October 4, 2012
The falling lines are the sloping centre lines that give the angle of the handrail at any moment.
In our example their are 3 types of handrail and falling lines:
1- The handrail on the non wreathed stair excluding the ramp
2- The ramp that changes the angle of the stair handrail to enable us to draw the tangent plane
3- The falling lines in the wreathed section, these 2 lines must meet at the intersection of the tangent planes
All these falling lines can be adjusted to and will change the shape of the handrail in space. The idea is to draw them to give the smoothest flowing curve as possible. With the tangent system the wreathed sections are always elliptical, so they are in fact automatically a smooth curve, the problem is to create a flowing transition between the lower falling line and upper falling line, while maintaining the elliptical center line within the wreath.
The best solution is not to use any ramps.
If you can arrange a stairs so that the angles of each flight, and therefore their falling lines, enter directly into the wreathed section and meet at the crossing of the tangent planes, you don’t need any ramps and the transition will be perfect.
On the other hand if the extension of the falling lines don’t meet at the crossing the angle the lower falling line enters the wreath must be adjusted with a ramp.
Ramps are always disgracious, to get the best possible solutions there are 4 constaints and 3 things to adjust:
Here are the constraints :
– The wreathed section the falling lines must join at the intersection of the 2 tangent planes
– The falling lines entering and leaving the wreath must be at the same angle as the non wreathed rails.
– The ramp section falling line that provides the transition from the non wreathed stair angle to the wreathed falling line should be as smoothly curve as possible.
– The handrail should be kept as close as possible to a constant height of 900mm above the steps.
Here are the 3 things you can play with:
– The angles of the falling lines in the wreathed section
– The shape of the ramps.
– The angle of the non wreathed handrails
In our example we only need a lower ramp as the upper non wreathed rail can be tweaked to have the same angle as the upper wreathed falling line.
To make the wreathed falling lines meet at the crossing of the tangent planes we have to adjust the lower wreathed falling line, and to make the lower non wreathed rail enter the wreath at the right angle we have to add a ramp.
The actual shape of the ramp is a matter of judgement.
The more gradual or less curved the ramp and therefor the transition the more graceful it will be.
It’s even possible to adjust the angle of the whole non wreathed lower rail and get rid of the ramp.
However doing this will modify the height of the handrail over the steps.
So to choose the exact shape of the ramp a compromise has to be made between the height of the rail and the curve of the ramp.
It’s a tricky subject to explain and I hope that I’ve been clear and helpful.
We could do a Q&A session on this when our sites are up and running.
All the best
March 7, 2014
As you may be aware, this youtube video was quite impressive to me.
First question I have is when you made what you called the “falling lines” if memory serves me correctly, you obtained the angle of the wreath in oblique position. Because these lines did not meet due to the rising turn, you had to connect the upper rising line to the lower rising line (axis line of both rails) and you obtained your angles you used for not only the template shape, but also for the end cuts. I don’t understand how you just picked a spot for it to connect to the lower rail (as shown by video). This is a very important line, so can you please explain how you did this and why, as it is the basis of the new template in oblique plane. I am learning CAD as I write this so those questions will come up later, but this line has me confused. My thinking is that the two lines have to be joined by that third line at a certain spot of tangency of that turn but I did not hear or see you reference that. Please explain your thinking on this if you will. This is at approx. 7min. 50 sec. in video that I am referring to. You will see that you inserted this line at no certain spot of the second lower axis line which dictates all angles.