Secondary mount and spider

The secondary mount was cut from a 2.75 inch diameter aluminium bar. To make the mount a bit lighter I also cut a piece out of the back of the mount. It cost me about 2.5 hours to do all the cutting. The secondary was glued to the mount with three 0.125 inch thickness, 0.8 inch wide silicone RTV.

To make the spider hub, I used a variation on Steve Swayze's design (link on my linkspage). I glued three pieces of 0.8x0.8x1.6 inch square aluminium tubing to each other. I glued a piece of 1.6x1.6 inch (2 mm thickness) metal to one of the tubes and drilled 1/4 inch holes, which I tapped for the adjustment bolts. The spider was made from 0.016 inch thickness, 0.5 inch wide metal banding, which I put through the upper and lower aluminium tube. The fact that the length of the tubing is twice the width, makes the spider excentric. When fastened, the secondary mount is very stable and very difficult to move.

The metal banding was attached to the struts with M6 bolts and locknuts as follows. The head was cut off the bolts. In the (threadless) ends where the head was cut off I cut notches with a hacksaw. It was quite a job to do this accurately, because the notches had to be exactly centered to keep the two bandings per arm precisely above each other. Transverse to the notches 2 mm wide holes were drilled. Holes of the same width were drilled into the ends of the pieces of metal banding to be used as spider arms. The banding was attached to the bolts with M2 bolts and nuts. The result is, that the secondary mount can be exactly position where I want to have it, with the bandings exactly above each other.


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Email: Jan van Gastel