ECL 115A
Engineering Case Library
Design of a Scotch Yoke Mechanism
Summary
been asked to design a replacement drive existing drive which was unsatisfactory. His reaction to the problem
mechanism for an
For six weeks the Scotch Yoke mechanism had operated beautifully. It had been giving a long, slender, induction coil a smooth, gentle oscillating motion of + 110° in a magnetic field at a rate of three cycles per minute-continuously. The output of the coil was repetitive within one
Then
seemed to happen very suddenly) the output readings began to be erratic and an examination of the Scotch Yoke indicated that it was chattering and "hanging up" momentarily at one point in its cycle and then "catching up" with a sudden rush. This malfunction caused some acute embarrassment to Aaron Baumgarten, the engineer responsible for part per 10
the
.
(it
design of the Scotch Yoke.
had been that it was not an especially demanding one and that it could be readily solved-and he had said so. For this reason, the malfunction of the Scotch
Aaron's
colleagues
a
Yoke gave wonderful
opportunity to pull his leg-and they did not waste the opportunity. He quickly reacted with corrective action which should
have been adequate but
fate, in the
form of
a technician (working on the night shift)
stepped
confound him and another occurred making corrective action necessary once again. This time all went well and the unit performed satisfactorily for four months. in
to
malfunction
He had
c 1969 by the Board of Trustees of Leland Stanford Junior University. Prepared by Mr. Aaron Baumgarten with support from the National Science Foundation through the Case Program, Design Division, Department of Mechanical Engineering.
2
imparted to the
Background
The
long,
induction
slender,
coil
one of the elements in the control system for the electron beam at the (Figure
1)
Stanford
is
Accelerator Center.
Linear
voltage induced
The
constitutes an
in this coil
input to a computer which acts to maintain
the
conditions
experiment. conditions
ECL 115A
is
prescribed
for
a
specific
The
maintenance of these important to the experimental
physicists because they represent a
known
datum which is used in the interpretation of the data accumulated during the
upon:
plastic
about
essentially
is
a
rod about one inch square and seventeen feet long on which a
been formed. The plastic rod had been formed by bonding plastic strips into a laminated rod having the desired cross-section. Plastic wheels which were bonded to the rod at regular intervals acted to support the rod in "bogey" wheels which were carried in a supporting cradle. The entire ensemble was then inserted between the pole pieces of a large di-pole electro magnet which was performing a gaging function by indicating the field strength of other magnets located in the actual electron beam. The coil was long enough to protrude from both ends of longitudinal
coil
has
the magnet, thereby providing a place to
attach
some
The
a.
such coil
driving means.
had been made to use
One attempt
limit
acceleration to b.
reliable.
The
First Scotch
gentle
drive
Yoke Design
Aaron suggested that kinematically, a (i.e., simple harmonic) motion would be sufficiently gentle and that mechanisms for generating such motion were well known and easy to build. For example, an electric motor driving any of the following devices (Figure 2) seemed well suited for the job.
A simple eccentric A Hypocycloid A Swash Plate
Exhibit A-l). This scheme was judged to be
c.
unsatisfactory because of its erratic behavior. The specific cause of this undesirable behavior was never firmly
d.
An
e.
A
the people involved
sudden
a
it.
sinusoidal
b.
the
oscillated in
impart
fabrication was not to exceed $500.
a.
Some of
to
run forever with zero maintenance.") A design goal of 10,000 hours of operation was agreed upon. of materials and shop c. The cost
motion
that
as
means were to be highly (As one man put it, "We want it to
of a drive motor coupled to the coil (see
thought
was to be
coil
way
a
switches to
periodically reverse the direction of
established.
with each reversal of
motion might be twisting the coil so that the end which was closest to the driving motor was out of phase with the end furthest from the motor. Others felt that the magnetic clutch in the drive might be slipping erratically. Everyone involved agreed-there was a problem to be solved. After some discussion it was decided that a new approach might be a good way to eliminate the problem and the following specifications for a new drive were agreed
experiment.
The induction
coil
acceleration
approximates f.
A
Linkage* Crank Mechanism (which
Isosceles
Slider
a sinusoidal
output)
Scotch Yoke Mechanism
*See: Elements
of Mechanism, Doughtie
&
James.
J.
Wiley
ECL 115A
4
Hypocycloid
Simple Eccentric
3-
Swash
Isosceles Linkage
Plate
input
3-
\\\\\
Slider
Scotch Yoke
Crank Figure 2
Sketches of Alternative Mechanisms
ECL 115A
5
There were other devices which were kinematically superior in terms of their acceleration characteristics. However, the
weeks of smooth, trouble-free operation, Aaron considered the case "closed".
estimated cost of manufacture in every case
Failure
of First Scotch Yoke
was higher.
The
initial
design concepts (Figure 3)
This comfortable frame of mind lasted for about six weeks until he received a
an eccentrically mounted circular disc cam. Such a cam would impart simple harmonic motion to a reciprocating follower which in turn could
phone
then drive the induction coil in a rotary oscillatory fashion through a rack and
fact
the
considered
of
use
This was an extremely attractive approach because each of the components was either easy to machine or could be pinion.
readily
purchased. However, after ways in which to make
considering several
positive
drive
this
(i.e.,
spring
loaded,
gravity loaded, face type groove, double acting follower) (Figure 3), Aaron felt that
Yoke configuration (Figure
the Scotch
was
more
a
The analysis
4)
desirable one.
decision was
of
the
made
dynamic was done
and a
mechanism
(Appendix A-l). This analysis indicated that the loads, friction forces and deflections which would result from normal operation were very small. On this basis, the design was completed (with much attention to cost of fabrication) and the drawings were released. (Exhibits A-2a through A-2c show some representative
Fabrication of the unit was uneventful
and was completed quickly (see Exhibit A-3). The original drive motor (Bodine
Type K-2; Frame Type KYC-22 RM B8122E-600M - Exhibit A-4) and the
mechanism
"Hey, your working right.
like,
isn't
You'd better get down here and fix it right away." A visual examination disclosed the that the horizontal rack (see Exhibit
A-3) had two scratch-like marks high on its periphery evidently created by the two
rows
of
bushings
balls
in
anti-friction
the
which supported
Cat. the
were coupled together through
Scotch
Yoke
mechanism.
Initial
operation was very good and after some
rack.
the
ball
In
addition to this, the vertical, hardened steel
yoke showed a series of horizontal light and dark rings along its central portion. The conclusion drawn from this evidence was that the vertical slider running on this shaft was chattering, and careful observation (visual and tactile) shaft
the
in
supported this conclusion. The chattering was so slight in magnitude that an observer looking at the bushing housing would suspect that chattering was there but couldn't
However, placing the on the bushing housing an observer to 'feel, quite a vibration which occurred as
be
enabled distinctly,
the slider
sure.
lightly
fingertips
moved up along
The
explanation
its shaft.
of
situation
this
which seemed most reasonable
details)
original coil
which sounded
call
coil-flipping
to
Aaron
was as follows: The friction force exerted by the slider on its shaft was reaching a value greater than he had originally Further,
estimated.
force was acting
the
when
highest
friction
the rack presented
It was the than more therefore a creating calculated value. This in turn was very high local load between the balls of
its
greatest
unsupported
being deflected
length.
6
Eccentric
ECL 115A
Cam
Spring Loaded Eccentric
Gravity Loaded
Cam
Eccentric
Face Type Groove
Double Acting Follower Eccentric
Cam
Cam
Eccentric
Figure 3
Sketch of Circular
Cam
Cam
ECL
8
the ball bushing and the "soft" rack (i.e., 303 Stainless Steel). This high local loading was responsible for the scratch-like marks observed on the rack. Once this action was started, it became progressively worse until enough free play was generated to cause the mechanism to malfunction. (Here, a malfunction means a rough oscillation of the induction coil which was reflected in nonrepeatable output readings from the
computer.)
To "fix it right away" Aaron had the mechanism brought back to the shop where an additional constraint was built into the framework in such a manner as to resist any upward deflection of the rack in its extended position (see Exhibit A-5). No such constraint was considered necessary for downward deflection because the unsupported length of rack was very short
when
it
experienced a downward force. In
His verbal request didn't prove to be
an effective way to communicate, however, because on Tuesday morning the unit was again found to be liberally covered with
was operated for several hours and ran smoothly - therefore it was put back into service where it performed well for several days. Over the weekend,
The
unit
however, one of the technicians on a night shift decided to help the mechanism along
by
liberally
oiling
the
bearings.
On
the
Monday morning Aaron noticed this fact and removed as much of the oil as he could - then told the supervising following
by
and
now
oil
the nylon bushings- were
grabbing their respective shafts so strongly that the operation of the
mechanism was
jumpy. Aaron then decided to go back to a ball bushing on the vertical slider and to replace the nylon bushings supporting the horizontal rack with similar bushings which had larger holes. The reasoning behind this move was that the horizontal bushings could have a very liberal clearance without seriously affecting the performance of the mechanism. With a liberal clearance it was visibly
possible to believe that even a recurrence of
the "oiling" procedure could be tolerated
without
adverse
affects
on
the
performance.
addition to this added constraint, the ball bushings were removed and replaced with
nylon bushings.
15A
I
The
vertical
presented
slider
a
different problem - in order to prevent wobbling of the slider a limited clearance between bushing and shaft was felt to be necessary. The alternative was to make the slider longer - but time did not permit.
One more
A
sign was put one and all to refrain from oiling the mechanism. These actions seemed to do the job, because the unit performed well.
thing was done:
in the reinstalled unit asking
Second Scotch Yoke
technician to instruct his people not to oil the device anymore.
because he knew in a
He took
it
was
moisture stabilized form, would absorb
water and swell. In this case the nylon bushing was not moisture stabilized and Aaron assumed that swelling could be caused by absorption of water.
oil
Sometime
this action
that nylon, unless
as well as by
later the
need for
a
second
Aaron decided to change its form in an attempt to avoid some of the faults of the first design. This meant abandoning the price ceiling which drive unit arose.
influenced the design of the in
light
of
his
considered to be
a
first unit,
but
was worthwhile thing to do experience
this
and
a
redesign was
started.
This time a
mechanism was divorced from rack was the and developed, more
any
carefully constrained
contact
with
bushings.
In
order to
any lingering doubts about maintaining geometric fidelity, the unit was made quite massive, (see Exhibits A-6a
eliminate
through A-6c)
following in a sense, the
philosophy of machine tool builders who achieve rigidity by making
traditionally
machines massive. One more thing was done to eliminate a theoretically negligible force which might have been gremlin-like in its nature. Whereas the first
their
Scotch
Yoke had
actuated
two
micro-switches (one each at the end of a half-cycle), the second design accomplished this switching
of
a
function by the interruption
beam of
light
focussed
on
a
photo-diode at the proper time (see Exhibit
This second drive remained in continuous, trouble-free operation for three months (except for the fact that the bulbs acting on the photo-diode switches needed changing one time.) A-7).
LIST
OF EXHIBITS
Exhibit A-3
Photograph, Limit Switch Setup Drawings of First Scotch Yoke (A,B,C) Photograph of First Scotch Yoke
Exhibit A-4
Drive Motor (Bodine Catalogue Pages)
Exhibit A-l
Exhibit A-2
Exhibit A-5 Exhibit A-6
Exhibit A-7
Drawing of Modified First Scotch Yoke Drawing of Second Scotch Yoke (A,B,C,D) Photograph of Second Scotch Yoke
Appendix A-l Dynamic Analysis of Scotch Yoke Appendix A-2 Design Data
ECL
115 A
ECL 115A
-K0O05 -.0 0 00
8750 UN* 002
_~ DIA.THRU.-CMAMF. BOTH 5 IDES ~ X 4^T |
!
^x>ee?-Two holes
AT ASSY.
DRILL t (2)
DOUJEL PlN.
PLACES
RACK. SUPPORT
WTL'.
^
3(74
EXHIBIT A-2b
PF ^00-»3>4 -OB ST.
Detail Drawing, First Scotch
Yoke
ECL
MLON
BUSH\N6
.34-3 O.D. P.F.
*Z-5fcl/N£-2B (Z)HOLE.b.
*
115 A
y DEEP'
+,0005
.ZSOO -r.ool
MTL*.
EXHIBIT A-2c
AL COO
T-C
Detail Drawing, First Scotch
Yoke
i.o.
ECL 115A The Type K-2 motor is characterized by laminations extending through to periphery of motor. This construction is especially well suited for motors which must be totally enclosed because it provides the most effective cooling with the greatest amount of magnetic
stock
MOTORS fractional/horsepower
Immediate Delivery
iron.
MODEL TYPE BALL BEARING MOTORS
REDUCER OUTPUT Speed
TorQue
Rpm
In.-Oz
0
9
•CAPACITOR (3-LEAD)— Normal Slip— 115 V.— 60 CY.—
5 7
93
Totally Enclosed
14.0
230 560
CY.—
840 839 838 837 836 835 834 833 832
300:1 180.1
72
KCI-23RM
1
30:1 18.1
KCI-26RM
12:1 6:1
600:1
861
81
300:1
7
65 43 12
120:1
860 859 858 857 856 855 820 819 818 817 816 815 814
B8122E-1800M B8122E-900M B8122E-600M"* B8130E-300M B8130E-180M B8130E-120M B8130E-72M
1
— 60
120:1
841
600:1
2.1
2 V.
62 37 18
900.1
4.1
40 67 200
6
Totally Enclosed
1800:1
B8262E-1800M B8262E-900M B8262E-600M B8262E-3O0M B8264E-180M B8264E-120M B8264E-30M B8270E-18M B8270E-06M
10
•SYNCHRONOUS CAPACITOR (3-LEAD)— 115
KCI-22RM
B8192E-1800M B8192E-900M B8192E-600M B8192E-300M B8194E-180M B8194E-120M B8194E-72M B8194E-30M B8200E-18M B8200E-12M B8200E-06M
1800:1
1.4
Totally Enclosed
Cartalog No.
842
120 100 95
07
•CAPACITOR (3-LEAO) — High Slip— 115 V.— 60 CY.
20 100 95 95 93
160 100 57
93 140 280
Model No.
Ratio
1
1.9
2 8
Type Frame
10 15 25
KCI-22RM
900:1
180:1
KCI-23RM
30:1
14 0
18:1
52
6:1
120 100 95 95 65 43
1800.1
26
72:1
KCI-26RM
KYC-22RM
900:1 600:1 300:1
KYC-26RM
180:1 120:1
863 862
MODEL TYPE BALL BEARING MOTORS
REDUCER OUTPUT Speed
Rpm 0.9 1.4 1.9
•CAPACITOR (3-LEAD) — Normal Slip— 115 V.-60 CY.-
5.7
93 14.0
Totally Enclosed
230
12:1
of lubricant supplied with
851
10
30:1
67
6
18:1
100 200
4
12:1
1
180:1
72:1
6:1
25.0 60
12
850 849 848 847
300.1
1800.1
21
KCI-22RC
1200:1
2
10 0
100 150 200 300 and container
600
40
15.0
821
900.1
120:1
110 105 95 85 54 32
KCI-23RB
854 853 852
32 18
y.o
table capacitor
1
10.0 17.0
3.0
CY.
1
7.0
6.0
— 60
6
1800
110 105 95 85 75 49
1.5
V.
827 826 825 824 823 822
72:1
57
1.0
Totally Enclosed
828'
180:1
30:1
1
B8192E-180OC B8192E-1200C B8192E-900C B8192E-300C B8192E-180C B8192E-120C B8192E-72C B8194E-30B B8194E-18B B8194E-12B B8194E-06B
300:1
18:1
4
Catalog No.
831
830 829
120:1
2.8
Model No.
900.1
8.6
2.1
KCI-22RC
1200:1
14.0
1.4
•SYNCHRONOUS CAPACITOR (3-LEAD) — 115
1800.1
66
1.1
Totally Enclosed
'
Type Frame
Ratio
110 105 95 75 70 46 26
93 140 280 0.7
•CAPACITOR (3-LEAD) — High Slip— 115 V.-60 CY.—
Gear
Torque In Oz
KCI-23RB
KYC-22RC
1200:1
846 845 844 843 813 812
900:1
811
600:1
66 40
30:1
2 6
12:1
0
9.1
810 809 808 807 806 805 804 803 802
1.3
6:1
801
2
300:1
1801 120 i_
1
72.1
KYC-23RB
18:1
B8262E-1800C B8262E-1200C B8262E-900C B8262E-600C B8262E-300C B8262E-180C B8262E-120C B8262E-72C B8264E-30B B8264E-18B B8264E-12B B8264E-06B B8122E-1800C B8122E-1200C B8122E-900C B8122E-600C B8122E-300C B8122E-180C B8122E-120C B8122E-72C B8124E-30B B8124E-18B B8124E-12B B8124E-09B B8124E-06B •
each motor.
BODINE ELECTRIC COMPANY
EXHIBIT A-4
Drive Motor (Bodine Catalogue Page)
Sheet
1
of 2
5.
ECL
K-2
type
The Type K-2 frame delivers considerably more power than motors pf clock type construction, and is especially adapted for use on instruments, control devices, and other equipment requiring relatively low output, and steady, trouble-free service.
motors
TYPE K-2
TYPE K-2
1
.
Holes
3. Ball
4.
Synchronous or Nonsynchronous
Can be
Stalled Indefi-
chined rabbeted joints. Oil lubricated ball bearings, standard for all rotor shafts, are carefully selected and electronically inspected for defects, quietness and cleanliness. Laminations are assembled between die cast clamping rings, and two rivets at each corner hold the stator assembly firmly together.
Designed
for continuous duty applications sturdy construction and exceptional reliability. All gearing is of the helical type, accurately hobbed to A. G. M. A. standards. Helical gearing increases load carrying capacity, reduces noise through smoother tooth action and produces more uniform pitch line velocity, as compared to spur-gears. Gear train is made up of individual gear and steel pinion assemblies, running and supported on hardened, accurately ground steel studs pressed into the gear housing to exact center distances. A laminated bakelite gear meshes with rotor pinion in the first stage. Gears in the intermediate positions are either bronze or steel. Grease lubricated gearing.
MODEL TYPE Torque
Rpm
In.-Oz.
TYPE K-2 Model
Type Frame
Thrust Bearing
Flange Type Thrust Bearing
requiring
Type K-2 motors are totally enclosed, having only a small bushed opening through which the terminal leads are brought out. End shields are die cast from zinc base alloy and are carefully fitted to stator rings by ma-
Speed
Bearing
Ball
2. Oil
nitely
• DIMENSIONS
with Helical Gear Reduction
Instantly Reversible
115 A
XH
Frame
c
K-22RM K-23RM K-26RM
4'%,
3H
254
"/,.
2%
3%
Shipping Wt. Oz.
XL
"A. 1
'%!
• DIMENSIONS
with Spur Gear Reduction
Catalog No.
No.
•CAPACITOR (3-LEAO) — Normal Slip 115 V.-60 CY.— Totally Enclosed 1550 1550
705 706
KCI-23 KCI-26
1.4 2.4
B8194E B8200E
•CAPACITOR (3-LEAD) — High Slip 115 V.— 60 CY. — Totally Enclosed 1
1200 1200
1
707 708
KCI-23 KCI-26
1.1
8
•SYNCHRONOUS CAPACITOR 115
1800 1800 3600 3600
V.— 60
CY.
— Totally
KYC-23 KYC-26 KYC-23 KYC-26
.35 .6
.18 .3
Suitarve capacitor and container
(3-
B8264E B8270E
701
B81 24E
B8130E B8138E B8144E
of
lubricant
supplied
.
t
-
Mounting Screw
drive shaft bearings in the gear
housing are lubricated by grease which has been selected for operation within the ordinary temperature range (about 40° F.). Two of the four case holding screws are extra long so that they may be passed into or through the mounting surface to hold the motor in place.
^ . i
—
4.
This Type K-2 speed reducer motor employs a small, but rugged, built-in spur gear speed
The gear and
!
:
j
Gear Reduction Assembly
'
DIMENSIONS
1
Holes
3.
reducer. The motor shaft rotates in ball bearings, while the slow speed drive shaft is supported, in a sleeve bearing. All pinions are steel; gears traveling at the higher speeds are made of bakelite for quietness; those at lower speeds of bronze to carry greater torques.
2
1
Pinion
Enclosed
703 702 704
Steel Rotor Shaft
2. Oil
LEAD)
with each motor.
•
.
'
\
.1672 -fit
—
Frame
K-22RC K-23RB
XH
c K-23 K-:e
"/,.
27,.
1
3 V,
2'%j
XL "/.«
XL
YB-
"/.«
IVSj
"/,«
1'/j2
Shipping Wt. Oz.
38 38
Shipping
Wl
Oz.
32
44
#
Dimensions are for reference only ans are correct For latest data request certified dimension sheet.
EXHIBIT A-4 Continued
at
date of publication.
Sheet 2 of 2
42 42 54
ECL 115A
ECL 115A
ECL 115A
t
oooC
.8H50 -.0000
t>IK
THRU
(4)
VERTICAL MATERIAL
SLIfcEJR :
EXHIBIT A-6c
304
WoLcs-
PF 500-IS5- O3
5. ST.
Detail Drawing, Second Scotch
Yoke
ECL 115A
^2 UHC - 2 B * J Oft? - POOR wove 4
/VYLON BUiHIN* -.542. 0.D-
RF.
6 - 32. UHC-TWR.0
1 3 ^4 .250 -ooo
DiA. 7W*|/.
i 6-32 UNC THRU (4)H0L£S
(?)ARtt
PF 900 -I3€ 'OA
^MflfL: EXHIBIT A-6d
ALUMDetail Drawing, Second Scotch
Yoke
UNC THRU. '
ECL USA
APPENDIX
ECL I15A
A-l
Flip
c.
lL
D^wie
~*
tt 'Polished
^tebl
1.4
.4-,
__
,
.MS
APPENDIX
ECL 115A
A-l
^U?-
Coil
-
Tye \y g
APPENDIX
ECL
A-l
\~L\"p
—
\ :
r
Coil
--ZZT"
x
r
4*
Dewc
^
1
15A
APPENDIX
ECL
A-l
PUP
Coil
D^wc
11 5
A
APPENDIX
ECL
A-l
x
115 A
4 APPENDIX
A-
ECL115A
1
0
fe
1
1 / .1
/
:
i
—
APPENDIX
ECL 115A
A-l
fn?
Coil,
/44
vm 3,
.£"92>
y *
1
9^ 9
oiru
/o *7a"
-a,
v*-
2
ir
4>
^
.00014 Jul***
(j.in^V
S
fc-CL
APPENDIX A-2
To cover an expanding on
the latest data
we
Ball Bushings,
line of
revised Dtila Sheets will be issued periodically giving
your
the sizes currently in production, If
latest
Data Sheet
is
J
1
5A
Attach Middle Page to Inside Back Cover
over 4 or 5 months old,
or write the factory suggest you contact your local representative (shown on back cover of catalog)
of
New
Catalog No. 4
requesting the latest information.
SUPPLEMENTARY DATA SHEET
engineering and Price Data effective January 1, 1963
No. 7
SUPERSEDES
Supplementary Dora Sheef No. 60
X-
SECTION
XX
BALL BUSHING ENGINEERING SPECIFICATIONS the Precision Series A, the Super-Precision Series
The following data cover
XA, the Commercial Grade
OPN Ball Bushings. The same basic dimensions with varying degrees of precision. They all have the same free-rolling characteristics. For more information refer to Index on inside back cover of the catalog. ADJ, and
Series B, the Adjustable Diameter Series five types are
made
Open Type
the
Series
Table #2
— PRECISION
A — Dimensions &
SERIES
WORKING
OUTSIDE DIAMETER
BOtE
LENGTH
NUMBER
A-61014 A-81420 A-I 22026 A- 162536
A-203242
.2500 .3750 .5000 .7500 1.000
1.500
A-324864
2,000
A-487296
A 64961 28
.5000 .6250 .8750 1.2500 1.5625
+ .0000
— .0005
1.2500
A-243848
A-406080
MAXIMUM PERMISSIBLE
.0000 -.0006
2.0000
.0000 -.0006
2.375
+ .0000 — .0008
2.500
-f-
—
+ .0000
— .0005 .0000 .0005
3.000
.0000 .0006
4.000
-
+ .0000
3.750
.0000
+ — .0012
4.500
.0000
5.000
+ .0000
6.000
— .0010 r
6.000
4.000
.0000
STAINLESS STEEL.
A
Scries
entirely of stainless steel.
They
and
.015
1.062
.000
+ .000
.5000 .6250 .8750
1.5625
.4990 .6240 .8740 1.2490 1.5615
20000
1.9983
2500
1
.000
.4989
2
375
1
3.000
1.99B7
3.000
2.4985
3.750
3.750
— .025 4
INCHES
2.250
4.500
2.9983
4.500
8.000
BUSHING
NUMBER
A -48
6.000
3.9976
6.000
2
— .0000 262
t-
— .000
3733
2.9982
.001
— .000
2
1
A-61014 A-81420 A- 12 2026 A-162536
-r .0005
465
344
A-203242
1.43
695
535
A-243B48
2.75
1100
850
A-324864
1710
1380
A-406080
2460
2000
A-487296
4400
3800
NOT NORMALLY RECOMMENDED
A-649612
-9*9 a travel life of 2 million inches .(See Catalog Page 18.)
Ball Bushings can be
made
obtained
»*• For normal fit
slightly larger shafts
mav
number (Example-XA-81420-SS). They to and including A- and XA-I6:536-SS.
SS following the part
— SUPER PRECISION
#3
BALL
BUSHING WEIGHT
+ .001
+ — .020
are identified by the suffix
Table
1
INCHES
- .030
"Based on
XA
1.875
.2490
.562 .875
—
-iW? "Based on a shaft hardness of Rock well 60C.
1.625
.2490 .3740 .4990 .7490 .9990
.437
+ .000
t
— .0008
BALL circuit:
INCHES
.750 .875 1.250 1.625 2.250 2.625
3.000
— .0010
3.000
-f .0000 .0004
BALL DIAMETEI
SHAFT DIA
D
c INCHES
INCHES A- 18 12
BETWEEN RETAINING RINGS
I
Load Ratings
RECOMMENDED HOUSING BORE
DISTANCE
BUSHING
BASED ON RETAINING RING THICKNESS SHOWN IN TABLE
to the
XA — Dimensions &
SERIES
he used with caution. (See Catalog
Pay
16.)
are available only in the smaller sizes
up
Load Ratings
DISTANCE OUTSIDE
WORKING
CONCEN-
BOM
BUSHING
BETWEEN
LENGTH
DIAMETER
TRICITY
c INCHES
INCHES XA-4812 XA-61014 XA-81420 XA- 122026 XA- 162536
.2500 .3750 .5000 .7500 1.000
XA-203242
1.2500
XA-243848
1.500
XA-324864
.5000 .6250 .8750 1.2500 1 .5625
.0000
— .0003
2.0000
2.375
.0000
-f — .0004
X
406080
A.
2.500
XA-487296 XA-6496128
3.750
—
3.000
+ —
4.000
+ .0000
4.500
.0000 .0006
2.250 2.625
1.875
1.2495
2.0000
1.250 1.625
+ .0000
— .D005
+ .0000
— .0005
3.000
.0000 .0006
4.000
#4
.015
+ .0000
5.000
— .0008
+ — .0010 oooo
6.000
+
.000 .025
BALL
WORKING BORE
.250
.500
B-6I0U
.3750
.6250
B
1
22026
B 162536
.750
.0000
.000
.875
B-
203 24 2
XA.24384B
+ .001
2.75
XA-324864
1.9994
3.000
1100
850
2.4993
3.750
1710
1380
XA-406080
2000
XA-487296
3800
XA-6496121
— .000
4.500
2.9992
4.500
6.000
3.9988
6.000
4400
.040
SERIES
Catalog Page
18.)
1For extreme precision, tolerance may be reduced.
B — Dimensions & Load Ratings
In lots of 250 or more
MAXIMUM
BETWEEN
PERMISSIBLE
RETAINING RINGS
SHAFT DIAMETEI
HOUSING BORE
BALL DIAMETEI
NORMAL
PRESS
FIT
NT
.2495
.2495
5000
.4980
.3745
.3740
.6250
.6230
BALL CIRCUITS
BALL
BUSHING WEIGHT
BUSHING
NUMBER
.875
1.750
.750
1.250
1.625
1.5625
2.250
2.0000
2.625
.000 -
.025
B-4812
B-61014 .0005
.020
.500
1.000
535
TOL.
.0015
8-81420
XA-203242
695
3.750
D INCHES B-4812
344
1.43
.000
GRADE
NUMBER
465
.0005 .0000
3.000
travel life of 2 million inches. (Set-
OUTSIDE DIAMETER*
f-
--
+ .000
— .030
01 STANCE
BUSHING
XA-4812 XA-61014 XA-81420 XA- 122026 XA- 162536
2460
-
— COMMERCIAL
262
46 109 207
.020
--
8.000
on a
NUMBER
22 38
2.375
1.4994
2.250
.000 -
6.0000
on a shaft hardness of Rockwell 60C.
Table
+ .000 •--
BUSHING
INCHES
INCHES
.5000 .6250 .8750 1.2500 1 .5625
+ .0000
BUSHING WEIGHT
BALL DIAMETEI
FIT
"li.2495 .3745 .4995 .7495 .9995
-—.0004
« « Based
ft ESS
.437 .562 .875 1.062 1.625
.875
.0010 * Based
D
.750
-
-f .oooo .0005
SHAFT DIAMETEI
(NCHES
TOL.
3.000
2.000
PERMISSIBLE
RETAINING RINGS
.8730
2500
1.2475
138
B-l
.9990
1.5625
1.5600
222
B-162536
.2490
2.0000
t.9970
400
B-
.4990
.7495
.7*90
.9995 1.2495
1
B-81420
.0000
.8750
.4995
1
22026
203242
.000 .030
2.375
The hearing 'Slight oul-of -roundness mav result from the heat-treatment of Series B bearings, making it difficult to measure the true O.D. normal or press jit. will return substantially to Us original roundness when inserted into the recommended housing bore far either
PAGE
1
Based on a shaft hardness of Kock »cll (>0C inches t.u e / life of 2 million .1 on a li m
liuu
i
jiuge 18).
ECL 15A 1
VPPENDIX A-2
Mounting Arrangements CARRIAGE IF
FIG.
16-PARALUL SHAFTS WITH ADJUSTMENT
A
linear travel carriage
mounted on three Ball
fixed shaft and Bushings, two of which ride on a parallel shaft which is the third on an adjustable set screws in an retained at each end by three can be used to oversize hole. The adjustments due to diametral clearance between
take out play
as for shaft alignthe shaft and bearings as well
ment.
PARALLEL SHAFTS ARE USED
IN
PRECISION APPLICATIONS, ACCURATE
ALIGNMENT
IS
When Ball Bushings carriage for linear travel,
IMPORTANT.
are used to it is
mount
a
frequently neces-
from rotating. Two sary to prevent the carriage may be used for this purpose. In
SECTION A-A
parallel shafts
precision applications where
little
or no play can
closely to be tolerated and the shafts are fitted exercised to assure the bearings, care must be
and posparallelism of the shafts or roughness may result. Shaft sible damage to the bearings accurate location,^ parallelism can be obtained by
FIG.
17-SINGLE SHAFT WITH LINKAGE GUIDE
FIG.
19— CARRIAGE ON
Bushings with an tatennediary and the
shaft mounted on two Ball between the shaft linkage to prevent relative rotation bearing housing during linear travel.
A
two Ball linear travel carriage mounted on proviBushings which ride on a fixed shaft, with riding on a guide sion for double or single rollers
A
rail to
FIG.
J
8— LONG AND SHORT
SINGLE SHAFT IN COMBINATION WITH A TORQUE ROLLER
prevent rotation of the carriage.
PARALLEL SHAFTS
mount, featuring two Ball Brings fixed shaft with an mounted on the carriage and riding on a long Bushing mounted on the mTermediate support, and a third Ball parallel shaft which is mounted fixed structure and riding on a
A
linear travel carriage
on the
carriage.
PAGE
12
THOMSON INDUSTRIES,
ALTERNATIVE MOUNTING USING U-CHANNEL & SINGLE ROLLER INC., Manhasset,
New York
— APPENDIX
ECL 115A
A-2
of the shaft mounting holes or by providing an
adjustment to permit proper alignment. Flexible
mounting of one of the Ball Bushings or a floating
arrangement of one of the shafts or Ball
Bushings can sometimes be used tive
as
an alterna-
arrangement. For information on flexible
Ball Bushing mounts cations in
see Page 15. For appli-
which both rigidity and extreme pre-
cision are required, individual
FIG. 2 1 —SPRING LOADED BALL BUSHINGS A floating Ball Bushing can be spring loaded in numerous ways to take out all shake or play resulting from the recommended diametral clearance between the shaft and the bearing. The spring force should be well in excess of the maximum load on the mechanism, but no more than the rolling load rating of the Ball
Boshing.
Ball Bushing
mounting blocks are recommended. This permits precise adjustment and alignment of
Bushings
to shafts. In
many
Ball
non-precision light
load applications the shafts can be finished to a diameter sufficiently undersize to allow for
amount
a reasonable
of shaft or bearing
misalignment. Instead of using two parallel shafts, preferable to
make
it
may be
use of a linkage or roller
guides to prevent rotation of the carriage on a
The accompanying illustrations sugfew of the many mounting arrangements
single shaft.
gest a
possible with
Ball Bushings.
FIG.
—
fIG. 20 TORQUE TRANSMISSION Torque can be transmitted to or from a free rolling linear motion by mounting the reciprocating part on a pair of parallel shafts which are secured in the rotating members.
22
FLOATING SHAFT
In applications where the load is always in one direction, one shaft can be rigidly mounted and the other allowed to float on rollers riding on hardened pads. In this arrangement, the shafts are self-aligning in one plane, but the pads must be dimensioned or shimmed to assure parallelism in the other plane.
CARRIAGE FIG.
23— PARALLEL
RESILIENT
A
linear
SHAFTS WITH A BALL BUSHING
MOUNTED travel
carriage
mounted on three Ball
Bushings, two of which are rigidly mounted in the carriage and ride on a fixed shaft, and a third in a standard resilient mount riding on a fixed parallel shaft. See Page 15.
THOMSON INDUSTRIES,
INC., Manhasset.
New York
PAGE
13
APPENDIX
ECL 115A
A-2
THE LOAD CAPACITY OF A BALL BUSHING AND SHAFT COMBINATION
INFLUENCED
IS
BY THE LIFE EXPECTANCY AND BY THE HARDNESS OF THE SHAFT Life expectancy is expressed in terms of the total inches of linear movement between the Hai l BusitlNd and the shaft during its operating life and is known as its Tmyi'1 Life. The shaft hardness is expressed in terms of the Rockwell "C" required for no grooving of the shall, (see last two paragraphs under "Hall Hushing Shafts." Page 16). The Rollins; Load Ratings given in l ahlcs 2 thru 6 on the Data Sheet are based on a shaft hardness of Rockwell 60C and a Travel Life of 2,000,000 inches, lo find the Allowable Load rapacity for other conditions of Travel I. ife or shaft hardness, the Rolling Load Ratings must be multiplied by the appropriate load correction factors Kl. and Chart 2 respectively. and Kn obtained from C hart To solve for other items refer to Table I. The Static Load Ratings given in Tables 2 thru 6 are based on a shaft hardness of Rockwell 60O and must be cot reeled by factor Kit when a softer shaft is used. They are given to indicate allowable non-Hrinell loads and arc to be used only in special cases where the expected Travel
TABLE
If yow with lo determine
is
And you know
Then solve
for
:
1
.
7
Allowohle lonH iapo< it y
n b
BAIL BUSHING
i.
Shaft bardnc**
Travel
li*-?
%>i»
t«q
Allowable load (opacity
ti
Rolling Load Rating m Kg
Ttavpl tiO
Potting load R-iting x K(|
and read
hnfdnftii
f. Sh'ift
x K||
Load Capacity req'd
a BALL BUSHING ti/« b Loud capacity rpq'd
expectancy
travel
life
from Chart
3
Minimum allowable buthinq
•i
land capacity req'd
b
Travel
Load Capacity Req'd
rcq'd
Ki
b.
BALI RUSHING Lend capacity
<
Travel
a.
Minimum oHowtblc shod hatdnest
life
*
KM
ihooic bu things with the nex< highest rating from Tab'et 7 thru 6
haidn"
Sheifl
t
4.
life
(iir-
o-iii
Load Capacity Req'd Rolling Lood Rating x
^
tile rue, 'd
and
'*-q"d
read
ChoM
*hoft
hardnei*
7
relatively low.
EXAMPLE:
IK siiim.s are to he used to support -halts in a mannei similar to that shown in Lie. !<>. I'age 12. The carriage weight is V0S which is equally dis tributes! on the thiee i-ushings. In operation the carriage is lo reciprocate on the shafts through a stroke of 2 int. hex ai a rale ol 300 complete cycles In Hie design ol a
a
mmm.
inaehme. ih;ec
moveable cairiagc on two
It.M
i
parallel
machine is based on an operating life of minimum. he hardened to Rockweii 55 HrsiilNCS si/c for the above Determine the minimum allowable Km
per
mii'.uie.
I
he design ol
'000 hoiu- and the
sli.ilis
the
<
m
a.i
'
!
application.
3
7
5
TRAVEL
10 LIFE
20
30
50 70 100
200
Lrom
the data given above
\
u
O u
PAGE
18
is
known
that:
.2
...i—
TM
x
Kn
.
60
50
.
40
.2
i
5 x
S4 pounds
.76
in Table 2 of the Data Sheet it is found Hushing No. A- 162536 for a " diameter shall is the minimum si/e which can be used in the above application.
that L
.10 1
Ki
Referring to the Rolling Load Ratings
.1 I
50 pounds
oad Capacity required per bushing
Load Capacity Req'd Rolling Load Rating ...
Q
O
it
I
- 4—
.3
«
2000
\ 60 mm. \ 3000 hi s. 2 16.000.000 inchc Travel life i <2".x2 x 300 ( is noted that, ii it Rockwell 55C • Referring lo Table Shaft hardness determining minimum allowable hushing si/e. the following formula is used i
.4
OOO
90 1
i
1
IN MILLIONS Of INCHES
ANSWER:
30
20
10
0
SHAFT HARDNESS, ROCKWELL C
THOMSON INDUSTRIES.
1
Rolling load Capacity
1
Life
1
INC.. Manhnswt. Wen- Yoik
I
K|
ffom
APPENDIX
ECL 15A
A-2
1
PLASTICS IN
SLIDING BEARINGS by GEORGE CARLYON Vice President, Manufacturing Cadillac Plastic
&
Chemical Co.
CADILLAC PLASTIC CO. 313 Corey
Way
80. San Francisco, Calif. 761-0740 From Peninsula 589-1833 REPRINTED by permission Publications,
February,
from
Inc.
of the copyright owner,
Repn nts
ortesy h co throug ila ble
DETROIT
AKRON
»,
ANAHEIM,
OHIO, 206
D<
YCO CORP
Market
E.
CAIIF., 1721
CHICAGO «, of
D.
Thompson
Magazine
AND WAREHOUSES
S.
3,
MICHIGAN, 15111 Second Ave.
INDIANAPOLIS
St.
LOS ANGELES
CLEVELAND 13. OHIO, 3333 Detroit Ave. DALLAS 7. TEXAS, 2546 Irving Blvd. DAVENPORT, IOWA, 1 14 Gaines St.
MILWAUKEE
III.,
FLINT, MICH., 1514
S.
Dort
FORT WORTH 1, TEXAS, GRAND RAPIDS, MICH., 33,
Form 81-0163
IND., 2505 E. Washington
LOUISVILLE
1517 Grand Ave.
57, CAIIF.,
2305 W. Beverly Blvd.
15, KY-, 1811 Berry Blvd. 3,
WISC, 517 No. Broadway
MINNEAPOLIS, MINN., 1607
OAKLAND 6,
Hwy.
1400 Henderson
1,
KANSAS CITY 8, MO.,
Raymond
727 W. Lake St. CINCINNATI 27. OHIO, 6710 Madison Rd.
HOUSTON,
for
1962.
OFFICES ava
F.
RESEARCH/DEVELOPMENT
St.
3015 S. Division TEXAS, 5031 Gulf Freeway
CALIF., 949
E.
S.
Hennepin
11th St.
SEATTLE, WASH., 2427 Sixth Ave., S. SO. SAN FRANCISCO 2, CALIF.. 313 Corey ST.
LOUIS, MO., 8680 Olive Rd.
TOLEDO
3,
OHIO, 1502 Monroe
St.
Way
ECL 115A
APPENDIX A-2
Ease
Plastics
Way
for
Sliding Bearing Design
By
GEORGE CARLYON
Manufacturing & Chemical Co. Division of Dayco Corporation Vice-President,
Cadillac Plastic
THE LOW FRICTION
plastics-nylon, Teflon
TFE, and Delrin acetal-are
well
known
as bear-
ing materials in sleeve and journal applications. They may be even more advantageous in plane surface
applications
where
relative
motion
is
linear or reciprocal, rather than rotational. Examples of such applications include machine
ways, elevator gibs, or slippers and actuatwide range of equipment. The conditions under which most plane sur-
tool
ing devices in a
FLUID POWER CYLINDERS
face bearings
work tend
of the plastic bearing
to
minimize limitations
materials and to favor
Speeds are, in most instances, with those normally encouncomparison low tered in journal bearing design. Loading often cyclical rather than continuous. Cooling is is their advantages. in
Drawings
indicate
range
of
sliding bearings might prove
applications
advantageous.
in
which
plastics
nearlv always less of a problem than
it
is
in
journal bearing design.
Thus, the limitations of plastic bearings in comparison with metal— lower heat distortion temperature, greater creep— become
less signifi-
cant.
At the same time, plastics are of particular value in sliding applications because of their
outstanding abrasion resistance. Plastics ways for machine tools, for example, provide long servicelife, eliminating the need to -scrape and resurface ways. Ease of replacement also reduces
free
need to provide large or intricate wearcompensation devices. The ability of plastics to operate without the
lubrication solves another of the major problems
APPENDIX
ECL 15A 1
A-2
dom TABLE
II
from
slip-stick.
Metal bear-
ing materials can offer, at best,
Design PV Limits*
a condition approaching no slip-
Velocity Ranges,
and then only by the use
stick,
fpm
of solid film or hydrostatic lubri100
0 to
3,000
Nylon
2,600
3,000
"Delirn"
acetal
"Teflon"
TFE fiuorocarbon
resin
200 to 400
to
200
100
Material
400 to 600
2,200
2,600
2,200
1,800
cation.
With present information, design of all ings
2,100
art.
resin
9,600
9,600
(reinforced compositions)
9,600
9,600
shapes of
Nemours,
good
Inc.,
from data compiled by E. 1. Du Pont de and Dixon Corporation. These are absolute maximums, and suggests selection of values about 75% of these maximums.
practice
and plate com-
testing
paratively uncomplicated.
These cular
plasties
value
to
are
the
of
parti-
designer
in the following situations:
abrasive in
sliding bearing design.
tually the only
way
Vir-
to provide
lubrication to linear bearing surfaces
is
by
hydrostatic or force-
substantially improves op-
of
oil,
eration.
Although design
Moreover, ing starts
machine design and eliminating a
number
points.
nate
stick-
for
criteria
in
many such
ap-
freedom from chatteris a primary considera-
tion.
Two
and
acetal,
of the plastics,
plane surface bearings are comparable bearings,
to
those
the
for
journal
significance
and
TFE
offer inherent free-
of potential trouble
Plastics
the
where
)
nectors,
simplifying
High
ambient
conditions; difficult or impossi-
slip is undesirable.
plications
attention,
corrosive
bearings, even a wiped-off coat
eliminate
tenance
or
ble lubrication; or
fed means. Use of plastics can
pumps, tubing conreceptacles, and main-
lubrication of plastic
(Initial
try"
range of standard
strip, sheet,
makes prototype * Established for sleeve journal bearings
and
Availability of low-friction
plastics in a
Not recommended
25,000
Fabric of TFE fiber
bear-
reciprocating
at best a "cut
is
mess,
also
can elimi-
inconvenience,
PLASTIC INSERTS FOR BEARING
and intermittant non-lubrication problems often associated with greases.
FIXTURE SLIDES
PLASTIC SLIPPER INSERT
PLASTIC INSERTS FOR BEARING
ELEVATOR GUIDES MACHINE TOOL WAYS
APPENDIX
ECL
A-2
TABLE
I
—
Properties of Plastic Bearing Materials
Materials' 1
Property
Acetal
Friction
of
on Steel
(Dynamic) Dry
Water Oil
Fatigue Endurance Limit
F)
0.15-0.40
0.04-0.25
0.15-0.35
0.14-0.19
0.04-0.08 (2)
0.1
0.02-0.1
0.04-0.05(2)
0.05-0.1
1
3,000(5)
—
185
500 600
150(6)
Continuous Duty Intermittent
250
Thermal Coefficient of
Expansion
-0.2
5,000(4)
1,400(3)
3,000
(psi)
(Max
Service Temperature
linear
'
"Teflon"
Uylon Coefficient
115 A
6.9 x
4.6 to 5 x 10
(in./in./°F)
1
0
5.5 x 10"'
•''
3.6 x 10''(7)
(77-212°F) PV Value
fpm)
(psi x
—
Continuous Duty-Max.
(8)
2,000-3,000
1,000
1,800-3,000
Dry
10.000(7)
30,000(9) 2,000-3,000
2,000-3,000
Water Lubrication
3,000-5,000
3,000-5,000
Oil, Initial
10,000-15,000
10,000-15,000
Oil, Wick Water Absorption
@
72°
F
(per cent by weight)
50 per cent
2-2.5
R.H.
100 per cent R.H.
8.5-8.8
Submerged
8.5-8.93
None None None
0.2
None None None
0.05
0.58 0.9
length Increase Caused by
Moisture
50 per
@
72°
F
(per cent)
0.5-0.6
cent R.H.
100 per cent
1.8-2.5
R.H.
1.8-2.5
Submerged
(mg from
after
1000
cycles
and CS-17 wheel) 73 F,
850-1800'
8,500-14,600
psi
1
10,000
'
families of polymers, properties of wh.ch may vary denylon and acetal are member, of comparatively broad include Cadco is sometimes shown. Nylons represented values of range hence a pending upon specific material selected, Values shown Co. deNemours DuPont E.I. » by produced N-l"; "Zytel 101." Acetal is represented by "Delrin" 500x.
Both
are intended as a theoretical design guide for bearing (2)
367 fpm and
(31
7MM
(4)
At 73° F and 100 per cent relative humidity.
(51
At 150° F and 100 per cent relative humidity.
(6)
Heat stabilized nylons
(7)
Filled
(8)
Some designers select
5
lb.
and
material selection.
load.
cycles.
e.g.
can be used to 275" F for continuous operation,
350°
for
intermittent
operation.
compositions.
75%
of these ratings.
However, prototype
actual feasibility.
(9)
20
50(7)
1000 gram load
Yield point at
(1)
0.35
8
6-8
Taber Abrasion
0.2
"Teflon" fiber
—
normally suggested for speeds up to 50 fpm.
testing
under
operating
conditions
must
determine
)
APPENDIX
ECL 115A A-2
Plastics
excellent in abrasion resistance. The static and dynamic co-
.
.
both
TFE
virtually
the
efficients of friction of
may
application of the criteria
and
are
acetal
load.
For the designer 'concerned
same. This eliminates stick-slip or jerky operation during starting or "inching-along," a major
adeach may have substantial apparticular any for vantages nonplication. If non-lubricated, prime slip-stick operation is a
problem with conventional ma-
rest at th
consideration, the choice of ma-
substantially improve the coefcients of friction for all three
would be
terials
TFE
or acetal.
plane surface applica-
terials in tions.
Even
lubrication
initial
will
most is abrasion important, the choice would be
materials. In those linear bear-
between nylon and Teflon.
may be ment may be even more marked.
resistance
If
If
high temperature operation is a prime requisite, Teflon might be extremely best. If loadings are
would be and variacetal between made the
high,
ous
filled
selection
TFE
Table No.
lists
available
properties of the three materials. particular interest in plane surface bearing design is the
Of
acetal.
where grease
applications
the improve-
applied,
PV
commonly
a
values,
ap-
plied criteria in sleeve bearing design, also have applicability
PV
plane surface bearings. to the product of the velocity in fpm and the bearing
in
refers
compositions. 1
ing
Although
high yield of high for a plastics material,
it
pressure
over the pro-
psi
in
Application of these limiting
when
shown
in
Table II)
plane
designing
surface
bearings ally all plastic sliding
a much less precise than in sleeve guide or accurate bearing design.
should be provided with a rigid
Normally the problem of load
nevertheless
is
low for
quite
metals. This suggests that virtu-
backing, usually of metal. And although acetal is the most rigid, with a modulus of 410,000, nylon
is
a
tougher
material
as
shown by its slightly lower modulus and high yield point. The Tabor abrasion tests also are of importance
to designers
concerned with plan surface applications, particularly because enclosing or of the difficulty of shielding surfaces in linear mo-
bearings,
is
plane surface bearings may be more acute than in sleeve journal bearings, although distribution of load usually is over in
a large area. Speeds generally are lower. The major problem
PV limits therefore, becomes one primarily of control of fric-
of
rail,
form the section of the neath it more than the
be-
rail
rest, in
essence creating a valley, 'f the shoe must continue to pass back and fortl over the valley it may create objectionable vibration. In such an application, therefore
might be advisable
it
make
to
metal, the shoe
rail of
the of plastic. Since total deformation
dependent upon
is
thick-
ness of material, deflection may be minimized by use of thin sections.
Of
is
least
af-
flow,
TFE
the
acetal
by cold
fected
under
plastics
three
the
The extremely high creep TFE may be minimized by the use of filled mate-
most.
rate of pure
employ
which
rials
graphite,
glass fibers or glass cloth as a
strength supporting body.
TFE may
Nylon, acetal and
be used in maximum environmental temperature of 150, 185, and 500F respectively. These materials are poor conductors of
Hence
heat.
it is
PV
design
when
advisable
applications are near limits,
some means
tional heat.
to
returns
same spot on a plastic the pad will, In time, de:
discussion,
jected bearing area.
factors (as
f
xmtinually
pad
or
cause problems. For a metal bearing shoo
i
instance
bearings,
surface
plane
with
creep ca
be substantially different. used Of the three most widely acetalTFE, materials-nylon,
under
deformation
time
long
maximum provide
to
for additional heat
dissipation.
Deformation With Time
Normally
it is
best practice to
always present in plastic materials. This is a mechanism of yielding similar to that experienced with metals at
use plastic for only one side of
gests that in adverse conditions
high temperatures. For
erated
where shielding or shrouding is impossible, nylon would be the
design purposes, additional de-
Two
than one per cent strain after a one year period reaches a magnitude ap-
possible:
proximately equal to that of the initial strain. To estimate total
use of liquids. In plane surface bearing applications, the latter
tion.
As the chart shows, nylon
has the greatest abrasion resistance, acetal the least. This sug-
preferred plastic. In addition
its
imbed
to
ability
to
(actually
foreign par-
absorb or engulf) effect ticles without significant
on
bearing
properties
further
recommend nylon where sives are present. This bility
characteristic
abra-
imbeda-
also
mini-
Cold flow
is
formation at
deformation,
practical
less
the
initial
strain
The
way
sign latitude
is
of allowing de-
by use
of appar-
mizes wear and scoring of the
ent modulus which
other surface. (Teflon also rates
modulus plus an allowance
is
prove dissipation of heat gen-
bv
the initial for
friction.
approaches
are
making bearing
sec-
other
tions as thin as practicable
backing them with metal,
method may be although
mav be multiplied by two. best
the bearing surface, with metal employed on the other to im-
even
oils,
liquids
and by
or
least acceptable,
water,
being
grease,
processed
APPENDIX
have
A-2
been
used.
successfully
The major problem, of course, is a method of retrieving and containing such liquids.
have
All three plastics
coeffi-
expansion
thermal
of
cients
several magnitudes greater than
metals (see Table
Thus,
1.)
if
from ambient substantial, adequate proviis sion must be made for this expansion. Other than providing coolant, two approaches may be temperature
rise
used. 1.
Since total expansion
is
a dependent upon thickness or size of the mateit may be minimized by use of thin
rial,
sections. 2.
this
If
undesirable
is
and tolerances must be held extremely close, is
it
possible to design the
mechanism
to give pre-
operation
cise
at
opti-
mum
top temperatures
after
a
period
of
less
precise operation during
warmup. And tics
since plas-
are such poor heat
conductors the time
is
warmup
usually short.
In an incredibly wide number of applications,
particularly in
the field of materials handling, the problem of sliding friction is
Unfortunately
considerable.
many such problems ble of solution
by
are incapa-
precise for-
mula, since operating conditions
may be
extremely erratic and
intermittent.
These areas include
buffer strips on conveyor chutes,
rub
rails,
chute linings or coat-
ings, etc.
As a general rule, nylon is probably the best material for rub rails and bumper strips, since the material
is
extremely
abrasion resistant and has a low coefficient of friction. Its
resistance
impact
and damping quality
enable the material to absorb
shock without damage.
Nylon has been used on such diverse items as ball grinder and piston feed chutes to eliminate
scoring or nicking of the product,
and
to protect the chutes.
ECL 115B
Some More
missing!
Troubles
At
clean out
After several months of good operation, the second Scotch Yoke mechanism began to transmit erratic signals once again. A visual examination did not indicate any obvious troubles, so each sub-assembly was disconnected and checked for excessive looseness or broken parts with no success. The motor was operated with no load: the rotation of the output shaft was observed to be smooth and the sound of the speed reducer was quiet and steady. At this point,
"Well -
it's
got
me
beat
-
Aaron
let's
said,
take the
whole unit back to the shop and we'll strip down piece by peice to see if we can find
it
anything."
An instrument-maker
did just that and
could find nothing wrong. "There's nothing left
to suspect but the speed reducer in the
motor-housing," said Aaron, "even though
seems to run smoothly and quietly." With this the instrument-maker picked up the motor and tried to turn the output it
by hand - and
making a shaft rasping noise as it did so. "You've got a stripped gear in there, mister," he said. "That's good," Aaron said, "at least I'll know what needs fixing." it
Aaron decided
tc
of the old grease so that he
could look for scuff or scratch marks on gears, shafts or the gear case walls,
and he
did find one gear with scratch marks on the
web. In order to determine
why
they were
there he re-assembled the gear train and
it
was then that he noticed that one shaft and one of its supporters were worn in a peculiar manner (see photographs Exhibit B-l) which permitted two gears to move out of mesh. This turned out to be the cause of the
latest
trouble; the
corrective
action
was to replace the motor/speed reducer combination with a new one of the same model - on the assumption that the observed wear had its beginning in an adverse combination of manufacturing tolerances which somehow had gotten by the motor manufacturer's Quality Control. The new motor/speed reducer failed in the same way - this time in a matter of a few weeks. During these few weeks, the original motor was returned to the manufacturer's engineering department for analysis (see taken
Exhibit B-2).
did turn,
With the
The speed reducer was quickly taken and every gear was looked at hopefully, but none of them had any teeth
failure of the
the decision was
made
second motor,
to redesign the drive
to the Scotch Yoke. While this decision
was
being implemented the unit was driven by a
motor of the same kind as the original one. As of this writing it has been operating for six weeks with no sign of trouble. third
apart
this point,
all
B EXHIBIT
B-l
OD N I
E
ELECTRIC
COMPANY 2500
W.
BRADLEY PLACE. CHICAGO. ILLINOIS 60618 AREA CODE 312-478-3515 TELEX 25-3646
ADDRESS REPLY J. F.
TO:
CADY
DISTRICT REPRESENTATIVE
1485 BAYSHORE BOULEVARD SAN FRANCISCO. CALIFORNIA 94124
March 27, 1969
PHONE, 415-467-8656
SLAC 0. Box 4349 Stanford, California 94305
P.
Attention; Mr.
Dear
Air.
A.
Baumgarten - Engr.
Baumgarten:
This will confirm our telephone conversation of March 26th. The motor you sent back to Bodine-Chicago Serial number 818RG046 We feel was inspected and evaluated by our engineering department. that the cause of failure can be pinpointed to two reasons: ,
#1.
The gearmotor was defective to begin with.... or
#2,
At some time during the life of the gearmotor the load was considerably in excess of the normal rated load.
In order to determine which of the bbove caused the motor to We are repairing the motor at fail we suggest the following: no-charge to Stanford, and returning it to you, making absolutely certain the motor is in first class condition before it is returned. Should it You can then test the motor under full load conditions. fail again, we will be certain that the motor is being misapplied, In this case our suggestion would be from a torque standpoint). ( to switch to the N-1RD gearmotor.
From previous tests and experience with this type of motor, it would appear that this is a case of simply too much load for this While the gears may stand up under these conditions, the motor. studs will not. It should be noted that this motor was subjected to over 2000 hours of operation in it's twelve weeks of use. If more than 2000 hours is desirable, a larger stronger motor should be used to give you a service factor, proportional to the expected life you desire.
Sheet
1
of 2
BO D
2500
W.
I
N E
BRADLEY PLACE, CHICAGO. ILLINOIS 60618 AREA CODE 312-478-3515 TELEX 25-3646
ADDRESS REPLY
TO;
CADY
J. F. OISTRICT REPRESENTATIVE
-"arch 27,
1969
1485 BAYSHORE BOULEVARD
SAN FRANCISCO. CALIFORNIA 94124 PHONE-.
415-467-8656 (
*age
2)
Motors and gearmotors are designed to give the For example: and 5000 hours of operation under nameplate 2500 user between find some that are designed to give more You'll conditions. to be placed in the category of special have they than this, but service as your present motor is. general service motors, not for 10,000 hours you should base requirement So, if you have a with a rating of four or five times motor on a your selection Normal being defined as conditions. your load under normal week,, days a eight hours a day, five On any application requiring more than One point of caution. 5000 hours of operation, the manufacturer should be consulted Items as to instructions on general maintenance of that motor. lubricants, and bearings to be watched very closely would be and in the case of DC motors* brushes and commutator wear. If we can We hope that you will find this information helpful. Stanford of Students be of any further service to you or the Univ. please feel free to call on us at your convenience.
Cordially,
F. Cady Company 1485 Bnyshore Blvd. San Francisco, Californ ia 94124
J.
Sheet 2 of 2
EXHIBIT B-2
FAILED ELECTRIC MOTOR
Sheet
1
of 3
Sheet 2 of 3
Sheet 3 of 3
„
ECL115
INSTRUCTOR'S NOTES
This case shows, not perfection, but
an
performed under
design job,
actual
constraints of time and
money,
for a single
The choice of the Scotch Yoke over the simple eccentric cam or the slider crank was a decision based on the author's personal experience. The merits and item.
shortcomings of these mechanisms, and the rational basis for engineering decisions, are fertile areas
The
of discussion.
particular configuration
Scotch Yoke chosen by the designer is not the only possible configuration— and perhaps not the "best" from the viewpoint of all engineers. The differences can be
examined in the light of design criterea which students would have to develop.
The suggested assignments
be
useful
drawing
exercises
in
and dimensions. Suggested assignments No. 4 and No. 5 are exercises in the application of beam deffinition
of the
may
detail
of
shapes
deflection theory.
1
of 2
ECL
„
SUGGESTED ASSIGNMENTS
for part
A
Review the various mechanisms shown in 2. Compare them on the basis of required number of parts, precision required of the parts, ease of manufacture
SUGGESTED QUESTIONS
for part
115
B
Estimate the highest torque imposed on
1.
6.
Fig.
the output gear by the operation of the
of the parts,
etc.
Scotch Yoke. 7.
Will
the
torque
on the output gear
reverse driving a cycle of operation?
Sketch
possible different configurations of the Scotch Yoke. Strive 2.
three
8.
What should the designer do now?
for simplicity of manufacture, accuracy of
performance, direct transmission of forces with the
least possible
bending, twisting, or
(Another part of this case, showing Dr. Banngarten's next step, is in preparation)
binding.
you as a detail designer have been asked to draw up the first yoke (part 2 of Exhibit 2a), the second yoke 3.
Assume
that
(part 2 of Exhibit 6a), or the frame (part
1
of Exhibit 6a). Estimate the time you will require to do this job; record the time
actually
used.
Use
the
sample
detail
drawings shown in Exhibits 2b, 2c, 6b, 6c, as models.
4.
Compare
the
stiffness
of the second
on the under unit force applied upwards or downwards by the crank at the positions of upwards and downwards motion of the crank. design to that of the
first
design,
basis of calculated deflections
Compare up-and-down motion of yoke, caused by its weight acting 5.
the at
different positions of the supporting rods,
the first and second designs of the Scotch Yoke mechanism. Assume that the calculation of deflection shown in for
Appendix
A refers to
the center position of
the yoke, and that the support rods in the later design are
3/8" diameter.
2 of 2
