RepRap Thermal Imaging

Ever since I wired up the heated build plate and extruder hot end to my RepRap, I’ve wanted to verify the thermal temperatures and heat distribution. For starters, I have used a cheap infrared thermometer, which is fine for verifying the temperatures, but not very well suited for verifying heat distribution.

Last week, I got my hands on a Fluke Ti25 Thermal Imager – perfect for getting a good look at the heat distribution!

My heat bed is a sandwich with Josef Prusa’s PCB heat bed on the bottom and a 4 mm glass plate covered in kapton on the top. My thermistor for sensing the temperature of the heat bed is taped to the bottom side of the PCB. As shown by the image below, the glass plate does a good job of evening out the heat from the PCB.

Prusa PCB Heat Bed

However, I was surprised to see how much the temperature of the kapton-covered glass surface lacks behind the temperature on the bottom side of the PCB (which, incidentally, is where my thermistor is placed). On the image above, the top is 85.8 C while the heat reflection by the bottom alu plate reads 92.8 C – nearly the same temperature sensed by my thermistor at that time. The top glass surface catches up to the bottom temperure eventually, but it takes as long as 5 minutes for it to become stable. This explains why some of my prints have had a hard time sticking to the heated build plate – it simply wasn’t warm enough, when I started the print.

J-Head MkII Nozzle

The image above is of my extruders hot end, a 0.5 mm J-head MkII (or should that be 0.4572 mm?). Again, I was quite surprised by the thermal imaging – the heater resistor goes as high as 302.3 C when heating the nozzle to 200 C! That’s quite a lot more than I would have expected – good thing I’ve used cement that can withstand 1100 C for gluing in the thermistor and resistor.


Finally, the image above is of my RAMPS 1.4, which has small EnzoTech MOS-C1 heatsinks mounted on all the Allegro A4988 stepper drivers. Notice how cool the heatsinks are – and notice how hot the PCB gets. Good thing those heatsinks were cheap…

5 thoughts on “RepRap Thermal Imaging”

  1. obs.: the hotter the fin gets, the better heat transfer is. EnzoTech MOS-C1 heatsink seems not working well. by the way, you work was great measuring heatbed temperatures!

  2. Hi Henrik,
    Stumbled across your interesting blog :-)
    When using thermal imaging you should be very careful about concluding on the absolute temperature. The measured temperature varies wildly with the emissivity constant of the material. For metal surfaces like copper the emissivity may be close to zero! Glass surfaces may be anything from transparent (measuring the temperature of the material below) to highly reflective (measuring the temperature of yourself :-)
    To measure the temperature of your heatbed, you could stick some pieces of matte 3M tape on it, which by experience increases accuracy.
    Your heatsinks are probably OK – as long the adhesive is not isolating it from the components.

  3. Hi Tommy,

    The glass surface was covered in matte kapton tape during the measurements. I have never heard about copper having a near-zero emissivity before – that could explain the odd readings of the heatsinks! Thanks.

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