An Ultimate Hand Scraped Surface Plate

That's what I hear, too. I think I would want to have a scraped straight edge to use along with the master level. Richard can tell you his way of doing it. Which I would trust before using a level to scrape to...
 
Two things that I observed. 1 I do not understand why they flaked the surface plate. Surface plates are normally scraped to 40 points per square inch or better and 70 percent contact. Also 4 tenths on a surface plate is like having the grand canyon on your plate. Plates are normally scraped to less than 1 tenth.
2 Machine ways are normally only flaked on surfaces that point down so they do not collect dirt and grime in the flakes that point up like we are seeing on the bridge port. That dirt and grime that is collected turns into lapping compound and speeds the wear on the machine.
 
So anyone want to hazard a guess how you might scrape plate to 90 millionths without a larger plate?
 
I watched a video where the they were rebuilding a large granite plate, it's on YouTube, I do remember them doing quadrants, and checking with surface gauges until all areas were the same
 
oil flaking is used for deeper oil pockets.
the oil pockets trap oil and use the oil as a bearing surface to reduce wear.
this process works off of the hydraulic principle that a liquid can't be compressed, it becomes a bearing surface.
oil is not likely to be put on this surface plate, nor will it be likely that the base will be incorporated into another machine.
my thought is that the flaking is purely decorative, and it's not serving it's intended purpose of trapping oil.
another purpose ,i suppose, is to look really cool-
that they nailed!
Yes, correct about the decorative scraping, it is quite superficial so far as depth is concerned I can see that it is done with the Biax flaker at a low angle; if a higher angle is used, it cuts way deeper and much narrower; I have seen this technique used by rebuilders for oil flaking the undersides of sliding elements with the re scrape of the exposed surfaces lightly flaked for decoration. I find it hard not to do the decorative stuff on my own work, but I do my best to not get carried away with it.
 
Thanks for sharing that, Jack. That is an awesome chunk of iron!

Was 4-tenths a typo, or did you mean 4 ten-thousandths?
Well, let's see. Scraped within 4/10" would be just less than 1/2". I think that would be kind of rough for a surface plate.
 
One would have to assume and imagine that it is 0.0004" over the entire 48"x96" area.
That's pretty good over that area. And who knows the method used in measurement.
For inspection grade you would want 0.0001"FIM
Toolroom grade would be 0.0002"
Those are tight numbers from the Starrett Spec, there are other specs out there that are looser.
 
How would you even scrape something that large? What would you use as a reference? Enlighten me please!

Surely you just pick it up and rub it on the other 8x4 foot surface plate you have blued up and go from their, errrrr yeah i see what ur saying :)

Stuart
 
Those are pretty loose specs from starrett, and 4 tenths is equal to 400 millionths, my new Standridge grade A inspection plate is accurate to .000050 or 50 millionths, grade AA lab plates are 25 millionths, or .000025 my plate is said to repeat to 25 millionths, the double a repeats to 17 millionths.
Another thing to note is that you can only expect a part you scrape to the surface plate to be half as accurate as the plates accuracy, in my case my tested parts would probably calibrate to a tenth, depending on how good it am lol.
 
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