EDIT:
Also, Mr. Dragon, sir, I say forget Allen head screws. Few things are as frustrating as an Allen head fastener that starts rounding out. I ordered a nice variety of stainless metric Torx screws (and stainless Keps nuts) and I couldn't be happier. To each as own, I suppose.
I would amend that to SS Allen BUTTON HEAD screws - Allen Head Cap Screws are fine in my experience. I've used the button heads and for a given thread size the Allen is a size or two smaller than the ones in the cap screws and as a result much more likely to get buggered up. Don't get me wrong, they look nice, but for utility the taller, uglier cap screws are more robust tool-wise.
-Pat
I like 'em just fine in my 3DP and on my whirry little flying things, and they hold up just fine even flying crashing at 50KPH or more.
The heads rarely round out unless I'm trying to drive them with worn out drivers.
We're talking panels on a plucking TE for Ifni's sake... not bulkheads on a Star Destroyer.
Also, I'll direct your attention to the PS in my original post...
Pssssst... replace them all with stainless steel hex-drive button head screws. Bring it into the 20th century, now that we're in the 21st.
mnem
*agitating-ily*
mnem
*agitating-ily-errr...*
The problem, as always, isn't the application and the in-service forces on the fastener, the problem is how good the 200lb gorilla with the Allen wrench in its mitt is at not over torquing small fasteners. I have to plead guilty here, as at the M3 kind of size I'm quite capable of ripping the heads off of small machine screws if I don't dial myself back a notch before tightening them. I am the argument for owning and using torque drivers for small fasteners. The single point contact design of Allen heads is fine at, say, M6 perhaps M8 and above but on those small fasteners there just isn't enough meat behind the single contact point to resist a properly hardened driver/wrench trying to shove the metal out of the way. If I'm too enthusiastic on tightening a small Allen screw it's always the socket that fails and rounds over, if I do the same on a Torx I strip the thread or rip the head off.
The big problem I have with Allen buttonheads is the global issue we all "conveniently ignore": especially with my "little whirry flying things", as they almost
all come directly from the lowest bidder factory in ShenZhen or GuangZhou...
...is the fact that you never know until you have them in hand whether they're going to be decent quality metal with properly forged hexes (on a button-head, if done correctly you can get 60-80% of optimal depth without weakening the screw shoulder) or cheapest possible with shallow hexes and made of case-hardened cheese or stainless cheese.
As for overtightening... yeah, my heli & quadcopter habits certainly did teach me to have respect for tiny screws. When you realize that your ~1kg 450-size heli hangs in the air from a single m2.5 screw through the main spur gear, it does make you stop & think
lest you overtighten and weaken the screw. Especially when you think about how much more the forces applied must be when you start throwing it around in acro flight.
Also, painful & expensive to have to replace critical flybar/head parts because you stripped out a screw head and can't get it out without drilling and destroying the part underneath.
EDIT: You do learn quick, as most of these are almost entirely made with m2 screws, as are pretty much any quadcopter that comes in under the 2 sticks rule.mnem