360mm First time mirror grind.

[Daniel-K]

What stage are you at with your mirror Dan?

on the cerium oxide stage its been in the cupboard in bubble wrap for a 3 months cause of work, pulled it out yesterday to check it and it has a few scratch's on nothing that would bother me. struggling with a ronchi test though i have a tester and gratings but cant seem to see anything when i look through them. this was our lap till i forgot about it and left out in the garage and the cold got to it and blew a chunk off it so i had to bin it, luckily our local society have gave us some pitch to finish it off with

[Rustysplit]

Getting the right position for the test can be a bit of a fiddle. I made my tester so that it had a wide flat area around the actual grating/light source. It helped in the initial set up as you could see the reflected light spot on the face of the tester and then adjust the tester/mirror mount to get nicely aligned. If you can leave the tester in position this helps alot. I added adj feet to my mirror stand to make it easier still.

My advice would be take your time and really look at the Ronchi pattern. When you first look at them it is easy to make a quick decision that they are fine. Look again and move the tester in and out and really examine what the lines are doing. A bit of patience and honesty with yourself here pays dividends. Pay particular attention to the edge. Watch for any sign of turned down edge or turned up, correct this as soon as you see it.

[Rustysplit]

The one thing I found that made a huge difference to the performance of the lap, was the hardness of the pitch. Too hard and it sort of glides about, just right and you can feel it "suck on" to the mirror and really feel the cerium oxide working.