Dick, Last word until you get a question... I don't understand the offset part. Do you draw two arcs: one the real centerline and another that is 3/8" shorter radius? Why the shorter radius arc? Ben Trousdale
--- In [email protected], Richard Karnes <rnk2202@...> wrote: > > Gents/Ladies -- > > A final word (from me) on spiral easements. > > You can really go off the deep end with the mathematics, calculating and > plotting equally-spaced offsets from the end of your tangent in order to plot > points that define the easement curve. (I used to do this in surveying > class, calculating and laying out spirals on the main Cornell quad.) > > So don't do that. > > Any stiff, springy, straight item (a spline) intrinsically conforms to a > least-energy curve when bent and held in place, provided that you don't > over-bend it so as to kink it. One of the best items to use is a metal rail, > the stouter the better. Plot your straight-track centerline and your curved > centerine of a particular radius. Make your radius about 3/8" smaller, but > from the same center point, such that the curve misses the straight by 3/8". > Then take a yard- or meter-length of .148 or .172 rail, spike the first six > inches along the end of the straight centerline in three places, so that one > edge of the rail base is against the centerline. Then flex the rail (spline) > by hand until the rail matches your curve, making sure that you allow enough > free length to avoid a reverse curve in your spline. Spike the rail to the > curve in three places over about six inches of length. Now draw your pencil > along the rail base to create your easement > centerline. Be careful not to move the rail as you do this --You may need > to hold it down with your other hand as you draw. Resist the urge to spike > the rail along the eased curve, as this can introduce unpleasant lateral > centerline excursions. > > For curves less than 33", use a 1/2" offset. For curves greater than 45", > use a 1/4" offset. Close enough for government work, as they say... > > Dick Karnes > ------------------------------------ Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/S-Scale/ <*> Your email settings: Individual Email | Traditional <*> To change settings online go to: http://groups.yahoo.com/group/S-Scale/join (Yahoo! ID required) <*> To change settings via email: [email protected] [email protected] <*> To unsubscribe from this group, send an email to: [email protected] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
