i think most any .5 will work. a difference of a mm or two should not matter. ugly but use hot melt to affix the lens in place. i did such for my leica. don't use super glue; it can fog the lens!!!!!
yes. many moons ago. i had a .25" square file, no heel, about an 80 degree face ! needless to say, everything i cut was a perfect disaster. in my defense, i didn't know what i was doing. then there was the "meeks book".
not sure if i ever cut that. one custom maker i worked for used repurposed blades from jrt engines. even in the annealed state were super miserable to cut
get yerself some windsor & newton china white. it comes in a tothpaste type tube. applied sparingly, it wont crack, flake, or rub off. the w/n version is the only brand i could conveniently rely on. dychem white has uses, but is a bit more tricky to deal with. jmho
my uneducated guess would be to first analyze the technique/s you're using to produce the ingot. are you using the same procedure from pour to pour? using the same procedure eliminates variables that can occur in the ingot. iv'e never done gold, but have experimented with silver, copper, and...
i like the border job. nice xcept for the corners. the scroll, uh, well,the leaf elements are a bit of overkill. yer cuttting seems fairly consistent. overall i'd give you a "b+". time at the bench-- you'll bee getting some a's
not much help . best to develop direct draw skill. saves a lot of time and reduces frustration. alternatively you can draw " gore sections", affix them, transfer and be dissatisfied. then repeat agai and again. seriously, develop direct draw skil.