Advice needed on what to do ...

[arvidj]

I think this might be the appropriate place to ask for advice on this subject. If not, let me know and well see about getting it moved.

As part of a Craig's List "take everything that is in the box or nothing" purchase I acquired what appear to be two cast iron 14 x 10 surface plates. One of the two has a cross hatched surface on one side, with the other three surfaces being flat. Even though they were wrapped in plastic wrap they seem to have have collected a little surface rust.

Before I do anything with them I was hoping to get some advice and\or a plan of attack to bring these back to a reasonable life. I have both a 12 x 18 x 3 and a 9 x 12 x 2 ubiquitous Grade B granite surface plate but do not have any scraping tools. I will be honest in that I am not looking to create AA grade plates out of them, just something a home hobbyist would find acceptable.

Any suggestions ... even starting with something as simple as "What should I do to just clean them up?" and "After you get them clean perform these test to assess how good\bad they might be." I am assuming that any planning beyond that would be based purely on speculation of condition, but feel free to "best case scenario and worst case scenario" if you have the time.




Thanks,
Arvid

 

[4GSR]

The plate with the grooves is a lapping plate. Not really considered a surface plate even though may have started out surfaced ground to a degree of flatness. The other one maybe some kind of "machined" flat. probably ground flat at one time or another. I would suggest covering the plate with mineral sprits or paint thinner and take a oil stone and hone the surface of the plate to remove any dings positive metal. Wipe clean it and your surface plate and lay the honed surface face down on your granite plate. Give it a little movement in a circular motion to "ring" it in. This should tell you if it fits snug to the granite plate or just rock around a little. Take a 0.001" feeler and run around all for edges to see if it goes under the edges any if at all. If not, you can pretty much say it is fairly flat to your surface plate. To check it closer, you need to get some Dykem hi-spot blue and check for a higher degree of flatness. Ken

 

[Richard King]

Ken is right on. They look like plates designed for bench work or granite plate lapping.. The non grove one looks like the type of plate they use to charge with diamond grit for lapping granite plates or they put sand paper on to flatten parts off a machine. Turn those plates over and take another picture. By turning them over you will show us the ribbed bottom. I suspect the have only 2 ribs and not several that are seen on a surface plate used to scrape machines. Those non ribbed plates will distort when flipped over. You might get them to hold .001" but not much better. Several years ago I did an experiment with them and discovered those non ripped plates will distort or bent to fit a concave or convex when turned over making it impossible scrape anything precision. Rich