Machine design, tập 84, số 10, 2012

July 19, 2012
A Penton Media Publication
Tune in to EngineeringTV.com

BASICS OF BALL
SPLINES, page 50
RESOLUTION AND
ACCURACY IN 3D
PRINTING, page 56

FASTER MOLDING
WITH HIGH-FLOW
POLYCARBONATES,
page 72
BETTER WAYS TO
ASSEMBLE PEEK
PARTS, page 80

Tips
& Traps
in
GD&T
Page 68


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VOLUME 84
ISSUE 10
JULY 19, 2012

MEDICAL INDUSTRY FOCUS
Authored by:

Lonny Wolgemuth

Senior Medical Market Specialist
Specialty Coating Systems Inc.
Indianapolis, Ind.
Edited by Stephen J. Mraz


Resources:
Specialty Coating Systems Inc., scscoatings.
com
For more information on parylene coatings,
scan this code or go to: http://machinedesign.
com/article/coatingadhesion-promoterspecialty-coatingsystems-0609

Many medical devices and their electronics need protection from moisture, chemical contamination, electrical
charges, and body fluids. Otherwise, patients and healthcare providers may be put at risk. One way biomedical
engineers provide this protection is by encapsulating
devices in a conformal coating, one made of a dielectric,
or poor conductor of electricity, such as silicone, acrylic,
urethane, or epoxy. But one of the best materials for this
purpose is parylene.

Parylene basics
Parylene is the generic name for a series of organic
polymers — poly(para-xylylene) polymers — used as
coatings. They are polycrystalline and linear in nature,
optically clear, and colorless. Parylene coatings have useful
dielectric and barrier properties and are chemically inert.
Three different types give engineers a range of dielectric
and other properties from which to choose. The coatings
contain no fillers, stabilizers, solvents, catalysts, or plasticizers, so they are not subject to any leaching, outgassing,

Protecting

MEDICAL
ELECTRONICS
with parylene

FEATURES

This biocompatible
conformal-coating material
protects medical devices
against fluids, chemicals, and
stray electrical charges.

rotary
50 Exploring
ball splines
Rotary ball splines can produce
submillimeter accuracy. However, the choice
of angular-contact or crossed-roller bearings
plays a critical role.

Parylene coatings are optically clear and do little
to change the look or dimensions of the underlying
component or part, as demonstrated in this photo of two
circuit boards. The top one is coated with parylene,
the bottom one isn’t.
20

MACHINE DESIGN.com

JULY 19, 2012

or extraction issues.
Parylene coatings are also compatible and stable in the presence of
bodily fluids and tissues, critical
factors in the medical-device
industry.
Parylene provides dryfilm lubricity with coefficients of
friction similar to that of PTFE
(Teflon), and dielectric strengths up
to 7,000 V at a mil (25 microns) of
coating thickness. No other material
can be applied as thinly as parylene
and provide the same levels of
protection.
Par ylene withstands all
common sterilization methods
— steam, ethylene oxide, electron
beam, hydrogen peroxide plasma,
and gamma radiation. It can be applied to most vacuum-stable materials, including
plastics, metals, ceramics, fabrics, paper, and even
granular materials. For example, parylene coatings
could be applied to microspheres or moisture-absorbent
powders.
Parylene can be selectively removed with plasma, lasers,
or strong abrasion, for instance, to repair devices. Parylene
is not soluble in harsh detergents and chemicals; in fact, it
protects components from such chemicals. Parylene is not

a “hard” coating, so excessive abrasion will remove it. However, most components coated with parylene do not abrade
or rub against other parts. If an application
does include abrasive contact, it is not a good
candidate for parylene.

Parylene has been
successfully used on implantable
electronics such as cardiac-assist devices,
neurostimulators, cochlear implants, and
pacemakers. It’s also been used to coat
nonelectronic medical devices as well,
including coronary and cerebral stents,
and catheters.

sublimating it directly to a vapor, and then heated again
until the dimer cracks into a monomeric vapor. This vapor
flows into an ambient-temperature deposition chamber
kept at a medium vacuum (0.1 torr) where it spontaneously polymerizes onto all surfaces, forming an ultrathin,
uniform film. No curing or additional steps are required.
The size of the coating chamber may be an issue if
Continued on page 22

A short history of parylene

Parylene deposition
Parylene coatings are applied using vapor-deposition polymerization (VDP) in a
vacuum chamber at room temperature. Film
deposition actually takes place on the molecular level, with the coating literally growing one molecule at a time. This lets parylene
penetrate and coat small cracks, crevices, and
openings, and protect even hidden surfaces

in areas where other coating methods such
as sprays and brushes cannot reach. Coating thickness is uniform, even on irregular
surfaces. And VDP is a clean, self-contained
process that uses no additional chemicals.
Parylene is deposited as a vapor, so it surrounds the target and perfectly follows its
contours, literally encapsulating it. Parylene
coatings are ultrathin and pinhole-free.
The only raw material used in the coating process is known as dimer. Technicians
place the powdered double-molecule dimer
into the vaporizing chamber at one end of
the coating machine. The dimer is heated,

In 1947, Michael Szwarc was pursuing his academic career in physical chemistry at the Univ. of Manchester, England. His interest in the
strength of individual chemical bonds led him to investigate a class of
aliphatic carbon-hydrogen bonds in which the carbon was directly attached to a benzene ring. While doing so, he heated gases of the simplest compounds having both benzene and carbon — toluene and the
xylenes — to high temperatures. He monitored both the decomposition products and rates of decomposition as a function of temperature.
With p-xylene only, a tan-colored deposit formed in the cooler
reaches of his glassware. The material has been described as a thin,
flimsy, tube-shaped mass, “the skin of a small snake.”
Szwarc correctly deduced that this film had been formed by polymerizing reaction products of the p-xylene, called p-xylylene. He also noticed
the new polymer’s physical properties and chemical inertness. This serendipitous polymerization was the world’s first vapor deposited poly(paraxylyene). Today its purer colorless form is called parylene N.
A few years later, William Franklin Gorham at Union Carbide Corp.
continued the research on parylene. By 1967, this work led to the availability of a new polymeric coating. “Parylenes” was the term used to describe both a new family of polymers and the vacuum-deposition process for applying them. In fact, Union Carbide developed over 20 types
of parylene, but only three were deemed commercially viable.

JULY 19, 2012

20

MACHINE DESIGN.com

Protecting medical
electronics with parylene
Parylene coatings give medical devices
the dielectric strength to resist stray
voltages as well as fluids and gases.

for designing
64 Options
the best hinge
Hinges with spring pins instead of solid pins
can lower costs and extend life.
CAD/CAM/CAE/FEA

Accuracy in

SPC leads
68 When
engineers astray

ADDITIVE

The quest for minimizing process variations
can lead to parts that are needlessly
expensive.

go with the flow
72 Polycarbonates
A new class of high-flow polycarbonate
copolymers meets or exceeds the physical

and mechanical properties of traditional
materials, and provides better molding
characteristics.

assembly techniques
80 Advanced
for high-performance plastics
Engineers switching from metal to plastic
need to revisit how they assemble the parts.

2

MACHINE DESIGN.com

JULY 19, 2012

21

MANUFACTURING
A common
mistake is to
confuse high
resolution with
accuracy.
In the realm of additive manufacturing,
what exactly are the
distinctions between
accuracy, repeatability,
and resolution? Accuracy
describes how closely a manufacturing machine’s output

conforms to a tolerance
within a specified dimensional range. Repeatability
captures the equipment’s
capability to produce consistent output, time after time.
And resolution refers to the
smallest measurement the
machine can reproduce.
These concepts are second
nature to designers and manufacturing engineers. Yet,
there is a widely held misconception about these measurement concepts as they
relate to additive manufacturing. Over the years, some
engineers have slid into using
resolution attributes — such
as layer thickness or dots per
inch — as a careless shorthand term for accuracy.
56

MACHINE DESIGN.com

Accuracy
in additive
manufacturing
The color maps reveal
that the top part — built
on a high-resolution
3D printer — is not as
accurate as the bottom
part, built using a
lower-resolution
setting on an FDM

system. Purples
and reds reveal that
the high-res printer
produced deviations
of ±0.020 in. or
more. Greens reveal
the FDM-built part
is mostly in the
±0.005-in. range.
Photo courtesy of T. A.
Grimm & Associates Inc.

A common mistake is to
confuse high resolution
with accuracy.

JULY 19, 2012

56
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Tips
& Traps
in
GD&T
ON THE COVER

DEPARTMENTS

Cover design by
R. L. Rubenking.

8 EDITORIAL
A better way to find stand-out engineers

10 EDITORIAL STAFF
12 LETTERS

16 SCANNING FOR IDEAS
Modular guarding system protects workers and equipment
One serious screwdriver

25 REPORTER’S NOTEBOOK
36 LOOKING BACK
43 SENSOR SENSE
Inclination and tilt detectors

44 COMMENTARY
The myth of Chinese and Indian engineers

47 INDUSTRIAL DESIGN
When symbols are just as important as good design

48 VANTAGE POINT
An educated workforce is key to reshoring

86 ORR ON ENGINEERING
How to make the path of least resistance work for you

88 SOFTWARE PRODUCTS
90 PRODUCT SPOTLIGHT

4

PRODUCTS
DATA FILES
AD INDEX
BUSINESS INDEX

CLASSIFIEDS
BUSINESS STAFF
BACKTALK
MACHINE DESIGN.com

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Motors

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Free eBook: Electric linear actuators,
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Recent advances in motion-control technology have given design engineers
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However, these developments have also complicated the process for determining
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EDITOR’S WEB PICKS

Tubing and hose guide

6

NewAge Industries has updated
its buying guide with 20 tips
on choosing plastic and rubber
tubing and reinforced hose. It
offers advice on critical aspects
of tubing and hose selection,
such as temperature, corrosion
resistance, flexibility, pressure
and vacuum requirements, and
reuse. Get a free copy at www.
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CAD models
Zero-Max’s downloadable 3D
CAD models of motion-control
components, previously for
Internet Explorer users, are

now compatible with Firefox
and Chrome Web browsers.
Intended to aid engineers when
configuring a system, product
models include flexible and
servo-shaft couplings, overhung
load adapters, gearboxes, torque
limiters, and linear actuators.
Download the models at www.
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concerns, choosing vendors, and legal
requirements. Learn more at www.tuv.
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Sealing site
Garlock has revamped its Web site
(www.garlock.com) with a focus
on seals and related hardware for
aerospace, chemical processing,
pharmaceutical, industrial, and pulpand-paper applications. It includes

an extensive archive of technical
articles; product info on compression
packings, diaphragms, gaskets,
hydraulic components, and expansion
joints; and a technical section with
engineering tools, product selectors,
and training resources. The site is also
compatibile with mobile phones and
tablets.

JULY 19, 2012

WATCH PRODUCT
OVERVIEW AND
TUTORIAL VIDEOS AT
YOUR CONVENIENCE
AutomationDirect’s Learn Web
site features industrial-control
product overviews and tutorials.
Topics range from PLCs and HMI
to motion control and sensors.
Recent Kickstart video uploads
include:

WERMA stack lights —
See the full line of stack-light
components and how they are
assembled; a wide variety of
visual and audible devices are
completely configurable.

Digital counter/
timer/tach —
Compact DIN-rail-mount unit
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flexibility.

Foot switches with
metal guards –
Use heavy-duty foot switches for
controls on rotating or spinning
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NITRA pneumatic
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couplings, and blow guns.
For a complete list of videos, visit
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IT’S MOTION
CONTROL VERSUS
MOTHER NATURE
ON CENTRE COURT.

©2010 Moog. All rights reserved.

RS# 106

WHEN IT COMES TO HIGH PERFORMANCE MOTION CONTROL, MOOG EXPERTS ARE THERE.
When design engineers sought the best way to control the new retractable roof at Wimbledon’s famed Centre Court, they turned
to Moog. The result was an innovative all-electric installation that provides 148 axes of control via high performance electric
actuators, servo motors, servo drives, closed-loop controls and software. Now, more than 1,100 metric tons (1,212 tons) of steel
and 5,200 square meters (17,060 square feet) of fabric move swiftly and safely to prevent rain delays.
Moog’s combination of motion control expertise and world-class solutions
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For more information call 866-580-7610.

How can we improve your machine design?
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WHAT MOVES YOUR WORLD

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EDITORIAL
A better way to find
stand-out engineers
There are K pegs. Each peg can hold discs in decreasing order of radius when
looked from bottom to top of the peg. There are N discs, which have radius 1
to N. Given the initial configuration of the pegs and the final configuration
of the pegs, output the moves required to transform from the initial to final
configuration ...
What you see above is part of a sample problem found on Facebook’s Web
site. Programmers looking for work at Facebook often start out by submitting

code to solve puzzlers like this one. Code that impresses the Facebook crowd
earns you a job interview over the phone. If that goes well, you’ll find yourself
in Facebook’s Menlo Park, Calif., facilities for an in-person evaluation. Facebook
says it has uncovered some of its most-able software engineers just by using its
Web site to ask for solutions to programming brain-teasers.
Whatever your opinion of Facebook social media, you have to give that company credit for coming up with an inexpensive way of finding good engineers.
Its methods stand in direct contrast to the practice of asking riddlelike questions
that have nothing to do with the job at hand, an interviewing technique popularized by Google and adopted by several other high-tech companies.
Employers, though, increasingly seem to be coming around to the idea that
responses to off-the-wall questions may say something about an applicant’s
quick-wittedness, but don’t really reveal much about how that person will get
a job done. So some organizations are now trying to find the real qualities that
predict good work performance. And many of them have concluded these
qualities have little to do with academic credentials or job resumes.
Engineering employers that still depend on brain-teasers to find technical talent might learn a few things from George Anders, a former Wall Street
Journal writer and book author. A lot of traditional talent-scouting systems
don’t work, he claims. Anders studied several professions to see how the best
employers found new hires who would likely turn into first-rate employees. He
summarized his findings in a book called The Rare Find. Two of the groups he
examined had an interesting insight: The Teach for America project and the
U. S. Army Special Forces both looked for evidence of one trait in particular —
resilience.
Teach for America sends teachers into low-income communities. It figures
educators who find success there must persist in the face of problems that might
crush less-committed individuals. So among other things, TFA is on the lookout for applicants who struggled in their first year of college but persevered and
eventually earned higher grades year after year.
Similarly, Army Special Forces drill sergeants these days aren’t particularly
impressed by candidates who do the most pushups or crank out fast times for
two-mile runs. They are more interested in who performs well with little sleep
during team problems where it’s important to think like a soldier. Guys who excel at pull-ups are still eliminated from the program if they get moody or hostile

when things don’t go their way.
I’d argue that resilience is just as important for many engineering tasks as
it is for teaching disadvantaged kids or gaining trust in a remote village. But it
doesn’t come up in many job interviews because hiring managers find it easier
to pull out a few head-scratcher problems than to spend time making a frank
assessment about what a job really entails.
— Leland Teschler, Editor
RS# 107
JULY 19, 2012


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WASHERS &
STAMPINGS

EDITORIAL STAFF

EDITOR
Leland E. Teschler


MANAGING EDITOR
Kenneth J. Korane


FREE CATALOG & BROCHURE

Call 1-888-WASHERS

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Stephen J. Mraz

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RS# 109

INDUSTRY COVERAGE:
AUTOMOTIVE, PACKAGING,
MEDICAL
Stephen J. Mraz

CAD/CAM, MANUFACTURING
Leslie Gordon

ELECTRICAL, ELECTRONICS
Robert J. Repas, Jr.

FASTENING & JOINING,
MATERIALS
Lindsey Frick

FLUID POWER
Kenneth J. Korane

MECHANICAL

Lindsey Frick
Kenneth J. Korane

EDITORIAL PRODUCTION
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Editorial Production Manager
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Art Director

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RS# 110
JULY 19, 2012


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ĚĞǀŝĐĞƐ͘^ƚĂŶĚĂƌĚĂŶĚĐƵƐƚŽŵŵŽƚŽƌŵŽĚĞůƐĂƌĞĂǀĂŝůĂďůĞǁŝƚŚŽƉƟŽŶƐ͘ŽŶƚĂĐƚƵƐƚŽĚŝƐĐƵƐƐ
Brushless DC Motor Features:
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RS# 111


LETTERS
Almost united on unions
I read with amusement the letters
sent to you concerning the question of engineers joining a union
(“ Time for Engineers to Think
About Unionizing? Jan. 19).
I was in an engineering union
several decades ago. It was for a
large railroad-car manufacturer
in the Rust Belt, which is no longer in business. (No, the union
didn’t bring it down.) As a designer and engineer-in-training,
I was required to join the union
based on my job description. It
was a good learning experience
on why engineers and unions
don’t mix. I won’t go into details
of the office culture or issues
with having hourly and salary
workers combined.
The issue that I had at the

time and still do today is that
the union had many constricting
work rules on how you get promoted and how people advance
within the organization. Professionals or not, you were treated
differently if you were in the
union. I found the whole process
to be nonproductive and inefficient for getting work done. I was
denied advancement, not based
on experience or productivity,
but on years of service. Union
people didn’t go to lunch with
nonunion. The entire culture was
counter to the teamwork environment required in the engineering profession.
During the summers, while
attending college, I worked in
a manufacturing plant that was
also unionized. I can honestly say
that the hourly union plant job
had more job satisfaction than
did engineers in the unionized
office. My opinion is that there is
no place for a union in the office
environment, let alone the engineering profession.
Joseph C. Dominick
There can be a period in an engineer’s career in which the individual is too young to retire
but old enough that a change
12

MACHINE DESIGN.com

Engineers still unified on some
things
Readers convey their
dislike of engineering
unions, although one offe r s a m o re - o p t i m i s t i c
v i e w. B u t r e a d e r s a r e
speaking with one voice
to criticize modern design
and the fact that form no
longer follows function.
They also seem to agree
that sustainability standards will do more harm
than good. We’ll see.

of employment is difficult or the
potential loss of benefits is too
great. Management can take
advantage of this situation by
withholding salar y increases.
Membership in a union could be
advantageous in this situation,
and a union could also provide
assistance against dismissal before eligibility to retire.
In my own career, I benefitted
from a union I did not even belong to. The factory employees
were represented by the United
A u t o Wo r k e r s U n i o n , w h i c h
negotiated ear ly retirement,
health-care benefits, and vacation and holiday times. The same
benefits were then granted by

management to salaried employees. Thus, there was no union of
salaried employees who had no
protection against age discrimination or arbitrary dismissal.
R Bruce Hopkins

No form and
too much function
As an industrial designer, I appreciated your recent commentary
(“Form Should Follow Function,
and More,” April 19). I suggest
that anyone involved in the design of any product that people
use read two books from the 70s.
One is How Things Don’t Work,
JULY 19, 2012

and the other is Design for the
Real World. Both books deal with
the same issues we need to deal
with today.
By the way, we have a 2005
German car purchased two years
ago. We are still trying to figure
out all of the technology/gadgets in the car. My son has the
same type of German car, but his
is a 2010. He will be trading it in
this year for a new one. He is a
top engineering manager working for one of the top computer
manufacturers, and he still hasn’t
figured out all the gimmicks and
features of this German driving

machine. But he paid for all of
them.
There is no evidence of a human-factors approach in these
two cars, just lots of interesting
things to look at and play with,
but hardly functional or germane
to driving. And who has the time
to figure out all of this?
If I buy something, no matter
what, I want to use it, not have to
go back to college for two years
and take another 60 credits, just
to repeat the exercise the next
time I buy a car.
As my teachers used to say:
M ake it simple enough for a
10-year old to figure out.
Manuel de Sa


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RS# 112

©2012 National Instruments. All rights reserved. CompactRIO, LabVIEW, National Instruments, NI, and ni.com are trademarks of National Instruments.
Other product and company names listed are trademarks or trade names of their respective companies. 05312


LETTERS
I just read your commentary and
now I think we are wired similarly.
I agree with all your comments.
At my firm, we are always talking
about form following function
and to design for use, not looks.
Cars today get too cluttered
because so many automakers are
competing to have the most “options” for mass marketing. I told

my spouse the other day that if I
could, I would get our next company vehicle with a hand-crank
starter. Less to go wrong, no batteries, and those cheap magnetos used to work pretty well.
All kidding aside, I enjoy controlling the functions of driving.
It’s not that difficult to clutch and
shift and hand crank the windows up and down, especially
when there’s little physical work
to do while sitting there anyway.
Larry Kooiker

Sustainability = Scam?
I want to thank you for your commentary on sustainability (“Do
We Need a Sustainability Standard? March 22). Unfortunately,
I think you are preaching to the
choir.
I appreciate your perspective,
but the idea of a sustainability
standard just sounds too good
to those politically correct nonproductive meddling by nonproducers. They firmly believe
we all, but especially everybody
else, will just have to buck le
down and throw more money
at another nonproblem (until it
dies from suffocation under its
own weight). By then, of course,
two new great sounding ideas
will have covered it up, and all
the money that can be squeezed
from the last idea will be taken.
The small companies that can’t

afford the extra cost and the drag
of more bureaucracy will have
closed up shop.
Remember when efficiency
meant doing more with less,
when economical meant costing less? Some day that common sense will again prevail. In
the meantime, keep up the good
work.
Wayne A. Strand
I do a lot of presentations about
Reduce, Recycle, and Reclaim
and I paraphrase another engineer (her name escapes me). She
wrote: “I cannot design anything
green. Everything will consume
resources. I can make my designs
greener, so they consume less
resources both when built and
when they run.”
Randy Mountcastle

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A n atomy of the
HUCK 360

®

®

PROBLEM :
CONVENTIONAL THREAD

BOLT

NUT

TRANSVERSE
VIBRATION

TRANSVERSE
V I B R A T I O N C O M P ARISON

Gap between the threads allows
for transverse movement.

CLAMP (LBF-THOUSANDS)

25
20

HUCK 36 0

15

OTHER VIBRA TIONRESISTANT
NUT DESIG NS

10
5
0

0

50

100

time

150

200

SOLUTION :
HUCK 360
250

No gap exists.
Threads are locked

(SECON D S )

BOLT

Once vibration begins,
clamp load quickly
decays with nuts and
bolts, while it holds
constant with the Huck 360.

RS# 114

NUT

preventing any
movement.