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MACHING FACILITY LAB MANUAL
MECH 200
October 2014
DEPARTMENT OF MECHANICAL ENGINEERING
RODNEY KATZ [email protected] REV 3
i
1 OBJECTIVES
To expose students to the basic workings and procedures required to produce
precision parts conforming to the specifications on engineering drawings using a
manual milling machine and a manual lathe.
The parts must be machined to the tolerances stated on the drawings without
being test fitted to their mating parts, i.e. the brass bushing must press fit into
the pillow block without deformation and/or excessive force. All parts will be assembled at the end of the Lab to produce a functioning “Rotor Assembly”.
This exercise is intended to replicate a real world manufacturing condition in
which various parts are produced from many different sources and a final assembly must be attained without having to rework the parts. To accomplish the above, students will appreciate the relevance of producing quality drawings which convey all the necessary details.
Some tolerances required in this machining lab are relatively tight and will
require particular attention to detail. Most parts can easily be machined to a
tolerance of ±0.004” (0.1mm) with the machining tools used in the shop.
The following example will give some physical size relevance to tolerances
and dimensions to be used in the machining of the Rotor Assembly parts:
o Average human hair = 0.0015” (0.04mm) thick
o Average sheet of paper = 0.004” ( 0.10mm) thick
Some positioning and diameter tolerances required in this machining lab will be +0.0000” –0.0005” which is about
1/3“ the thickness of an average human hair.
This lab will also give the student an appreciation of the care, time and cost
required to produce parts with tight tolerances. Therefore in the design process
tight tolerances should be kept to a minimum and only used when necessary.
Lab Safety
Students must be familiar with and conform to the
Machining/Design Facility
Use Policy in Appendix A
ii
TABLE OF CONTENTS
1 OBJECTIVES ........................................ I
2 MANUAL LATHE .................................. 1
2.1 LATHE SAFETY PROCEDURES ................................................................................ 2
2.2 USE AND CARE OF THE MILLING MACHINE .............................................................. 2
2.3 GENERAL TECHNIQUES FOR TURNING ON A MANUAL LATHE ..................................... 3
3 MANUAL MILLING MACHINE .................. 6
3.1 MILLING MACHINE SAFETY PROCEDURES ............................................................... 7
3.2 USE AND CARE OF THE MILLING MACHINE .............................................................. 7
3.3 HOW TO CHANGE A MILLING TOOL ........................................................................... 8
3.3.1 REMOVING THE TOOL ..................................................................................... 8
3.3.2 LOADING A TOOL ............................................................................................ 9
3.4 GENERAL TECHNIQUES USED FOR MILLING ............................................................ 9
4 THE PROJECT ................................... 11
4.1 ALUMINUM ROTOR TURNED ON THE LATHE ........................................................... 11
4.1.1 TURNING ALUMINUM ROTOR ......................................................................... 11
4.1.2 DRILLING THE SHAFT HOLE ........................................................................... 13
4.1.3 CUTTING OFF THE ROTOR ............................................................................ 14
4.1.4 FACING THE ROTOR TO FINISHED LENGTH...................................................... 14
4.1.5 BORING THE RECESS IN THE ROTOR .............................................................. 15
4.2 BRASS BUSHING TURNED ON THE LATHE .............................................................. 16
4.2.1 DRILLING AND REAMING THE BUSHING BORE .................................................. 18
4.2.2 CUTTING THE BRASH BUSHING OFF ............................................................... 19
4.2.3 FACING THE BUSHING TO FINISHED LENGTH ................................................... 19
4.3 PILLOW BLOCKS ON THE MILLING MACHINE .......................................................... 20
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4.3.1 SETTING THE X-Y DATUM CORNER OF THE VISE ............................................. 20
4.3.2 PREPARATION OF STOCK FOR PILLOW BLOCKS .............................................. 22
4.3.3 MILLING OF PILLOW BLOCKS ......................................................................... 22
4.3.4 BORING THE BUSHING HOLE ......................................................................... 25
4.3.5 MILLING THE SIDE RECESSES ....................................................................... 27
4.3.6 DRILLING SCREW CLEARANCE HOLES ............................................................ 28
4.4 CNC MACHINING OF THE BASE PLATE ................................................................. 29
5 WORKS CITED .................................. 30
6 REVISION HISTORY ........................... 30
7 APPENDIX A: MACHINING & DESIGN FACILITY USE POLICY A
7.1 SAFETY ............................................................................................................... A
7.2 FACILITY DRESS CODE .......................................................................................... A
7.3 GENERAL ............................................................................................................. B
7.4 MECHANICAL ENGINEERING MACHINING FACILITY STANDARDS ................................. B
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TABLE OF FIGURES
FIGURE 1: MANUAL LATHE [1] ............................................................................................. 1
FIGURE 2: MAXIMUM PROTRUSION FROM THE CHUCK WITHOUT THE END SUPPORTED............... 4
FIGURE 3: CORRECT TOOL POSITIONING ON A LATHE ............................................................ 5
FIGURE 4: MILLING MACHINE USED IN THIS LAB IS CALLED A “BRIDGEPORT” STYLE KNEE MILL ... 6
FIGURE 5: CORRECT METHOD FOR MEASURING DRILL DIAMETER WITH A CALIPER .................... 9
FIGURE 6: VISE CLAMPING OF PARTS IN SERIES AND PARALLEL ............................................ 10
FIGURE 7: FEATURES OF THE ROTOR ................................................................................. 11
FIGURE 8: MACHINING STEPS FOR ALUMINUM ROTOR .......................................................... 12
FIGURE 9: CORRECT DRILL DEPTH FOR THE CENTER DRILL .................................................. 13
FIGURE 10: CUTOFF TOOL POSITIONING ............................................................................. 14
FIGURE 11: FACING THE ROTOR ........................................................................................ 15
FIGURE 12: BORING TOOL SETUP ON LEFT AND ROTOR WITH FINISHED BORE ON RIGHT .......... 16
FIGURE 13: TURNING OF BRASS BUSHING .......................................................................... 17
FIGURE 14: REAMER USED FOR PRECISION DRILLING .......................................................... 18
FIGURE 15: MILL AXES OF MOTION .................................................................................... 20
FIGURE 16: DATUM CORNER OF VISE AND THE X-Y COORDINATES ....................................... 21
FIGURE 17: LEFT DISPLAYS SETTING X DATUM AND RIGHT THE Y DATUM ............................... 22
FIGURE 18: STEPS FOR MILLING PILLOW BLOCKS ................................................................ 24
FIGURE 19: TOP VIEW OF CLIMB MILLING AND CONVENTIONAL MILLING .................................. 25
FIGURE 20: VISE CLAMPING WITH ALIGNMENT USING MAGNETS ............................................ 26
FIGURE 21: AFTER PILLOW BLOCK HAS 0.5” HOLE MILLED .................................................... 26
FIGURE 22: CUTTER COMPENSATION ................................................................................ 27
FIGURE 23: STEPS FOR MILLING SIDE RECESSES IN PILLOW BLOCK ....................................... 28
1
2 MANUAL LATHE
FIGURE 1: MANUAL LATHE [1]
2
2.1 LATHE SAFETY PROCEDURES
Only one student to operate the machine at any one time. Multiple people
operating a machine at once can cause confusion and inadvertent operations
which can endanger the other operator. Non-operating members of the group
can watch, advise the operator and add coolant to the work piece if required.
Lathe operator and observers must always stand to the side of the chuck, out of
the line of rotation.
Always remove the chuck key from the lathe chuck immediately after use and
replace it in the chuck key holder (on the back splash guard). Do not ever leave
the chuck key in the lathe chuck while your hand is not holding it. If a chuck
key is left in the chuck and the lathe is turned on the results can be very serious.
Always ensure the work piece is held securely in the chuck. Ask if uncertain.
Always wait for the lathe chuck to come to a complete stop before touching the
chuck or work piece.
Never remove swarf (long stringy cuttings) from the lathe tool or work piece with
your fingers. These can cause nasty cuts to your hands and fingers. Use the long
nosed pliers, a dental pick and/or air gun to remove the swarf and cuttings.
Do not allow an accumulation of swarf in the vicinity of the chuck and the work
area. Back out of the work and remove it to the under tray or scrap bucket.
Remove the lathe tool when drilling or using the tailstock. Also remove any drills
from the drill chuck or the pointed live center when they are not being used.
Always stop the lathe while changing tools.
Ask the instructor before using sandpaper or a hand file on the lathe.
2.2 USE AND CARE OF THE MILLING MACHINE
Refer to Figure 1 and familiarize yourself with the names and parts of the lathe.
Oil the lathe first. Use the lubrication injector pump located on the apron of the
machine , two shots required
Only change lathe speeds when the lathe is off. When changing speeds using
the gears, always first turn the chuck by hand ensuring the gears are properly
engaged before switching the lathe back on.
3
Do not machine excessively close to the chuck. Keep the cutting tool tip a
minimum of 1/8” away from the chuck.
Ensure that sufficient stock is held in the chuck to prevent the work piece from
being pulled out of the chuck while being machined.
Use caution when using the long nosed pliers to remove swarf from around the
work piece and cutting tool; do not knock pliers against the cutting tool or chuck.
Use caution when placing any metal tools near the lathe cutting tools that are not
in use. The lathe cutting tools used in this shop are expensive tungsten carbide
inserts which have very sharp brittle tips and can be damaged easily if knocked
against other metal objects. Therefore, do not place the chuck key on the
headstock ledge; return it immediately to its designated holder on the back panel.
Do not allow any tools or measuring instruments to protrude from the lathe
headstock ledge, as they could accidentally drop onto the rotating chuck.
2.3 GENERAL TECHNIQUES FOR TURNING ON A MANUAL LATHE
Pay close attention to the job at hand and the details. Failure to do so will often
result in a finished part not conforming to specification. This is often only
recognized at the completion of the part or worse yet in the final assembly
resulting in a time consuming re-make or rework of the part.
There is no “Undo” command in machining
Removal, cutting or machining of material on a lathe with a lathe tool is referred
to as “turning.”
Always clean the chuck jaws with a shop cloth before installing the work to
prevent eccentric chucking and indenting of the work piece by previous cuttings.
Always ensure the work piece is rotating at full speed when engaging the cutting
tool into the work piece or exiting the cutting tool from the work piece. Do not
stop the chuck rotation with the cutting tool in the work piece or when it is
touching the work piece.
Always move the lathe tool to its cutting position off of the work piece then
proceed with the cut into the work piece.
Feeding in or out the “X” axis, determines the diameter of the work piece.
Feeding in the carriage in the “Z” direction determines the length of the part.
4
Have the least amount of material protruding from the chuck as possible in order
to machine the part. Rigidity is the key factor to achieving a good machined
finish on the part.
FIGURE 2: MAXIMUM PROTRUSION FROM THE CHUCK WITHOUT THE END SUPPORTED
A general rule: Do not have more than 2 times the diameter of the work
protruding from the chuck, and a minimum length of one times the diameter held
in the chuck, as seen in Figure 2. If more of the work piece is to protrude from the
chuck, a live center must be used to support the end, consult the instructor for
additional guidance.
The cutting tool must be centered with respect to the center of the spindle, seen
below in Figure 3. When the tool tip is set to the spindle center height, a cut
depth of 0.100” translates to a diameter change of 0.200”. The digital readouts
(DRO’s) on the lathes are set to read in diameter (DIA).
5
FIGURE 3: CORRECT TOOL POSITIONING ON A LATHE
Backlash is the play or slack between the driving screw element and the driven
nut element that occurs when an overshoot and short backup is made while
turning an axis into position. To eliminate backlash while turning into a desired
position, the turning wheel must be backed out approx. half a turn from the
original input direction and then repositioned again to the desired position.
A small initial cut and measurement must always be made on the diameter of the
“X” axis and another on the “Z” axis to establish a datum point from which the
diameter and length can be set. This is a crucial measurement as all subsequent
measurements will be based on these initial measurements.
When measuring the diameter of the part in the chuck, move the carriage out of
the way to allow unconfined access to the part.
Use two hands when feeding during a cut. This will result in more control and will
provide a uniform finish on the work piece.
6
3 MANUAL MILLING MACHINE
FIGURE 4: MILLING MACHINE USED IN THIS LAB IS CALLED A “BRIDGEPORT” STYLE KNEE
MILL
7
3.1 MILLING MACHINE SAFETY PROCEDURES
Only one student to operate the machine at any one time. Multiple people
working on a machine cause confusion and inadvertent operations which can
endanger the other operator. Non-operating members of the group can watch,
advise the operator and can add coolant to the work piece (part being machined)
if required.
Always shut-off the Mill before removing parts from the vise or measuring parts in
the vise. Immediately and gently apply the break to stop the spindle rotation after
switching off the motor, do not let the spindle coast to a halt. This ensures the
cutter is stationary when the operator needs to handle or measure the work.
Remove the draw bar wrench immediately after use and replace it on the
provided peg. Always check to ensure the draw bar wrench is not on top of the
mill prior to switching on the motor.
If the cutter will not release easily from the collet after loosening, use a cloth
around the cutter to protect your hands and fingers while removing the cutter.
Do not use fingers to clear away chips. Use the air gun, but with caution and
consideration for others.
If you are uncertain about the set-up for machining your part ask the instructor.
3.2 USE AND CARE OF THE MILLING MACHINE
Refer to Figure 4 to become familiar with the names and parts of the Manual
Knee Mill.
Oil the Mill first using the hydraulic oiler on the side of the machine before use
(one pump is sufficient).
Change the speed of the Mill only while the motor is running. This is due to the
infinitely variable speed drive belt and pulley configuration (similar to that used
in an infinitely variable speed snowmobile transmission.)
When changing the machine speed between high and low the machine must
be off. This leaver is located on the upper right hand side of the machine.
Ensure the “Way Lock Levers” are loose when moving any of the X, Y or Z
axes. These levers can be tightened if required to prevent movement.
The compressed air can be used to clean the Mill but do not blow directly into
the slides of the machine.
8
Coolant can be used liberally on the machine; any excess coolant sprayed on
the floor must be cleaned up immediately to prevent a slipping hazard.
All machines must be thoroughly cleaned and excess coolant dried off after use. There should be no visible chips on the vise, or milling table. In between the milling table slots should be cleaned with compressed air.
There are five different metal recycling bins in the shop. Be sure you are
placing the correct metal scrap into the appropriate bin or YOU will have to
spend your personal time separating out the metal scraps! Note: there are
two aluminum recycling bins one for shavings and the other for solid pieces.
If the machine is making a strange noise, vibrating, or is not cutting as it
should always stop and check for the cause or ask the instructor for
assistance. Do not proceed with machining until the problem is solved.
Never use a milling cutter in a drill cut.
3.3 HOW TO CHANGE A MILLING TOOL
When removing cutting tools or the drill chuck from the collet, place the plastic
tray below the tool. This prevents the tools and the vise from being damaged
when they are “tapped” out, and accidentally dropped onto the mill.
Always place tools on the plastic trays on the mill table. This prevents the steel
tools from “dinging” the precision ground mill table.
Do not place the collets on the plastic trays; instead return immediately to their
home on the work bench.
3.3.1 REMOVING THE TOOL
Apply the machine brake and turn the wrench ½ a turn to loosen the
drawbar bolt on top of the machine. This will loosen the draw bar which
protrudes down the center of the machine and secures the collet.
Place your hand below the tool and tap the top of the drawbar with a rubber
mallet this will cause the tool to come out of the machine. If the tool does not
release right away then keep one hand below the tool and with the other
loosen the bolt a little more and tap the drawbar again with the mallet.
Once the tool is removed, continue to loosen the bolt by hand until the collet
drops out.
9
3.3.2 LOADING A TOOL
Place collet into the machine with one hand and hand tighten the drawbar bolt
with the other hand until the collet is fully engaged with the machine draw bar.
Place the tool into the collet and continue to hand tighten the bolt. If the tool does
not fit into the collet, slightly loosen the bolt to allow the tool entry into the collet.
Place hand on the milling machine brake and tighten the drawbar bolt with the
wrench between 1/4 to 1/3 of a turn, MAXIMUM past finger tight.
3.4 GENERAL TECHNIQUES USED FOR MILLING
Pay close attention to the job at hand and the details. Failure to do so will often
result in a finished part not conforming to specifications. This is often only
recognized at the completion of the part or worse yet in the final assembly
resulting in a time consuming remaking or reworking of the part.
Note: There is no “Undo” command in machining
Ensure the vise jaws and machine base are thoroughly clean before installing
parts (use the air-gun or shop towels if necessary). A tiny metal chip left
sandwiched between the part and the vise jaw or parallels could result in a part
not being square and can also leave indentations in the part.
Always check the diameter of the drill with a caliper to verify it is the correct size.
Previous users may have incorrectly replaced the drill in the drill index. The
accurate method of measuring a drill is to measure across the cutting flutes tips
using the broad section of the dial caliper as shown in Figure 6.
FIGURE 5: CORRECT METHOD FOR MEASURING DRILL DIAMETER WITH A CALIPER
10
De-burr and remove all sharp corners of parts with a file after milling or cutting.
This will ensure parts sit properly when re-installed in the vise, also for safety and
cosmetic reasons.
Only clamp one part at time. If it is necessary to clamp more than one part at a
time to improve efficiency, only clamp in series, not in parallel as seen in Figure
6. Parts clamped in parallel cannot be held with even force and can cause one
part to loosen during milling.
Parts clamped in series Parts clamped in parallel
- Recommended - - Not Recommended -
FIGURE 6: VISE CLAMPING OF PARTS IN SERIES AND PARALLEL
Most parts clamped in the vise only require the vise handle to be tightened
approx. 1/4 of a turn past finger tight. This exerts a clamping force of approx.
2000lb on the part.
Always ensure the cutter is rotating when bringing it into contact with the work
piece. This prevents the cutter edges from being damaged.
When making a finish cut in one axis always lock the opposite axis table using
the locking handles. This will prevent any drift and chatter occurring in the
opposite axis. Remember to unlock the handles after.
Before removing the finished part from the vise, measure it to ensure that it is
accurate and meets specifications. If additional machining is required and the
part has been removed from the vise it can be difficult to achieve repeatable
alignment resulting in parts not meeting specification.
Scribe an “X” in the upper left corner of the part, in order to allow reinstallation in
the vice with the same orientation when additional machining is required.
11
4 THE PROJECT
4.1 ALUMINUM ROTOR TURNED ON THE LATHE
The Rotor will be machined from Aluminum 6061-T6, 11/2” diameter bar stock. Each
piece is a minimum of 2” long to ensure that a sufficient amount of material can be held
in the chuck for safety and rigidity.
4.1.1 TURNING ALUMINUM ROTOR
The features of the rotor and associated names are displayed below in Figure 7.
FIGURE 7: FEATURES OF THE ROTOR
Set the lathe to 1075 rpm or 860 rpm, gear speed combo A-3. Place the
aluminum designated lathe tool in the quick-change tool holder. See Figure 8 for
the machining steps of the aluminum rotor.
Place the 11/2” diameter aluminum bar in the chuck with approx. 1
1/2” protruding.
Make a face cut of 0.010” and set the Digital Read Out (DRO) on the “Z” to
0.000. This is the datum point for the length (Z) of the part.
Make a small skim cut (approx. 0.25” long in the Z axis) on the diameter of the
work piece, and move the lathe tool back off the part in the “Z” axis not moving
the position of the “X” axis.
12
STEP 1: Initial facing cut and set Z
datum to zero
STEP 2: Skim cut and set X to
measured diameter value
STEP 3: Turn OD to 1.450” and face a
depth of 1.250”
STEP 4: Rough stock removal: turn OD
to 1.250” and face 0.490”
STEP 5: Rough stock removal: Turn
OD to 1.050” and face 0.490”
STEP 6: Rough stock removal: turn OD
to 0.850” and face 0.490”
STEP 7:
Final diameter stock removal. turn od to a final diameter of
0.750” and face 0.490”
STEP 8: Final shoulder face cut in Z to a width of 0.500” and a final
diameter in X of 0.750”
STEP 9: Chamfer both outside edges
using the chamfer tool
FIGURE 8: MACHINING STEPS FOR ALUMINUM ROTOR
13
Measure the diameter of this cut with the dial calipers, and input this value into
the DRO for the “X” axis.
Turn the diameter to 1.450” ±0.005” and to a length of 1.250”.
Refer to Figure 8 for the steps to turn the boss to 0.750” diameter by 0.500” long.
Only turn to 0.480” ±0.010” in length (Z axis) for the rough cuts.
The final 0.500” length cut of the boss will be made using a facing cut by
positioning the Z axis at 0.500” ±0.005” and feeding into X to 0.750” ±0.005”.
Remove the tool from the quick-change tool holder and replace with the
chamfering tool and lightly chamfer the two corners as required. Note: These
corners are only “cosmetic” chamfers, and therefore do not need to be accurate.
4.1.2 DRILLING THE SHAFT HOLE
A center drill is always used in a lathe drilling operation. When a center drill hole
is not used, the drill could deflect to the side resulting in an off center hole.
Insert the center drill chuck into the tail stock and drill a hole in the aluminum
work piece to the depth shown in Figure 9 (half way up the second taper).
Replace the center drill with a 1/4’’ diameter drill and clear any remaining chips
from the rotor. Drill a ¼” hole approx. 11/4’’ deep, backing out every
3/8’’ to clear
the cuttings and inject coolant down the hole.
All holes should be deburred, to do this insert the countersink tool in the drill
chuck, gently bringing it into contact with the part. Rotate the chuck by hand. This
will remove the burr at the entrance of the hole and create a small chamfer.
FIGURE 9: CORRECT DRILL DEPTH FOR THE CENTER DRILL
14
4.1.3 CUTTING OFF THE ROTOR
Insert the cut-off tool into the tool holder and align its front right tip to the front
face of the part as shown in Figure 10. Make sure to not touch the tool tip to
the part without the machine moving. Use a piece of square metal to achieve
proper alignment. Move the “Z” carriage forward to approx. Z=1.050” and feed
the cut-off tool into the work at a medium, steady pace ensuring coolant is being
injected liberally into the cut-off groove. Once the cut-off tool penetrates to the
drilled hole the part will simply fall away. Do not attempt to catch it.
FIGURE 10: CUTOFF TOOL POSITIONING
4.1.4 FACING THE ROTOR TO FINISHED LENGTH
Remove the bar stock from the chuck and insert the rotor part as shown in Figure
11. Shim stock (brass foil) can be wrapped around the part in order to prevent
the hard jaws of the chuck from indenting the part.
Insert the regular lathe tool (diamond shaped) into tool holder and face the part,
removing as little material as possible. Back the tool out in the “X” axis without
moving the “Z” carriage.
Measure the total length of the part and input this value into the “Z” DRO.
Move the “Z” carriage to 1.00” and face the part. This will produce the 1.00”
finished length of the part.
15
FIGURE 11: FACING THE ROTOR
Insert the chamfering tool and turn a small cosmetic chamfer on the part.
4.1.5 BORING THE RECESS IN THE ROTOR
Insert the boring tool into the tool holder. Take a brass shim and measure it with
a caliper. Place the brass shim on the face of the rotor and very lightly touch the
tip of the boring tool to the front face of the part near the center with the lathe
turned off, see Figure 12. Set the DRO in “Z” to the thickness of the shim.
Move the tip of the boring tool out in the “X” axis approx. 1/8” beyond the center
hole and bore in the “Z” axis to a maximum depth of 0.240”. Repeat this
operation increasing the diameter of the bore by approx. 0.200” per cut.
After the 2nd cut, back out the boring tool in the “Z” axis, ensuring not to move
the “X’ axis from its last cut. Measure the internal diameter of the bored hole, and
input this value in “X” DRO. Continue boring out the recess in increments of
approx. 0.100” until a diameter of 1.000” ±0.005” is achieved.
Return the tip of the boring tool to the center of the part “X” = 0.000” at a depth of
“Z” = 0.250” ±0.005” and feed the tool out to a diameter of 0.995”. Retract the tool
in the “Z”, shown in Figure 12. The tool is only taken to 0.995” diameter so it does
not contact the inner diameter wall, which would produce chatter marks.
16
The internal chamfer on the 1.000” bore diameter can be achieved by feeding the
boring tool in at a 45 degree angle. (Internal chamfers cannot be turned using the
regular lathe tool).
FIGURE 12: BORING TOOL SETUP ON LEFT AND ROTOR WITH FINISHED BORE ON RIGHT
4.2 BRASS BUSHING TURNED ON THE LATHE
The brass bushing will be machined from Brass 3/4” diameter bar stock. The stock piece
must be a minimum of 11/2” long to ensure that a sufficient amount of material can be
held in the chuck for safety and rigidity.
Note: The brass bar stock is 0.750” diameter therefore the “0.75” Nom.” diameter
section of the bushing is already to size and does not require machining. (Nom.
is short for nominal which means: leave the pre-sized stock at its original size or
as it comes from the supplier). Keeping nominal sizes in mind and using when
feasible will save time and expense in designing and manufacturing parts.
Using the diamond shaped lathe tool face the work piece and set the DRO to
Z=0.000”.
Make a small skim cut (approx. 0.250” long) on the diameter of the work piece
and move the lathe tool back off the part in the “Z” axis without moving the
position of the “X” axis. Measure the diameter of this cut with the calipers and
input this value into the DRO for the “X” axis.
Turn the shoulder of the bushing to 0.510” ±0.005” diameter and 0.440” deep in
approx. 0.100” diameter increments, as shown in Figure 13.
17
STEP 1: Initial facing cut and set Z
datum to zero
STEP 2: Skim cut and set X to
measured diameter value.
STEP 3: Turn OD to .650” and face a
depth of .440”
STEP 4: Turn OD to .510” and face
0.440”. Measure diameter with micrometer and re-input into
DRO.
STEP 5: Turn OD to .505” and face
0.440”. Measure diameter with micrometer again and re-
input, if necessary.
STEP 6: Final diameter stock removal. Turn od to a final diameter of
0.502” and face 0.440”
STEP 7: Turn down step on leading
edge to OD of 0.490” and to a depth of 0.070”
STEP 8: Final shoulder face cut in Z to a width of 0.450” and a final
diameter in X of 0.480”
STEP 9: Chamfer both outside edges
using the chamfer tool
FIGURE 13: TURNING OF BRASS BUSHING
18
In order to obtain the high tolerance on the bushing O.D. (0.5020”, + 0.0005”,
-0.0000”) a micrometer must be used to measure the O.D. Input this micrometer
measured diameter into the DRO.
Turn the bushing down to 0.505” diameter and measure it again using the
micrometer, if it reads different to the DRO reading then update the DRO with
this latest measurement.
Make a cut to O.503” diameter and measure again with a micrometer.
Now cut diameter to the required size 0.5020”, +0.0005, -0.0000” and check the
size using the micrometer.
Position the tool at “Z”= 0.450” and feed in the “X” axis to a diameter of 0.480”.
This will face cut a clean square shoulder and produce an undercut at the
junction of the flange and the shoulder.
Turn the small reduced diameter of 0.490” x 0.07 depth from the end of the part.
This reduced diameter is designed into the part to allow for ease of initial
insertion of the bushing into the pillow block bore.
Insert the chamfering tool. Cut the small chamfers on the front edge and the
shoulder edge.
4.2.1 DRILLING AND REAMING THE BUSHING BORE
Refer to the Section 4.1.2, “Drilling the Shaft Hole” for initial drilling then Section
4.3.4 “Boring the Bushing Hole” for creating the precision hole with a reamer.
As this is a precision hole of 0.2510” ±0.0003 it must be reamed to attain the
tolerances required. A hole of approx. 0.240” diameter is drilled to a depth of
0.750”, drilling in increments of approx. 1/4” deep and retracting to clear the
cuttings (this is called peck drilling).
FIGURE 14: REAMER USED FOR PRECISION DRILLING
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Insert the 0.2510” diameter reamer into the drill chuck and change the lathe
speed to 275 or 220 rpm depending on the lathe being used. Note: More cutting
flutes on the tool require slower rotational speeds of the machine.
While applying coolant, slowly feed the reamer into the drilled hole until the
reamer bottoms out. Retract slowly. Do not lock the tailstock.
4.2.2 CUTTING THE BRASH BUSHING OFF
It is important that all the necessary operations are performed on the working
side of the part prior to it being separated from the initial stock piece. It is often
very difficult to hold the part in this orientation again and maintain concentricity.
Refer to 4.1.3 “Cutting Off the Rotor”.
Cut the bushing off longer than stated in the drawing, to a length of 0.600”
±0.010”. This extra length will allow a small amount of material to be removed for
a facing cut. The cut-off tool might not produce a flat smooth face on the part.
4.2.3 FACING THE BUSHING TO FINISHED LENGTH
Refer to 4.1.4 “Facing the Rotor to Finished Length”. This method is repeated
only using the brass bushing
Face the bushing to a length of 0.575” and chamfer O.D. using the chamfering
tool and lightly chamfer the I.D. using the countersink tool in the drill chuck.
The completed part should now conform to the drawing.
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4.3 PILLOW BLOCKS ON THE MILLING MACHINE
4.3.1 SETTING THE X-Y DATUM CORNER OF THE VISE
Instructions for setting the Digital Read Out (DRO) systems are located on the
individual machines. Note: All rotary dials on the machines and dimensions are
in inches.
FIGURE 15: MILL AXES OF MOTION
The Mill uses an XYZ Cartesian plane axis system as displayed in Figure 15. The
directions refer to the relative movement of the cutting tool, not the milling
table.
The milling machine vise must first be initialized to obtain a datum corner. This is
usually the top left corner of the vise back jaw as shown in Figure 16. Note: The
top left corner is commonly used as the machining datum; therefore it is also
useful to dimension parts on the drawings from this corner.
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FIGURE 16: DATUM CORNER OF VISE AND THE X-Y COORDINATES
Install the 1/2” collet into the Mill spindle and install the 0.200” diameter probe
Edge Finder into the collet with approx. 1” total protruding. Note: The Edge
Finder probe is 0.200” diameter therefore a radius of 0.100” is used to set the X
and Y positions with respect to the edge of the vise.
An “Edge Finder” centripetal probe will be used to accurately locate the datum
corner of the vise with respect to the center of the Mill spindle, seen in Figure 17.
Open the vise up and clamp a sample piece of material approx. ¾” up the jaws of
the vice. It is very important to zero the machine with material clamped in the
vice, otherwise “Y” axis positioning will be off approximately 0.0015” when parts
are clamped.
Turn the Mill on, setting the speed to approx. 1800 RPM.
Position the Edge Finder as shown in Figure 17 on the left and move the Y table
slowly towards the Edge Finder until the Edge Finder probe is barely touching the
edge of the vise. Continue slowly moving the Y table in the same direction until
the Edge Finder probe flicks to the side (running eccentric with respect to the
body). This position will be Y = -0.100”, set the DRO to Y -0.100.
Repeat this operation to confirm that the correct position has been obtained.
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FIGURE 17: LEFT DISPLAYS SETTING X DATUM AND RIGHT THE Y DATUM
Move the X table with respect Edge Finder shown in Figure 17 on the right, and
repeat the above two steps. This position will be X= -0.100”, input this position to
the DRO.
Note: There are other methods to locate datum edges, enquire with the shop
instructor for more information.
4.3.2 PREPARATION OF STOCK FOR PILLOW BLOCKS
The pillow blocks will be made from aluminum 6061-T6 bar stock 1/2” x 2 “.
Cut one piece 3 3/8” ±
1/16” long using the Metal Cutting Chop Saw.
Remove all burrs using a file and deburring tool.
4.3.3 MILLING OF PILLOW BLOCKS
4.3.3.1 SQUARING-UP BLOCKS
Install the 1/2” wide parallels in the vise and place the work piece on top of the
parallels. Lightly clamp the work piece and hit it with the rubber mallet to ensure it
is well seated on the parallels, then tighten up the vise. A second hit with the
mallet may be necessary to ensure good seating of the part.
With the machine turned on set the manual mill to approx. 2000 rpm.
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Use a 1/2” diameter two flute, HSS (high speed steel) milling cutter to “end mill”
the top face of the aluminum block as shown Figure 18, Step 1. Move the work
piece under the cutter and slowly move it up using the Z axis crank handle until
the cutter contacts. Set the Z dial to “0”, then raise the table approx. 0.100” (one
full revolution = 0.100”) for the first cut, this will be a “plunge mill.” Traverse the
table back and forward to remove all the material on this plane.
Remove an additional 0.025” of material in the Z for a finishing cut. Remove the
work piece from the vise and de-burr edges.
Replace the work piece in the vise with the last machined side facing down.
Remove approx. 0.100” of material in the Z axis in two cuts.
Move the work piece in the X axis approx. 3” away from the cutter. Do not move
the Z axis from its last cutting position and measure the height of the work piece
using a caliper then reenter the Z datum as measured.
Crank the table up the required amount and mill the work piece to its finished
height of 1.750” ± 0.005”. This completes Step 2 in Figure 18. Always check the
work piece to ensure that it is square and the correct dimension has been
obtained before proceeding to the next step.
Place the work piece in the vise as shown in Figure 18, Step 3 with the bottom of
the milling cutter protruding approx. 3/8” below the work piece. This will reduce
tool deflection.
Using the “Y” axis table “side mill” the part removing a maximum of 0.125” per
pass. Make the last cut a “climb mill” removing less than .005” of material using
a slow steady feed rate. This will produce a superior finish.
Climb milling is used on manual milling machines only when machining soft
metals and plastics. Do not use climb milling when milling steel, conventional
milling is used when milling steel on a manual milling machine. Climb milling is
used predominantly in CNC machining on all metals and materials, this is due to
a negligible amount of “backlash” on these machines. Note: Backlash is the
play between the driving screw and driven nut of the machine.
Remove the part and de-burr the last cut edge. Insert the work piece with the
opposite end (unfinished end) protruding approx. 1/2’’. Side mill this edge
removing the least amount of material to obtain a completely finished edge
making the last cut a climb mill removing less than 0.005’’. Total length of part
should measure approx. 3 1/4” long. This completes Step 3.
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Outline of pillow blocks in bar stock
STEP 1: End milling 1st edge
STEP 2: End milling of 2nd edge
STEP 3: Side milling using climb milling for finishing
cut
STEP 4: Scribe line thru center and cut with band saw
STEP 5: End mill the pillow blocks individually
FIGURE 18: STEPS FOR MILLING PILLOW BLOCKS
.500
25
Note: “Climb milling” is when the work piece travels with the direction of the cutter
rotation. “Conventional milling” is when the work piece travels against the rotation of
the cutter, shown in Figure 19.
FIGURE 19: TOP VIEW OF CLIMB MILLING AND CONVENTIONAL MILLING
Remove the part from the vise and scribe a line dividing the part into two equal
sections lengthwise. Using the Band Saw cut the part in two through this line.
Consult the instructor on the safe and correct use of the Band Saw prior to use.
Place one of the previously cut pieces in the vise protruding approx. 1/2’’ with the
rough cut edge facing up as shown in Figure 18, Step 5. Face mill this piece to a
height of 1.425” ±0.005”. Repeat this step for the 2nd piece. De-burr with a file
and check to ensure the part is square.
4.3.4 BORING THE BUSHING HOLE
When a precise diameter hole is to be plunge bored with an end mill or reamer, a hole
must first be drilled approx. 85% of the diameter of the finished hole size. Precision
diameter holes can be bored using various techniques:
Reaming
Plunging into the work with a calibrated diameter end mill
The center hole of the bushing was created using a reaming tool and the pillow block
hole will be plunged into with a calibrated end mill tool.
Clamp one block in the vise as shown in Figure 20 butting the block up to the
magnet on the left side of the back jaw. The magnet acts as the position stop for
the X axis.) Note: The hole boring operation will be done while the pillow blocks
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are in a rectangular shape (prior to removing the material on the side) because
this allows a more accommodating shape when clamping the part in the vise.
FIGURE 20: VISE CLAMPING WITH ALIGNMENT USING MAGNETS
Do not use excessive force when clamping as the vise is capable of exerting
thousands of pounds of force on the part which can force the back jaw (“Y”
datum) backwards up to 0.004”. (This will happen on even the best vises). This
will result in the final milled hole position of 1.000” ± 0.0005” to be out of
tolerance, ultimately causing the rotor assembly to bind.
Insert the drill chuck in the spindle and then load a 7/16” diameter drill into the
drill chuck. Turn the mill on and set the speed to approx. 1000 rpm. Position
X:0.875”, Y:-1.000” ensuring the table locks are engaged. Remove the part and
repeat the drilling process for the 2nd block.
Insert the designated 1/2” diameter end mill into the collet. Turn on the mill and
set the speed to approx. 1800 rpm. Plunge the cutter through the drilled hole
using the knee “Z” feed. Repeat for the 2nd block. The finished product appears in
Figure 21.
FIGURE 21: AFTER PILLOW BLOCK HAS 0.5” HOLE MILLED
The Instructor will check the hole height position relative to the base using the
dial indicator installed on the height gauge.
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4.3.5 MILLING THE SIDE RECESSES
In order to mill the side recesses of the pillow blocks a “cutter radius offset” will be
used as shown in Figure 22. The cutter radius offset, also commonly referred to as
cutter compensation, is used to compensate for the cutting tool radius and must be
offset from the cut line. Milling the side recesses in the pillow blocks will use a
combination of side milling and end milling.
Lines will be scribed on the blocks to give a visual reference when milling this
step. As the student becomes more proficient with cutter tool offsets the scribing
of visual references will not be necessary. Using the height gauge on the surface
plate with the scriber tip, scribe lines in
the position as shown in Figure 23,
Step 1.
Place the work piece in the vise
vertically and ensure the cutter will not
make contact with the vise.
While the spindle is rotating, bring the
tip of the cutter lightly into contact with
the top of the block using the “Z” crank
handle. Move off the work in the XY
plane and zero the “Z”.
Using a 1/2” diameter end mill cutter
the radius offset will be 0.250”. The
initial cut will be cutting along the Y
axis. The roughing cut in the X should
be a depth of 0.350” therefore the
initial X position should be:
Starting Position = Cut Depth – Cutter
Compensation
Starting Position = 0.350” – 0.250” = 0.100”
Move to X: 0.100”, Z:-0.250” and lock the X axis. Cut completely through the
width (0.5”) of the pillow block as shown in Figure 23, Step 2.
Increment the “Z” with the cutter to the side of the block. In this case do not
plunge the cutter into the block. Remove approx. 0.250” vertically in “Z” with each
cut until the depth of approx. -0.780” is reached.
FIGURE 22: CUTTER COMPENSATION
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Now make a finishing cut using climb milling which will result in a superior finish
on the side. As shown in Figure 23, Step 3 moves to the final position of
X: 0.375” and Z:-0.800”.
Now adjust the X position and complete the second recess.
Step 1: Scribed lines for milling side recesses
Step 2: 1st cut to rough out material at X:0.100”
Step 3: Position of cutter for clean-up cut showing
cutter offset position
Step 4: Position of cutter for clean-up cut showing
cutter offset position
FIGURE 23: STEPS FOR MILLING SIDE RECESSES IN PILLOW BLOCK
4.3.6 DRILLING SCREW CLEARANCE HOLES
A general rule for determining screw clearance holes: Drill is approx. 5% larger than the
outer diameter of the screw. For example, #10 screw = 0.190 O.D. 0.190” x 1.05 =
0.200”. As there is no 0.200”diameter drill select the next larger size = 0.201 diameter
(#7 drill). See the “Common Tap and Clearance Drill Sizes” chart located in the design
lab for more information.
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Install the drill chuck into the spindle. Using a #7 drill (0.201” diameter) to make
loose clearance holes into the pillow blocks. Note: Ensure that the parallels
under the part are set to the side as far as possible to avoid drilling into them.
Turn the machine on and change the speed to approx. 1500 rpm.
Note: A tool offset is not used when drilling holes as holes are only point positions with
the drill being centered to the machine spindle.
4.4 CNC MACHINING OF THE BASE PLATE
The base plate machining will be a demonstration of CNC (computer numerical control)
machining by the shop instructor. This demonstration will replicate a production method
of machining the base plate. All milling edges, faces and drilled holes will be machined
using a fixture plate and a single machine set-up. The base plate will be machined from
a piece of 1/4” x 2.5” extruded aluminum cut to approx. 3.75” long.
Initially two 0.200” diameter holes will be drilled through the plate in the positions
shown in the drawing. These two holes will serve as the machining fixture holes
and hold the base plate in place during the CNC milling operation. Note: since
fixture holes were incorporated into the design the work piece did not need to be
clamped to a vise during machining. These simple holes allow full access to five
sides of the work piece without having to remove and replace the work into the
machine vise. This exponentially saves machining time!
The CNC machine will cut out the outside contour first and then mill a 0.050”
deep pocket. This pocket is to create a flat surface for the pillow blocks to mate
to in order to assure alignment. Aluminum extrusion does not often come
perfectly flat; instead it can contain a slight convex or concave surface.
Four tap drill holes will be drilled into the base plate in the positions indicated on
the drawing using a #20 drill. (See Tap Drill Chart on the Design Lab walls for the
selection of tap drill sizes). Note: Using CAD software “Hole Wizard” tool often
results in components being over engineered. For example calling for 80%
thread engagement when only 60% is required. Simple errors like this greatly
increase the cost of machining. When designing a part first decide the
appropriate fit required then select the drill needed from the chart.
These holes will be tapped (internally threaded) using a #10-32 tap. All holes and
edges are to be de-burred to assure a good mating surface of pillow block and
base plate and also to prevent a person from cutting themselves while
assembling components.
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5 WORKS CITED
[1] Dorian Tool Catalog, 2014.
6 REVISION HISTORY
Revision #: Date: Author:
1 October 11, 2002 Rodney Katz
2 October 06, 2014 Travis McKay & Jana Strain
3 October 15, 2014 Rodney Katz
A
7 APPENDIX A: MACHINING & DESIGN FACILITY USE POLICY
7.1 SAFETY
Safe working procedures must be adhered to al all times.
Familiarization with the document: Department of Mechanical Engineering Basic
Safety Regulations for Instructors and Students is required. A copy is on hand in
the Facility as well as at:
http://www.uvic.ca/engineering/mechanical/assets/docs/forms/ME%20Safety%202010.pdf
When entering the shop for machining the first action is to sign into the “Machine
Equipment Sign in Book”.
Safety glasses must be worn at all times while using any tools and equipment or
observing others machining
Rushing is the main cause of accidents. Care and attention must be exercised so
as not to cause injury to yourself or others.
Any equipment or area requiring attention or which may cause a hazardous
situation must be addressed immediately or reported to the Shop Supervisor.
Shop personnel must be consulted before using any tool or method considered
unsafe or with which a user is not familiar. Users are encouraged to ask
questions at any time.
7.2 FACILITY DRESS CODE
No open toe footwear is permitted
No sleeveless shirts are permitted; at minimum a T-shirt is required. Long
sleeves are recommended to avoid metal chips from irritating or burning the skin.
All loose jewelry and rings must be removed before using moving equipment.
Including earrings and necklaces because they can be pulled into the machine.
Long hair must be tied back and up above the neck line, then constrained.
Any loose hair is a major risk to personal safety; please see the shop walls for
stories of fatal incidents that occurred as a result of long loose hair.
B
7.3 GENERAL
Care must be exercised so as not to cause damage or undue wear and tear to
the facility. This includes protecting and maintaining equipment and fixtures as
instructed by lab instructors and supervisors.
Users of equipment must clean all areas of work and equipment after use to the
level at which it was found. Machine tools and equipment used for the projects
are to be thoroughly cleaned after use. Workbenches and the areas surrounding
the equipment must be swept and vacuumed after use.
Hand tools taken from the racks must be placed back following their use.
All tools or materials borrowed from the Design Facility must be signed out with
consent of the equipment must be swept and vacuumed after use.
Hand tools taken facility personnel.
7.4 MECHANICAL ENGINEERING MACHINING FACILITY STANDARDS
Drawings must be made for all work being performed in the Design Facility and
submitted to the Facility personnel prior to commencing with any work.
Only course related or approved projects can be worked on in the Design
Facility.
Machine Tools, equipment, and supplies in Room B111 are for use by the Design
Facility Personnel only. Please consult first with the Facility personnel if you
require supplies or tools from Room B111.