Acer-Ferrous Toolworks Sector

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.

International orders:  Please contact us for a quote using first class mail, which is a significant savings compared to Priority mail.

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

12 Responses

    1. We do, yes. Please contact us for a quote, as we can often ship first class mail at a significantly lower price than Priority Mail, which is what the check out process in our store will use.

  1. I really would like to be notified of any future videos on the sector or any thing else. Thank You, Michael

    1. The sectors are made here is the United States. I can ship internationally worldwide. I would suggest for the sector to contact me directly for a first class mail quote, which is a good bit less expensive than Priority Mail that my web site will calculate. The sector meets the weight/value limitations for first class mail.

  2. Just got my sector, it was just what I was looking for. Amazing quality and packaged very nicely.
    I’m very pleased I splurged to buy this. Nice work.

  3. If the sides of each arm of your sector are parallel to each other, then theorems of geometry can easily prove that the inside and outside angles are exactly the same and you do not need the 6 degree adjustment.

    1. You are correct. However, the sides of the sector are not parallel to each other which necessitates the 6 degree compensation. Because the scales on the sector radiate outward from the pivot point, we tapered the arms to make them fit and also reduce the weight of the tool.

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