Myron Ferguson | March 10, 2017


YouTube Video // Drywall, Tile, Flooring

Drywall Arches: Simple, Segmented, and Elliptical

 

Part 1: Simple radius arch

 

Points of reference:

  • Height: top of arch above floor. All arches in a house will typically share this number. The height will be two inches below the header. 
  • Rise: distance from height down to where the curve begins. For a doorway that is 36 inches wide, the rise will be 18 inches and the run will be 36 inches. 
  • Spring line: where the rise hits the outside edge. Where the curve becomes straight. 
  • Run: width or arch. 

 

How to do it:

  • Mark the center of the opening
  • Draw a plumb line up to the height Mark. 
  • Measure down 18 inches from the height Mark. This Mark will be the pivot point for drawing the radius. 
  • Partially set a drywall screw into the pivot point 
  • Use a piece of wire bend to the correct length to draw the radius beginning at the top and swinging the pencil left and right. 
  • Draw a level line at the bottom of the arch — the spring line. 

That is how to draw the simplest—and least common—arch.

Why is the easiest arch to draw the least used? Because it is hard to make a radius arch look like the other arches in the room if the widths are not all the same. Different spring lines in the same room look like after-thoughts. 

A half-circle arch closes off a substantial amount of walking space, causing headache potential. 

 

 

Part 2: Drawing a segmented arch:

 

A segmented arch is one that uses a portion of the radius from a larger circle. Segmented arches allow you to keep height and spring line consistent. In this example, the height will be the same as the radius arch was — two inches below the header. 

  • Mark height
  • Determine where the spring line will be (figure the rise). Myron chooses seven inches. 
  • Determine what the radius of the segment of the circle will be.  

One way is with a construction calculator:

  • Run=36
  • Rise=7
  • Radius = 26-3/4 inches. 

Another way is to use the formula:

  • Measure down from the height 26-3/4 inches
  • Partially drive a drywall screw
  • Pre end a piece of wire at 26-3/4 in
  • Swing a line left and right from the center until the line intersects the spring line. 
  • This allows you to keep a consistent spring line height with slightly different radii 
  • This also provides a definite point of transition from curve to straight. 

 

 

Draw an ellipse:

 

Step by step:

  • Measure to find the center
  • Plumb up
  • Mark height
  • Mark the rise (7 inches again)
  • Draw  the level spring line
  • Get a piece of string with a knot at either end, 36 inches apart (or whatever the run is). 
  • On an elliptical arch, this is called the major axis. 
  • Half of 36 is 18 and that is called the minor axis

 

—Myron Ferguson, aka That Drywall Guy, points out on his website that over 80% of the visible interior of a home is covered with drywall, and  "The bitterness of poor quality remains long after the sweetness of low price is forgotten."

Amen, brother.

 

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