
tMainatind at Madison, Wiscosin in cooperathm with the University of Wisconsin See outmei in Small Sawmil Improvent Working Plan, March 1930, for explanation of indexing system proposed
UNIVERSITY OF FLORIDA
mandrel. Turn the stick down until theLf-ree 31262089269764e
opposite the track by turning the mandrel-P~ulley; do not try tq turn by pulling the stick. Measure the distance from the stick to the string, marking the point on the stick from which the measurement is taken. Turn the stick over, by turning the Pulley, until the unclamped end is again opposite the rail, and -measure from-the marked point to the string. The distance at the deck end should be 1/16 inch less than at the opposite position. Adjust to the required position by slewing the mandrel, in mills provided with adjusting screws, or by slewing the husk when such mechanism is lacking. In slowing the mandrel before adjusting the box nearest the saw, relieve the other boxes so as not to strain the mandrel.
The use of lag screws to anchor the husk to the mudsills is not recommended. Bolts from the tie plates or husk should extend through the mudsills and heavy washers should be used at each end of the bolt. A plate or block on the top of each mudill fixed between the track and husk adds rigidity.
C. J. Telford,
Mimeo. No. R899-20' -2-