Screw decisions for assembly

[deadofmind]

You can have the most expensive screws on the market, if your plastic screw wells are not up to the task, it will still only take about 5 open/close cycles to ruin those screw wells.

I would like to know if EvilDragon has spoken to the manufacturer about this.

 

[Rockthesmurf]

A common theme on the Pandora board:

Community member A : Hey, why don't we add XXXXXXX, it only costs $1 - $2, it is so little it really makes little to no difference.

Other members : That sounds okay, I mean it only matters to a small percent of people, but it is only $1 - $2 dollars.

You loop the above for 50-100 ideas and you add $100-$200 to the Pandora cost. Yes I admit we may not have had 50-100 of these sorts of ideas yet, but ED has previously stated on these boards that these 'little' extras do add up. In terms of is it a good idea to discuss this stuff; absolutely! Good to get a rounded view of it, give ED some food for thought. In terms of is it good to actually follow through with; well that is based on whether it is really needed, and you can't really do that directly by saying 'is it worth $1-$2 per Pandora', because there are probably a lot of things which are worth $1-$2, but together they push the price of the Pandora up sufficiently that it all seems pointless. Think of it more like if ED offers two Pyras, standard for $500 and elite for $600, and the difference with elite isn't specification but instead a bunch of small things (better screws, light sensor for brightness adjustment, metal inlays for screws to go into) would many people actually go for the elite? Oh no; please don't start a poll for this!

Anyway... I am sure the above isn't anything people don't already know. In terms of screws, it is somewhat interesting; not something I had ever thought of before, interesting to see the pro's and con's of the various head types.

 

[God Ginrai]

How much do we want to spend on having great screws so we can avoid wear and tear that eventually makes you have to replace a 10 EUR case after opening it too many times?

After all, while I like the idea of a hardware hacker friendly device a lot, I'm not a hardware hacker myself and I assume that most of the community is not. So even if it only costs 2 EUR extra per Pyra to get extremely wear-resistant screws, I'm not sure if it is worth it -- it may be better to let those who want to do a lot of open/close cycles buy a couple of spare cases, instead of letting everyone pay for a near-optimal screw system that in the majority of cases is complete overkill.

Honestly, if adding better screw assembly only took 2 EUR, I wouldn't mind paying it. I honestly don't even plan to modify my Pyra aside from maybe changing the SoC, or printing a new case or buttons. However, for that low of a price on my unit, I wouldn't mind paying that bit of extra to make the device easier for those who do.

-God Ginrai

 

[WizardStan]

Also that's assuming we go with some supreme screw assembly far beyond what we actually need. If we just swap the screws for Robertson or torx or even a hex that would solve arguably the biggest problem without increasing the cost at all.

 

[slaeshjag]

The biggest issue isn't the screw head. I've never been close to stripping the head on any of the screws in my pandora, and I'm not known for using the correct size screwdriver. The case broke much sooner.

 

[fusion_power]

You can have the most expensive screws on the market, if your plastic screw wells are not up to the task, it will still only take about 5 open/close cycles to ruin those screw wells.

Exactly, that's why the idea with metal inlays came in, where you can avoid to directly screw into plastic. Would make the Pyra much more durable and allows alot of disassembling passes for our tinkerer friends.

 

[WizardStan]

The biggest issue isn't the screw head. I've never been close to stripping the head on any of the screws in my pandora, and I'm not known for using the correct size screwdriver. The case broke much sooner.

The plastic breaks because you need to apply a downward force while extracting the screw upward: the channel takes a lot of pressure and that's directly a result of using Phillips screw heads. Change the screw head to something designed to be removed and you don't need to push down any more thus cutting the amount of stress on the case in half at least.

 

[God Ginrai]

Can we just use nuts? I don't have to exert downward force when I use a socket wrench.

-God Ginrai

 

[levi]

It would perhaps help if we stopped using the ambiguous term 'stripped screw'. You can strip heads, or you can strip threads - the former is achieved by torque over pressure exceeding a certain value and the screwdriver head slipping out and damaging the screw head, the latter through excessive downward pressure breaking the plastic. In the former only the screw is damaged, in the latter only the case is.


They can both result from the inexpert removal of a difficult to remove screw. The phillips head is part of the reason I ended up stripping the head of one of the screws in my Pandora, but the main reason is that the head of the screw was too large for the well it sat in. I knew to not apply enough pressure to strip the threads, but I needed to increase the torque until, it turned out the driver head slipped.


My only objection to pozidrive screws is that availability of the drivers in precision format. I've managed to find one, but it alone costs almost as much as a complete set of phillips precision screwdrivers that comes with some free flatheads too. Hex might be a better choice, as small hex keys are easy to come by. But as I said I also think sticking with phillips is fine if the well is machined properly.

 

[God Ginrai]

The term isn't really ambiguous. The threads on the screw won't strip in a device like Pyra. The threads on the device would. Hence, a stripped screw is one where the head is stripped.

EDIT: Now that I think about it, using nuts could actually be very useful. There wouldn't be any plastic threads to strip.

-God Ginrai

 

[WizardStan]

To be fair we have been using them interchangeably even if we shouldn't have been; talking about the stripped head and the stripped threads in the channel simply as "stripped screw".

 

[Yoyobuae]

The one problem I had with Pandora's screws was finding an adequately sized screwdriver. For Pandora's screws a "close enough" fit screwdriver won't cut it (but it will cut "into" it ).

Initially I was expecting the screw heads to be a similar fit as desktop PC case, thinking screwdrivers which work for those also worked for Pandora. Instead I needed a much smaller screwdriver, and was lucky to find one with the right fit. I can imagine how other users might not be able to find the right screwdriver and then easily strip the screw.

 

[zonova]

I have no idea how this works but, in the pyra, could we possibly have the screw holes themselves be made of metal? Like, washers or something? So you couldn't easily just strip the holes, and you could just meld or glue or fix the washer/metal-hole into the plastic case?

 

[levi]

That's what Fusion_Power and B-Zar were talking about on the last page. Normally in my experience of such things on e.g. multimeter battery covers the part is flanged to stop it twisting, and it's force fitted into a precisely corresponding hole in the case. I suppose you could glue a smooth receptacle into a round hole, but I'm honestly not sure what glues would stand up to such torques if the screw has seized (which is another reason why the part in multimeters is generally made out of brass).


On consideration, perhaps there's some moulding technique where you start with the brass receptacles in the mould, and mould around them. That would be more reliable than hammering them into brittle plastic.

 

[God Ginrai]

If there are sockets for these, then I would really like to have these:

-God Ginrai

 

[levi]

You have some nuts, posting those pictures here

 

[Grench]

Ahem - those nuts are not appropriate for the application. Try these instead:

http://www.mcmaster.com/#clip-on-nuts/=rw9hd7

As for the machine screw to go into them - I prefer torx types myself.

 

[God Ginrai]

I don't get it... why do they need a clip?

-God Ginrai

 

[comradekingu]

The way i see it is good screws not being an extra amount of pennies, but the lack thereof being a - amount of pennies from the total. As with the case, that is really not a good way to save.

Casemodders have great use for replacement screens, as do hardware hackers, but having good quality screws is good for both. Just because the case can be replaced and is cheap, its a costly affair for the omission of good quality screws. And it feels wrong on every level there is.

Replacement screws i have at the ready, cases not so much. I see a reason for having many, but poor screws isnt one. Being able to 3d-print helps of course, but it doesnt make the default screws any better.

I will argue that not skimping on screws is good even if you never have opened the case, because you might have to. Every repair that can be carried out by the user is good. Additionally, for headquarter repairs, it makes them cheaper, since every time a screw is stripped it means a hassle for ED, which just isnt worth it for anyone.

TL;DR screws that are easy to strip in screw-wells is just not up to par. At least i expect the metal to be harder, and possibly the screw to be better. Very little involvement for huge reward.

 

[Grench]

I don't get it... why do they need a clip?

-God Ginrai

Screw enters from the bottom of the device.  Current design is to have it thread into a pillar of plastic on the upper case.

Replacing the pillar of plastic with something metal is a good idea - you get that, right?

In order to have that metal interface it has to anchor to the UNDER side of the upper case plastics and stay put during assembly.  Clip on nuts would clip to the plastic (replacing the pillar) and hold-put during assembly and not fall out on the floor.

If standard hex nuts were used - how wold they interface with and hold onto the upper plastics?

More realistically, if this is to be done 'right', plastic (carbon fiber?) pillars should be OK.  However, to make a set of reusable threads in soft material, it would be better to machine out a set of coarse and deep threads (thread depth/cut not screw length).  Then use a matching screw.  Think of a wood/deck screw with the point removed going into a pre-tapped socket.

The Pandora's screws were relatively fine threaded machine screws - not much depth to the thread AND they were expected to self-thread.

Conversely - machine threading the screw holes on every case would probably add $5 to each case.  The outcome would be robust, but a tap drilling robot would have to be set up to tap out each screw pillar in the top plastics.