Metals Units 45-75
Structure
1 to 15 to dense to open, how much space in between grit
grade scale
A to Z
Describe a thread designated as M 56 X 5.5
M-Metric Nominal size-56 Pitch-5.5 Pitch dia tolerance-19g Outside dia tolerance-56g
How is a grinding wheel dressed when grinding a vertical surface..why is it necessary
dress side of wheel to give clearance
What is the purpose of the backlash eliminator?
eliminates backlash between the nut and the table lead screw
3 factors that affect the efficiency of a milling operation
excessive heat, abrasion, and chipping or crumbling of cutting edges
What are the features of a plain vise
may be bolted to the table so that the jaws are parallel or at right angles to the axis of the spindle
How is the pitch designated for metric threads
millimeters
vertical milling machine can be used for
milling boring,drilling, and reaming
State the purpose of a follower rest
move with the carriage to prevent work from springing up
feed =
number of teeth in cutter x cut per tooth
How deep should a roughing cut be
one-half the total amount removed from the workpiece in one cut
Why are rotary tables used?
permits the milling of radii and circular slots
numbers for wheel
prefix of manufacturer, abrasive type,grain size,concentration,bond type,bond modification,depth of abrasive,manufacturers record
Define the process of knurling
process of impressing a diamond-shaped or straight-line pattern into the workpiece to improve its appearance
Define truing
process of making the grinding wheel round and concentric with its spindle axis
What is the purpose of a headstock spindle (part of the lathe)
provides a drive through gears from the motor to the work-holding device
What is the purpose of the cross slide (part of the lathe)
provides a manual or automatic cross movement for the cutting tool
What purpose do T-slots serve
receive bolts for clamping workpieces
4 purposes of grinding fluids
reduction of heat,lubrication, removal of swarf, and control of grinding dust
State purpose of rough and finish turning
rough turning removes the most metal as possible in the shortest length of time. Finish turning follows rough turning, produces a smooth finish surface and cuts the work to an accurate size.
How is grain determined and why is it important
say you have a #8 grain size, it would pass through a screen having eight meshes per linear inch and would be 1/8 inch across, IMPORTANT because undersize grains in a wheel will fail to do their share of the work
finishing cuts you use a ______ feed
slower
roll dresses
small grinding wheel mounted to wear the diamond grit down
What is the purpose of a light trial cut at the end of the workpiece
so the work is the appropriate length and doesn't need extra supported
two flute end mill
2 teeth
How far may work extend beyond the chuck jaws before it must be supported
3 times the diameter extending beyond the chucks jaws
At what maximum speed should a 3.50 in cemented carbide milling cutter revolve to machine cast iron
50-80 ft/min
What common ratios are found on rotary tables
72:1 80:1 90:1 120:1 larger ratios found on larger tables
State two methods by which indexable carbide inserts are held in a tool holder
Cam action and clamp
Name two common materials from which end mills are made
Carbide, and cast iron
boring
Enlarges the hole slightly and making it rounder and straighter
7 main causes of milling cutter failure and state how they can be minimized
Excessive heat (add coolant), Abrasion (follow rules CS and feeds), chipping or crumbling, Clogging (two coolant nozzles), Built up edges (good cutting fluid), work hardening (break up the glaze), and Cratering (tool surface treatments)
OD, ID
Outside Diameter Inside Diameter
3 types of vertical milling
Ram type, 2 axis control, and heavy duty
Why is it necessary that the taper on the lathe spindle nose and the mating taper in the chuck be thoroughly cleaned before mounting
Steel chips or dirt will destroy the accuracy of the spindle nose and mating taper in the chuck
Why is the selection of the grade of wheel important to the grinding operation
Wheels which are to hard do not release the grains readily; consequently the grains become dull and don't cut effectively
3 manufactured abrasive and why they are used extensively used today
aluminum oxide (used for grinding the hardest steels), silicon carbide (used for grinding materials with low tensile strength, and boron carbide (next to diamond second hardest material and cost less)
most common wheel used to grind
aluminum oxide, second common silicon carbide
Name four natural abrasives
aluminum oxide, silicon carbide, boron carbide, and diamond
define chip per tooth
amount of material that should be removed by each tooth of tooth of the cutter
What should be done to prevent the cutting tool from binding in a deep groove
apply cutting fluid to the
What is the purpose of a multi thread
are used when it is necessary to obtain an increase in lead and a deep, coarse thread cannot be cut
Describe the cutting action of zirconia-alumina abrasive
as it cuts and becomes dull the dull particles fall off and sharp ones replace the old ones
Why should a hole be bored before it is reamed
bc boring takes most of the material and reaming takes a little bit and touches it up
Why should chips not be cleaned with a cloth
because if someone picks that rag up they might get cut
How can the tap be kept in alignment when tapping on a vertical mill
by mounting the tap in the vise
How is the size of a lathe designed
by the largest work diameter that can be swung over the lathe ways
What can happen if an extensively heavy cut is taken or too fast a feed is used
can cause the cutter to break
What precautions must be taken when turning work supported by solid centers
care must be taken (adjusting and lubricating)
Know the parts of a lathe
carriage headstock look at picture on pg 354
What are two requirements that must be met to enable a lathe cutting tool to cut
certain angles and clearances
CBN
cubic boron nitride manufactured diamond
How large should a face milling cutter be in relation to the width of the work
cutter should be 1 inch larger than width of work
Define CS and state how it is expressed
cutting speed and can be defined at which the rate at which a point on the work circumference travels past the cutting tool.
CSx4/D
cutting speed x 4 divided by diameter
facing
cutting to square outside edges (cross slide used to make facing cuts)
What is a template
determines the accuracy of the form produced
Explain how the ratio of 40:1 is determined on a standard cutting head
divide 40 by the number of divisions to be cut
Name three methods of holding cutters on a milling machine?
fixture, vertical milling attachment, and arbors
Why are aluminum oxide and silicon carbide abrasives used?
for high tensile strength material and silicon is used for low tensile strength materials.
Why are four-jaw chucks used
for work that must remain absolutely true , and they can hold round square or irregularly shaped workpieces
What are the basic functions of a grinding wheel?
generation of cylindrical,flat and curved surfaces, removal of stock, production of highly finished surfaces, cutting-off operations, and production of sharp edges and points
Describe the principle of crush-form dressing
grounding the crush roll to the right tolerance over and over
Factors to consider when the grade of wheel is being selected for a particular job
hardness of the material, area of contact, condition of the machine, speed of grinding wheel and the machine, rate of feed , and operator characteristics
collets
hold end mills tools
Why is the table alignment so important to most milling operations
if not aligned right the keyway will not be milled parallel to the axis of the shaft
Why is proper CS important
if the CS is to high the blade dulls quickly, if it's to low time will be lost during the cutting process
Why is is important that the vise be aligned with the tabel travel
if the head is not 90 degrees the holes wont be square
Why is the proper balance of the grinding wheel essential
improper balance will affect the surface finish and accuracy of the work
lathe feeds in
inch per revolution
climb cutting can
increase cutter life by 50%
How has the role of grinding changed over the years
initially they were used on hardened work, today grinding is applied extensively to the production of unhardened parts
State the purpose of the mandrel
is a precise tool, when pressed into the hole of a workpiece, provide centers for a machining operation
Define the structure of a grinding wheel and state how it is indicated
is the density of the wheel, indicated by numbers from 1 to 15
Define dressing
is the process of removing the dull grains and particles
What is the function of the bond and how does it affect the grade of the wheel
is to hold the abrasive grains together in the form of the wheel, the grade of the wheel is determined by how strong the bond is
What is the purpose of the compound rest (part of lathe)
it can be swiveled to any angle for tapering turning operations
vertical mill look at picture of the parts
knee, base, column, spindle, head, ram
List the advantages of the taper attachment
lathe center remains alignment,setup is simple, length of workpiece does not matter, wider range of tapers may be produced
Describe 3 types of standard tool holders and state the purpose of each
left-hand offset tool holder (offset to the right) is designed for machining work close to the chuck designated by the letter L, Right-hand offset tool holder (offset to the left) used for machining work close to the tailstock designated by the letter R. Straight tool holder can be used to take cuts in either direction designated by the letter "S"
Define lead
longitudinal distance the helix advances axially in one complete revolution of the work
grain size
lower the number the less grit
vitrified bond
made of clay at a high temp
What precaution should be taken before drilling holes on a vertical mill
make sure workpiece is held secure and holes are in the right place
turning
makes the diameter get smaller when you cut
How may the live center be checked for trueness after it has been mounted on the spindle
start the lathe and observe if the center is true, but for complete accuracy use a dial indicator
What type of cutter should be used to machine a large surface
suitable fly cutter should be used
How should work be checked for defects
test wheel before use, be sure it's mounted properly, see the wheel guard covers at least half the wheel
List advantages of an electromagnetic chuck
the holding power of the may be varied to suit the area of contact and thickness of the work, special switch neutralizes the residual magnetism in the chuck, allows the work to be removed easier
How is the pitch designated for UNC threads
the pitch is the distance from a point on one thread to a corresponding thread point on the next thread
Describe the process of face milling
the process of milling flat surfaces that are at right angles
Define helix
theoretical line generated on a cylindrical surface
List four purposes of threads
to fasten devices such a screws and bolts,provide accurate measurement,to transmit motion, to increase force
Why should the table saddle be locked before machining
to prevent movement during cut
Why is wearing safety glasses and not wearing loose clothing important
to protect your eye and so your clothes don't get caught in a machine
State three purposes of facing a workpiece
to provide a true,flat surface, square with the axis of work, to provide an accurate surface, to cut the work to a required length
purpose of reaming in a lathe
to quickly obtain an accurately sized hole
What is the purpose of a follower rest
travels with the carriage to prevent work from springing up
List the operations that can be performed on a lathe
turning, tapering,form turning,threading,facing,drilling,boring,grinding, and polishing
What factors affect the selection of the proper wheel structure
type of material being ground, area of contact, finish required, and method of cooling
For what purpose is direct indexing used
used for quick indexing of the workpiece
Uses for Boron carbide
used in the manufacture of precision gages and sand blast nozzles
what it the purpose of an arbor
used to hold the cutter during machining operation
Chuck cradle
used to support chucks when you switch them
What is the purpose of a steadyrest
used to support long work held in a chuck
Define worm and worm gear and describe their use
used when a great ratio reduction is required between the driving and driven shafts worm-cylinder on which is cut a single or multiple start ACME thread angle ranges from 14.5 to 30 Worm gear- teeth on a worm gear are machined on a peripheral groove
rough stock
want to remove it fast but leave some stock for fishing cut
4 points to be observed in grinding care
when not in use should be stored properly, wheels should be tested for cracks prior to use, select the proper type of wheel for the job, and grinding wheels should be properly mounted and operated at the recommended speed
Describe climb milling
when the cutter and the workpiece are going in the same direction
Conventional milling
when the cutter and workpiece are going opposite
end mill
will cut on end of it and outside
List two most important things to remember about filing in a lathe
work should only be filed in a lathe only to remove a small amount of material, and always remove the cutting tool from the toolholder before filing
