Spring Loaded Caliper

by ianjohnson, published

Spring Loaded Caliper by ianjohnson Jun 7, 2013
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A mount to add bearings and a spring to a caliper so you can measure filament as it runs between the bearings. There is a mounting arm so you can add it to a filament winder, or set it up between two spools to check the size or deviation of some filament. It works best if you have some good guidance for the filament before and after the caliper, because the filament will tend to slip off the bearings to one side or the other.


I added a version that has a built in filament guide and a wider mounting plate.


In addition to the printed parts you will need:

4" Pittsburgh caliper from Harbor Freight
2 608 bearings
2 M8 x 20 bolts
2 M8 Nuts
4 small sharp screws
1 small spring, about 1.5" long.

The part with the mounting arm goes on the fixed jaw of the caliper, and the smaller part goes on the sliding part. There are small starter holes for the screws which hold the spring.

You can try to drill through the steel caliper jaws, but I found that loading it up with superglue works fine. Just make sure that the bearings stay flat and aligned with each other. If one ends up cocked at a little bit of an angle, it will push the filament out to one side and the measurement will change as the filament moves from one side of the bearing to another.

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Bummer. I printed this and I have the exact same calliper that's in the pictures, yet it doesn't even come close to fitting into the slots on the printed part. What gives?

There's a small door (top, ridged) on the caliper that allows the values to be read from a microcontroller such as Arduino.

Here's some info on how to hook it up: https://sites.google.com/site/marthalprojects/home/arduino/arduino-reads-digital-caliperhttps://sites.google.com/site/...

You read my mind! How about having feedback to the filament extrusion setup?

That measurement would need to be made right at the nozzle where the plastic is still melted. I'm working on using a linear CCD and a laser to measure it, but so far I can't get a reading from the sensor into the Arduino. I'm a little stumped because the wiring and code seem to be correct.

The laser/sensor would feed a PID routine that would adjust a stepper/puller to keep the diameter as close to constant as possible coming out of the nozzle. The plastic at that point would be larger than 1.75 because it wouldn't be stretched out yet. The spring loaded caliper behind the puller would tell you if you hit the target.

I've read a bit about interfacing the caliper with the arduino, but I don't understand most of it yet. The value there would be generating a graph of the diameter over the course of the batch. I don't know anything about programming on the PC side of things, I'm still learning how to get the Arduino to do what I want.