There are lots of different types of calipers, but I am specifically talking about the ones used to measure wall thickness on a turned piece. This isn’t much of a problem in most bowls, because you can feel your way around, but it does become a problem on hollow forms and deep vases, where the fingers are just not long enough.

I made my first set from some plywood, and I won’t claim originality on the design. In fact, I picked up the idea from Frederick Williamson’s site.


They are simple to make. All parts are drawn onto a piece of paper, cut out the parts, glue onto plywood and cut them out with a scroll saw or jig saw. What to watch out for when designing the parts:

  1. In order to line up the tips of the calipers, one of the pieces must be split in half and “wrapped” around the other one by way of an additional part. In the picture above, it’s the lower arm.
  2. Make sure the openings for your fingers are large enough, otherwise you’ll struggle every time you use them.
  3. The joint needs to have as much surface area as possible. This will allow proper alignment and least amount of friction.

These work fine and I still use them on a regular basis, especially on smaller pieces. They do have a few shortcomings, though. Firstly they are not long enough to go into deep hollowed forms. And secondly, the shape of the arms means that there are quite a few spaces where I cannot reach, e.g. close to the opening on a hollowed form.

A bit of searching around, and I realized that the calipers offered by Axminster will do the job, but at a price. Since I have all of the required metal working tools, I made the second set also myself:


These are made from a sheet of aluminium about 4 -5mm thick. Essentially the same principles apply as above, except these are not meant to be held like scissors. These are meant to be set to a specific wall thickness and then you feel your way around to see where your walls are thicker than that. Here’s a close-up shot of the handle part:


As you can see the gap is set with the allen head screw by way of adjusting the nut. The rubber band holds the two arms together, but allows them to spread where you have thicker walls. The arms are shaped so that just about any shape can be measured.

Although they don’t deliver quantitative measurements, the do work very well. There are a few things I’d improve:

  1. Adjusting the nut is a bit fiddly. I might replace this with a bigger, custom made nut.
  2. Aluminium is quite a soft metal, and in consequence these have to be used very carefully to avoid bending the long arms, which would distort your measurement.
  3. The place where the semi-circular arm pieces are joined together is not really solid. At some point I will open this again, make some small grooves on both sides, fill it with CA glue and then stick it together, that should remove any play in this area.

Feel free to copy. If you have any improvements, I’d love to learn about them.