14 CIRCULAR 558, U, S. DEPARTMENT OF AGRICULTURE 
RECTION OF OPTIMUM MILE SPEED T@ Dian iEiinrs 
OF, CYLINDER 
The comparison was made of two medium-sized hammer mills in 
processing the seed of blue wild-rye and tall oatgrass. The specifica- 
tions for these mills are given in table 1. One has swinging hammers, 
the other solid hammers. Preliminary trials were made to determine 
optimum cylinder speed for each mill, and then trials at not less than 
100 r. p. m. above and below the optimum speeds were made. The 
detailed data are not presented, but when optimum speeds were used 
with correct screen size, the mills showed no essential difference. It 
was found that the optimum speed of the 22-inch cylinder was 940 
r. p. m. for blue wild-rye and 900 r. p. m. for tall oatgrass, whereas, 
the corresponding speeds with the 26-inch cylinder were 730 and 720 
Yr. p.m., respectively. In other words, the small cylinder was used at 
approximately 25 percent greater speed than the larger cylinder. It 
therefore appears that the periphery speed of the cylinder in feet per 
minute determines the effectiveness of the operation. The circum- 
ference of the 22-inch cylinder was 5.759 feet; that of the 26-inch 
cylinder was 6.807 feet or 18 percent greater. The periphery speed of 
the smaller cylinder at 940 r. p.m. was 5,413 feet per minute and that 
of the larger cylinder at 730 r. p. m. was 4,969 feet, a difference of only 
8.9 percent in favor of the smaller cylinder. This difference could, no 
doubt, be reduced, since the variation of +25 r. p. m. must be al- 
lowed when determining optimum cylinder speed. 
The presumption is that for medium-sized mills, other conditions 
being equal the speed of operation should vary from the optima 
recommended in table 3 by about 40 r. p. m. for each inch of differ- 
ence in diameter of the cylinder, being decreased with increases in 
diameter, and vice versa. 
It should be noted that the area of screen was 68 square inches 
oreater in the 26-inch mill, the effect of which was not determined. 
This mill also had 364 square inches of a }-inch screen spot-welded 
in the hood, which may have been effective in the work. However, 
the data are taken to indicate that these differences are less significant 
than the periphery speed of the cylinder. 
SUMMARY 
This circular reports methods of processing seed to remove awns 
and other appendages from species that have been restricted in their 
use because of the difficulty of planting them with ordinary machinery. 
Seed of the following species adapted to the Pacific Northwest were 
processed: Bluebunch wheatgrass (Agropyron spicatum), blue wild-rye 
(Elymus glaucus), Canada wild-rye (£. canadensis), Siberian wild-rye 
(EH. sibiricus), tall oatgrass (Arrhenatherum elatius), bulbous barley 
(Hordeum bulbosum), squirreltail (Sitanion hystrix), alfileria (Hrodium 
cicutarium) and virgins-bower (Clematis ligusticifolia). 
Processing was done by milling threshed seed in a hammer mill 
and cleaning it with a seed cleaner. 
Seed can be successfully milled if the speed of the hammer-mill 
cylinder is reduced to less than half the normal grinding speed, the 
correct size of screen used, and the mill fed at the full rate. 
