Here is an interesting video on flattening a cast iron hand plane by hand scraping. (Flat to 0.0002" - Stanley No.5 Jackplane hand scraped...) Richard Moore - Engineering at Home
Hand scraping is a process to “flatten” metal/steel usually large machinery where the parts are too big to be put on a surface grinder and where the surfaces are bearing surfaces and will be rubbing against other flat steel surfaces and need to hold microscopic bit of oil for lubrication.
Scraping is a series of scrape marks to flatten metal and leaving micro divots that will hold oil for lubrication.
The poster freely admits, that the project in the video is way overkill for “flattening” the sole of the plane. He is a metal worker and is scraping for practice and because he can.
But it does dramatically demonstrate why we need to flatten/smooth new stones. Look at the screen shot of the sole of the plane. The blue spots are the flat spots and the grey middle is a concave area, (Red Arrow).
Imagine that is your stone, The flat spots are smooth, and the middle is not. As the stone wears the bevel and edge of a razor honed on the stone will contact the rough low spots in the middle.
For soft waterstones, it is important to get a new stone smooth and flat, most are not, then to smooth and remove swarf with use, refresh lap.
For hard naturals it is critical to smooth/flatten a new stone, so you are not honing on the rough middle. Hard stones are difficult to lap flat and often a rough middle remains. Once flatten smooth, it may never need flattening again in its lifetime, when use for finishing razors.
It is not critical that the stones are “dead flat”, but smooth and flat-ish. The razor bevel, (bearing surface) is only a millimeter or two wide, the spine much less. There is no harm in making a stone Dead Flat, (few really are) but it is a lot of work, and even if you were to make a stone Dead Flat, after the first use, it is no longer flat, all stones wear.
Hand scraping is a process to “flatten” metal/steel usually large machinery where the parts are too big to be put on a surface grinder and where the surfaces are bearing surfaces and will be rubbing against other flat steel surfaces and need to hold microscopic bit of oil for lubrication.
Scraping is a series of scrape marks to flatten metal and leaving micro divots that will hold oil for lubrication.
The poster freely admits, that the project in the video is way overkill for “flattening” the sole of the plane. He is a metal worker and is scraping for practice and because he can.
But it does dramatically demonstrate why we need to flatten/smooth new stones. Look at the screen shot of the sole of the plane. The blue spots are the flat spots and the grey middle is a concave area, (Red Arrow).
Imagine that is your stone, The flat spots are smooth, and the middle is not. As the stone wears the bevel and edge of a razor honed on the stone will contact the rough low spots in the middle.
For soft waterstones, it is important to get a new stone smooth and flat, most are not, then to smooth and remove swarf with use, refresh lap.
For hard naturals it is critical to smooth/flatten a new stone, so you are not honing on the rough middle. Hard stones are difficult to lap flat and often a rough middle remains. Once flatten smooth, it may never need flattening again in its lifetime, when use for finishing razors.
It is not critical that the stones are “dead flat”, but smooth and flat-ish. The razor bevel, (bearing surface) is only a millimeter or two wide, the spine much less. There is no harm in making a stone Dead Flat, (few really are) but it is a lot of work, and even if you were to make a stone Dead Flat, after the first use, it is no longer flat, all stones wear.
