Machinist precision grinding and grinding wheels practice questions (429A).

Five free practice questions on precision grinding and grinding wheels: block G of the Red Seal 429A Machinist exam, about 11 of its 135 questions. They are in the exam's format: four options, one correct answer. Answer each one before opening the explanation. No account, no email.

01The questions

1. Procedural · Plans operation of grinding machines

   Which wheel marking suits finish grinding a hardened tool-steel die plate on a surface grinder?

   1. A60-H8-V
   2. C60-H8-V
   3. A60-R8-V
   4. A24-H8-V
   Show the answer

   A. Correct. A is aluminum oxide, the abrasive for steels; 60 is a medium grain that leaves a good ground finish; H is a soft grade, which lets dull grains break away on hard work instead of rubbing and burning; 8 is a medium structure; V is the vitrified bond used for precision grinding.

   Why not the others

   B. C is silicon carbide, the usual choice for cast iron, non-ferrous metals and carbide. For hardened steel the conventional abrasive is aluminum oxide, as in A60-H8-V.

   C. R is a hard grade. A hard wheel holds its dulled grains on hardened steel, so it glazes and burns the work; hard work needs a soft grade such as H.

   D. 24 is a coarse grain for heavy stock removal and leaves a rough surface. A finishing pass on a die plate calls for a finer grain, such as 60.

2. Procedural · Sets up work holding devices for precision grinding machines

   A small steel block sits on a single pole strip of a magnetic chuck and shifts when the wheel touches it. What change gives it a secure hold?

   1. Shim it on paper so it seats evenly.
   2. Raise it on a solid steel parallel.
   3. Set it to bridge two or more poles.
   4. Move it to the middle of the chuck face.
   Show the answer

   C. Correct. Holding force comes from magnetic flux passing from one pole through the work and into the next. A part on a single pole strip has almost no flux path; set across the insulating lines so it spans poles, it is pulled down hard. Small parts are also blocked in with thinner steel pieces.

   Why not the others

   A. Paper adds an air gap between the part and the chuck, and an air gap cuts magnetic holding force sharply. The cure is to make the part bridge two or more poles.

   B. A solid steel parallel lying across the poles carries most of the flux itself and passes little up into the part on top. Laminated parallels are made for that job; the direct fix is to set the part across two or more poles.

   D. Moving the part along the chuck does not help while it still sits on one pole strip; the hold depends on how many poles it bridges, so it will shift just as easily in the middle.

3. Procedural · Selects precision grinding machine speeds and feeds

   A 400 mm wheel is grinding a 40 mm diameter shaft on a cylindrical grinder. The chart gives a work surface speed of 18 m/min. What work speed is set, to the nearest rpm?

   1. 14 rpm
   2. 143 rpm
   3. 450 rpm
   4. 286 rpm
   Show the answer

   B. Correct. Work speed uses the work's diameter: rpm = (1 000 × CS) ÷ (π × D) = (1 000 × 18) ÷ (3.1416 × 40) = 18 000 ÷ 125.66 = 143 rpm.

   Why not the others

   A. This puts the 400 mm wheel diameter into the formula. The work speed is set from the work's own diameter, 40 mm, which gives 143 rpm.

   C. This leaves π out: 18 000 ÷ 40 = 450. Dividing by π × D is what turns the surface speed into revolutions; the answer is 143 rpm.

   D. This uses the 20 mm radius instead of the 40 mm diameter, doubling the result. With the diameter, (1 000 × 18) ÷ (3.1416 × 40) = 143 rpm.

4. Procedural · Grinds internal and external cylindrical and tapered surfaces

   A single-point diamond set pointing straight at the wheel's centre chatters as it dresses and leaves an uneven face. What change corrects the set-up?

   1. Slow the diamond's traverse across the face.
   2. Cant it to point against the wheel's rotation.
   3. Cant it to point with the wheel's rotation.
   4. Raise it above the wheel's centre height.
   Show the answer

   C. Correct. Tilted so its point trails in the direction the wheel turns (a drag angle), the diamond rides the face instead of being driven into it, so it stops digging in and chattering. Turning it slightly in its holder from time to time also keeps the point sharp.

   Why not the others

   A. Traverse rate decides how open or fine the dressed face is, not whether the point digs in. Cant the diamond to point with the rotation.

   B. Pointing into the oncoming wheel lets the face drive into the diamond, so it digs in and chatters worse. The point should trail with the rotation.

   D. Above centre is the wrong way: a dresser is set at or slightly below the wheel's centre line, and raising it makes digging in more likely. The cure is a drag angle with the rotation.

5. Recall · Finishes holes using a honing machine

   In honing a bore, what sets the cross-hatch angle of the finish?

   1. The grit size of the honing stones.
   2. The pressure applied to the honing stones.
   3. The ratio of stroke to rotation speed.
   4. The length of the stones in the hone.
   Show the answer

   C. Correct. Each abrasive grain traces a helix whose angle depends on how fast the hone strokes compared with how fast it turns. A faster stroke at the same rpm opens up the cross-hatch angle, so the stroke is matched to the rpm for the pattern specified.

   Why not the others

   A. Grit size controls how deep the scratches are, and so the roughness, not the angle at which they cross. The angle comes from the stroke speed compared with the rotation speed.

   B. Stone pressure governs the rate of stock removal and, if excessive, distortion of the bore. The cross-hatch angle comes from the ratio of stroke speed to rotation speed.

   D. Stone length affects how well the hone bridges and corrects the shape of the bore, not the angle of the scratch pattern. That angle is set by stroke speed against rotation speed.

02Answer key

03What block G covers

Block G covers precision grinding: surface grinders, cylindrical and internal grinding, tool and cutter grinding, and honing. It includes choosing a wheel from its marking, ring testing and mounting it, truing and dressing, magnetic chucks and other work holding, work speeds and feeds, and reading faults such as loading, glazing and chatter from the wheel and the finish.

The Red Seal Occupational Standard names this block “Machines using precision grinding machines”. It carries 8.1% of the exam, about 11 of the 135 questions, split across two tasks. The share column is each task's weight within the block, as the standard publishes it.

04What the questions turn on

Loaded or glazed

A loaded wheel shows bright specks of metal packed into its face, typical of soft, ductile steel on a fine, dense wheel. A glazed wheel is evenly shiny with no metal in it, because the grains have worn flat.

Truing is not dressing

Truing cuts the wheel until its face runs concentric with the spindle and has the shape the job needs. Dressing sharpens and opens the cutting face. Read the fault described to decide which one it calls for.

A dead note means reject

A sound vitrified wheel gives a clear ring all the way round when tapped. A dead note at one spot points to a crack. The wheel is not mounted or run: tag it, set it aside and report it.

Why you spark out

Under infeed the wheel, work and machine spring slightly, so less comes off than the dial shows. Passes with no added infeed let that deflection relax and grind away the remaining stock for true size.

05The other blocks

The 429A exam has eight blocks. Each has its own page of free questions:

The 429A Machinist practice exam page describes the full question bank. How these questions are written and checked: how our questions are made. Found a mistake? Tell us and we will fix it.