Spent last couple of days working on the rear tail light fitting, first day, progress was made which came to an abrupt end, the second day was very productive mainly because of the experience of the first day.
On the first day I cut out the shape of the fitting from the 3mm road sign and then tried to solder/weld the 2mm vertical element to it. It would not take properly and if I got it hot enough to take it moved so it had to be re-done. Also the clamps I was using were aluminium and were first acting as a heat sink and second when they got hot they expanded and no longer clamped the two parts together.
It was very frustrating. I think the road sign is dural rather than aluminium either that or the easyweld stuff does not like joining dissimilar thickness materials, because the heat transfer and cool down is different. I decided therefore to re-make the whole thing in 2mm sheet aluminium.
I was very aware that this is not a very vibration resistant or robust choice so my design concentrated on light weight (so that vibration would not be such an issue) and wherever possible maximizing the section to provide rigidity. All 4 mounting points would also have to be rubber mounted which means that the top hat sections I turned up to mount the under seat tray would have to be re-made to a different design. (good job I bought 2 metres of 25mm aluminium bar)
I also realized that the design I was contemplating on the first day would not work because the number plate hanger bracket was too far forward and would end up either touching the rear tyre on full suspension deflection or it would have to be angled so far out of the vertical as to be hopelessly illegal.
I had previously machined up some plugs to go in the truncated frame rails these were tapped 6mm to take a male/ female 25mm x 25mm vibration mount. There are also 2 projection welded 6mm nuts on the rear seat support which hold the seat latch. So I have 2 mounting points approximately horizontal and two approximately vertical.
The complexity is that the frame rails are not parallel but rather taper inwards and point slightly downwards and the seat latch bolts are not symmetrical around the centre-line of the bike. Added to that I have not yet made the seat itself and I want the light unit to fit flush to the bottom of the seat unit. Getting the slope of the light unit to fit to a non-existent seat was therefore a bit challenging.
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