# Hand-held case/enclosure design using CAD tools

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#### Nicholas Kinar

Jan 1, 1970
0
Hello--

I am working on a custom electronics system which ultimately requires a
hand-held case design. Consequently, I am wondering if anyone would
know of a good book, paper or tutorial on electronics case design.

How would I align the circuit board inside the case with the outside of
the case? How do I create standoffs for the circuit board? How do I
effectively deal with the routing of wires inside of the case? Perhaps
there are more general books that are available on this type of design.
Does anyone have a suggestion?

As an aside, I am also curious as to how it might be possible to design
an enclosure for an electro-optical system. How would I integrate
lenses and an optical system into the enclosure? Are there standard
mounting parts for lenses which I can model in a CAD program (and then
produce using rapid prototyping), or would I simply purchase

I've posted something similar on the comp.cad.pro-engineer newsgroup,
but for this posting on sci.electronics.design, I've widened the net to
be broader than just using the Pro/Engineer software. I hope that this
posting should be interesting to a broader group of individuals.

Are there any resources out there on this type of design? Perhaps this
is not of interest to those working in electronics (after all, case
design is sometimes more often done by mechanical and industrial
engineers), but perhaps there are some "important"
books/papers/tutorials on how to do this.

Nicholas

D

#### David L. Jones

Jan 1, 1970
0
Nicholas said:
Hello--

I am working on a custom electronics system which ultimately requires
a hand-held case design. Consequently, I am wondering if anyone would
know of a good book, paper or tutorial on electronics case design.

How would I align the circuit board inside the case with the outside
of the case? How do I create standoffs for the circuit board? How do
I effectively deal with the routing of wires inside of the case? Perhaps
there are more general books that are available on this type
of design. Does anyone have a suggestion?

As an aside, I am also curious as to how it might be possible to
design an enclosure for an electro-optical system. How would I
integrate lenses and an optical system into the enclosure? Are there
standard mounting parts for lenses which I can model in a CAD program
(and then produce using rapid prototyping), or would I simply purchase

I've posted something similar on the comp.cad.pro-engineer newsgroup,
but for this posting on sci.electronics.design, I've widened the net
to be broader than just using the Pro/Engineer software. I hope that
this posting should be interesting to a broader group of individuals.

Are there any resources out there on this type of design? Perhaps
this is not of interest to those working in electronics (after all,
case design is sometimes more often done by mechanical and industrial
engineers), but perhaps there are some "important"
books/papers/tutorials on how to do this.

I doubt you'll find a book our there on this that really covers what you
want. It's not really possible, there are an infinite numbers of variations
possible and every design has it's own unique set of requirements.

Generally speaking, wiring is not a good thing, and you should try to avoid
it if possible. A well designed product will for example (if possible) have
just the PCB with PCB mount connectors that align with holes in the case.
This is cheaper and more reliable.

Lens systems are pretty much a custom thing. e.g. look at security passive
IR sensors and you'll see every design is unique and custom.

The best way to learn this stuff is to take things apart and see how others
have done it. Then when it comes time for your own design you can
incorporate various ideas into your own case.

Electronics designers who don't for example have good in-house mechnaical
CAD designers will often resort to off-the-shelf cases for their products,
and these can have have built in PCB stand-off's, front panel windows,
battery holders etc. So you pick a suitable case from the countless ones
available and then design your PCB and product around that case. This isn't
really suited to very high volume manufacture, but is great for low to
medium volume production.

Dave.

N

#### Nicholas Kinar

Jan 1, 1970
0

I doubt you'll find a book our there on this that really covers what you
want. It's not really possible, there are an infinite numbers of variations
possible and every design has it's own unique set of requirements.

Ah, I think that you are right. There is a diverse number of products
out there.

Generally speaking, wiring is not a good thing, and you should try to avoid
it if possible. A well designed product will for example (if possible) have
just the PCB with PCB mount connectors that align with holes in the case.
This is cheaper and more reliable.

I've done this once before, but I've found that alignment is sometimes
really tricky. I suppose that a few revisions of the PCB might be
necessary sometimes.

Lens systems are pretty much a custom thing. e.g. look at security passive
IR sensors and you'll see every design is unique and custom.

The best way to learn this stuff is to take things apart and see how others
have done it. Then when it comes time for your own design you can
incorporate various ideas into your own case.

Agreed. I'll take a look at some similar stuff.
Electronics designers who don't for example have good in-house mechnaical
CAD designers will often resort to off-the-shelf cases for their products,
and these can have have built in PCB stand-off's, front panel windows,
battery holders etc. So you pick a suitable case from the countless ones
available and then design your PCB and product around that case. This isn't
really suited to very high volume manufacture, but is great for low to
medium volume production.

Dave.

I've done this a few times, and this works really well for most
circuits. However, if I need to interface to electro-optical or
electro-mechanical components, the design becomes increasingly
challenging, especially when the system needs to be ultra-portable. I'm
either going to have to use a off-the-shelf case, or I will have to look
into developing my own custom design.

Thanks, David.

N

#### Nicholas Kinar

Jan 1, 1970
0
Peter,

Look at commercially-available cases from PacTec, Hammond, Bud and
many others - some will have mechanical drawings of their products on
their website, which should give you some ideas of how things are
normally done.

I suppose that it is best to learn from imitation.

As for making things on the board match holes in the case, or vice
versa, all I can say is to measure carefully. Then carefully measure.
Then print the board and panel layout to scale, and see if they fit.
Then adjust things till they do fit. Repeat as needed.

It is vital that you actually have the parts you will be using on hand
while laying out the board and enclosure.

I agree that parts always need to be on hand when doing the layout.
I've had a number of interesting experiences when I haven't followed
this simple design suggestion. The tricky thing with some through-hole
components is that often the part will appear to fit on the 1:1 scale
layout, and then it will have to be forcefully pushed on the PCB with a
pair of pliers. I've broken one or two parts using this method.

Nicholas

S

#### Spehro Pefhany

Jan 1, 1970
0
Hello--

I am working on a custom electronics system which ultimately requires a
hand-held case design. Consequently, I am wondering if anyone would
know of a good book, paper or tutorial on electronics case design.

This book is pretty good for injection-molded parts:-

http://www.amazon.com/gp/product/1569901295?ie=UTF8&tag=speffcom-20

As is this one:

http://www.amazon.com/gp/product/1569903506?ie=UTF8&tag=speffcom-20

There are some others-- although a single 6' shelf will hold most of
the decent books on this subject, IMHO.

As others have said, look at existing parts and try to visualize how
the mold opens, how each part gets ejected, and the reason for every
single detail on the parts. Small differences like inserting a
deliberate narrow groove where parts fit together (so things don't
have to line up perfectly) can make the difference between a
cheap-looking product and a nice-looking one.

You really have to pay a lot of attention to details such as wall
thickness, rib height-to-width ratio, material, shrinkage (often
several percent, and varies with material, additives, process
conditions etc.), draft (VERY important- just about everything has to
be slightly angled so it will come out of the mold), and what kind of
side action is required to do things like make holes on sides.
How would I align the circuit board inside the case with the outside of
the case?

One way which doesn't use much material or space is to have part of
the mounting boss protrude into the PCB mounting hole, but there are
many, many ways. High volume consumer goods often uses snaps, but they
How do I create standoffs for the circuit board?

A boss, preferably with gussets to strengthen it. Design it for a
specific type of screw. And put it on the back of the case and/or
under label so the shrink marks won't show.
How do I
effectively deal with the routing of wires inside of the case?

Try to avoid them entirely. Failing that, you can use clips and such
like. It may be possible to make the kind you need without involving
side action, particularly if you can cover up a hole to the outside
with a label or something (eg. another part). A "crossover" (metal
from mold halves meet to seal off plastic flow) is generally far
preferable to side action (eg. a hydraulically actuated moving core)
Perhaps
there are more general books that are available on this type of design.
Does anyone have a suggestion?

You can't possibly acquire the design skills that an experienced
mechanical engineer has, plus industrial design skills, plus specific
knowledge of plastic part design and manufacturing in just one or two
books, or just a month or two of study. Knowing a thing or two about
mold design also helps.

N

#### Nico Coesel

Jan 1, 1970
0
Nicholas Kinar said:
Hello--

I am working on a custom electronics system which ultimately requires a
hand-held case design. Consequently, I am wondering if anyone would
know of a good book, paper or tutorial on electronics case design.

Perhaps you can ask these questions as well on a forum about 'solid
works' (a popular piece of software for designing housings).

D

#### David L. Jones

Jan 1, 1970
0
Nicholas said:

Ah, I think that you are right. There is a diverse number of products
out there.

I've done this once before, but I've found that alignment is sometimes
really tricky. I suppose that a few revisions of the PCB might be
necessary sometimes.

That's where todays 3D MCAD features of PCB programs like Altum Designer can
be useful:
(the good stuff starts about half way through)
Helps get your PCB/Case design right the first time with more complicated
projects.
Many case and part/connector suppliers will provide 3D models on their
website, so you can just import them and do your clearance/fit checking
fairly easily. Hammond are one case supplier that provide 3D models for all
their cases for example.
Check out an early quick 3D mockup for a new little project I'm working on
for example:
http://www.edn.com/blog/980000298/post/1570043757.html
Agreed. I'll take a look at some similar stuff.

I've done this a few times, and this works really well for most
circuits. However, if I need to interface to electro-optical or
electro-mechanical components, the design becomes increasingly
challenging, especially when the system needs to be ultra-portable. I'm
either going to have to use a off-the-shelf case, or I will have
to look into developing my own custom design.

If you want to do your own cases easily then this mod and their software
might help:
http://www.emachineshop.com/
Their software is easy enough for non mechanical guys like me to start
producing something useful in 5 minutes.
Designing your own case that looks good and works well takes skill, time and
money though, so I'd exhaust all the off-the-shelf cases first before
resorting to that option.

Dave.

N

#### Nicholas Kinar

Jan 1, 1970
0
Thanks, David!

That's where todays 3D MCAD features of PCB programs like Altum Designer can
be useful:
(the good stuff starts about half way through)
Helps get your PCB/Case design right the first time with more complicated
projects.
Many case and part/connector suppliers will provide 3D models on their
website, so you can just import them and do your clearance/fit checking
fairly easily. Hammond are one case supplier that provide 3D models for all
their cases for example.
Check out an early quick 3D mockup for a new little project I'm working on
for example:
http://www.edn.com/blog/980000298/post/1570043757.html

I had a look at the You Tube video, and Altium Designer makes me very
excited. In the past, I've been using Eagle Cad to do most of my design
work but it might be time for a change. I'll take a look at Altium and
see if it will fit my needs.

I had no idea that you have a blog, David! I think that your project is
really neat, and I would like to do something similar to what you have
done with the custom case. I've bookmarked your video blog for further
reference.

Which MCAD are you using? Does the MCAD interface with Altium? (I am
assuming that you are using Altium.) According to the You Tube video,
there should be a way to exchange data between the two software packages.

Which manufacturing house is producing your case? What would be the
cost of manufacturing? I'm currently situated in Canada, but I think
that most product facilities for plastics closest to where I am located
are in the United States.

Once again, thanks David.

Nicholas

If you want to do your own cases easily then this mod and their software
might help:
http://www.emachineshop.com/
Their software is easy enough for non mechanical guys like me to start
producing something useful in 5 minutes.
Designing your own case that looks good and works well takes skill, time and
money though, so I'd exhaust all the off-the-shelf cases first before
resorting to that option.

Dave.

Yeah,

N

#### Nicholas Kinar

Jan 1, 1970
0
Yup, just doing this... again.... take mechanical drawing and
electrical drawing, lay on top of one another, place on sunny
window, look for errors.

George H.

This seems to have been a rite of passage for all those who work in
electronics. It's part of the engineering experience. Maybe we learn
something from doing it every time. At least I know that such a process
helps to drain printer ink cartridges, but oh well...

Nicholas

N

#### Nicholas Kinar

Jan 1, 1970
0

Great titles! I absolutely love the covers on these books. Although
there is always a word of warning about "judging a book by its cover," I
think that these are excellent titles. I'll consider ordering them.

One way which doesn't use much material or space is to have part of
the mounting boss protrude into the PCB mounting hole, but there are
many, many ways. High volume consumer goods often uses snaps, but they

A boss, preferably with gussets to strengthen it. Design it for a
specific type of screw. And put it on the back of the case and/or
under label so the shrink marks won't show.

Ah, neat ideas!

Try to avoid them entirely. Failing that, you can use clips and such
like. It may be possible to make the kind you need without involving
side action, particularly if you can cover up a hole to the outside
with a label or something (eg. another part). A "crossover" (metal
from mold halves meet to seal off plastic flow) is generally far
preferable to side action (eg. a hydraulically actuated moving core)

I'm creating a hand-held ground-based remote sensing system for
determining the physical properties of environmental materials. This
requires attaching transducers to the circuit board. The transducers
that I have been using in previous prototypes unfortunately require the
use of wires. Clips are a good idea. In my previous circuits, I simply
left the wires to slop around in the box. This was really not a good
idea because I soon found that after the circuit was transported,
vibrations would create a big tangled mess.

You can't possibly acquire the design skills that an experienced
mechanical engineer has, plus industrial design skills, plus specific
knowledge of plastic part design and manufacturing in just one or two
books, or just a month or two of study. Knowing a thing or two about
mold design also helps.

Sigh, I understand the truth in these words. However, because I am a
researcher working in the context of a university to do research and
also develop a product, I have a vested interest in also learning about
new things. Of course, if I was doing this for a company, then it would
make good sense to hire a mechanical engineer with some experience in
the field. Moreover, purchasing a few books may provide an enlightening
experience, and it will simply give me some interesting summer reading!

Spehro, thank you for this post and for the good book titles. I'll be
sure to learn a lot during this summer.

N

#### Nicholas Kinar

Jan 1, 1970
0
Nico said:
Perhaps you can ask these questions as well on a forum about 'solid
works' (a popular piece of software for designing housings).

I'll give SolidWorks a try. Thanks, Nico.

S

#### Spehro Pefhany

Jan 1, 1970
0
I'll give SolidWorks a try. Thanks, Nico.

Both Solidworks and Altium are $thousands, but if you can afford a mold or three, that probably seems quite cheap. ;-) D #### David L. Jones Jan 1, 1970 0 Nicholas said: I had a look at the You Tube video, and Altium Designer makes me very excited. In the past, I've been using Eagle Cad to do most of my design work but it might be time for a change. I'll take a look at Altium and see if it will fit my needs. I had no idea that you have a blog, David! I think that your project is really neat, and I would like to do something similar to what you have done with the custom case. I've bookmarked your video blog for further reference. Which MCAD are you using? Well, I don't actually use MCAD myself, that's not my area. At work we have mech guys who do the 3D models for us, not sure which package they use. But if the model is available from the manufacturer then it's easy for me to attach this to the component myself. Does the MCAD interface with Altium? (I am assuming that you are using Altium.) According to the You Tube video, there should be a way to exchange data between the two software packages. Yes, it uses the STEP file format. So if your MCAD package supports STEP then you are in business. Which manufacturing house is producing your case? What would be the cost of manufacturing? I'm currently situated in Canada, but I think that most product facilities for plastics closest to where I am located are in the United States. It's an off-the-shelf case from Hamond, I just pulled that 3D model from their website. See what I said about the ease of designing products around existing cases! They also so custom mods to their cases (cutout/slots etc) for a fee. Dave. N #### Nicholas Kinar Jan 1, 1970 0 Both Solidworks and Altium are$thousands, but if you can afford a
mold or three, that probably seems quite cheap. ;-)

installation, so it wouldn't hurt perhaps trying it out for a while.

Concerning the actual production of the case, I may also have access to
a rapid prototyping machine (there's such a machine in one of our
engineering lab), so I wouldn't think about trying out a very expensive
mold until I've learned something about actually working with plastics.

Thanks, Spehro!

N

#### Nicholas Kinar

Jan 1, 1970
0
Well, I don't actually use MCAD myself, that's not my area. At work we have
mech guys who do the 3D models for us, not sure which package they use. But
if the model is available from the manufacturer then it's easy for me to
attach this to the component myself.

Ah, the luxury of having engineers who are competent with mechanical things.

Yes, it uses the STEP file format. So if your MCAD package supports STEP

For years, I've used Eagle CAD. I don't think that this software
package supports anything remotely related to STEP.

It's an off-the-shelf case from Hamond, I just pulled that 3D model from
their website. See what I said about the ease of designing products around
existing cases! They also so custom mods to their cases (cutout/slots etc)
for a fee.

It would be a good idea to simply pull a model and then change some of
its aspects. Because I have access to a rapid prototyping machine, this
might give me an ability to learn from the model and then make my own
version of it.

Thanks, David.

N

#### Nicholas Kinar

Jan 1, 1970
0
If the sensors are outside the case, on cables, I'd put connectors on
the cables, and matching PC-mount connectors on the PC board, located
so that they can be accessed from outside the case (protruding through
the front or rear panel.) There are screw terminal strips that could
be mounted on the PC board so that they could be accessed from outside
the case, for individual wire connections (but I prefer connectors -
once you get things connected correctly, you can disconnect and
reconnect the cables without worrying about the correct wire order.)

My remote sensing system will be used in an outdoor environment - so I
am going to have to ensure that the connectors are waterproofed to
prevent rain and snow from getting into the case. This was a problem
with some of my earlier prototypes.

In the past, I actually used a case from Hammond plastics and created a
circuit board with holes to fit the stand-offs. I cut holes in the case
for the USB connector and power jack - but the holes also allowed for
rain and snow to enter the case. This caused the circuit to
malfunction. I thought at first that if the circuit is hand-held, there
should be a good possibility of keeping the circuit dry, but the weather
thought otherwise.

I don't know if this is a logical idea, but my initial thought was to
produce an electronics case which also incorporated the transducers. So
the transducers would fit into a recess at the front of the case, and
the case would be designed to have a trigger grip.

I need to also produce a stationary version of the remote sensing
system. The system will be interfaced to a datalogger and then left out
in a location which is exposed to the elements.

I think that perhaps the circuit could be placed into an off-the-shelf
case, and then the transducers could be placed into a "cradle" designed
using mechanical CAD software and produced using rapid-prototyping
technology. Connectors on the outside of the case will be used to
interface the transducers to the circuit.
While it is good to learn new things, don't lose track of the actual
job you started on.

version of SolidWorks, and in addition, there is a rapid-prototyping
machine in one of our labs. My initial idea was to learn some of the
basics of how to use SolidWorks and then produce an electronics case on
the rapid-prototyping machine. I suppose that the more toys you might
have access to, the more likely it is to get carried away.

Of course, my first concern is the design and operation of the circuit,
as it should always be.

Thanks, Peter.

N

#### Nico Coesel

Jan 1, 1970
0
Nicholas Kinar said:
installation, so it wouldn't hurt perhaps trying it out for a while.

Concerning the actual production of the case, I may also have access to
a rapid prototyping machine (there's such a machine in one of our
engineering lab), so I wouldn't think about trying out a very expensive
mold until I've learned something about actually working with plastics.

I your company has such a machine, chances are they have a license for
Solid Works as well.

N

#### Nicholas Kinar

Jan 1, 1970
0
Yes, they do. It seems that SolidWorks is *always* used with rapid
prototyping machines.

Thanks, Nico.

N

#### Nicholas Kinar

Jan 1, 1970
0
If not SolidWorks at least AutoCAD or Inventor or some other program.

Bob

Yes, thanks, Bob. All of these program *can* do some mechanical design
work.

Nicholas

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