Trammel Point Method

Trammel points, which are used to scribe a circle or radius, consist of two points mounted on a beam (typically a piece of wood) and designed to slide along the beam to increase or decrease the radius. Typically, one of the points is a pencil or pen, while the other is usually a metal point used to anchor the centre of the circle or the radius. The size of the radius can be adjusted by sliding the marking point along the beam to the desired length and locking it into position. 

 

Trammel Point Method for Squaring a Room and Finding the Centre:

1. Measure the width of the room from top to bottom left of centre (Line A). 

2. Find the centre of Line A and mark it (Point B).

3. Measure the width of the room from top to bottom right of centre (Line C).

4. Find the centre of Line C and mark it (Point D).

5. Adjust for any difference in centre between Point B & Point D. For example, if Point B is one inch different than Point D, divide the difference by two to establish the new centre point of Line A

6. Snap a line the length of the room from Point B through Point D. This is now Line E.

7. Find the centre point of Line E and mark it Point F.

8. From Point F, use trammel point at fixed position on flat board to mark through Line E left of centre, and mark it Point G.

9. From Point F, use trammel point at the same fixed position on flat board to mark through Line E right of centre and mark Point H.

10. From Point G, use trammel point at a fixed position on flat board draw arc above Line E. Mark this Arc I.

11. From Point G, use trammel point at the same fixed position on flat board draw arc below Line E. Mark this Arc J.

12. From Point H, use trammel point at the same fixed position on flat board draw arc above Line E. Mark this Arc K.

13. From point H, use trammel point at the same fixed position on flat board draw arc below Line E. Mark this Arc L.

14. Where Arc I and Arc K intersect, mark it Point M.

15. Where Arc J and Arc L intersect, mark it Point N.

16. Snap a line from Point M through Point N, and mark it Line O.

17. Where Line O intersects Line E is the centre of the room. Line E and Line O also form a 90-degree angle.