Making a Small Caliper

A Toolmaker's Bag of Tricks

A Toolmaker's Bag of Tricks

Dick Young decribes how he made a small caliper

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A Toolmaker's Bag of Tricks

By Dick Young:

On October 26, 1941 I was joined in marriage to my wife, DeLoris. We settled into an apartment in Moorhead, MN and I was employed by a local machine shop geared to serve the general public. On December 7, 1941 the bombing of Pearl Harbor shook the whole world.

The owner of the shop where I worked, Wes Withnell, recognized that there was a lack of qualified machinists available to serve the war effort and thought it wise to convert his shop into a training center for aspiring machine operators.

Though I was still quite young, early training at home and a position at the Grand Forks Foundry helped prepare me to achieve a position as shop foreman. Part of the job required that I teach practical machining techniques to the trainees.

One young man was learning to sharpen tools and tested them by machining down a fairly large piece of shafting. The work-piece was not for a particular use, but only to practice on. Knowing the shaft was of a high quality material, I stopped him from machining it completely away. I decided to slice the shaft into slabs to be used for other purposes and for some odd reason had a desire to make a slide caliper.

Though I could easily purchase one, the thought of making a caliper stuck in my mind. With no other direct purpose for the slabs I salvaged, I decided to proceed with my plans.

My first task was to machine the material to a uniform thickness, but thin enough so the tool would not be bulky in my pocket. The job of cutting the basic outside shape of the caliper was a relatively simple process and went quickly. Cutting the V-shape of the slide in the main body of the caliper, and the slide itself proved to be a bit more of a challenge. The slide needed to move freely but remain in alignment with the body for the full length of the bearing area. Any “slop”, even very slight, may allow the jaws to move out of parallel and give false measurements. Fortunately my care in machining paid off and the caliper had a tight, but freely gliding action. I also included a cam-action thumb lock to maintain a dimension I may check.

The real challenge came in laying out and marking the measuring lines. Those who have used pocket slide calipers know they are capable of inside and outside measuring. To make sure my caliper was effective for both, I had to take great care in laying out the lines in respect to the jaw configuration.

I scribed the lines in the standard design of a ruler. Each inch was divided into 1/32” segments, and the lines varied in length from halves, quarters, eighths, sixteenths and thirty-seconds of an inch for easy identification. To make the lines I held the work piece in a shaper vice and made a stop block to measure the placement of each line using an inside micrometer. The scribing tool had to be extremely sharp to achieve the thinnest lines possible for accurate measuring. Since the machines I had to use were manual, (no CNC in those days) and every movement of the machine was directed by me, I had plenty of chances to make a mistake that could ruin the work I had previously done.

Thankfully, everything came out right and the caliper was very accurate. It has been one of my most regularly used tools since 1941. At the time of this writing, this caliper has been in existence for 66 years, and has been used in all the shops I have worked in over my life. Though it shows some wear from years of use, it still is a functional tool.

To the tool and die maker, the ability to make special tools adds greatly to our bag of tricks.

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"Making response to customers a top priority since 1947"