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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.

Plane hand scraping.jpg
After you have used a stone, or even after a few laps it's not flat anymore.
It will develop a low spot in the middle or a high spot, depending on how you hone.
If you just go up ad down the stone you will get a low spot. If you use sweeping rolling x strokes, and rotate the stone, you will end up with a convex stone.
I prefer a slight high spot over a low spot.
This is a coticule I lapped after only one use. As you can see the pencle marks will get removed from the sentre first, so no low spot.
If you know how to take advantage of this shape you don't even need to lap it again.
I have hand scraped a few cast iron beds and it is a tedious chore. Other than the word flat, I am not sure I find it very relevant to my razor hones however since it does not create a flat surface at all, only a flat bearing surface for something else to glide very flat upon. As you noted, the divots holding oil. There are different kinds of “flat” and surface contact matters with the razors more than bearing surface flat. Otherwise those old slightly crowned razor hones would have never worked 100+ years ago. You should try hand scraping - it will give you a great appreciation for the pursuit of machining flats.
Yea, I am sure folks that really make things flat, like those that re-surface/calibrate and certify surface reference plates flat, are “amused” at the obsession of some for honing stone “flatness” and shade tree Mark I eyeball Certification/calibration “tools” used, to Certify/proclaim a honing stone “Dead Flat”, as if it mattered to hone a razor.

Really, we are more concerned with Surface Roughness, not flatness. Yes, the easiest way to make a stone uniformly smooth is to flatten it, but you can, and lord knows millions have, for hundreds of years, honed razors to a high level of keeness and comfort with stones that were not dead flat, but smooth.

As others have proven, you can hone razors to a high level of keeness with stones that are intentionally convexed, and clearly not flat. It is up to you and your face to decide if that is better and worth the effort, same goes for Lapping Arks Dead Flat.


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As a side note, I’ve seen images of people using a Japanese ‘sen’ or scraper on engine blocks. I actually have one and chatted with Alex Gilmore about it and he said that it was probably made for scraping metal.

In Japan, they use a lot of convex hones, but not for sharpening, sharpening stones are flat. Convex hones are used on the ura (concave) side of swords, knives, scissors, etc. I need to build a form to smooth mine out, the surface is pretty worn
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"Scraping" metal for flatness (usually on the carrier surfaces of machine tools) isn't related at all to flattening hones. I don't use edged tools to flatten my stones, and ways scrapers are edged.

It's not just the flatness that counts, the main purpose is to have oil retention to prevent wear. Otherwise they would be polished.....
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