Jeff Morgan - Wile E. Coyote School of Telescope Making
Quote: I got to thinking about how much weight it could bear. Instead of the alt-az cradle I would place a Schaefer AT-9 equatorial head on top to carry a 8" f/12 refractor. Total weight for head, counterweights, and tube would be about 180 pounds.
Quote:Typical allowable stresses for such species would be a few thousand psi, and hence if a tripod is well-detailed (more on that below), adequate strength to support a few hundred pounds of load is possible. But care must be taken to check all the various modes of failure, e.g., the tripod shown could fail in bearing at the bolts that attach the legs to the pier. In this region, the area resisting compression is reduced because of the bolt holes, and hence the net area (i.e., cross-sectional area minus the projected area of the bolt hole) must be used to compute allowable force from the usual formula of force = strength times area.Determining the various failure modes requires a fair amount of judgment and experience. In the picture provided, I can see potential for a bearing failure at the bolt-leg junction, at the connectors that hold the platform to the base (that would likely be a compression failure perpendicular to the grain, and that failure mode involves a much lower strength for wood members), a gross overturning problem because the center of rigidity of the tripod may not coincide vertically with the center of mass of the OTA, etc., etc, etc.
Quote:I wonder if one were to reinforce the hub holes with flange bearings and/or sleeve bearings? Or increase the diameter of the carriage bolts? Given the depth of the required hole, the limiting factor would be the availability of extra-length drill bits.On the spreader, again I would try re-enforcing the wood-wood joints with bronze bearings. Here the wood thickness is not that great, so it would be easy to increase bolt/bearing sizes.
Quote:Hope this helps...