Electronics > Projects, Designs, and Technical Stuff
Very small and thin transparent enclosure
jmaja:
That might be a good option for the heatshrink, but I also need to have a stiff option that allows changing the battery and different kind of installation.
I took a quick survey of what I found on my desk. Two scientific calculators from the 80's. Phillips had M2x5 machine screws that seemed to screw into thread inserts. Casio had 2x6.5 mm thread forming screws into plastic. My old Samsung S4 Mini had M1.4x4 machine screws that probably screw into metal frame (didn't open it just took one screw out). MR16 LED "bulb" had M2x4 machine holding the PCB and screwing into metal (aluminium?) frame.
All of these seem to open and tighten just fine.
reboots:
Be aware that custom-machined polycarbonate, particularly using screw closures, may lead to serious problems with stress concentration and cracking. Do not allow your machine shop to use any kind of process coolant or lubricant other than water.
I recommend producing a set of prototype enclosures of the final intended design, using material from your expected production supplier, and torture-testing them for as long as possible to make sure that e.g. thermal cycling won't cause stress cracking at the screw threads.
I have had some luck with Plastite trilobular thread-forming screws in molded polycarbonate enclosures.
The calculator enclosures you mentioned are likely made from ABS or similar plastic, which is softer and less prone to stress concentration.
jmaja:
--- Quote from: reboots on April 13, 2019, 07:36:26 pm ---Be aware that custom-machined polycarbonate, particularly using screw closures, may lead to serious problems with stress concentration and cracking. Do not allow your machine shop to use any kind of process coolant or lubricant other than water.
I recommend producing a set of prototype enclosures of the final intended design, using material from your expected production supplier, and torture-testing them for as long as possible to make sure that e.g. thermal cycling won't cause stress cracking at the screw threads.
I have had some luck with Plastite trilobular thread-forming screws in molded polycarbonate enclosures.
The calculator enclosures you mentioned are likely made from ABS or similar plastic, which is softer and less prone to stress concentration.
--- End quote ---
Are threads cut to PC the most likely problem? Would using a recession for a nut or a thread insert make these problems less likely? This thread insert would be thin enough (even when recessed): https://www.tappex.co.uk/products/brass-threaded-inserts/microbarb
The first enclosure prototype will be made tomorrow. If that seems feasible, the plan is to make ~20 and test them for 6 months before going further.
Nusa:
If you design your case to have interlocking hinges arrangement on opposing sides (or even all four sides), you wouldn't need screws at all. Wire pins through the hinges would keep it closed. Easily removed for battery changes.
reboots:
--- Quote from: jmaja on April 15, 2019, 05:15:45 am ---Are threads cut to PC the most likely problem? Would using a recession for a nut or a thread insert make these problems less likely? This thread insert would be thin enough (even when recessed): https://www.tappex.co.uk/products/brass-threaded-inserts/microbarb
--- End quote ---
I have not used threaded inserts in polycarbonate, so I can't say. I would try oversized holes with minimal barb engagement, just enough to keep the inserts placed. I know some manufactures of polycarbonate enclosures use inserts, but those might be overmolded.
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