Drawing a horizontal scroll.

The Monkey's tail geometry.



Drawing a Monkey’s tail introduction.

There are many different ways of drawing the wreathing volute or Monkeys tail. one of my personal favourites is demonstrated below. This gives a fairly consistent result and even using modern cad software to achieve a smother end result, this will give you a good starting point and scale from which to start. When recreating or matching existing scrolls for replacement this will generally get you very close if not spot on. Due to the different number of ways to draw the scroll you may not always find the original way in which it was drawn.

Should you be lucky enough to have access to modern scanning equipment, by understand the basic geometry and knowing the starting point of each of the segments you can normally get an almost exact copy. I have used this method a number of times when replacing missing parts, luckily living in London many neighbours have the similar handrail from which to get measurements. There are also other tell tail signs to look for, more often than not you can find the original hole in the floorboards that the newel post was bolted down through, giving you a position for the centre of the cap part of the Monkey’s tail.

On this page at the top we have a video showing how to set out the Monkey tail geometry, beneath that we have the stage by stage  drawings with instructions that you can work through or at the bottom of the page we have a pdf download that you can print out to work from and the basic geometry as shown in Diagram 2 in cad format, you can drop these straight into your cad drawings, scale them to suit and then start at Diagram 3.

We will be showing hot to draw the riser faces and nosing lines in an additional section coming shortly.

Drawing the horizontal scroll.

Diagram 1.

To draw the handrail scroll you will first need to determine the over all width of the scroll (E). This will be calculated by measuring the distance between the centre line of the handrail run coming down the flight (B) and the centre line of the farthest offset spindle round the scroll. The distance between these is (A). once you have this dimension you can add the width of the handrail profile (D) to obtain the over all width of the handrail scroll (E).

N.B. When you are using these drawings to get the riser line for the curtail, a good starting dimension for distance (E) is either 1 1/3 times the going or 5 times the handrail width. This does not always work but will get you up and running.

Drawing a handrail horizontal scroll

Diagram 2.

Once you have your over all width you can start drawing the horizontal scroll. This is achieved by drawing a line the width of the scroll (E) and dividing it into 8 equal segments. Line F-G

Scroll drawing D2-FG

Spring a line from point (F) equal to one segment through 90º to point (H) and draw a line from (F) to (H)

Scroll drawing D2-H

Draw a line from (G) to (H), then spring an arc from the centre of (F-G)  to touch and at 90º to line (G-H) to create point (J).

Scroll drawing D2-J

Draw an arc from point (G) using (J) as its centre through 90º to create point (K). Then draw a line from (J) to (K)

Scroll drawing D2-K

Draw a line parallel to (F-G) from point (H) to intersect with line (J-K) to create point (L) this will be the second arc centre for of the scroll.

Scroll drawing D2-L

From point (K) draw a line at 90º to line (H-G) to intersect with line (F-G) to create point (M)

Scroll drawing D2-M

Draw a line from point (L) through the intersection of (H-G) and (M-K) then from point (J) draw another line through the same intersection of (H-G) and (M-K) to create point (N). This will give you lines from which you can get some centres for the arcs that create the scroll.

Scroll drawing D2-N

To get the other centres. From Point (N) draw a line perpendicular to line (H-L) until it intersects with the line from point (L) to line (F-G) then through 90º to line (J-N) then again to line (L to (F-G) and once more top line (J-N). this will create the points (P-Q-R-S)

Scroll drawing D2-J-N
Scroll drawing D2-P-S

Diagram 3.

Now we have the drawing points we can set these over the treads to draw the curtail tread ends, Nosings, Monkey’s tail etc.

To line the drawing geometry up we will need to mark the handrail centre line distance from point (G) and (K) we will call these (Y) and (Z) respectively. We can now align these over the handrail centre lines, in this example we will set the handrail over riser 1 in a traditional spindle position, this being the front of the spindle aligns with the riser face. Therefore the centre line of the first spindle will be ½ a spindles width into the flight from riser face 1.

Scroll drawing D3-align

With the handrail centre lines set out we can overlay the handrail centre lines of the drawing geometry, over the handrail centre lines on the tread plans.

Scroll drawing D3-aligned

With all the setting out geometry in place we can now draw the the Monkey’s tail. We already have the first curve drawn (G-K) this was drawn to get point (k) we can draw the other side of the handrail by springing another line from Point (J) to half the handrail width short of centre line (Y) or in this instance 36mm. It is also worth springing the centre line through as this can be used for setting the spindle positions and during manufacture of the component parts. During manufacture this will be the wreathing 90º bend leading into the monkey’s tail, from this point forward will be the tail itself.

I have added in the handrail coming down the flight for ease of reference.

Scroll drawing D3-90-bend

Now you can continue round, moving to point (L) as the centre of radius for the next quadrant, point (N) for the third quadrant and point (P) for the fourth.

I normally stop at this point on the larger profiles and continue the circle from point (P) to act as the “bun” part of the monkey’s tail. This will then allow the profile to blend back into the lead in part of the tail. This also leaves some lead in at the start of the tail for if the tail has to start pitching before the wreathing 90º part.

Scroll drawing D3-final

This will work in a lot of situations. Once you have the geometry if you use a cad programme for drawing your stairs this can be scaled very easily, this will save you having to redraw the basic geometry, therefore you can start at diagram 3 as you will still have to align it over your stringer and nosing centre lines and draw the handrail to width from the centre line.

The last stage is drawing the feature tread end to set under the Monkey’s tail. We will cover the options for this in another lesson.

N.B. When a larger offset is used for the feature tread it may be desirable to divide the starting width (F-G) into 10 or 12 equal parts.

We are starting to add more pre drawn examples and will give examples of how the layout will change by dividing by 10 or 12. The sample page for these with the first one available for download can be found Here.

Have a look at the Monkey’s tail gallery for some design ideas.

Download in PDF format:

Drawing-a-handrail-horizontal-scroll.pdf (60 downloads)

Monkey_tail_44_8_Plan

Download cad files with all three options on.

The image opposit shows the drawings included in this file.

 

Download .3DM

Monkeys-tail-8-10-12-3dm.zip Membership Required: Basic or Full

 

Download .dwg

Monkeys-tail-8-10-12-dwg.zip Membership Required: Basic or Full

 

Download .igs

Monkeys-tail-8-10-12-igs.zip Membership Required: Basic or Full
Monkeys tail Geometry 8-10-12