Machinist lathe turning, tapers and threading practice questions (429A).

Five free practice questions on lathe turning, tapers and threading: block E of the Red Seal 429A Machinist exam, about 28 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 · Sets up tooling for conventional lathes

   After a 60° threading tool is clamped in the toolpost on centre height, how is it set square to the work?

   1. Square the toolholder to the cross-slide by eye.
   2. Align it with the point of the tailstock centre.
   3. Align its flank with the compound swung to 29°.
   4. Set it in a centre gauge held against the work.
   Show the answer

   D. Correct. The centre gauge's edge is held against the work and the tool is swivelled until its 60° point sits evenly in the gauge's V with no light on either side. Both flanks then meet the work at the same angle to its axis.

   Why not the others

   A. Squaring by eye is not accurate enough: a small error tilts the thread form so one flank is steeper than the other. A centre gauge against the work sets the point square.

   B. The tailstock centre point sets the tool's height, which has already been done. Squareness to the work's axis is set with a centre gauge.

   C. The compound's angle sets the direction the tool is fed in, not how the tool sits relative to the work. The point must still be squared with a centre gauge, or the thread flanks will lean.

2. Procedural · Sets up workpiece on conventional lathe

   A rough casting has its bore position laid out as a scribed circle on its face. How is it set in a four-jaw chuck before boring?

   1. Indicate the rough outside until it runs true.
   2. Centre it by the rings scribed on the chuck face.
   3. Adjust jaws until a surface gauge follows the circle.
   4. Run a dial indicator's contact around the scribed line.
   Show the answer

   C. Correct. The layout circle is the reference for the bore. With the scriber point of a surface gauge set just off the line, the spindle is turned by hand and the jaws adjusted until the point follows the circle all the way round.

   Why not the others

   A. Truing the rough outside centres the casting's skin, which may not be concentric with where the bore has to be. The scribed circle is the reference, followed with a surface gauge.

   B. The rings on the chuck face only help place the jaws roughly; they say nothing about where the laid-out circle sits. Set the circle true with a surface gauge.

   D. A dial indicator reads the height of a surface, and a scribed line on a flat face has no height to read. A surface gauge point is set to the line by eye as the work turns.

3. Procedural · Turns external surfaces using a conventional lathe

   After a trial cut, a diameter measures 50.42 mm and the drawing calls for 50.00 mm. The cross-slide dial reads radius, so the tool moves in by the amount shown. How much is fed in?

   1. 0.840 mm
   2. 0.105 mm
   3. 0.210 mm
   4. 0.420 mm
   Show the answer

   C. Correct. The diameter is 0.42 mm oversize, and every 0.01 mm the tool moves in takes 0.02 mm off the diameter. On a dial that reads radius, feed half the diameter excess: 0.42 ÷ 2 = 0.21 mm.

   Why not the others

   A. This doubles the excess instead of halving it and would take 1.68 mm off the diameter. On a radius-reading dial the infeed is half the diameter excess, 0.21 mm.

   B. This halves the excess twice. The dial reads radius, so the diameter excess is halved once: 0.42 ÷ 2 = 0.21 mm. Feeding 0.105 mm leaves the shaft 0.21 mm oversize.

   D. This would be right on a dial that reads diameter. On a radius-reading dial, 0.42 mm of infeed removes 0.84 mm from the diameter and leaves the shaft 0.42 mm undersize.

4. Recall · Turns tapers using a conventional lathe

   To what taper per foot is the taper attachment set for cutting an NPT pipe thread?

   1. 0.750 in. per foot
   2. 0.600 in. per foot
   3. 3.500 in. per foot
   4. 0.250 in. per foot
   Show the answer

   A. Correct. NPT threads taper 1 in 16 on the diameter, 0.750 in. per foot, about 1° 47′ each side of the axis. The attachment is set to that taper, and the threading tool is still set square to the work axis, not to the tapered surface.

   Why not the others

   B. 0.600 in. per foot is the Jarno taper, a series of machine-tool tapers. NPT pipe threads taper 1 in 16 on the diameter, 0.750 in. per foot.

   C. 3.500 in. per foot (7/24) is the steep, self-releasing taper of milling-machine spindles and tool holders, held by a drawbar. A pipe thread tapers far less, 0.750 in. per foot.

   D. 0.250 in. per foot is the taper of standard taper pins and their reamers. Pipe threads taper 1 in 16 on the diameter, 0.750 in. per foot.

5. Procedural · Cuts threads using a conventional lathe

   To four decimal places, what is the depth of an external 3/4–10 UNC thread?

   1. 0.0541 in.
   2. 0.0750 in.
   3. 0.0613 in.
   4. 0.0650 in.
   Show the answer

   C. Correct. External thread depth = 0.6134 × P, with P = 1 ÷ 10 = 0.1000 in.: 0.6134 × 0.1000 = 0.0613 in. This is the radial depth; the finished thread is sized over wires or with a thread micrometer.

   Why not the others

   A. 0.5413 × P is the depth of an internal thread. An external thread is cut deeper: 0.6134 × 0.1000 = 0.0613 in.

   B. 0.75 × P appears in some references for depth or compound infeed, but it is not the external thread depth on the formula sheet. Use 0.6134 × 0.1000 = 0.0613 in.

   D. 0.6495 × P (0.06495 here) is the factor in the metric pitch-diameter formula, MD − 0.6495 × P, not a thread depth on the formula sheet. External depth is 0.6134 × 0.1000 = 0.0613 in.

02Answer key

03What block E covers

Block E is the conventional lathe, set-up and operation. Set-up covers work holding in chucks, collets, on faceplates and between centres, tooling and tool height, steady and follower rests, taper attachments, and speeds and feeds. Operation covers facing, turning, drilling, boring, reaming, taper turning, knurling, grooving, single-point threading and parting off.

The Red Seal Occupational Standard names this block “Machines using conventional lathes”. It carries 20.7% of the exam, about 28 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

Tool height from a pinched rule

A thin rule pinched between the tool point and round work lies tangent where they touch. Its top leans toward the operator when the tool is below centre, away when above, and stands upright when the tool is on centre.

Compound angle is half the taper

The compound rest is set to half the included angle. The tangent of the setting is half the difference in diameters divided by the taper length, because the tool cuts one side of the work.

Pick the speed step below

Work out rpm from the chart cutting speed and the work diameter. When the lathe has no step at that figure, take the nearest speed below it, which keeps the surface speed within the chart value.

Feed the thread with the compound

For a 60° thread the compound is swung to about 29° and every infeed is made with it. The tool then cuts mainly on its leading edge, so the chip flows freely with less tearing and chatter.

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.