GINNING PIMA COTTON IN AEIZONA 7 
All rollers should be grooved to prevent motes or small defective 
seeds from hanging on the fixed knife, causing crimp or cut cotton. 
The grooves are V-shaped, being one-eighth of an inch wide, three- 
sixteenths of an inch deep, and IV2 inches apart. These grooves 
should never be allowed to close. The direction of the grooves is 
diagonal and opposite to the direction of the leather strips, making 
one turn in the length of the roller. 
Gins with a 40-inch roller and a short moAung knife are consid- 
ered preferable. Longer rollers have a tendency to give, or buckle, 
in the center, causing the cotton to wad between the fixed knife and 
the roller. The moving knife if too long frequently buckles in the 
middle when it strikes an accumulation of seed cotton. To avoid 
this the moving knife in some long-roller gins is made in two or three 
pieces, but the mechanism for driving a three-bladed knife is more 
complicated and difficult to repair than that with the knife in one 
piece. At the point where the sections of the moving knives pass 
each other a groove becomes worn in the roller, because at this point 
a little seed cotton often hangs on the fixed knife. As a result some 
of the seeds are often crushed and delivered with the lint cotton. 
The rapidity or rate of ginning is largely dependent on the pres- 
sure of the fixed knife on the roller. With longer rollers it is more 
difficult to get an even pressure along the full length of the knife 
without danger of its buckling in the center. With long rollers, there- 
fore, less pressure must be used and a thinner sheet of cotton turned 
out, which reduces efficiency. This is proved by the fact that the 
output per hour from gins with 40-inch rollers equals or exceeds 
that from longer roller types and with less trouble than is likely to 
occur with them. The added cost of walrus leather on the longer 
rollers is another objection to the use of this type. 
SETTING THE FIXED KNIFE 
Though most gin stands are built so as to allow for different ad- 
justments of the fixed knife, there is no occasion in practice to make 
any such adjustments. This feature of gin operation can be greatly 
simplified by a proper setting of the knife, which remains fixed. One 
way of doing this is to remove the clamps which in some gins are 
intended to hold the fixed knife against the roller and to replace 
them by a single bar of quarter-inch steel, 3 inches wide. Using the 
same bolts the fixed knife, preferably with a single beveled edge, 
should be clamped against the rabbet of the top cross rail with the 
straight side to the roller in a position that will bring the edge of the 
fixed knife one-sixteenth of an inch below the center of the roller. 
The desired pressure of the roller against the knife is obtained 
by adjusting the roller boxes. Care must be taken to adjust both 
ends so as to have equal pressure on the Avhole length of the roller, 
causing the cotton to come over the roller steadily. By eliminating 
the small clamps and giving the knife a fixed relation to the roller, 
there is no chance of missetting the knife, and all the gin stands can 
be given the same adjustment, which is essential to 'uniform results 
in ginning and the uniform appearance of the cotton. 
If the fixed knife is set above the center of the roller there is 
danger that in trying to bring the moving knife close to it, in order 
to avoid cracking the seed, the moving knife will rub against the 
