The K-20 Project

The K-20 Project

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2/24/2007 - The Secondary Cage Part II: The Focuser Board

In the last entry, I talked about how important it is to have the Secondary Cage a light as possible.  Well, when you're hanging 2+ lbs. of eyepieces off the focuser, the one place you don't want to scimp is the focuser board.  It MUST remain rigid enough so it doesn't sag under the weight of the focuser and eyepieces.  That said, you still do not want to use a 1/2 thick piece of plywood, it's simply too heavy.  The solution?  Make a CURVED focuser board that matches the radius of the inside of the cage rings.  A slight curve in the board results in a VERY rigid and strong board, yet it only has to be about 1/4 inch thick.  We decided to take some maple veneer and laminate it into a 1/4 inch thick piece of plywood.  By placing the entire stack in a jig with the correct curve and clamping while the glue dries, we should get a nicely finished curved focuser board that weighs a fraction of a "full thickness" straight board.

ENTRY PICTURES


Making the jig. Here we are using a router to cut out the numerous arcs that will be used to make the upper and lower curved clamping surfaces. The lower arc will match the radius of the inside of the cage rings. A nice trick to using a router with a 1/4 inch wide bit (which is also the width of the finished focuser board) is that in one pass, you cut the correct radius for BOTH halves of the jig!	Stacking and aligning the lower half of the jig.

Lower half of the jig is ready to start laying down the plies of maple veneer.	The completed jig. I don't have any pictures of the actual lamination because well, my hands were covered with glue and Mr. Camera doesn't like things like glue. The lower photo is the jig all clamped up (and it will remain this way for at least a few days) with the soon-to-be focuser board inside.