Nav Tower repair

20130715-195644.jpgAs you may recall from my Ryedale rally report, I finished the race with the bike looking very sorry for itself after the nav-tower fractured.  It’s not an exceptionally complex structure so I decided to replace the aluminium alloy plates with  carbon fibre.  I checked with various sources but noone had a CAD drawing for the mount, so while I am working on making up a CAD drawing, I needed a way to get the structure fixed as soon as possible.

I acquired an A3 sheet of 2mm pre-preg carbon fibre.  While it’s 0/90 degree weave might not be perfect for this application, as it would allow some twisting flex, I was confident that the additional aluminium cross bracing and support would minimise that.

I started off by flattening out the fractured plates as best as I could, and found that they fitted together pretty well.  Certainly, as this is a simple support the measurements weren’t critical beyond ensuring the holes were the right distance apart for a few key components.

I then cut the A3 carbon fibre sheet in half and sandwiched the resulting two pieces between the best of the two fractured plates and a piece of wood.  Using the bolt holes in the alloy plate as a template, I drilled through both carbon fibre sheets and the piece of wood, inserting a bolt and clamping it down with fat washers and a nut each time.

This gave me a nice solid piece to work with, and ensured all the holes were in the right place.  I then traced around the alloy plate with a dremel to cut out the carbon fibre.  The resulting piece is a little wider than the original in places, but nothing that can’t be sanded down a bit more to make it a better fit.

Once mounted up and with the additional, fatter alloy spacers/braces in place, the whole mount is certainly stiff and strong enough for me.  I could maybe have saved a few more grams or made it a little stiffer if I’d been pickier with the lay-up of the weave, but it’s more than adequate for my purposes as it is.



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