Milling and Drilling Operations Questions and Answers

Answer: B

They should remain parallel to each other.

A plate cam is milled on a vertical milling machine with the cam blank on a dividing head. The dividing head spindle and the vertical head spindle are tilted to the same angle, keeping the axis of the blank parallel to the axis of the end mill. As the blank is rotated and fed, the end mill then cuts the cam profile square across the blank's face, and the angle of tilt sets the lead (rise) of the cam.

If the axes were inclined to each other the cutter would cut the profile at a slant. 'Opposite' and 'vertical and inclined' do not describe a fixed geometric relationship at all.

Answer: C

The indexing head is used to drill holes on pitch circle diameter.

An indexing (dividing) head holds the work and rotates it through precise fractions of a turn, using a worm and worm wheel (usually 40:1) and an index plate. That is how a milling machine divides a circle into equal parts: cutting the teeth of gears, the flutes of reamers, the flats of a nut, or drilling equally spaced holes on a pitch circle.

It does nothing to the cutting speed or the surface finish; those depend on the spindle speed, the feed and the cutter. So 'All of the above' is also wrong.

Answer: D

The answer is None of the above, because all three statements are true.

Gang milling uses two or more cutters mounted together on the same arbor of a horizontal milling machine, so that several surfaces are machined in one pass. The cutters may be of the same or different diameters and widths, depending on the profile and the heights of the surfaces to be cut, and each cutter is mounted on the arbor.

Since none of the first three statements is false, none of them can be 'not true', which leaves 'None of the above'. Straddle milling is the special case of two side-and-face cutters spaced apart to machine two parallel faces at once.

Answer: C

Solid milling cutters are made from HSS.

High speed steel is tough enough to be made into a one-piece cutter with many fine teeth, and it can be ground and resharpened easily. That is why plain, side-and-face, slitting, form and end mills are commonly solid HSS.

Carbide and ceramic are too brittle and costly to make whole cutters of most sizes; they are used as brazed tips or indexable inserts in the cutter body (small solid carbide end mills are the exception). Stellite is a cast cobalt alloy used for tool tips and hard-facing, not for solid cutters.

Answer: C

The answer is the Multi station drill machine.

A multi-station drilling machine holds several workpieces at once, each in its own fixture at a station on an indexing table or transfer line. All the stations work at the same time, and at each index every part moves on to the next station, so several workpieces are drilled together and a finished part comes off at each cycle.

A gang drilling machine is a row of independent single-spindle columns on a common table; it is meant for a sequence of different operations (drill, ream, tap) on a job moved by hand from one spindle to the next. A pillar drill has a single spindle and drills one workpiece at a time.

Answer: A

Back taper is a slight decrease in diameter from front to back in the body of the drill.

A twist drill is made very slightly smaller in diameter towards the shank, along the fluted body, typically by a few hundredths of a millimetre per 100 mm. This back taper keeps the lands from rubbing on the wall of the hole behind the cutting point, reducing friction, heat and the risk of the drill seizing.

A decrease from back to front would make the drill wedge tighter as it goes deeper. The taper is on the body, where the drill is in the hole; the shank is either straight or carries a Morse taper for holding, which is a different thing.

Answer: D

The process is Spot facing.

Spot facing machines a small, flat, circular seat square to the hole axis around the mouth of a drilled hole, usually on a rough casting or forging, so that a bolt head, nut or washer bears evenly on it.

Counter boring enlarges the hole to a definite depth to sink the bolt head below the surface, which is deeper than a spot face. Counter sinking makes a conical recess for a countersunk screw head. Reaming finishes the hole to an accurate size and does not produce a seat.

Answer: A

The drill size is 9.75 mm.

Before reaming, the hole is drilled smaller than the finished size to leave a reaming allowance. Using the workshop formula

\[ \begin{aligned} \text{drill size} &= \text{reamed size} - (\text{undersize} + \text{oversize}) \\ &= 10 - (0.2 + 0.05) = 9.75\ \text{mm} \end{aligned} \]

9.8 mm subtracts only the undersize and leaves out the oversize a drill tends to cut. 10.25 mm is larger than the reamer, which would leave nothing to ream, and 9.85 mm subtracts the difference of the two allowances (0.2 − 0.05) instead of their sum.