Spring Loaded Caliper
by ianjohnson, published
I added a version that has a built in filament guide and a wider mounting plate.
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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/...
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.
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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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