Archive for March 5th, 2019
That’s a staged shot with a quilt square from the top of the pile. You’d (well, Mary’d) sew along the lines, not across a finished square.
The remaining deep shadows under the foot require an LED with an imaging lens on a gooseneck; precise piecing requires feeding fabric into the needle with alignment exactly where those shadows fall.
The light levels look harsh and shadowy on the bare base:
The shadow extending leftward from the needle comes from the arm’s shadow of the rear LED bar. The hotspot specular reflections of both LED arrays aren’t quite as glaring in real life, but a matte surface finish would be better.
The needle LEDs sit on the bottom of the heatsink inside the endcap:
The COB LED PCB has a weird pink tint, perhaps due to the silicone filter passing all the yellow and blue light downward, with red light reflected into the PCB.
After one iteration, I settled on a 20 Ω 1 W ballast resistor:
It drops 3.6 V to provide 180 mA of needle LED current and dissipates 640 mW, with the LEDs burning about 1.5 W to raise the heatsink just above room temperature. The extrusion on the rear arm is pleasantly warm and the resistors seem happy enough.
Looks good to us and it’s much much much better than the feeble Juki needle LED.