07-08-2014, 08:29 AM
(07-07-2014, 10:38 PM)f350ca Wrote: Looking at possibilities for bearings on the shaft that supports the paddles on a paddle wheel boat. Im thinking of using something like 2 1/2 inch heavy wall pipe (will fit through the headstock on the lathe). Its a relatively low torque load over a long shaft (about 8 feet between the bearings). Expect something in the order of 200 rpm.
I don't have any thoughts on poured bearings, but here is a comment on shaft design. 8 feet between bearings for a 2.5" hollow shaft is a long way.
At 200 rpm I suspect you will be well below the critical speed unless you have considerable mass mounted on the shaft, but straightness might be an issue. Commercial pipe isn't all that straight. Even with turned ends for the bearings, there is likely to be a lot of "run-out" due to straightness issues with the pipe (unless you are able to turn centers on an 8 foot shaft. Weight mounted on the shaft will also generate deflection - which is amplified by the time it reaches the bearings - flexing of the boat frame also comes into play. Bottom line - you may want to consider some type of "self-aligning" bearing design to avoid shaft binding when in operation. One solution is a spherical mount for the bearing - these are commercially available in both ball bearings and sleeve bearings. Some will accommodate up to 3 degrees of misalignment are even rated for submerged operation. The problem is cost: new mounted bearings of this type in the 2" size run around $400. You might be able to find used / salvaged bearings.
Terry S.