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Saturday, 20 September 2014

Weird Revit Railing Stuff - Part 3 - Rail Offsets


Rail Offsets

Following on from my earlier post (Top Rail Transitions) about the subtle differences between old and new style railings, here is another weird difference.  In my attempts to get the transitions working properly on the inside railing, I played around with the railing offsets in plan at the stair half landing.  Each railing type gave different result - rather than try to explain what is happening, here are the offsets and outcomes for each type in the situation where the risers on a half landing are staggered by one tread (which should be buildable).

Old Style Railing (no top rails)

When the railing sketch exactly follows the edges of the stairs and landing, none of the types work, as we have seen previously.  


So, with the old style railing (no top rail), I first offset the sketch line on the landing by 16mm.
 This was enough to get the transition to the upper run railing section working, but not the lower run.
16mm offset landing sketch line
Section view - 16mm offset landing sketch line
 So then I tried increasing the sketch by 1mm to 17mm, which fixed the lower transition too

 Sadly the mitred joints show in 3D views
17mm offset landing sketch line
Section view - 17mm offset landing sketch line

From the section it can be seen that the transition only works because the 17mm allows the underside of the sloping rail to get to the correct height before the 50mm width of the rail turns the corner (different size rails and different stair angles would need different offset dimensions).

NB. notice how the section view shows old style rails solid in elevation when selected.
 

Top Rail Only - Transition = Simple

16 or 17mm offsets do not work at all for the new top rail type, even though the geometry is exactly the same
Section view - 17mm offset Top rail only
If you increase the offset by another 7mm (to 24mm) it still does not work

In this example it even leaves a gap between the horizontal and upper sloping rail (with corresponding warning message).  There is a mismatch between plan and 3D view.

 However, add another 1mm to the offset (up to 25mm) and it works again
 And it even works in plan
And in 3D it does not show the mitre joints (unlike old style rails)


So it seems that you have to increase the offset in plan by another 8mm to make it work as a Top Rail compared to the old style railings - even though the geometry should work without that 8mm.  WHY the difference?


But it gets worse . . . . .

Top Rail Only - Transition = Simple

Try changing the Top Rail to have "None" transition, and it breaks again - this time leaving a gap between both sloping runs and horizontal landing rail.




At least the broken plan section and 3D view are consistent (unlike the broken rail Simple transition where plan and 3D do not match)

Just add one more mm and it behaves again.  Crazy Huh?



The moral of the tale is that there is no consistency between old and new style railings; nor between different transitions in the new style Top Rails;  and quite often no consistency between plan, section and 3D.  And if you try playing around with these same settings you will most likely get different results to those shown here - because there are so many hidden settings that it is really tricky knowing which change you made does what.  Each time I tried this on a different stair in a different project I got different results.

At worst, I would like to see the new Top Rails achieve successful transitions within the same dimensions as the old railings.  At best I would like to be able to make successful transitions within much tighter constraints as they can actually achieve on site.




Reference:
Top Rail Properties in Revit Railings
Weird Stuff in Railings - part 1 - Top Rail Transitions
Weird Stuff in Railings - part 2 - Railing Extents 

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