Last post in this series was on May 21st, so I must say I've dropped the ball. It ain't over yet though! Welcome back.
In that last post from so very long ago I described dealing with issues of the fixing pin, osae-bo, being misaligned to the upper surface of the sub blade, or osae-gane. With that out of the way, the next step is to fit the main blade to the dai.
The process I use is not too different than what most other people do. Here are some of the tools I bring to bear for this process:
![]()
To the left is a specialized kote-nomi, or trowel chisel, used for cleaning up the surface of the tsutsumi, a ledge found at the mouth opening on some Japanese plane bodies. Next to it is a bottom-scraping chisel, or soko-zarai nomi, and next to that a mouth opening chisel or kuchi-kiri nomi. Then a few Japanese files which are quite handy at times. Missing from the picture is a scraping plane and thin chisels, but they'll show up later on, don't worry.
I use a mechanical pencil to mark the ura side of the plane blade:
![]()
I realize that for some, this use of a mechanical pencil represents an unacceptable deviation from 'historical practice' - - perhaps I should have ground my own ink from charcoal - - however I hope for a certain forbearance, and that we may let such transgressions slide for the time being. It seems to me if historical practice is to be our guide to what we do today then we would never have moved on from stone tools in the first place, but I do digress....
I spray a bit of camellia oil onto the ura as well, and rub it around a bit with my finger, creating a thin oily layer infused with the pencil graphite. I find this marks the bed of the plane blade more effectively than either the pencil or oil alone:
![]()
You want a thin layer of oil, just slightly damp, not dripping.
Then it is a matter of tapping the blade down so as to leave marks behind on the bed at the points of contact:
![]()
Note: with this particular plane, I am discarding the sub-blade and will be using it as a single knife plane (ichimai-ba), so the osae-bo has been removed. Even if you are keeping the sub-blade, you can optionally remove the fixing pin anyway to facilitate work on this area.
Usually when you start out with this process to marking the contact points between the blade and the dai, the points of contact obtained are fewer and not located in an even distribution across the bed. Later, as you improve the fit, the marks will become more evenly distributed. This is just like the machinist's art of scraping machine beds and ways.
The critical points of contact for the blade are the areas immediately under the osae-mizo (grooves at the sides of the bed) and the lower portion of the mouth, essentially a U-shaped area, shown in green on the drawing below:
![]()
The area that is not green on the plane bed is not critical to the fit and can be given a slight clearance. That way you can reduce the area with which you need to obtain a close fit.
Japanese plane blades are tapered in thickness as well as width. It is generally the case that as one fits the blade further and further into the dai, points of interference will arise on the sides of the blade. One doesn't want a tight fit on the sides of the grooves against the plane blade however. There needs to be room to wiggle the blade in making adjustments, and if the blade were a tight fit and the plane sat on a shelf for a while, and the humidity dropped significantly, the dai could shrink against the blade. This can make the blade quite difficult to remove, or, in extreme cases, can cause the dai to split. Flatsawn dai are obviously more vulnerable in this regard.
Back to the marks just created by tapping the blade down into place - remove the marks with the tool of choice. In the early stages you can be a bit more aggressive with the material removal, however take care not to be in any sort of hurry with this process. Fitting a blade to a dai is not one of those activities where one wants to rush to meet deadlines, be halfway through that 6-pack of cold ones, or you are in a distracted state otherwise. It's all about being methodical, patient, and observant. If you find yourself losing the wa during the work, then take a break, leave it for some other time.
I tend to favor the soko-zarai nomi for most of the fitting work:
![]()
The sides of the osae-mizo can be dealt with using slim chisels:
![]()
![]()
Whenever working near the osae-mizo, take care not to cut into the ramp surface which presses down on the blade. It needs to be kept scrupulously flat and unmarred.
As mentioned above, as you move along in the fitting process, the points of contact become more widely distributed across the bed:
![]()
You can see that the marks lower down are within a couple of millimeters of the tsutsumi ledge.
As the blade gets further and further down, you will likely run into a situation where the blade starts to press against the lowest part of the mouth and the tsutsumi, which will cause the dai to bulge in that area:
![]()
A slight bit of bulging is okay, but you don't want too much. It is possible to split the dai if the pressure there is too great, and an overly tight fit makes the plane blade harder to adjust, which, if you use a metal plane adjusting hammer, will lead to the head of the blade getting deformed from the hammer strikes. It's just like joinery - there is a 'just right' fit, and too tight or too loose a fit are undesirable outcomes.
Trouble is, it is hard to assess visually what the exact situation is down low in the mouth:
![]()
One can see that the bulge is greatest in the middle, but not much more than that. The bulge could be caused by the blade pressing against the lower part of the mouth or the upper area of the tsutsumi, hard to determine which case it is. Also, the blade fit should be getting pretty snug at this point so ascertaining the interference points by feel alone is not on the cards.
The solution I have come up with is again not echoed by hallowed tradition, unless you are a machinist, in which case this is most certainly old school: feeler gauges.
A gauge can be slipped in and the entire interface between tsutsumi and blade bevel can be inspected. To the right:
![]()
Middle:
![]()
And left:
![]()
If you find a tighter area, the adjustment can then be made to the tsutsumi. The feeler gauges will allow you to determine the degree of fit, and locate the tight spots quite precisely, even the location of the tight spots on uphill portions of the tsutsumi. If there are no points of interference found during the check, then one can conclude that the plane is tight against the bed and continue working on that area. Eventually the blade bevel will meet the tsutsumi.
For adjusting the tsutsumi, the best tool is the special-purpose kote-nomi:
![]()
After adjusting, I obtained an even 0.003" gap between the blade bevel and the tsutsumi:
![]()
Back then to fitting the blade and scraping the bed to obtain a good fit. As you get closer, you make ever finer adjustments. The last few percent of fit take the most time, so take your time, enjoy the process.
Getting closer:
![]()
Now, a few adjustments later, we are down to a 0.002" gap to the tsutsumi:
![]()
As the blade gets close to the mouth opening, you will be able to see how even the mouth opening is:
![]()
You can see that the gap is tighter in the middle of the blade. There are two possible causes for this:
I hold a thin gauge block (1/8"/3mm) on the koppa-gaeshi surface to see if I can get an idea as to how flat and straight the mouth opening is:
![]()
With the gauge pressed down to the left, a closer look shows that the mouth along the koppa-gaeshi is clearly not flat:
![]()
Needs a li'l bit of fettlin'.
I set up a paring block, carefully positioning it:
![]()
Kuchi kiri time:
![]()
I'm just clearing the bulged area in the middle and trying to leave a clean flat surface behind. A regular thin paring chisel can work fine for planes without the tsutsumi.
Afterward, we have an even gap across the mouth opening:
![]()
Now down to 0.001" all along the bevel and the blade is close to the point of emergence:
![]()
The dai shows widely distributed marks, except in the middle where I've deliberately made a little extra room:
![]()
Once the blade is at the point where it will protrude from the dai's lower surface, you will need to flatten any bulge that resulted on that lower surface. There will inevitably be some bulging from a good fit, but it should not be excessive, and this goes doubly so if you are fitting a sub-blade later on, as this blade will accentuate the press-down of the main blade against the bed. Checking the dai lower surface is performed with a straightedge, either a wooden one or a metal one which has a notch to clear the blade edge.
I use a scraping plane, dai-naoshi-ganna, to flatten the dai behind the mouth:
![]()
A wooden square can be most helpful for guiding the scraping plane near the mouth - you want to take care not to run the scraping plane blade into your plane blade.
It is possible that you'll find, once the blade is all the way down, that one of the trimmed mimi on the main blade wasn't trimmed enough in an earlier step, so you may have to go back and trim it again and resharpen. I found this with the plane shown above. You need a little space at both corners of the blade so shavings don't back up in that area.
Next time I'll look at fitting the sub-blade, osae-gane, to the main blade and dai. We're close to the end of this series. Hope you'll tune back in later. Thanks for visiting.
In that last post from so very long ago I described dealing with issues of the fixing pin, osae-bo, being misaligned to the upper surface of the sub blade, or osae-gane. With that out of the way, the next step is to fit the main blade to the dai.
The process I use is not too different than what most other people do. Here are some of the tools I bring to bear for this process:
To the left is a specialized kote-nomi, or trowel chisel, used for cleaning up the surface of the tsutsumi, a ledge found at the mouth opening on some Japanese plane bodies. Next to it is a bottom-scraping chisel, or soko-zarai nomi, and next to that a mouth opening chisel or kuchi-kiri nomi. Then a few Japanese files which are quite handy at times. Missing from the picture is a scraping plane and thin chisels, but they'll show up later on, don't worry.
I use a mechanical pencil to mark the ura side of the plane blade:
I realize that for some, this use of a mechanical pencil represents an unacceptable deviation from 'historical practice' - - perhaps I should have ground my own ink from charcoal - - however I hope for a certain forbearance, and that we may let such transgressions slide for the time being. It seems to me if historical practice is to be our guide to what we do today then we would never have moved on from stone tools in the first place, but I do digress....
I spray a bit of camellia oil onto the ura as well, and rub it around a bit with my finger, creating a thin oily layer infused with the pencil graphite. I find this marks the bed of the plane blade more effectively than either the pencil or oil alone:
You want a thin layer of oil, just slightly damp, not dripping.
Then it is a matter of tapping the blade down so as to leave marks behind on the bed at the points of contact:
Note: with this particular plane, I am discarding the sub-blade and will be using it as a single knife plane (ichimai-ba), so the osae-bo has been removed. Even if you are keeping the sub-blade, you can optionally remove the fixing pin anyway to facilitate work on this area.
Usually when you start out with this process to marking the contact points between the blade and the dai, the points of contact obtained are fewer and not located in an even distribution across the bed. Later, as you improve the fit, the marks will become more evenly distributed. This is just like the machinist's art of scraping machine beds and ways.
The critical points of contact for the blade are the areas immediately under the osae-mizo (grooves at the sides of the bed) and the lower portion of the mouth, essentially a U-shaped area, shown in green on the drawing below:
The area that is not green on the plane bed is not critical to the fit and can be given a slight clearance. That way you can reduce the area with which you need to obtain a close fit.
Japanese plane blades are tapered in thickness as well as width. It is generally the case that as one fits the blade further and further into the dai, points of interference will arise on the sides of the blade. One doesn't want a tight fit on the sides of the grooves against the plane blade however. There needs to be room to wiggle the blade in making adjustments, and if the blade were a tight fit and the plane sat on a shelf for a while, and the humidity dropped significantly, the dai could shrink against the blade. This can make the blade quite difficult to remove, or, in extreme cases, can cause the dai to split. Flatsawn dai are obviously more vulnerable in this regard.
Back to the marks just created by tapping the blade down into place - remove the marks with the tool of choice. In the early stages you can be a bit more aggressive with the material removal, however take care not to be in any sort of hurry with this process. Fitting a blade to a dai is not one of those activities where one wants to rush to meet deadlines, be halfway through that 6-pack of cold ones, or you are in a distracted state otherwise. It's all about being methodical, patient, and observant. If you find yourself losing the wa during the work, then take a break, leave it for some other time.
I tend to favor the soko-zarai nomi for most of the fitting work:
The sides of the osae-mizo can be dealt with using slim chisels:
Whenever working near the osae-mizo, take care not to cut into the ramp surface which presses down on the blade. It needs to be kept scrupulously flat and unmarred.
As mentioned above, as you move along in the fitting process, the points of contact become more widely distributed across the bed:
You can see that the marks lower down are within a couple of millimeters of the tsutsumi ledge.
As the blade gets further and further down, you will likely run into a situation where the blade starts to press against the lowest part of the mouth and the tsutsumi, which will cause the dai to bulge in that area:
A slight bit of bulging is okay, but you don't want too much. It is possible to split the dai if the pressure there is too great, and an overly tight fit makes the plane blade harder to adjust, which, if you use a metal plane adjusting hammer, will lead to the head of the blade getting deformed from the hammer strikes. It's just like joinery - there is a 'just right' fit, and too tight or too loose a fit are undesirable outcomes.
Trouble is, it is hard to assess visually what the exact situation is down low in the mouth:
One can see that the bulge is greatest in the middle, but not much more than that. The bulge could be caused by the blade pressing against the lower part of the mouth or the upper area of the tsutsumi, hard to determine which case it is. Also, the blade fit should be getting pretty snug at this point so ascertaining the interference points by feel alone is not on the cards.
The solution I have come up with is again not echoed by hallowed tradition, unless you are a machinist, in which case this is most certainly old school: feeler gauges.
A gauge can be slipped in and the entire interface between tsutsumi and blade bevel can be inspected. To the right:
Middle:
And left:
If you find a tighter area, the adjustment can then be made to the tsutsumi. The feeler gauges will allow you to determine the degree of fit, and locate the tight spots quite precisely, even the location of the tight spots on uphill portions of the tsutsumi. If there are no points of interference found during the check, then one can conclude that the plane is tight against the bed and continue working on that area. Eventually the blade bevel will meet the tsutsumi.
For adjusting the tsutsumi, the best tool is the special-purpose kote-nomi:
After adjusting, I obtained an even 0.003" gap between the blade bevel and the tsutsumi:
Back then to fitting the blade and scraping the bed to obtain a good fit. As you get closer, you make ever finer adjustments. The last few percent of fit take the most time, so take your time, enjoy the process.
Getting closer:
Now, a few adjustments later, we are down to a 0.002" gap to the tsutsumi:
As the blade gets close to the mouth opening, you will be able to see how even the mouth opening is:
You can see that the gap is tighter in the middle of the blade. There are two possible causes for this:
- the plane bed is crowned ('high centered') and pressing the blade up in that area
- the lead edge of the mouth (a surfaced called the koppa gaeshi) is not flat
I hold a thin gauge block (1/8"/3mm) on the koppa-gaeshi surface to see if I can get an idea as to how flat and straight the mouth opening is:
With the gauge pressed down to the left, a closer look shows that the mouth along the koppa-gaeshi is clearly not flat:
Needs a li'l bit of fettlin'.
I set up a paring block, carefully positioning it:
Kuchi kiri time:
I'm just clearing the bulged area in the middle and trying to leave a clean flat surface behind. A regular thin paring chisel can work fine for planes without the tsutsumi.
Afterward, we have an even gap across the mouth opening:
Now down to 0.001" all along the bevel and the blade is close to the point of emergence:
The dai shows widely distributed marks, except in the middle where I've deliberately made a little extra room:
Once the blade is at the point where it will protrude from the dai's lower surface, you will need to flatten any bulge that resulted on that lower surface. There will inevitably be some bulging from a good fit, but it should not be excessive, and this goes doubly so if you are fitting a sub-blade later on, as this blade will accentuate the press-down of the main blade against the bed. Checking the dai lower surface is performed with a straightedge, either a wooden one or a metal one which has a notch to clear the blade edge.
I use a scraping plane, dai-naoshi-ganna, to flatten the dai behind the mouth:
A wooden square can be most helpful for guiding the scraping plane near the mouth - you want to take care not to run the scraping plane blade into your plane blade.
It is possible that you'll find, once the blade is all the way down, that one of the trimmed mimi on the main blade wasn't trimmed enough in an earlier step, so you may have to go back and trim it again and resharpen. I found this with the plane shown above. You need a little space at both corners of the blade so shavings don't back up in that area.
Next time I'll look at fitting the sub-blade, osae-gane, to the main blade and dai. We're close to the end of this series. Hope you'll tune back in later. Thanks for visiting.