Technology and our changing world high Technology

Review questions.

1. 
   Whatkind of blade should beused when hacksawing brass tubing?
   
2. 
   How do you position the piece in the horizontal band saw to cut it to tiieproper length?
   
3. 
   Why should you place your work over a soft surface when cutting with the cold chisel?
   

DRILLING
A common but very important operation in metalworking is the drilling or cutting of round holes.
Drilling is die first step in installing the screw, bolts, and rivets needed to fasten parts together.


Drilling Machines and Equipment
A bench or floor type drill press is the most common machine for drilling operations. The largest workpiece a drill press can handle is determined by measuring the distance from the drill chuck and bit to the support column.
A chuck holds straight-shank twist drills. The shank is the aid that fits into the chuck, or holda. On larga drill presses, a taper-shank drill fits directory into the spindle or is held by a sleeve or socket.
The electric hand drill has a pistol-grip handle on which the on-off switch is located. Light electric hand drills take straight-shank drills up to 'A” in diameter. Heavier ones may take twist drills up !4”. The manual hand drill is used mudi the same as the electric hand drill. Hand drills usually found in school shops can take drills up to ³4”.
A drill press vise is used to hold workpieces. Otha clamping and holding devices such as wrenches, pliers, and C-clamps are also useful for safely holding work to be drilled. A V-block is used when drilling round stock.
Twist drills are made of high-speed steel. They are marked HS or HSS. Straight shanks fit into a chuck. Taper-shank drills are used on larga drilling machines and lathes.
Customary drill sizes shown by number, letter, and fraction. Numba (wire gauge) sizes range in diameter from the smallest, No. 80 to the largest, No.1 .Letter sizes range from the smallest, A, to the largest, Z. Fractional sizes range from 1 /64” upwards by 64 ths. Fractional drills are used for most work. Sometimes numba and letter drills are needed for accurate tapping or reaming.
Common metric sets of drills range in size from 1 mm to 12 mm.