Machining and Cutting Tools Questions and Answers

Answer: D

Pitch of a power hacksaw blade means the number of teeth per inch.

Hacksaw blades are specified by teeth per inch (25 mm). A coarse power hacksaw blade has about 4 to 6 teeth per inch, a medium one 10 to 14, and fine blades 18 to 32. The same count is often written as teeth per 25 mm.

Teeth per 10 mm, per 20 mm or per 10 cm are not units used to grade blades. Strictly, pitch is the distance between adjacent teeth, but trade usage states it as a teeth-per-inch count, which is the reading the question takes.

Answer: A

The pilot helps finish concentric holes.

A pilot is a plain, uncut extension on the front of a reamer, a counterbore or a spot-facer. It fits into an existing hole and guides the tool so that the reamed or counterbored hole stays concentric and in line with it.

Chips are removed by the flutes, not the pilot. Holding the tool in a tap wrench or in the machine spindle is the job of the shank: a square end for a wrench, or a straight or Morse taper shank for the spindle.

Answer: C

A die nut is used for chasing and conditioning damaged threads.

A die nut is a solid, hexagonal die turned with a spanner. It is not adjustable and is not meant to cut a thread from a plain rod; it runs over an existing external thread to clean it, remove burrs and restore thread that has been bruised or rusted.

New threads are cut with an adjustable circular split die in a die stock. Improving surface finish is not its stated purpose; the die nut reforms the thread profile.

Answer: C

The cutting fluid for aluminium is kerosene.

Aluminium is soft and tends to stick to the cutting edge, forming a built-up edge. Kerosene, or paraffin, is a thin oil that wets the surface well, prevents the chips welding to the tool and gives a good finish, which is why trade practice lists it for aluminium.

Water alone does not lubricate and promotes corrosion. An air jet only clears chips and cools slightly. Ethanol is not used as a cutting fluid in workshop practice.

Answer: D

The part of a file that is not hardened and tempered is the tang.

The body, edges and heel carry the cut teeth or bear against the work, so they are hardened to keep the teeth sharp. The tang only fits into the handle. It is left soft so that it is tough rather than brittle and will not snap when the handle is driven on or when the file is levered sideways.

The heel is the part of the body next to the tang and is hardened like the rest of the body. The edge is either cut or a hardened 'safe edge' without teeth.

Answer: B

The key gives excessive clearance angle as the cause of tool chatter.

Clearance is ground below the cutting edge so the flank does not rub on the work. If it is made too large, too little metal is left behind the edge to support it. The weakened edge deflects and springs back under the cutting force, and the tool vibrates against the work, which is chatter.

Too small a clearance makes the flank rub, causing heat, wear and a poor finish rather than vibration. Rake angle mainly controls chip flow and cutting force; a very large rake also weakens the edge, but the trade texts this paper follows list excessive clearance as the cause.

Answer: B

The prick punch used for witness marks is ground to 60 degrees.

Prick punches are made with two point angles. The fine 30 degree point makes light marks used to locate the leg of a pair of dividers. The 60 degree point makes the bolder marks punched along a scribed line as witness marks, so that the line can still be seen if the scribed mark is rubbed off.

90 degrees is the angle of a centre punch, which makes a large mark to start a drill. 20 degrees is not a standard punch angle, and the 30 degree prick punch is for divider marks, not witness marks.

Answer: D

The item that is not a tool is the box file.

A box file is an office folder for storing papers. Its name contains the word 'file', which is the trap.

The other three are fitter's files, cutting tools with rows of hardened teeth: a hand file is a flat file of uniform width with one safe edge, a flat file tapers in width and thickness towards the tip, and a curved-tooth file has arc-shaped teeth for soft metals such as aluminium.

Answer: B

An engineer's vice is specified by the width of its jaws.

A bench vice is sold as, for example, a 100 mm, 125 mm or 150 mm vice, and that figure is the width of the jaws, the length of the gripping face measured across the vice.

The maximum opening also matters to the user, but it is a secondary figure, not the size by which the vice is named. The length of the movable jaw and the height of the vice are not used to specify it.

Answer: A

The key's answer is a negative rake angle.

The harder and stronger the work material, the smaller the rake angle should be, because a small rake leaves more metal behind the cutting edge. With a negative rake the cutting force pushes the edge into compression instead of bending it, which suits hard, high carbon steel and the brittle carbide tool tips used to machine it.

A large positive rake is for soft, ductile metals such as aluminium and copper. Zero rake is typical for brass. The key takes the carbide-tool case; with a high speed steel tool, a small positive rake is the usual choice for high carbon steel, which is why that option is a near miss.