=33.= There are three types of head-frame construction--_the_ =A=
_type_, the _square type without an inclined brace_, and the _square
type with an inclined brace_.
=34. A Type of Head-Frame=.--Fig. 32 shows the construction of a
triangular, or =A=-shaped, head-frame of which (_a_) is a side
elevation and (_b_) an end view. This particular frame is largely
used at anthracite mines, but the type is one quite commonly used for
timber frames, though the details of construction vary in different
localities. The height of the frame is from 30 to 50 feet, and with
direct-acting engines this height should be sufficient to allow a play
of at least two-thirds of a revolution between the cage landing and the
overwinding point. The posts _a_ are parallel to the hoisting rope _b_
as it hangs down the shaft and the inclined brace _c_, which resists
any thrust that would tend to rotate the head-frame, is parallel to the
resultant pull of the two parts of this rope _b_; the inclined braces
_d_ stiffen the frame and help support the cross-timbers _m_ that
support the cage guides _e_. The sills _f_ are made of three pieces of
timber 8 inches by 14 inches in cross-section. The posts _a_ rest in
cast-iron shoes _g_ that are firmly bolted to the posts and sills. The
inclined braces _c_, _d_ are fitted with cast-iron shoes _h_, _i_. The
post _a_ and the two braces _c_, _d_ are held in place at the top of
the frame by the casting _j_, which also supports the pillow-block _k_.
The posts _a_ and the brace _c_ are made up of two pieces of timber
each 8 inches by 14 inches in cross-section. The brace _d_ consists
of one piece of timber 8 inches by 14 inches in cross-section. The
transverse braces _l_ consist of two pieces of timber 6 inches by 14
inches in cross-section, bolted through the timbers _a_ and _c_. The
supports _m_ for the guides are single pieces of 8" × 8" timber. The
center post, as shown in Fig. 32 (_b_), is braced by the two pieces
_n_, _o_, which are supported by two timbers _p_, _q_ bolted to the two
outside posts. The posts _a_ and the inclined braces _c_ are further
braced by the tie-rods _r_, _s_, _t_, and _u_, all of which are fitted
with turnbuckles, as shown at _v_. The different posts are firmly
bolted together, the bolts being fitted with cast-iron washers.
[Illustration: (_a_) (_b_)