February 15, 2007

          Tucson Model Yacht Club
                Tucson, Arizona

Builders Corner

Mast Fitting

At Tucson Model Yacht Club we have been making new mast fitting for our fleet of EC12 boats. Until recently we have been making the gooseneck/vang fitting as shown in Bob Well's article Foxy lady V. After some thought I came up with this new fitting that is easier to make and needs no fine adjustment to make the boom pivot smoothly. The drawing in figure 1 shows the fitting with all dimensions. It is made from 3/8" thick aluminum, (if you can, try and get a good grade of aluminum as it is easier to machine and will give a better finish). Start by marking out the outline and the hole locations. The next step is to drill all the holes using a smaller pilot drill (the use of a drill press is essential in getting all the holes parallel to the work piece). The notch that forms the mast contour is started be drilling a 1/8" hole the length of the fitting and them using a hacksaw, cut out the unwanted material, finish with a file or dremel tool . To get a good fit to the mast, wrap a strip of fine emery cloth or wet and dry sand paper around a piece of mast and use this as a file. ( I start by forming the notch because if a mistake is made you haven't lost much) Next, cut out the U shape. This can be done by drilling a series of holes to one side of the vertical layout line, make two horizontal saw cuts and then using a coping saw, cut through the series of holes and the piece will fall free. Finish by filing all surfaces to the layout lines. The next step is to drill all the hole to the correct size. The size of the two holes for the pivot shaft will depend on the shaft size and bushings used. I use two nylon shoulder washer (obtainable from any good ACE hardware store) that fit a 3/16 dia brass rod or tube. The clamping bar is made from a piece of 1/8 thick aluminum cut and filled to fit inside the extruded mast. The two holes are best located by inserting the clamp bar into the mast and then position the fitting on the mast and spot drill through using a 1.85mm dia drill or nearest equivalent. Remove the clamp bar from the mast, complete the two holes and thread both holes using a #2-56 tap.

Finally chamfer all corners, sand smooth and polish as required. Assemble the fitting to the mast using two #2-56 x 1/4" long brass or stainless screws.
Figure 1 shows the detail and Figure 2 shows the completed assembly.