Hi there, all,
Despite some trepidation about offering my latest efforts alongside the posts of the stalwarts of Mad Modders, I've decided to have a go. If only because some Modders may be able to tell me where I went wrong and how they would tackle the job. So, here goes:
A friend managed to damage a rather high quality binocular loup and asked me if I might be able to fix it for him. I said I'd attempt a repair, strictly on a 'best efforts' basis with no guarantee, but that wouldn't be a quick job - I'd have to finish some other jobs first and also to make some tooling and fixtures along the way.
In this first post, I'll describe the diagnosis, identify the damaged part and summarise my repair plan. (Photos at the end of the post.)
The loup comprises a pair of magnifying optics which mount on to a bar with an adjustment for inter-ocular distance. That bar, in turn, mounts on to a head-band. The optics resemble rifle sights but have a shorter focal distance (about 30 cms) and the mounting bar is shaped to angle their optical axes to converge at that distance.
My friend had managed to drop the loup which had caused it to become 'boss-eyed'. I gave the loup a thorough inspection and was relieved to find no damage to the optics units themselves but the mount that attaches one optic to the bar had been distorted by the impact. This component (aka 'the mount') is shown in the photos. It is plastic, I assume it is a moulding, and it has a stepped hole through which the ocular end of the optic fits, retained by a threaded ring and an M2 grub-screw. On its upper flat face, there is a tongue that is a sliding fit in a slot in the mounting bar where it is secured with a washer and a plastic-headed M2 thumb-screw. The tongue on the damaged component had suffered a permanent twist which had caused the loup to become 'boss-eyed'.
I don't have facilities for plastic moulding so the only way I could see to make a replacement mount was to hew it from solid. My measurements suggested that 8 mm sheet would be the suitable raw material and I opted for Delrin (I'll come back to choice of material later in this thread). I bought a piece of Delrin sheet on eBay - it was billed as 8 mm but turned out to be nearer 9 mm which had me scratching my head at first! I sawed off a 1" wide strip using my table saw and divided that into 1½" lengths. This gave me five blanks (aka 'dominos').
I decided that it would be easier for me to make a matched pair of mounts than to exactly duplicate the undamaged original. So I resolved to work on all five dominos in parallel in the hope of achieving two usable mounts rather than having to start over if I suffered any problems along the way. The tongue seemed to be the trickiest feature so I opted to start with that, then progress to the stepped hole and finally to profile the mount to something like the originals.
As Bob says, 'OK, photos':