INTRO
So, this project started like this, I found the youtube channel of this nice lady that was doing bat rescues. she would film some of the rescues and put them up for people to watch. It turned out she was local, and I offered to do a few potential upgrades.
So, we have a collapsible net like the one here and the net is also on a telescopic extension arm. alas, bats having wings meant they often were hanging very high up trees or other structures. so the next natural thing was to attach this pole with some tape a longer pole, ideally an extendible one, ...or two. it turns out holding a small net on top of a wobbly pole 8-10 meter straight up in the air, while trying to catch a bat that doesn't take too kindly on the idea of getting caught could be a challenge. so some upgrades were in order.
First upgrade was to get a nice telescopic flag pole, a nice aluminium one that could do +6 meters. now she could tape the net extension to the flag pole and get another 2 meters of hight. less wobbly but still not all that great. so it would have been great to have a way of holding the net in an angle on top of the pole. like one of those gopro mounts, just stronger.
you can get an idea of the flag pole and the actual head here
STEEL?
So I did a prototype hinge, something solid and strong with quick lock and release capability. simple enough right? maybe...
This is the one I made, it's thin chromoly steel sheets, it's strong, it locks very very well, to the point I'm convinced it will break before it slips. aaaaaand it's heavy, way too heavy for the application. 200grams on top of a 8 meter lever means a LOT of force. oh well, I have like 5 different projects that can use a hinge like this, it won't go to waste. but we need something lighter, much lighter, and really didn't need to be that strong.
This is the one I made, it's thin chromoly steel sheets, it's strong, it locks very very well, to the point I'm convinced it will break before it slips. aaaaaand it's heavy, way too heavy for the application. 200grams on top of a 8 meter lever means a LOT of force. oh well, I have like 5 different projects that can use a hinge like this, it won't go to waste. but we need something lighter, much lighter, and really didn't need to be that strong.
PVC PERHAPS?
I had some PVC tubes available but no other types of plastic sheets at the time. figured I do a prototype and see if I can make the same thing out of plastic. To get some sheets out of the pipe sections, I cut the PVC tubes lengthwise and unroll them with the help of a heat gun. Now to get really flat sheets I would sandwich each piece between two thick aluminium offcuts, clamp, and slowly heat till PVC would spread flat. then I could cool the whole thing down and extract my nice and flat plastic sheet. needed 12 of these.
Then made some patterns and cut out the hinge sections. also need to cut out some spacers. then used some more PVC tubes to make a body to hold the whole thing together. to lock it I wanted to use a quick release mechanism but had to forgo that in the interest of time. so used a wing nut and two wide washers to get a solid locking action. one side has a screw that attaches to the tip of the flag pole, the other side has a tight slide-fit to hold the net frame.
It turned out quite solid in the whole 270 degrees of movements. but just for good measures I had made the hinge so it could be flipped around and at 270 degrees it would sit on the other piece directly and hence reduce the force on the hinge. while at it I made a fix attachment as well, just in case.
This prototype worked well for one rescue season, even got featured in some of the rescues. but alas, nothing goes "that smoothly". we had a record-hot summer and at one point the pole was left in the car in the sun with the net attached. the heat and added force was enough to deform the PVC. unsurprisingly, what can be heat-formed can also get heat-un-formed. oh well, maybe using metals wasn't a bad idea after all?
ALUMINIUM OR ALUMINUM?
In the past I had tried to source some aluminum with no success. I hear its only available in US and it's export is illegal. so, the next best thing was locally grown aluminium.
Working with aluminium has some unique challenges, specially thin sheets of it. it's gummy, has tendency to "cold weld" and to weld it you need a TIG welder, and usually can't be heat-hardened. I had temporary access to a TIG welder so I decided to give it a go. maybe I could make it work with some additional tricks.
POLYCARBONATE (PC)
So, need a plastic that is not gummy (like PE or PP), not weak or heat sensitive (like PS or ABS), easy to source as sheet for me (unlike POM or PTFE) and it needed to be though. very few non-exotic plastics are left to chose from and polycarbonate was the obvious choice. aside from one minor caveat of requiring DCM for fusion welding. DCM being a bit of a controlled solvent, is hard to buy. I could have extracted it out of paint stripper but that requires some glassware that I don't have and rather not get at this point. so, no gluing, at least I can do some minor heat forming. 
Bought a small sheet of 4mm polycarbonate and did the usual cut-outs and drilling, and sanding. not bad!, looks promising I thought.... so, let's go further.
A thin steel sheath and a bit of sanding, heating and some epoxy to fill all the gaps... damn it! now that I have epoxy on it, it's not going in. (that's what she said...). some cursing later I got it in and it looks good! I mean I have epoxy all over but that cleans easy enough.
I wonder what these few odd looking marks are though?
.....FUCK, are these cracks? yeah, yeah they are cracks..... FUUUUU....*flips-tha-table
