8 BULLETIN 1319, U. S. DEPARTMENT OF AGRICULTURE 
roller. The closest approach of the moving knife should be to the 
edge of the fixed knife and not to the surface of the roller. If the 
moving knife rubs against the roller, the surface of the roller will 
be roughened so that the cotton will adhere and be carried under the 
roller, which is called " backlashing." The roller often is moistened 
with a wet cloth or swab to stop backlashing, but the surface soon 
gets rough again by the rubbing of the moving knife. 
The pressure of the fixed knife on the roller should be just 
enough to pull the cotton over in a continuous sheet at a steady rate. 
(PL VII.) Too much pressure will produce extreme heat, causing 
the fiber to fold or crumple and giving the cotton a rough appear- 
ance. Samples of such cotton also are likely to appear somewhat 
darker in color on account of the shadows that are cast by the uneven 
surface. 
HOW THE KNIVES FUNCTION IN GINNING 
The moving knife passes through a short arc, the middle of which 
should be at the edge of the fixed knife, the space between the knives 
increasing until the moving knife reaches the top of the stroke. 
When the moving knife is down, the cotton comes in contact with 
the roller and the lint is carried under the fixed knife. Some of the 
fiber separates from the seed the first time the moving knife goes 
up, while some of it still adheres to the seed. The remaining fiber 
draws the seed back as the moving knife goes down and again 
passes under the fixed knife until stopped by the seed ; but with 
the next upward stroke of the moving knife the seed usually is 
knocked away, and the lint is free to pass over the roller. 
When the overlap of the moving knife (its swing above the 
edge of the fixed knife) is too short, more strokes of the moving 
knife are required to separate the seed. Meantime more cotton may 
be accumulating under the fixed knife, and a thick sheet may be 
formed which comes over the roller in a badly crimped or rough 
condition. (PL VIII.) With a longer overlap of the moving knife 
the cotton goes through more quickly, and since there is then less 
accumulation of cotton under the fixed knife the fiber comes over the 
roller in a thinner sheet, giving it a much smoother appearance. 
When the moving knife has only a short overlap, the upper surface 
of the sheet of cotton coming over the roller usually is much smoother 
than the lower surface which lies against the roller, the roughness 
of the sheet of fiber being due to the accumulation and crumpling 
that occur. (PL IX.) 
ADJUSTMENT OF THE MOVING KNIFE 
The overlap of the moving knife should be at least three-quarters 
of an inch when the length of the staple is from 1% to l^J inches. 
If the fiber is shorter, the moving knife should be lowered to reduce 
the overlap, while for a longer staple the knife should be raised to 
increase the overlap. The speed of the roller should be 100 revolu- 
tions and that of the moving knife TOO revolutions per minute. 
At these speeds the gins will stay set, and unnecessary wear on the 
roller and moving parts will be eliminated. Greater speeds heat the 
moving parts and tend to prevent the seed cotton from coming in 
contact with the gin roller. 
