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I bought a Japanese plane a few years ago, and didn't really spend a lot of time researching before I started using and sharpening it. Now that I have a little more time for woodworking again, I unpacked the plane and noticed that the flat part of the back (ura?) of the plane blade is very large compared to 'model' photos online. Additionally, when I try to flatten the back, the left-most and right-most part of the edge doesn't get sharpened, as the back must be a bit convex?

Can I fix these two issues somehow? While googling I found some references to 'tapping out' the blade but I'm not quite sure how to proceed or whether it can even fix my problem. Ideally I'd like a link to a comprehensive guide or similar.

Here's a photo of my blade (ignore the sharpie lines). The large and uneven flat part on the back of my blade

This is the back of a 'model' blade (https://brianholcombewoodworker.com). enter image description here

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  • Hi welcome to SE. The concavity part is easy, you just need to sharpen that out. The cause is the thing you need to look at most. Are you sharpening on waterstones? If so there's a good likelihood one or more of them need flattening (waterstones can go out of flat quickly, some very quickly).
    – Graphus
    Sep 8, 2018 at 17:07

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the flat part of the back (ura?) of the plane blade is very large compared to 'model' photos online.

This isn't really an issue, or at least in practice it doesn't have to be. The purpose of the hollow, the urasuki, as you know is to reduce the time and effort required in working the flat of the iron during sharpening (and in Japanese irons the steel on this part of the iron is generally very hard indeed, so it takes quite some effort to abrade).

When newly formed the hollow is generally exactly as shown in the 'model' example in the Question, perfectly symmetrical and uniform. But with use the iron has to be specifically maintained for the urasuki to remain this way and (perhaps surprisingly) this was not always done.

Numerous vintage and antique irons show ura that are anything but textbook after regular use and wear:

Vintage Japanese irons, non-textbook urasuki

This topic is covered in this post on Wilbur Pan's site, The historic record.

As you can see the page includes a photo of Toshio Odate who it would appear was not particularly concerned by this, so I don't think you need to be either.

Additionally, when I try to flatten the back, the left-most and right-most part of the edge doesn't get sharpened, as the back must be a bit convex?

If the extreme left and right of the edge isn't being abraded I think it's telling you that your sharpening media (or the surface that supports it) aren't dead flat and that's what you need to look at. Once it/they are dead flat as you sharpen the middle of the edge will wear away and eventually the two ends of the edges will start to be abraded again.

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  • Thanks a lot! Recently I've been flattening my (synthetic) waterstone after every usage, but it's quite possible or even likely that I didn't do this a few years ago. I'll spend some more time sharpening then, to make sure I get rid of the convexity.
    – grapher
    Sep 9, 2018 at 18:04
  • Yes if you didn't flatten regularly previously one or more of your stones would certainly have been dished to some degree, and honing on a curved surface leads to raised edges. Your stones now, being flat, are showing this up. A slightly curved edge like you have isn't always fatal if the honing surface maintains that same curvature (one reason many old European stones, which are generally much slower wearing than waterstones, are found to be dished) but obviously you need to continue to use that hone or you run into honing difficulties. It's much simpler to just keep everything flat.
    – Graphus
    Sep 10, 2018 at 11:23

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