What controls the Baluster Per Tread spacing?

[patricks]

Trying to create a spiral stair, and wondering what controls the baluster spacing when Baluster Per Tread is used?

When sketching the spiral stair, the treads/risers were created according to the Tread Depth instance parameter, which measures along the center arc of the stair run to determine the placement of each riser line. I then changed the angle between each riser line to be an even 30 degrees according to a particular stair manufacturer.

When I created the railing and set it to 1 baluster per tread, the baluster does not occur in the same place on each tread, and in fact I have 2 balusters on at least one tread. Could this be because I changed the angle of the riser lines to make each tread be deeper than the dimension shown in the stair's instance properties?

*edit* and now I just placed another railing of the same type, on another spiral stair and there are 2 balusters per tread on EVERY tread of the stair, despite the rail being set to only 1 baluster per tread!

[cliff collins]

I suspect that the "baluster per tread" rule was programmed for straight stairs--and it probably uses the default 11" deep tread as a constant.

With a spiral stair, the treads are pie shaped, and thus Revit's calculations are thrown off.

Phil Read did a really amazing presentation on Revit stairs at AU 2009.
I think there was some examples on spiral/organic shaped stairs which may be helpful?

Here is a link:

http://au.autodesk.com/?nd=class&session_id=5380

cheers......

[gwnelson]

All I've ever seen is the baluster spacing fighting with the #/tread - and there is no clear winner. My solution is to make excuses for Revit & not show stairs & railings too closely.

[patricks]

hah yeah I won't really be showing this railing, since it should come shipped with the pre-fab stair anyway.

I did change the stair tread spacing to the actual arc length of my treads along the run sketch line, which turned out to be 8.xxx" for 30-degree treads, and that changed the baluster per tread to be correct.

Now the problem is that the baluster hits the tread in the center of the tread's outer edge. I see no way to change the spacing to be at one corner or another corner (as it would really be built), short of changing it back to normal baluster spacing (not per tread) and make the spacing equal the arc length of the tread outer edge. Then of course I would need a separate railing type for every diameter of spiral stair.