Undercarriage Asssitant - Finding Angles and Sight Lines
In Windsor chair making, it is sometimes helpful to know the angles and sight lines (direction of lean) for holes. An example of this is for spindle holes in a chair seat, where each hole needs to line up with a point on a bow, or arm.
On this bow back chair, the position of the holes on the seat and the bow are marked.To find the sight line and angle, draw out the pinch rod and push the points slightly into the wood each end. Fix the rod in place, using the clip on the brass rod.
Take a laser (details at the end) and place this on the seat, with the laser switched on. Move the laser around the seat until the projected line runs along the seat and directly up the rod. It may be best to have the tape facing the laser, so that it is easier to see the line.
In this position, if you look along the line towards the pinch rod, it will appear vertical. This line along the seat is known as the sight line and is the direction in which the rod (and future spindle) is leaning.
Mark the line on the seat.
To find the angle of the hole/spindle, place a bevel gauge along the sight line and adjust the blade until it is parallel to the rod. This is the angle for the hole. You can measure the angle with a tool such as a Bevel Monkey.