Enclosure design review
Enclosure design review
(OP)
Hello Engineers!
I'm working on the design of an enclosure for electronic stuff.
Being an electronic engineer, I've check tips and articles on plastic injection to get something realistic and not too expensive to produce. But now I'm getting to a point where i need some help to review my design.
If you check the attached drawing you'll see a flat bottom with many ribs (do I need all of them?). The electronic pcb is holded on the side ribs (+ few points inside). Behind you'll see the holding "ring".
I plan to use 2 screws and some "snap" stuff (in the front) to close the enclosures...
I'm also worring about the tightness of the assembly (shall I add an "o-ring" in the assembly profile?)
But now my question is about the draft angle on the ribs and walls. Where should I take the reference plan from? Would it be the top assembly face? Or the flat bottom face?
Please give me some comments!
Any link to technical documentation (or example) would be welcome too!
Thanks in advance for your replies!
Ivan
I'm working on the design of an enclosure for electronic stuff.
Being an electronic engineer, I've check tips and articles on plastic injection to get something realistic and not too expensive to produce. But now I'm getting to a point where i need some help to review my design.
If you check the attached drawing you'll see a flat bottom with many ribs (do I need all of them?). The electronic pcb is holded on the side ribs (+ few points inside). Behind you'll see the holding "ring".
I plan to use 2 screws and some "snap" stuff (in the front) to close the enclosures...
I'm also worring about the tightness of the assembly (shall I add an "o-ring" in the assembly profile?)
But now my question is about the draft angle on the ribs and walls. Where should I take the reference plan from? Would it be the top assembly face? Or the flat bottom face?
Please give me some comments!
Any link to technical documentation (or example) would be welcome too!
Thanks in advance for your replies!
Ivan






RE: Enclosure design review
I have no idea if the ribs are excessive or inadequate as I have no idea of the loads and temperature or material or expected life.
I have no idea if you require an "O" ring as I don't know what quality of seal you require.
If you need a tight seal, remember plastics creep with time and some plastics solvent stress crack in the presence of some rubbers.
Regards
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RE: Enclosure design review
Here are some more details about the parts:
The part is the base of a display attached on the front tube of a bike (or bicycle).
The load on the part is not much, just as someone pushing on buttons. The temperature range is given by the outdoor condition (-10°C to 40°C).
The enclosure should be tight against water splach (eavy rain).
And I will talk to a moulder and material supplier next week. I'm trying to be there as prepared as possible!
Should the green face be the reference for the draft angle?
Thanks for your interest
Regards
RE: Enclosure design review
Regards
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RE: Enclosure design review
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Enclosure design review
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RE: Enclosure design review
Imho: First thoughts:
You have a very complicated part requiring a very complicated tool - side cores etc. (for complicated read expensive!)
I would remove all but the functional ribs as most of the assembly stifness will be due to box shape when the other half is fixed. Ribs are time-consuming to put in, give sink marks on the visible faces and waste material. They can be put in at a later date if really required. (ribs should be no more than 0.6 x wall thickness for amorphous materials such as ABS) Cored out pillars are cheaper to produce in the tool than ribs.
I would seriously look at the clamp ring arrangement with a view to making the tool "open and shut". To make a separate saddle bracket tool would be cheaper than trying to mould all in one as drawn.
Harry
RE: Enclosure design review
The few ribs needed to hold the pcb in place with the right angle will be kept, the other ribs will removed.
Regarding the bracket, Harry, do you mean it would be cheaper to make 2 parts assembled (e.g. with screw)?
(We plan to produce about 3 to 5000 pieces)
I will post a new design soon!
Thanks again for your help!
RE: Enclosure design review
If you had shown that design to a molder he would likely have quoted you several dollars per piece rather than several dimes.
You will get a bit of water resistance (splashes) from the piece as you have it, but certainly not water proof. Adding a rounded "lip" to the entire surround may help... some snap-together alarm keyfobs have this, like the entire DEI line (Clifford, Viper, etc.). For the buttons, you'll need to design your rubber membrane carefully with this requirement in mind. That hole on the side is a possible water entry point, particularly if you're using some form of power connector there (notorious for not being "to spec" in placement or size)... a grommet may be necessary.
As Pud suggested, replace those solid pillars with cored ones, as if you're going to put a screw in it... which will also give you a possible screw-down location for the PCB if it's decided later you want some more stability from key presses. The ribs coming off of the pillars do not need to be long at all (about as long as the shortest ones you now have).
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Enclosure design review
What do you mean by "rounded lip"? Can you explain it a bit more?
As for the buttons, I'm not yet done with the design and difficulties... I'll be back with more questions soon!!!
Thanks
RE: Enclosure design review
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Enclosure design review
RE: Enclosure design review
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Enclosure design review
Regards
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Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
RE: Enclosure design review
After visiting a protoype & tooling company, I'm back with my design modified (see side-cut view attached).
The housing woulod be made of Polycarbonate. The wall are 2mm thick. No "ribs" are needed. The bottom and upper shell fit together within a small straight slot and 2 or 3 screws.
I need advice about the buttons interface. I plan to use "rubber style" soft polymere for the "membrane". It should press the button with a max of 0.2mm course.
Would my design be "water resistant"?
Would it be possible to mount it in?
Any advice how to have this function done?
Thanks again for all your advices and ideas!
With my best regards
Ivan
Ivan, Owner
STEIMER ROBOTICS
RE: Enclosure design review
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Enclosure design review
It is relatively expensive, relatively hard to mould and unpredictable in performance due it's strong tendency to solvent stress crack i the presence of some very common chemicals.
It has good UV, rigidity and toughness under good conditions.
The plasticisers in PVC and some other elastomers can solvent stress crack it.
Many lubricants stress crack it.
ABS seemed a reasonable choice. Polypropylene would also be a reasonable choice unless you want to glue it.
Regards
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RE: Enclosure design review
I'm with Pat on the ABS. Less potential processing errors to give you a crud product. Colours will be cheaper too as lower melt temp. If you need transparent then acrylic or SAN.
Cheers
H
Good luck.
RE: Enclosure design review
We choose PC for the UV and rigidity. Is ABS as good for outdoor condition?
If cheaper and easier to manufacture, then I'll change to ABS of course!
Can we easely glue on ABS?
There will be a glass to protect the LCD, we plan to use PC again. It's the best transparent material, isn't right?
Regarding the button, I've a question about sharpness.
What would be the sharpness value of such "rubber" (very flexible) material?
I've heard about possible sharpness class A 30 to 80. What would be the hard one, 30 or 80??? (I don't know this unit...)
Thanks again for your advices!
Best regards
Ivan, Owner
STEIMER ROBOTICS
RE: Enclosure design review
ASA is better.
PC is best transparent material? There is no best transparent plastic like there is no best metal. What is best depends on what you want to do with it. Gold makes a poor crankshaft for a high output engine and magnesium makes poor electrical contact breaker points.
Certainly a correctly coated PC window will perform well as a lens on an outdoors instrument. High impact acrylic might also work. Unmodified acrylic will be excellent IF there is no real impact involved
If the lens is to be PC and glued in, then PC makes sense for the body due to compatibility when gluing.
Mar resistant sheet PC has much better overall properties than injection moulded PC components for reasons of the protection from solvents and scratching from the coating and the much higher molecular weight.
This is the first we have heard of a clear lens being included.
Regards
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RE: Enclosure design review
The lens is supposed to be glued on the upper shell...
Regarding flexible button, what sharpness could be rubber?
Any idea about the unit?
Ivan, Owner
STEIMER ROBOTICS
RE: Enclosure design review
I think that maybe you mis-heard it as sharpness! Rubber hardness is usually specified as "Shore Hardness" A through D and the lower the number the softer it is.
Trevor Clarke. (R & D) Scientific Instruments.Somerset. UK
SW2007x64 SP3.0 Pentium P4 3.6Ghz, 4Gb Ram ATI FireGL V7100 Driver: 8.323.0.0
SW2007x32 SP4.0 Pentium P4 3.6Ghz, 2Gb Ram NVIDIA Quadro FX 500 Driver: 6.14.10.7756
RE: Enclosure design review
Sorry for my poor english!
Thanks for your correction!
Ivan, Owner
STEIMER ROBOTICS
RE: Enclosure design review
Hardness of rubber required can be very subjective, to use an idiom, sometimes you just need to suck it and see which means you need to try it out to get the taste or feel of undefinable qualities.
The suppliers of the elastomers should be able to advise and supply samples of the correct thickness for you to get a feel for it.
Regards
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RE: Enclosure design review
I've touched samples but they were not the right shape neither the correct thickness.
Hopefully I'll get some samples in time...
Ivan, Owner
STEIMER ROBOTICS
RE: Enclosure design review
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RE: Enclosure design review
I've got the protoypes done. It looks very good and luckly the hardness of the button was ok (I did guess a hardness Shore A 40). The buttons are easy to assemble, it makes a water tight interface and it can even push to activate the swicthes!!!
Now I've a new problem: the lense's reflexion... When the sun shines straight on it, there's no way to see the lcd...
I thought it's due to 2 reasons:
a. the PC lense is not coated
b. the lense shape (flat)
What can I do to improve the visibilty?
I'm not sure I can afford the coating (the part should be very cheap to produce) and if I change the shape then the LCD will looks deformed...
Thanks for your help, my success is yours too!
best regards
Ivan
Ivan, Owner
STEIMER ROBOTICS
RE: Enclosure design review
I'm still interested in treatment for hardness and reflection...
I will ask our supplier what they can do to improve reflection and hardness!
Thanks everyone for your help!
I'll give some feedback when injection machines will be running!
Best regards
Ivan
Ivan, Owner
STEIMER ROBOTICS
RE: Enclosure design review
Good to hear that the project seems to be progressing well. You could try getting the windows cut from some pre-treated polycarbonate sheet similar to this, available in the UK but I guess it can be sourced anywhere if you know what to ask for:
h
Is it possible to get the LCD with a built in back-light, it may not cost a lot more in quantity, but it would improve the readability and is a bonus if it ever needs to read in the dark!
Trevor Clarke. (R & D) Scientific Instruments.Somerset. UK
SW2007x64 SP3.0 Pentium P4 3.6Ghz, 4Gb Ram ATI FireGL V7100 Driver: 8.323.0.0
SW2007x32 SP4.0 Pentium P4 3.6Ghz, 2Gb Ram NVIDIA Quadro FX 500 Driver: 6.14.10.7756
RE: Enclosure design review
I am not up to date on scratch resistant coatings, but the coatings used for car headlights should do. Your PC supplier can probably give advice as to the current state of the art suppliers
Regards
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