Structural parts, Uni directional glass

Routing uni troughs

Posted by Paul

One of the hardest things to do on the build is to cut perfectly good bulkheads. Not physically difficult but emotionally. Of course this is all just in your mind, and I imagine drilling through hull holes will be equally difficult to do given that the idea of building the hulls so strong and then drilling holes in them is counter intuitive. Nevertheless, in order to create a spanning uni rope across the rear bulkhead in the way that the engineers designed, it is necessary to trim the rear bulkhead so that the trough is a smooth arc. Uni like any glass is weakened when it is sharply turned on a corner. So to avoid this a nice smooth curve is cut in the rear bulkhead and the sharp corners taken off bulkhead 5. This is not necessary on bulkheads 4 and 6.

bh7 cut portbh7 stencilbh7 cut sb

bh5 after cutbh5 before cut

Once I had trimmed the bulkheads I set about routing out 25mm troughs in bulkhead 4 and 6 and 15mm troughs in bulkheads 5 and 7. (For bulkhead 6 I routed the trough before I glue the top half of the bulkhead on as it is easier to reach before it is on, but I will need to glue it up before I can do the uni rope). As with all things it is often better to do some trial runs on offcuts first, which I did to set the router fences, and once I was happy with it I set about doing the actual bulkhead troughs. I also rolled a section of uni about 650mm wide, half a roll width, and fit it into the slot nicely. Of course when it is wet it may be a little thicker with the resin but I am sure it will still fit very well.

It took me all day to trim the bulkheads then play around with the router and test cut a panel and then to rout the slot into the 4 bulkheads. For the saloon wall with the cabin top contour, I have routed that part separately before I glue it on as it is easier to reach, and also routed the rest of the bulkhead sides that it will meet up with. I will have to glue that up before I can lay its uni down.

bh topsuni trough

The router can not get right down to the end of the bulkhead near the hull panel tops so I did this last part with a chisel (and hammer). The idea is to taper the trough down to nothing and a chisel is a good way to achieve this. A tip here is to use the back of the chisel so it does not try to dig deeper with its blade, it is easier to control the depth of the cut backwards. Another tip is to keep the balsa chips (sawdust) as it is very effective in soaking up any spills of resin or hardener (unmixed) on your workshop floor, although if don’t follow my lead you may not have the kind of spills I have been having!

With all the uni troughs cut I may start on the uni wet out and fill tomorrow. It may be too difficult to get the uni wet, rolled and in on my own during the open time, even though you use the ADR not the West on these tapes because of the longer open time and less heat generated in the troughs.

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Paul