Sunday, March 23, 2014

3D Printed Dial Calipers

3D printing initially interested me because of its ability to create physical parts very quickly with nearly any geometry. By the time I had access to a 3D printer the ability to print virtually any shape had already been well proven and had even become common place. I was then introduced to the idea that multiple parts could be printed together, assembled, and captured. This may seem like a new concept but it is merely a new way of looking at 3D printing. The printer doesn't care how many pieces its printing, or even if they are connected.

I had seen adjustable wrenches printed already assembled. In the same fashion, I designed a c-clamp to try my hand at this concept. The camp worked perfectly. So then the question became "What's next?"

Dial Calipers. Yes. That sounded more than complicated enough with its gears, dials, and half dozen moving parts. I guess the irony of 3D printing a precision measurement tool with, what is normally considered, an imprecise manufacturing method was just too good to resist. But just to clear, 3D printing accuracy can range from +/-0.001" to +/-0.015 or more depending on the printer. Its typically not as bad as most people think... But it can be.

This dial caliper was designed to open to 4" with 9 different moving pieces that would all be printed together, already assembled. It would have a working thumb wheel, inside/outside jaws and a depth gauge. I also included a cam lock for the dial so the 'zero' position could be adjusted. Since this would be 3D printed I didn't see any reason to put the graduations below 0.005". In hindsight, graduations down to 0.0025" wouldn't have been completely pointless.

While cleaning away the support material I had my doubts as to if this would even work. It took a bit of work to free up all the various moving pieces but they all came free.

Fresh from cleaning, I went to show the calipers to one of my friends. He looked at me with half confusion and half pity with a look that said "...why did you do this?.." Then we had a little conversion about how the calipers would be horrifically inaccurate which ended with him handing me a random piece of steel rod stock he had been machining. He asked me to measure it. I zeroed the calipers, measured the diameter, and read off the number: 1.997". He then measured it with a proper set of Starrett digital calipers: 1.9975". He just looked at me and said "How did you do that?" Admittedly, I was a bit lucky there. Further testing showed accuracies in the +/-0.0025" were more common.

I want to be clear that this is just a proof of concept and is not in anyway intended as some functional production model. There are gaps between all the moving parts on the order of 0.01". The dial has 0.05" of backlash due to slop in the gear train. The plastic (actually, resin) that its printed out of is wildly temperature sensitive.

Accepting these facts, its a pretty cool device. Everything works as intended, its no bigger than normal calipers, and it looks cool. Every time I see this I'm reminded how steampunk it looks. Maybe someday I'll make a version out of stainless steel and brass.

STL files on Thingiverse.


  1. These 3D printed tools are terrific! Would you be interested in having them featured on the Stratasys blog? (They are a great example of the prototypes possible with Objet PolyJet technology.) Please be in touch via the Stratasys Facebook page:
    --Kate (from the Stratasys social media team)