Upgrading the printhead. 

I've been thinking about how to best improve the printing speed. This is where having AI as a sounding board is helpful, and its how I use it. The purpose of this project, and any of my projects, is to give me a task and allow me to learn by doing and its not the end product, entirely. 

In my past projects one of the difficulties is that I had no one to ask questions of. Its very difficult in an esoteric project to find someone else who's tickled by the particular niche I'm interested in and here I've found asking an AI to be helpful even if its just allowing me to come up with the answer by forming the quesiton.

I digress, right now the printer's DMax (darkest print) takes around 3 seconds of UV exposure. This makes printing .... very slow. But I knew that, its cyanotype (later Van Dykes), and you know that going in, but if I want to scale this to larger prints and smaller pixel sizes, the 3 seconds means days for large prints. So I went over my problem with Gemini and learned a few things.

FIrst, I was putting the LEDs 15mm from the surface because I thought that would cut on any fringing. I guess that's a common misconception, AI said to move it 5mm away. Then I was noodling about the width of the printhead. Right now its 100mm, enough for 4 UV LEDs mounted on star heatsinks. What if I made my own heatsink? Quick look at JLPCB showed Aluminum PCBs are about as cheap as normal PCBs. Ok, now I just need to buy loose LEDs. 

Looking at Amazon I couldn't find the LEDs I've been using by themselves. So I looked at DigiKey, whoa... I found 380nm LEDs with a 30 degree AOV for like $5 each. Right now I've been using 120 degree AOV LEDs. I've tested some lenses to focus those down, but I don't think its reasonable to get the accuracy I need from 3D Printed parts and cheap optics. I figured in the end, loses due to cheap lenses (<$100 ea) and other things it probably would even out. But 30mm? I just need to move the LEDs closer. 

So I turn to Gemini, I gave it the specs on both the LEDs I've been using and the new one and asked, with the new one and moving it to 5mm away, given the old needed 3 secs, what is the rough new exposure? 

0.3ms ... milliseconds.  

The LEDs came in a couple of days ago and I replaced a star LED with the new one, and blasted a new sheet with it. I kept the LED roughly 5mm away from it, and used 4.4V, (down from 5V) so the LED drew .7A, so ~ 70% of full power. At 1/2 second, it looked like it bleached the cyanotype away. So, now I wait for the aluminum PCBs, at the worst, I can use the old printhead and just replace those LEDs with the new one, and print a new 5mm distance.