Thanks for all the help and advice here on the forum. Job - almost - done as I'm waiting the threaded nut insert ordered via the link at the start of this thread. The hole in the controller is just big enough to allow the mount knurled nut to be screwed in a couple of threads. The plastic is thicker than I thought, so it is quite firm but I'll open up the controller again and fit the insert when it arrives. Plenty strong enough to use carefully in the meantime with my Samsung Galaxy Tab A 7 inch tablet.
Things I learnt doing this mod:
- I just couldn't find this type of threaded not insert in imperial size here in the UK. I'm sure there must be one somewhere, but I gave up and ordered from the link. Shame about the postage cost, but there is a lot of water between the USA and the UK!
- The cost of the DJI Inspire 1 tablet mount via the DJI shop is reasonable - until you add the postage cost which is half as much again! However, very quick delivery and I was able to track the delivery man to my doorstep and it was delivered at the listed time.
- I measured and marked as suggested in the thread, but I found that my marled point was a fraction lower than that shown in the guide - just a tiny distance above the 45 degree 'flash' line on the controller. About 1/16 inch or a couple of mm.
- I made a small 'pilot mark' using the pointy end of a Leatherman blade intending to drill with my electric tool. However, as the plastic was fairly soft I decided to use the small flat-bladed Leatherman screwdriver to 'drill' a hole about 1/8 inch in diameter. Just a half turn of the blade at a time and cleaning out the 'swarf' as I went. Eventually, the blade penetrated the plastic dead centre in the gap in the web inside the controller. Yes, I did move the wires out of the way before I started and I put my finger where the screwdriver blade was going to exit. Better to have a sore finger than a damaged wire - ha! As I was really slow and gentle 'drilling' through, there really wasn't any chance that I was going to stab myself.
- I offered up the mount to make sure the hole was in the right place and it all looked good. I wasn't big enough to take the mount spindle yet, but I could see everything was OK.
- To make room for a bigger hole and eventually the insert, I used a pair if pointed-nose pliers to 'roll' each half of the plastic 'web' out of the way. This seemed to be a fairly non-violent way to do this, as the plastic 'tears' quite easily at its base. I was VERY careful to make sure the wires were clear and that I didn't catch anything as I twisted the pliers.
- I now used another tool on the Leatherman to enlarge the hole slowly. No idea what it's for, but it has a sharp point with a slightly chamfered 'blade' and it gets slightly wider up the short blade. I gradually enlarged the hole until the mount spindle would fit and this allowed me to fit the mount retaining screw through the lanyard hole. All good so far and it felt fairly firm, but I enlarged the hole a little bit and screwed in the mount knurled nut a couple of threads to make it firmer. I read that somebody else had done this at it worked for them.
- I could have made the hole a bit bigger and screwed the nut in all the way, but as I'm going to fit the insert when I get it, I didn't bother.
- I feel that 'drilling' with the various Leatherman tools was a more gentle process that using a powered tool and as it was a slow process, gave me more control of what I was doing. Other multi-tools are available ........
So, thanks again for the advice. Goodness knows why they put that flimsy mount on the 3S controller, but all looking professional with the new mount!