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Gordon Rayner
scholastic sledgehammer
Reged: 03/24/07
Posts: 965
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Re: Recommend reclining chair for binocular viewing?
07/04/09 08:24 PM
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For use of a straight view binocular with a reclining lawn chair , one needs several axes of rotation in the mount. One of those is a hinge, with a vertical axis , as the first motion outboard of the p-gram. This axis is parallel to the azimuth axis , atop the tripod, around which the entire p-gram rotates.
As Rick Miseroy has pointed out, the starting torque for the azimuth axis should be larger than the starting torque for the hinge axis. Otherwise, one must grab the p-gram with one hand, while turning around the hinge axis with the other hand.
So, we should add starting friction to the azimuth axis, while tending to make the hinge move more freely. Perhaps Dobson az bearings should be squeezed together, or the screws or hose clamps surrounding a PVC C-tube around an aluminum pipe or shaft should be tightened.
One might examine the hybrid Dobson plate-bronze bushings az mount in AMATEUR TELESCOPE MAKING, edited by Stephen F. Tonkin, (Springer, 1999), in the chapter on a p-mount. One might increase the disc size and pad location radius, and/ or change to a less slippery combination than Teflon and pebbled Formica.
Consider the rudder on a small sailboat. Its fittings, such as pintles, may be useful for the hinge axis.
I coincidentally found yesterday 3 aluminum fittings, 2 inches long ,with 1/2 inch reamed holes lengthwise. One side is flat, parallel to the holes, and the other side is a half-cylinder, also parallel to the holes. The ends are milled flat. They seem to be good mates for some 1/2 inch shoulder bolts, threaded only at the end, titanium, which I have had for a long time. When I saw them, I thought "p-mount hinge!". I only need to drill and tap one or two mounting holes, perpendicular to the hinge hole axis. Has anyone seen an off-the -shelf equivalent to these fittings? Near equivalents could be made from rectangular aluminum bar, in a milling machine or in a lathe with a 4-jaw chuck. Making the half-cylinder side , for clearance, may not be necessary.
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