Heh, comments before I even had a chance to explain what I was doing (or trying to do).
If you watch the first closeup video, you can see me giving an initial markup to see where it was bearing, and indicating to see how deep the lowest spot was.
The pits were about 0.0035” deep, but the rest of the plate seemed pretty flat to begin with. I didn't bother putting the whole thing on my granite plate to indicate for real, but just locally indicating over the surface it appeared the rest of the plate was within about a thou or so of flat.
As Rich said, three and half thou is a lot, so I was trying to do very heavy roughing: no gaps between the lines, long strokes, and no blue ups until you’ve scraped off all the yellow. I could and (probably should) have gone even heavier but I did want to show how things were progressing. It's not easy doing and showing at the same time.
While I could have gone slightly longer, I lengthened my stroke to about a half inch before I started and left it there throughout the entire session. I don’t like going much longer than that because it’s so easy to catch an edge.
In the beginning of the second closeup video (plate scrape 2) you see me give the bearing areas some extra attention, then covering the entire surface from both directions. It’s easier to read the markup after you create the checkerboard pattern at least once (you get points in the markup, not smears).
The first “real” markup was at about 7s in. It showed pretty much the same contour but I was more confident in the result.
Next I started what Rich referred to as “blind” “paint scraping”. From 7s to 12s in the video you see me trying to go slow enough that my strokes are touching. I did crosses rather than circles because I find it easier to go straight down rather than creating holes (I’m trying to get the entire surface down to the bottom of those small pits, but since it started out relatively flat I wanted to scrape as evenly as possible). It’s “blind” because I do multiple passes just scraping off all the yellow without blueing up.
I had the the scraper cranked up to full speed, but my old biax has a steel casing and weighs about twice as much as the modern ones. In my defense, it’s HARD to go slow enough to keep the scrapes touching and still keep things even and scrape straight down.
At 12s in you see me checking my progress. The pits were now only 0.002” deep so I was almost halfway there. Then I did the same blind process again and got it within about a thou (you can see me checking at 19s).
Only then did I stop attacking the entire surface and start going after areas of blue only, still with heavy crosses. Now I’m removing all the areas of blue (black) ink only, not the entire surface.
I called it a day shortly afterward as I was still pretty tired from last week, and both the plate and the scraper are pretty dang heavy. With only a shallow hole remaining in the middle I should be able to complete the roughing and get to 5 PPI over the entire surface with only another couple passes.
Regarding the stones: they removed the burrs quickly for me which is all I really was asking of them. I accidentally gave away my last small Cherry brand Japanese oilstone at the class without realizing it. I’ve got a broken small wedge shaped one, but on a 10x15 surface the larger stones seemed easier and quicker to me. Anyway, not sure what the concern is with my stones. I saw and felt burrs before stoning and didn't after — what more would you want?
I aim to get the entire surface looking like Chris’s angle plate, but the larger surface will likely take (considerably) longer. I’ve only spent a few hours roughing so far.
Lastly, I’ve got reasonably thick skin, but I’d love to see someone else publish their scraping progress for public criticism. It’s hardly fair that I'm the only one with my posterior in the wind. <laugh>
