Getting Gold: A Gold-Mining Handbook for Practical Men

by J. C. F. Johnson

18 lb.	hammers are used for			3 in. boring bars.
16 lb.	”	”	”	2½ in. ”
14 lb.	”	”	”	2 & 1¾ in. ”
5-7 lb.	”	”	”	1 in. ”

The boring bars may be made of 1¹∕₈ inch bar iron of various lengths, with steel bits up to 3 inches. A bit should bore from 18 feet to 24 feet with each steeling, and requires to be sharpened once for every foot bored.

3	men with a	3-inch	bar should bore	4	feet.
3	”	2½ ”	”	6	”
3	”	2 ”	”	8	”
3	”	1¾ ”	”	12	”
2	”	1 ”	”	8	”

per day of 10 hours in hard granite.

Power, etc., Required To Work Rock Drills.

H-P.	Diameter of Air Cylinder.	Diameter of Steam Cylinder.	Stroke.	No. of 3-inch Drills driven.
	Inches.	Inches.	Inches.
6	8	8½	12	1
10	10	10½	16	2
12	12	12¼	22	3
16	13	13	24	4
20	14½	14½	28	5
30	17½	17½	36	8
40	20	20	36	11
60	22	24	60	15

Power Required to Work Double Steam and Air Cylinders.

H-P.	Diameter of Air Cylinder.	Diameter of Steam Cylinder.	Stroke.	No. of 3-inch Rock Drills driven.
	Inches.	Inches.	Inches.
28	12	12	22	7
32	13	13	24	8
40	14½	14½	28	10
60	17½	17½	36	15
80	20	20	36	22
120	22	24	60	30

DURABILITY OF ROPES.