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| Mark 2 Truss Tube |
This truss was designed as a cheap replacement for ultralight carbon fiber tubes. The first incarnation of the design, although light and stiff enough, was too fragile. It was based upon a frame of balsa wood which was soaked in PVA glue. This new design improves greatly upon the toughness of the previous, and its ability to withstand bangs or knocks. I have used the same format as before. however the cross members now have reinforcing ribs on the back face. Also more attention has been payed to grain direction. The main improvement however is the use of a thin layer of Fibreglass along the spines of the truss. 1/ I first drew out a template on a large board covered in wallpaper liner. This template formed the basis for the three sides of the triangular truss. 2/ Strips of balsa were cut and layed out on the template. The spines were laid lengthways and the crossmembers with ribs glued to the spines. 3/ The three sides were left to dry, then chamfered (sanded) with 60 degree edges. 4/ The three bonded sides were now stuck together to form a triangular section tube. 5/ The end pieces with 6mm dowel holes were then glued on. The jig had dowels inset into it, so that each truss is identical. 6/ All sharp edges were sanded. 7/ A layer of thin fiberglass was laid along the spines running the length of the truss, where the truss is most likely to be abused. 8/ The whole lot was spray painted black. 9/Iron washers were attatched over the dowel holes to act as clamps for the magnet. This is the method previously implemented. What I have ended up with is an extremely light tube (Lenght=105cm, Weight = 60g) which is now also fairly tough. My end goal is to achieve the same performance as a carbon tube at a fraction of the cost. This design is coming very close to achieving this. For my 20in scope I am planning on the truss tubes to each weigh 250g. (2m long) It may be commented upon that this process is of course time consuming. Hopefully this is offset by the fact that they are cheap to manufacture. |