Quilting is widely known as one of the hottest hobbies around, with supermodels and buff young men falling over each other to get to their sewing machines. But did you know that it's literally hot? Since getting my thermal camera a few days ago (see previous blog post) by far the most amazing thing I've seen is this video of our quilting robot in action. It is stitching the Selenium square on a periodic table quilt (see future blog post).
What you're seeing is the sewing head (the boxy thing moving around in the upper half of the frame) putting stitches down into the fabric and batting stack near the bottom of the frame. First it futzes around for a while making small letters, then it goes much faster making big letters, and leaving a totally unmistakable glowing trail. That glow is showing the heat generated by the friction of the needle against the fabric and thick batting, which persists for 5-10 seconds, long enough to see the shape of whole letters. You can tell that there's no visible-light contribution to the image (i.e. you're not seeing the thread at all) because towards the end of the video the early parts are completely invisible. You are seeing heat and only heat.
I really had no idea that there would be that much localized heat generated simply by stitching! Quantitatively, immediately after stitching the fabric seems to be about 10F (5C) degrees hotter than the surrounding fabric.
For reference, here is a normal visible-light video, framed about the same, of the next square (bromine) being stitched.