volume 3 unit 3

What two change gears do you need to machine metric threads on a lathe? Where do you mount the gears?

(1) 50-tooth gear on the spindle. (2)127-tooth gear on the lead screw.

What three conditions must be met before machining threads on a lathe?

(1) Proper work preparation. (2)Correct tool setup. (3)Proper lathe gearing.

What is the repeat accuracy of the quick-change tool post?

0.0001″.

How much back-rake should a rough threading tool have?

0°.

When you rough-drill a hole for hand reaming, how much material should you leave? For machine reaming?

1/32″; 0.010 to 0.015″.

What is the recommended rpm range for tapping by power?

10 to 30.

What is the included angle of a Unified thread?

60°

What feature do American Standard NPTs have in common with Unified threads?

60° included angles.

If you want to machine a double-lead thread having 16 TPI, at how many TPI should you gear the lathe to get the correct TPI?

8 TPI.

When you cut threads on a lathe, how far does the tool move per revolution of the workpiece?

A distance equal to the lead of the thread.

How do you set a tool post grinder at center height?

Align the centering holes in the grinding wheel spindle with the headstock center.

At what height should you set the point of the threading tool in relation to the work?

At center height.

What's the major difference between machining metric threads and Unified Threads?

At the end of each cut, back out the cutting tool and stop the machine, but never disengage the split nut

What's the procedure to follow if the knurling rollers double track at the start of a knurling operation?

Back the knurling tool away with the cross slide, reposition it, and start again in a new spot.

Why should you take lighter cuts during internal threading operations?

Because the cutter extends farther out of the tool post.

How do you keep a tap from turning when you are tapping threads by power in the lathe?

By resting a tap wrench on the compound rest.

How can you mount a taper shank drill in a tailstock if the tapers between the drill and tailstock are different?

By using a socket reducer.

How do you adjust tool bits to center height when you are using a multiple tool holder?

By using shims.

In the thread designation M9 × 1.25-5H, what does 5H mean?

Close fit internal thread.

Name the patterns and pitches available on knurling tools.

Diamond and straight; fine, medium, and coarse

What important considerations should you remember when knurling?

Don't allow the workpiece to rotate if the knurling tool is touching it and the carriage travel has stopped because rings will form on the workpiece; don't stop the workpiece without relieving the knurling tool pressure because the pressure may distort or spring the work; keep the knurling tool and work well oiled throughout the operation; check the tailstock center frequently because the pressure of the knurling operation may cause the center to loosen slightly; and always ensure the setup is rigid so you don't damage the chuck or ruin the workpiece.

What's the tap size limitation for tapping by power versus hand?

Don't power tap with taps under ½″ in diameter.

For external and internal grinding with a tool post grinder, how should the grinding wheel and workpiece rotate?

For external cylindrical grinding, set the workpiece and the grinding wheel so they rotate in the opposite direction at the point of contact; for internal grinding, the wheel and the workpiece run in the same direction at the point of contact.

What is the purpose of left-hand threads?

For use in applications where right-hand threads could loosen during operation.

How do you prepare and set up a cutting tool to cut an Acme thread on the lathe?

Grind the tool to fit the Acme thread gage and to fit a thread one pitch size smaller than the thread to be cut. Ensure it has 3 to 6° side clearance, and a 0° side and back rake; use the Acme thread gage to square the tool with the workpiece and set the compound rest parallel to the ways.

What spindle speed should you use for machine reaming?

Half the drilling speed for a hole of the same diameter.

What methods can you use to mount drills in a lathe?

In a drill chuck or tailstock spindle, or floated on dead center.

What is the procedure for cutting a thread with a geometric die?

Insert the chasers into the correct slots; set the rough cut and set the finish cut; cut the threads with the rough cut setting; and reset for the finish cut and complete the cut.

What are some of the differences between external and internal threading on a lathe?

Internal threading has cutter clearance restrictions and it requires you to mount the threading in a boring bar.

For a ¼-20-UNC thread, what should the pitch diameter measurement over the wires be if the diameter of the wires is 0.029″? Show all calculations.

M = 0.2612". 0.087 0.07577 - 0.250 0.029) (3 201.5155 - 0.250

How do you prepare the workpiece for machining left-hand threads?

Machine an undercut at the starting point (make it at least as wide as and slightly deeper than the single thread depth) and chamfer the side nearest the start.

How do you set up a diamond dresser for dressing and truing a tool post grinder?

Mount it in a holder clamped to the drive plate, and then set the point of the diamond at the center height and angle it 10 to 15° in the direction of wheel rotation.

How do American Standard NPTs differ from Unified threads?

NPTs are machined on a taper of ¾″ per foot.

How are grinding wheels for internal grinding mounted?

On tapered shafts called quills.

Why should you grind two threading tools?

One for roughing cuts; another for finishing cuts.

How do you position the compound rest for machining square threads and how do you feed the tool bit into the workpiece?

Parallel to the ways; perpendicular to the work.

What's the difference between pitch and pitch diameter?

Pitch is the distance from a point on one thread profile to a point on the next thread measured parallel to the axis; pitch diameter is the diameter of an imaginary cylinder concentric with the thread axis.

For what operations are center rests used?

Prevent slender stock from springing; provide auxiliary support to permit heavier cuts; and provide support for drilling, boring, or internal work.

What are some advantages of boring?

Produces round and concentric holes; you can bore true holes for reaming; you can finish bore holes to any size and leave allowance for reaming; you can produce odd-sized holes.

What's the purpose of recessing a workpiece?

Provides room for tool runout, seats for snap rings and O-rings, and lubrication channels.

Which method of cutting multiple threads is especially adapted to cutting Acme and square threads?

Set the compound rest parallel to the ways.

What's the procedure for starting a knurl between layout lines?

Set up the work, lathe, and knurling tool as usual; swing the compound rest to the right 5° to reduce the starting pressure; position the knurling tool slightly to the left of the right-hand layout line and start the knurl by forcing the corner of the roller into the work surface; move the carriage by hand and, if the knurl is tracking properly, extend the knurl to the right-hand layout line; move the knurling tool clear of the work and position it parallel to the work surface by swinging the compound rest back to the left 5°; and finish knurling the workpiece by using the same technique as ordinary knurling.

What's the spindle rpm for threading?

Slower than regular turning speeds for the type of metal being machined.

What is the cause of a bell-mouthed hole? How do you correct it?

Spring in the boring bar, a dull tool, or too heavy a cut; by occasionally feeding the tool out of the hole at the same setting you used to fed it into the hole, sharpening the tool, or reducing feed or depth of cut.

How should you prepare a hole for an internal taper pipe threading operation?

Straight bore it to a diameter equal to, or slightly larger than, the minor diameter of the small end of the mating thread.

What is the lead angle of a thread?

The angle made by the helix of the thread at the pitch diameter.

What governs the amount of end relief ground on a boring tool?

The diameter of the hole.

What's the difference between a follower rest and center rest?

The follower rest has only two jaws and is mounted to the carriage; the center rest has three jaws and is mounted to the ways.

What size runout groove should you machine on a workpiece before cutting threads?

The groove should be slightly wider than the thread pitch, and depth should be equal to or slightly greater than the thread depth.

What does the side relief angle of a thread depend on?

The helix angle of the thread.

How do you set the compound rest for internal threading?

The normal position is 29° to 30° to the left of the perpendicular position; but if clearance between the compound rest and work occur, position it 180° from normal position.

Describe an Acme thread.

The thread depth is equal to one-half the pitch plus clearance allowance, and the sides form an include dangle of 29°.

Describe a square thread.

The thread sides are parallel and the depth is equal to the width of the space between the teeth on external threads.

What's the difference between a threading tool designed for cutting external square threads and a cutting tool designed for cutting internal square threads?

The width is slightly more than ½P; the width is slightly less than ½P.

How does the boring speed compare to the turning speed on material of the same diameter as the hole?

They are the same.

Describe the thread gage and thread micrometer methods of measuring threads.

Threaded plug gage is one of the most exact methods of checking internal threads; thread micrometers are highly accurate thread measuring tools that measure threads at their pitch diameters.

For what purpose is knurling used?

To make impressions into the work surface for decoration, provide a gripping surface, and increase diameter.

What's the purpose of the dovetails on a quick-change tool post?

To provide a positive hold and accurate setting for multiple tool holders.

Describe multiple threads. Why are they used?

Two or more threads that run parallel to each other around a surface; where parts must assemble quickly without loss of strength; and where a nut and shaft must tighten quickly.

What should you do to protect the work surface when using the center rest on ground work?

Use copper shims between the work and center rest jaws.

What's the quickest and easiest method of cutting multiple threads?

Use the thread-chasing dial.

What's the major difference between machining right-hand threads and left-hand threads?

When you machine left-hand threads, you cut away from the headstock instead of toward the headstock.

How do you check the form of a threading tool?

With a 60° center gage.

How do you check internal tapers?

With a taper plug gage, the mating part, or a protractor.

How do you position the cutting tool for machining taper pipe threads?

With the center gage aligned with the straight portion of the pipe, not with the taper.

How close can you set a cutting tool when you use a micrometer stop?

Within 0.001″.

What does each position in thread designation ¼-28 UNF-3B mean?

¼ = nominal diameter. 28 = number of TPI. UNF = Unified fine. 3 = thread class (lowest tolerance of the three classes). B = internal thread.