Precision Machining Technology - Section 5 - section 8
List three benefits fo holding a workpiece between centers.
1) The workpiece can easily be removed, flipped, and replaced with a high degree of repeatability and accuracy. 2) A diameter to be machined end-to-end will maintain concentricity and have very little runout. 3) It provides even support on both ends of a workpiece and makes for a more rigid setup with less deflection.
List and briefly describe the two different types of knurling tools.
Bump-type tools which apply pressure asymmetrically, and clamp-type tools which apply pressure on opposing sides of a part.
How can a tap be aligned when threading a hole on the lathe?
By countersinking the hole, by using a dead center to help align, and by using a spring-loaded tap center.
How can tool binding be overcome when cutting deep grooves or cutting off large diameters?
By cutting to a partial depth and then widening the groove to provide clearance.
List the two basic knurl patterns.
Diamond and straight-line
List three safety precautions relating to clothing that should be observed during lathe operation.
1) Long hair should be tied up. 2) Long sleeves should be rolled up above the elbows. 3) Watches, rings and other jewelry should not be worn.
In what units are the feed rates measured for lathe operations?
Inches Per Revolution, and Feed per revolution in inches
Which two tool posts are the most efficient if several tools are to be used?
Indexable tool posts, and Quick-change toolposts
list two application fo Acme threads.
Jacks, Large valves, Vises, and lathe lead screw.
How is knurling different from other lathe operations?
Knurling applies pressure to raise the surface, and does not generally remove materiel.
Which device may be used for either tool holding or work-holding?
Tailstock.
What part of the lathe is used to feed the tool during facing.
The Cross-Slide
What are the two main components of the carriage?
The Saddle and the Apron.
List the four main parts of the engine lathe.
The bed, the headstock, the tailstock, and the carriage.
List two advantages of using a self-centering chuck.
The jaws of a self centering chuck advances and retracts simultaneously, making them quicker and easier to use.
What feature of a lathe cutting tool has a direct effect on the surface finish?
The tool's nose radius.
What are the two main purposes of the lathe spindle?
To hold and rotate the workpiece during machining.
What two functions can the lathe tailstock perform?
To secure work-holding accessories, and to hold cutting tools for performing hole-making operations.
What is the purpose of the lead screw of a lathe?
To transmit motion to the carriage for thread cutting operations.
what type of thread is machined on a tapered diameter and is used to create leak-proof joints?
pipe thread
what dimension of the thread is mesured by using a thread micrometer or the three-wire method?
pitch diameter
what is the reason for feeding the cutting tool at the above angle?
the compound rest is set approximately 1/2 the included angle of the thread so that one cutting edge is dominate when removing material.
why should the depth of cut be reduced for each pass of the thread is cut deeper?
because of the large amount of tool contact and potential for work piece and tool flex
what mesuring tool is used to visually inspect the form, or shpae, fo an external thread?
comparator
what feature of mating threads determines the class of fit?
determined by the clearance between the mating thread flanks.
the distance of actual contact of two mating threads measured along the length of the two threads is the _______.
flank.
What type of mandrel would be ideal for gripping a workpiece on an accurately machined, but odd-sized hole?
An expansion mandrel.
What function does the compound rest serve?
As an adjustable mounting base for the tool posts.
When facing, why should the tool not be fed past the center of the workpiece?
Because the direction of impact on the cutting tool is reversed when one moves past the center of a rotating workpiece.
Why must extra care be taken when performing boring operations?
Because the tool is out of sight, and can more easily collide by accident.
Define the swing and the bed length of a lathe.
"Swing" is the largest diameter workpiece that can be mounted in the spindle without touching the ways. Bed length is measured from the headstock to the end of the bed.
Calculate spindle RPM and machining time for cutting a 1.5" diameter which is 4" long at 225 SFPM using a feed rate of 0.004".
(225 SFPM • 12") ÷ 1.5"•π = 573 RPM 4" ÷ (0.004" • 573 RPM) = 1.75 Minutes OR 4" ÷ 0.004" = 1000 rotations 1000 ÷ 573 RPM = 1.75 Minutes
destermine the approzimate compound-rest in -feed for cutting a 1 1/2-12 UNG 2A thread.
0.0583
A lathe cross slide uses a diameter--reading micrometer collar. if the cross slide is advanced by 0.150", what depth of cut would result?
0.075
If a 0.050" depth of cut is taken on the diameter of a workpiece, by how much will the diameter be reduced?
0.100"
List three characteristics of a workpiece that would make a mandrel the ideal work-holding device.
1) The workpiece features a straight hole or bore all the way through it's center. 2) It is desired that the outside diameter be concentric to the bore. 3) It is desirable to machine the entire outside surface of the part without removing it from the chuck.
What are two reasons for center drilling on the lathe?
1) To create a bearing surface for the lathe centers. 2) to create a starting point that will center a twist-drill.
List three potential advantages of using an independent chuck for a work-holding situation.
1) Workpiece can be centered more accurately by manual adjustment. 2) Non-symmetrical shapes can be clamped in the chuck. 3) The workpiece can be purposefully offset within the chuck.
What are two reasons boring may be selected to produce a hole instead of drilling and reaming?
1)The boring tool may be adjusted to any desired hole-size. 2)Boring can produce larger diameter holes than drills or reamers. 3)Boring can more accurately correct eccentricities.
The standard taper in most lathe tailstocks is what?
A Morse taper, which allows taper-shank tools such as chucks, drills, reamers, and counterbores to be used.
Explain the differences between the two auxiliary devices in the previous question.
A Steady Rest is fixed at one location on the lathe bed, while the Follow Rest is attached to the moving carriage.
The most common variation of the above chuck has how many jaws?
A Universal Three Jaw Chuck
Name the device that is used to transmit the spindle power to the workpiece when held between centers.
A drive dog.
Briefly define form cutting.
Form cutting produces contoured surfaces using specially shaped tools to achieve the desired form.
How do grooving and cutoff speeds compare to turning speeds?
Greatly reduced, 1/3-1/4 of normal speeds.
What two materials are most commonly used for lathe cutting tools?
High speeds steel, and carbide steel.
what is the name for the rotating device that transmits power to the carriage for thread-cutting motion?
Lead Screw
Is a left-handed or right-handed tool normally used for facing?
Left-handed
Name the type of tailstock center that would be selected to support a workpiece for most lathe operations.
Live centers
What part of the lathe is used to set the feed rate of the cutting tool?
Quick Change Gear Box
Should a left or right-handed tool be used when turning towards the headstock?
Right handed
Are deeper cuts used for roughing or finishing operations?
Roughing
Name two material shapes that can be properly held in a four-jaw chuck.
Round, octagonal, and square stock.
Name two material shapes that can be properly held in a three-jaw chuck.
Round, triangular, and hexagonal stock.
how many classes of fit are there int he Unified National system?
Six
What two auxiliary devices which can be used to stabilize long, slender workpieces for turning operations?
Steady Rest and Follower Rest
What is the special name for the type of jaw-type chuck that has a mechanism to move the jaws simultaneously?
Universal Chucks
When and how should chips be removed from the work and cutting tool?
Using a brush, pliers, or chip hook, and only when the spindle has come to a complete stop.
How can hole depth be controlled during drilling operations?
Using graduations on the quill and hand-wheel.
When drilling and reaming on the lathe, how are the tools usually fed into the workpiece?
Using the tailstock and quill-feed.
determine the major diameter limits for the following threads using the Machienry's Handbook
a. 1/2-20 UNC 2A Upper: 0.4987 Lower: 0.4906 b. 3/4-16 UNF 3A Upper: 0.7485 Lower: 0.7391 c. 1-8 UNC 2A Upper:0.9980 Lower: 0.9830 d. 1/4 12 UNF 3A Upper:1.2482 Lower: 1.2368
determine the minor diameter limits for the following threads using the Machienry's Handbook
a. 1/2-20 UNC 2B Upper: 0.4570 Lower: 0.4460 b. 3/4-16 UNF 3B Upper: 0.6960 Lower: 0.6820 c. 1-8 UNC 2B Upper:0.8900 Lower: 0.8650 d. 1/4 12 UNF 3B Upper:1.1780 Lower: 1.1600
determine the pitch diameter limits for the following threads using the Machienry's Handbook
a. 1/2-20 UNC 2B Upper: 0.4675 Lower: 0.4459 b. 3/4-16 UNF 3A Upper: 0.7094 Lower: 0.7056 c. 1-8 UNC 2B Upper:0.9276 Lower: 0.9188 d. 1/4 12 UNF 3A Upper:1.1959 Lower: 1.1913
name the device used to track the timing of half-nut lever engagement.
the timing of the half-nut engagement is monitored by the rotating mark on the thread dial.
