Acer-Ferrous Toolworks Sector

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We have now added the Acer-Ferrous Toolworks Sector to our product line.  This tool was a collaboration between Acer-Ferrous Toolworks and Red Rose Reproductions and has been under development for many months.  Read on to learn how this ancient tool design can be an asset in your shop.

The sector is a proportioning tool that, in conjunction with a pair of dividers, can be used to figure various mathematical calculations. It was in use dating from the 16th century into the 19th century when it was largely replaced by the slide rule. This modern rendition is meant for the woodworker looking to simplify many mathematical problems. It consists of two rulers joined by a hinge.   The rulers have scales engraved on them along with small holes at each numerical point to capture the tips of the dividers. Here is a brief description of each scale and its uses.

  • “L” scale, line of lines.  This scale is used to divide a specific length into equal divisions and to scale up or down proportions. It also has the golden ratio proportion and can be used to figure the radius, diameter, or circumference of a circle given any one.
  • “P” scale, Line of Polygons.  Any polygon from 4 to 12 sides can quickly be created from the known radius of the circle.
  • “C” scale, Line of Chords. Used to set the sector precisely to any angle from 6 degrees to 90 degrees.
  • “T” scale, Line of Tangents.  used to determine the sight line and resultant angles of compound angles.  This is useful in chair construction where the legs have rake and splay. 

These sectors are made of black anodized aluminum scales with brass hinges.  The markings are laser engraved on and are bright and easy to read.  Overall length is about 13 inches.  Each comes with a spanner wrench to adjust the hinge stiffness as needed.  There is a 26 page instruction booklet included with each sector. Note: Dividers are not included with the sector.

Price is $195 plus shipping.  They can be purchased here.

Below are several videos showing how each scale on the sector is used.  They are really quite easy and intuitive to learn to use, and eliminate many chances for error since no calculations need to be done longhand.

The Sector and its Uses