180 GRAVEL AND PLACER MINING IN ALASKA. [bull. 26: 
heptagonal, and octagonal tumblers and per cent of saving of vvea 
over the square type. The wear and tear of bucket pins and bush 
ings is almost entirely the result of the deflection of the buckets i 
rounding the tumblers. A slight amount of wear is occasioned b 
deflections back of the lower tumbler as the buckets come in contac 
with the material. These last deflections, however, would be prevente 
by rollers such as are suggested in a paragraph on page 184 discussin. 
the respective merits of the spud and headline. 
If, instead of square upper and lower tumblers, pentagonal, hexagc 
nal, heptagonal, or octagonal tumblers are used the saving of wear o 
bucket pins and bushings would be approximately 40, 66, 86, and 10 
per cent, respectively. 
There is but one serious objection to the use of a lower tumbler o 
more numerous faces, i. e., greater size and weight. The great savin 
in wear of the bucket pins and bushings will, when fully appreciated 
result in the use of both upper and lower tumblers of more numerou I 
faces. (See PL XXXIII, .4.) 
One dredge manager of much experience has suggested the use o 
a round lower tumbler of large diameter with buckets of short pitch 
claiming that buckets seldom lie flat on tumbler faces when excavat 
ing, but frequently ride the corners between the faces. This difficult; ; 
has been observed by the writer on many Occasions. A too rapi . 
feeding of buckets resulted in considerable spilling of material upo. 
the buckets about to round the lower tumbler. The spilled materia; 
lodged between the buckets and the tumbler faces and destroyed, tern 
porarily, their proper relation. The use of the round lower tumble 
would have the additional advantage of preventing surging (se 
p. 184). 
Until recently it has not- been generally regarded as good practic 
to lower the digging ladder to more than 45° from the horizonta 
because of supposed disadvantages in such manipulation. Recen : 
installations provide an idler at the rear end of the well to preven 
the buckets from dragging on the chutes and the save-all gratings a 
the ladder is lowered more than 45° from horizontal. This devic 
permits greater working depths with a given length of ladder am 
makes deeper ground available for the dredge. PI. XXXIII, B 
illustrates diggings at a low angle. There is a marked diversity o< 
opinion among managers as to the relative merits of the trommel am 
shaking screen. The trommel advocates have claimed better mechan 
ism, cheaper maintenance, more efficient screening when material is a 
all tenacious, and economy in power. The advocates of the shaking 
screen have claimed larger capacity with given weight, higher per 
centage of gold saving because of better opportunities for amalgama 
tion by impact, and easier and better distribution of material over th< 
gold-saving surfaces. 
