In shaft sinking, the same support, slightly modified, is used without the trolly. The arrangement adopted in this case is shown in Fig. 29, Plate VII. The central bar is held firmly in its position by a cross stretcher bar set against the sides of the shaft. The arms are made to revolve upon this bar to allow the holes to be bored in the positions required. When all the holes have been bored, the support, with the machines, is hauled up, by means of a chain attached to the central bar, out of the way of the blast. With this support, the time of fixing, raising, and lowering is reduced to a minimum; while the facility with which the machines may be slid along and fixed to the arm, and the positions of the latter changed, allows the boring to be carried on rapidly.
For open work, as in quarrying, where the stretcher bar cannot be used, the tripod stand is adopted.
_The Dubois-François Carriage._--The support commonly used in France and in Belgium consists of a kind of carriage carrying bars upon which the drills are set. This carriage is used in drivings of all kinds; but it is particularly suitable for tunnelling. It has been adopted, with but slight modification, in the St. Gothard tunnel, and in several other important works of the like character.
A modification of the carriage is shown in Figs. 30 and 31. Being designed for ordinary mining operations, it carries but two machines; but it will be readily perceived that, by increasing the number of vertical screws, the same support may be made to carry a larger number. It consists essentially of a vertical frame of flat bar iron _a b c d_, 8 feet in length, and 4 feet 9 inches in height above the rails, the hinder portion of which rests upon a cast-iron plate _e f g h_, carried upon two wheels; on this are fixed the two uprights _l_, _l′_, which, being bound to the upper part by a transverse bar _m m′_, form a framing to serve as a support to the two vertical screws _p′_, _q′_. The front framing is formed of two longitudinals _b c_ and _b′ c′_ and the uprights _a_, _a′_, and the vertical screws _p_, _q_, which are connected to the upper part by the single piece _a d_. This framing is supported below upon a small trolly with four wheels, connected to the two longitudinals of the framing by a pivot bolt _n_ of ~T~ form, the bar of the ~T~ being inserted into the elongated openings _o_ cut through the middle of the curved portion of the longitudinals. The cast-iron plate behind, the use of which is only to give stability to the carriage, carries above it, by means of the two curved pieces _h_, _h′_, a wrought-iron plate V, upon which the small tools needed for repairs are kept. Two screws, _s_, _s′_, carried by lugs cast upon the back of the plate, serve, by turning them down upon the rails, to fix the carriage, the latter being slightly lifted by the screws.