How to Duplicate Contours with a Drafting Compass

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Sometimes tools can frustrate you. A friend of mine bought a plastic contour gauge to duplicate the contours on the wall to a board he would use as the side of a custom shelf he was building. He wanted the board to sit flush without damaging the wall trim in his rented apartment. Unfortunately, he ended up with a cut that was totally out of fit. I imagined that probably the teeth of his contour tool were not tight enough, hence losing the pattern when picked up. Or the tines were too thick to capture detail.

So, when he reached out to me for help, I gave him this simple and easy method of scribing with a drafting compass. I learned it from an old friend of mine who has been doing carpentry for the last 40 years. The method works like charm and made my friend could not help but marvel at how easy he scribed the patterns onto the board. Needless to say that he felt a little stupid, but he was happy to learn another way to duplicate contours from the wall using just a drafting compass.

Tools you will need

Sanding sponge

Precision drafting compass

Circular saw or miter saw

Jigsaw

Steps for Scribing Patterns with Drafting Compass

Time needed: 10 minutes.

The following is the six-step process of using a precision drafting compass to transfer the contours of a surface to the board you want to fit.

  1. Step 1: Make a 45 degree bevel cut

    Make a 45 degree bevel cut with a miter saw or circular saw on the edge of the board that will sit on the contoured surface. The beveled edge must not be seen from the outside when you fit the board. Although this step is optional, it is a very useful tip when working with thick wood or boards. It minimizes how much a jigsaw will work since it reduces the cross-section across which the saw will cut. This allows you to guide the blade of the jigsaw a lot better than if you were cutting through the entire thickness. This cutting tip also reduces the depth of cut by half hence reducing the stress on your jigsaw. The advantage is that mitering the edge of the board makes cutting easier without compromising structural integrity.

  2. Step 2: Set the precision compass

    Bring out the guide and the lead of your compass so that tool does not come into contact with the irregular surface you want to trace. Also, set apart the guide and the lead of your drafting compass

  3. Step 3: Transfer the contours to the board.

    While holding the board or lumber you want to fit against the contoured surface, run the compass at a consistent angle such that the guide moves along the contoured surface while the lead scribes the board to transfer the pattern. Use the same consistent downward motion and make a dark line on the board so that when you go to cut, you will have a definite line. The lead will draw on the board exactly what the guide reads from the irregular surface.

  4. Step 4: Cut along the scribed contour line with a jig saw.

    Place the board on the jigsaw table and cut gently along the scribed line with a jig saw. Be careful to ensure that you guide the jigsaw blade accurately.

  5. Step 5: Clean the cut with a sanding sponge

    Once you have made the cut with the jig saw blade, use a sanding sponge or any other sander to gently smooth out the cut to get a clean cut. If you do not sand, you will end up with a rough cut that may not fit perfectly.

  6. Step 6: Fit the board

    Now fit your board onto the contoured surface. It should fit near perfectly if not perfect. This is how you use a compass to scribe contours onto a board when you do not have a contour gauge or when the contour tool fails to live up to its name.

Julius

Julius is an electrical engineer by profession who used to work at a solar microgrid firm as an O&M supervisor. While there, he realized that having the right tools for the trade is equal to getting the job half done. That's when he started this blog to talk about tools.

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