"Machine Tool Reconditioning" is a good book, but pretty expensive if all you want to do is learn basic scraping technique. I think Lindsay Publications has done a reprint about scraping that's a lot cheaper and will give you the basic idea.
Here's a summary, sort of:
Grind the teeth off the end of an old flat file (one about 5/8" wide), back an inch or so, and grind the end to a slight convex radius, perpendicular up and down. Stone the end to a good finish, keeping square corners top and bottom. That's your scraping tool.
Say you want to scrape a cast-iron angle plate. Get some Dykem Hi-Spot Blue or similar (a small tube will last you a LONG time). Take a tiny dab on your finger and rub it onto the surface of the angle plate you want to check, until there's a uniform very thin blue coating. Place that surface on your granite surface plate (or other flat reference surface), and slide it back and forth a couple of inches. Pick it up and look. You will see shiny spots where there was contact. Put the angle plate in a vise or similar, and with your scraping tool, scrape off the shiny spots. Rub the blue back over the scraped areas (you probably won't need to add more blue yet, just rub what's already on the surface back over the spots), and repeat the slide-on-the-surface-plate routine. Looks to see where the shiny spots are. Scrape 'em off. Repeat. And repeat. And repeat.... Eventually you'll be getting shiny spots all over the surface. Depending on how far you want to go, you can get more and more of them, closer and closer together. If you can get about 30 per square inch, over the entire surface, you have done very well and it's "enough."
The process is very meditative. It also takes forever, and because it's so slow it's difficult to screw it up too badly before you notice.
That's just doing a single flat plane. Things get more "interesting" when you want to get two surfaces perpendicular to each other, or scrape a dovetail way, or any of a number of other things. When things get "big," of course, you have to start bringing the reference surface to the work instead of the other way around, and sometimes you want to put the blue on the reference plate and look for blue spots on the work, and no end of other variations.
The first time you do this, you will also discover that you have been made a member of the Royal Order of the Blue Finger, as that Dykem spotting blue will attach itself to your skin with a persistance that will astound you. Denatured alcohol cuts it as well as anything.
[This message has been edited by SGW (edited 10-30-2001).]
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