staircase stretch out or development.
Current Kno project,
Keep an eye on this for the next few days. O.K. maybe weeks or months! This is an important part of producing stairs and I will provide as much information to explain this as I can.
Using the stretch out, to draw the plan view.
How to draw geometric staircase plans, introduction.
This may be the most important stage of designing a geometric staircase, by not drawing the stretch out, you are likely to have problems once the stairs are made and installed on site, This can be an extremly expensive, time consuming and a design compromising mistake.
The staircase stretch out is used to show the flow of the handrail and help calculate the spindle, riser and stringer face positions.
This makes positioning the winder risers very easy, the risers may be drawn at a constant distance apart in a straigh line and then folded around the handrail centre line to give the riser positions on plan or drawn equally spaced on plan and then elevated to the stretch out to create the handrail flow.
This will also show why it is an advantage to add the diminishing flyers before the winders.
Having a good understanding of this process, will allow you to acheive the desired layout in the drawing stage.
In this article.
We show how to use the stretchout for setting the winder postions.
How so space the spindles around the winders.
How the handrail flow and the stringer bottom cut are determined from the stretch out.
Remove the guess work.
With a pre-determined formula it makes the process of drawing the stairs a lot quicker and improves the end result.
Here I will give a few examples of how this may be achieved, different projects may require different methods dependant on the final look, space or personal choice.
This is one of the most important stages in drawing a geometric staircase and will help void problems in the design, before they happen.
Nb.
Before starting any stretch out, confirm the spindle spacing on the straight goings, to ensure the spacing is within the legal maximum.
The maximum legal spacing between spindles is at the thinnest point of the spindle or the greatest distance between any part of adjacent spindles. In this diagram, I have shown what would happen if using turned spindles as opposed to square sticks, with a maximum legal spacing of 100mm – 4″.
Without confirming the spacing at this stage you may have to draw the stairs again if the spacing is over size.
As you can see, with straight sticks we are within the legal maximum space allowed, with turned spindles that have a minimum Ø of 20mm 3/4″ the distance between spinldes is over the maximum allowed spacing and therefore illegal.
The examples.
In these example I will tag each example with a letter followed by the criteria used to get the result.
This will allow you to decide which criteria best suits your project and compare the different ways of achieving your layout.
Example A – Stretch out.
Example A, Still to come: This example in video format, 3D model of this example.
Straight flight with half space winders and diminishing flyers, using the stretch out to give riser postions.
To Follow.
Example A – Plan.
Straight flight with half space winders and diminishing flyers, using the plan view with equally spaced spindles to get the stretch out.
Example B.
Straight flight with half space winders, no diminishing flyers.
Example C.
Straight flight with half space landing. Handrail coming to horizontal mid turn.
Example D.
Straight flight with half space landing. Handrail staying at same pitch as flights through turn.
Example E
Spiral stairs with landing. How to flow the handrail across the landings on spiral flights.
Example F.
How the stretch out is used to determine the bottom cut line for the stringer.
Example G. – Top of flight.
Stringer fascia transition. how the bottom of the stringer flows into the ceiling line at the top of a flight.
Example G. Bottom of flight.
Stringer fascia transition. how the bottom of the stringer flows into the ceiling line at the bottom of a flight.
Example F.
Putting the curves into the handrail tangents.
Stretch out basics.
Handrail centre line stretch out.
This handrail centre line is the most common point for creating a stretch out, this will show the flow of the handrail through the flight and how the flights link together throughout the staircase.
Set the spindle positions and confirm they have space to sit on the treads as required, before going into production.
From a handrailers point of view, the handrail is the house and the staircase the foundations upon which that house is built.
Trying to build a mansion on bungalow foundations just isn’t going to work. You will end up with a bungalow, or a mansion that doesn’t sit over the foundations.
Starting the plan view.
When starting to draw the plan view, it is good practice to use the handrail centre line as the edge of the staircase.
The stringer face and nosings are easily added to this once the handrail flow has been drawn.
Example “A” details.
In this example I am going to use a flight consisting of:
Handrail centre lines B and C, one going apart.
16 rise and goings, to include 7 winders.
16 rises at 190.3mm – 7 ½”
16 goings at 262mm – 10 ¼”
28mm thick treads.
35mm – 1 3/8″ square spindles.
When using turned spindles, work with the thinnest part of the turn.
We will allow for winders that encroach into flyer area, creating diminishing flyers either side of the turn.
This allows the change of pitch to be divorced from the change in direction; creating a smother transition and a constant handrail pitch through the turn.
Risers points through inner drum turn.
We know that the distance between the handrail centre lines is equal to one going.
The distance between spindles on the straight flight is ½ a going.
To keep the spindle spacing through the turn as close as possible to the straight flight, we will use multples of a half going.
We have 7 winders to fit into the 180º turn, therefore we need 7 X ½ a going.
7 X 1/2 X 262 = 917mm Along the tangents.
So the winder stretch out line A for the winders is 917mm.
This is drawn perpendicular to the staight handrail centre line and at a tangent to the handrail 90º through the turn.
Draw a line A and set it centrally above the straight handrail centre lines B and C (dia 1).
Divide line A by 7 for the number of rises. (dia 2).
To see how this looks at pitch on the 2D stretch out, we can carry the riser postion lines up through the goings lines, that are spaced apart by a single rise each (dia 3).
With the winder stretch out drawn and divided, the next stage is to mark the divisions onto the tangents.
The riser division points along the mid turn tangent A are already sitting in position, those ouside of the staight handrail tangents B and C, will be sprung from where tangent A crosses tangents B and C at junctions E and F.
From these points describe an arc from each of the division points along tangent A through 90º to tangents B and C (dia 4).
You will notice riser points 7 – 10 are not set over the handrail centre line, to place these in their correct position.
Draw a line fron the riser point on the tangent lines til it crosses the handrail centre line perpendicularly (dia 5).
With the riser points set over the handrail centre line, the centre line for the turn winders and diminishing straights can be added to the straight flight section.
This is acheived by bringing the handrail centre line through the turn with riser points 5 to 12 in to meet the straight risers 5 and 12 (dia 6).
When we look at the full staircase stretch out, you can see we have staight pitch lines both up through the straight sections and across the risers through the turn section (dia 7).
I have also added the same diagram but with the going and rise lines trimmed away from the staircase stretch out, this gives a clearer view of the goings and rises (dia 7a).
Now we can offset the handrail centre line into the flight void by half a spindles width, this will be the stringer face position (line sf) .
In this example we are using 35mm spindles, therefore the offset distance is 17.5mm (dia 8).
Riser points around outer strings.
Option A.
Equal division.
(dia 9a)
To get the riser points around the outer wall string. Offset to the handrail centre line between the straight risers at each end of the winders, to half the width of the flight, this offset line is commonly referred to as the walk line.
This walk line can now be divided by the required number of rises.
The riser lines can now be drawn in with a line from the wall string through the walk line and handrail centre line dividing points, continue the line though till it contacts the stringer face line SF.
Confirm that wherever the walk line is described, that each going is equal to or greater than the goings through the straight sections of the flight.
Option B.
One going of straight before winders.
(dia 9b)
Draw a straight line J from the each of the last risers on the straight sections, equal in length to a straight going and set centrally in the width of the flight.
Describe an arc between the ends of these two lines, using the same centre point as for the handrail centre line arc.
Divide the walk line arc by the number of rises required.
The riser lines can now be drawn in with a line from the wall string through the walk line and handrail centre line dividing points, continue the line though till it contacts the stringer face line SF.
Confirm that wherever the walk line is described, that each going is equal to or greater than the goings through the straight sections of the flight.
This method has two benefits.
- The riser lines through the arc are closer to perpendicular to the handrail centre line, this means the spindles do not rotate off the centre line as much.
- the transition between straight goings and winders is more gradual.
Options A and B overlayed to show the difference (dia 9c).
setting the spindles.
Now we have the riser face positions we can position the spindles along the handrail centre line .
For this examble I will use option B from above as this is the preferred option.
The spindles are of 35mm square stock.
We will use the traditional spindle postion for tread mounted spindles on cut string stairs (dia 10).
The straight goings will have the first spindles set with one face over the riser line and one face over the stringer face.
The second spindle on each tread will be set with one face on the centre of the going and a second face set over the stringer face (dia 10).
As you can see, the spindles cross the riser lines around the corners, the good thing is we know from the stretch out that the handrail flows through the turn, the risers are in the correct position for a constant handrail height and we have some space to move the spindles about on the treads, How much space? Is another thing, to determine the space available we can offset the riser lines by the nosing distance.
In this example we are working with 28mm 1 1/8″ (dia 11).
With the nosings drawn on, a final tweek to the spindle positions to keep the spacing as even as possible (dia 12).
In this example the winders are set in place from the stretch out, in the next example we will use the winder positions to control the handrail height in the stretch out.
Handrail base and spindles.
The last part to check is the width of the handrail base over the width of the spindles, this is to ensure that the handrail base covers the spindle top as it goes through any turns.
By offsetting the handrail centre line by half the handrail base each side you will see where you may have problems, should the spindle extend outside of the handrail base at any point the a lerger handrail base will have to be used.
Ideally there should be a minimum 3mm 1/8″ border either side of the spindles.
