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Homemade Scaling Caliper for Drawing

July 10, 2017

I was browsing around on the internet this morning looking at drawing tools, and I stumbled across a youtube video of a fellow making a proportional drawing caliper. I’ve used these before, but lost the one I had bought some time ago. This sounded like a good project to fuss around with.

A drawing caliper is a measuring device made of two crossing sticks that allows you to scale up a measured distance depending on where you attach their intersection point. For example, if you set the small end to be 1 inch apart, with the center screw set to 2X, the points at the other end will be 2 inches apart. As long as that intersecting point stays the same, all your measurements will have the same proportion.

There are commercial calipers you can buy, such as this one from AccuraSee, but the one in Jen’s video looked pretty easy to make, and it was; however, I discovered a problem with three of the hole placements.

I decided to make mine out of two strips of balsa wood (3/32″ thick), being easy to cut and shape and not too flimsy. A 6/32″ screw and wingnut holds the pieces together. I printed out Jen’s diagram that he linked to on the video, and used that as a template for the balsa (1″ wide, 9″ long.) I drilled 5 holes according to his diagram, and tested the scaling by lining up the two ends with two rulers. The 1:1 scale in the center was easy to test since it’s in the direct center of the 9 inch strip. Hole #2 also measured out correctly by scaling up 1 inch to 2 inches on the other end, as you can see above. There was a problem, however, with the three other holes not being placed correctly. The 3rd hole should have read 3 inches, but instead I got 3 5/8 inches. hole #4 was 4 7/16, and hole #5 was 5 9/16.

I needed to make a new caliper with those three holes in different spots, and to do that I cut a slot between the three holes with this opening moved slightly forward (towards hole #2.) That way I can adjust the placement of the screw to figure out the new location. Doing this, I discovered hole #3 needed to move 1mm in Jen’s diagram, hole #4 moves 3mm, and hole #5 moves 4mm. Just that tiny adjustment made a huge difference on the other end.

I made marks on the balsa strip where the new holes needed to be, and cut and shaped two new strips of balsa. Now the calipers scale correctly in measurements of 1:1 up to 1:5. Below is Jen’s diagram that I’ve marked up with red lines showing the new placements. You can print this out, and see for yourself if it works to your liking. Balsa doesn’t drill very well, so I may make a new one later out of stronger wood, like oak.

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