Hi Jim,

I've been around for quite a while, but never felt I had much of anything to contribute. Time to try and give some back to all the great contributors on this forum.

I don't think the precision is there to get that last <0.1mm on the calculations.

I have ran the calcs through an excel sheet for both the spiral staircase and for some I did exploring making a dynamic reducer after looking at perryman's thread, but in each case the calcs are correct but lacking on Sketchup due to rounding errors.

I'm going to explore factoring of the calcs to reduce the rounding error, but I feel the final solutions will always come up minutely short.

In saying that, the incomplete geometry is only really visible when zoomed in, so for a lot of models it will not be a problem. For me though, this lack of complete accuracy is driving me mad for a solution.

Jim,

I have been making my own DC Spiral Stair myself.
For the handrail, I have ignored much of the existing geometry and created the handrail guides independently based on a derived n-sided polygon.

You cannot use trig calcs based on pure circles to get your railing length & angle as ultimately you are not making true arcs / circles, just a representation of such from a collection of vectors, hence your calcs will never be spot on (i.e. the curve is longer than the chord).

Be careful when calculating your unknown angle for the railing sections. You have used atan, but your unknown length is the adjacent, not the hypotenuse. Hence you should use asin.

Also watch out for the use of actuals for your calcs, rather than relying on your attribute settings as they can substantially different (e.g. in your model with the rise at 7" and the height at 98", your true rise is a little over 7.5").

I also noted that the component instances does not reset after repeated sizing using the height attribute. When going to attach the file I found it had grown to 8 mb. A quick purge from the model Info > Statistics dialog reined it back to 272 kb. Component count going from +300 to 18

Spiral Stair DC mod 1.skp

HTH, Jon.