In the previous post on ha-ganna sharpening I started to talk about having difficulties getting a good cut with my 60 degree blade. My other blades all cut fairly well. Yet despite trying a few different sharpening techniques, and doing my best to get a really sharp edge, the 60 degree blade continued to cut poorly. So I started to think a lot about how the blade was cutting through the wood. When you use ha-ganna you are always cutting across the grain. With a cross grain cut the more you can slice through the wood with a shear cut the cleaner and easier the cut will be. Particularly with certain soft woods a shear cut can really help to get a clean slice. Imagine using a chisel to cut across endgrain. If you hold the chisel so that you are cutting perpendicular to the grain the cut takes more force and it usually less clean than if you shear across the grain with the blade at a slight angle. This is especially the case as the blade starts to get dull.
As I was thinking about all this I decided to model my blades in sketchup. I also started to search around the internet for any information I could possibly find on ha-ganna. One thing I noticed was that blades from another maker looked like they were forged at tighter angles than my own. The angle of my 60 degree blade is actually really close to 60 degrees. Several of the blades that I found online for cutting 60 degree kumiko, looked like they were forged more like 45 degrees. So I started wondering how the forged angle of the blade would affect the cutting edge geometry. If the blade is formed at a tighter angle like 45 would that still give a workable edge geometry for cutting 60 degree kumiko? And how would it compare to my current blade?
I ended up reaching out to a friend who had ordered some ha-ganna from Japan a while back. He ordered his set from a different supplier so I was curious if his blades differed from mine. He sent me some photos of his blades and sure enough the blade he has for cutting 60 degree kumiko is forged at a much tighter angle, around 44 degrees. Thanks for the help Shaun Davis!
In contrast, here is the forged angle of my 60 degree blade
Here I measured the angle of the sharpening stone I’m using for this blade, and you can see it’s right around 61 degrees.
Both Shaun’s and my blades’ were sold as 60 degree ha-ganna. Yet clearly the angle they were forged at is drastically different.
From here I decided to model the blades in Sketchup to get an idea for how the forged angle would affect the edge geometry of the blade. Below is an image from sketchup showing a model of my current 60 degree ha-ganna blade next to one with a forged angle of 45 degrees like Shaun’s. I set both at the same angle as they would be if they were in dai (plane block), and both have bevels that produce a 60 degree cut in a imaginary piece of wood.
Here is the blade forged at 60 degrees, producing a cut at 60 degrees.
And here is a blade like Shaun’s, forged at 45 degrees but producing a cut at 60 degrees.
The edge geometry of each blade as it would slice through an imaginary piece of wood, is completely different. The blade on the left (forged at 60 degrees) has a strong vertical attack. While the blade on the right (forged at 45 degrees) has much more of a shearing cut action.
It seems to me that the shearing cut would produce a much better cut. Particularly since it’s going to slice the fibers at the surface of the wood first, helping prevent tearing of fibers. It’s my guess that this is the main culprit behind my own difficulties getting a clean cut with my 60 degree ha-ganna blade. I’ve seen numerous videos of people cutting really soft wood like sugi (Japanese cedar) using ha-ganna with beautiful, clean results. Yet no matter how much I tried I couldn’t achieve anything like that using my 60 degree blade.
My general takeaway from all this is that it’s best for a blade to be forged at a tighter angle than the desired cutting angle. I could certainly be wrong, but clearly the difference between my blades and Shaun’s are quite large. Also the effect on cutting ability and edge geometry is clearly affected by what kind of angle the blade is forged at.
To test this theory a bit more I modelled my 60 degree blade with an edge geometry for cutting 45 degree kumiko. (45 degree kumiko ha-ganna leave a 90 degree cut in the wood). Below on the right is the 60 degree blade producing a 60 degree cut. On the left is the same 60 degree blade producing a 90 degree cut. The edge geometry is completely different.
Here’s the 6o degree blade, producing a 60 degree cut.
And here is the 60 degree blade producing a 45 degree cut.
Finally I couldn’t help but put this to the test a bit. So I took my 60 degree blade and reshaped the blade to produce a 90 degree cut (as described above). And it worked great. It cut really smoothly, leaving no tearout or jagged grain in even really soft sugi.
Below is the modified 60 degree blade, along with the blade that I bought for cutting 45 degree kumiko pieces. Both make an actual cut of 90 degrees through the wood, but clearly the edge geometry is vastly different. (The blade sold as “for 45 degree kumiko” is forged at a 90 degree angle).
So I’m really curious how the blacksmith who made my blades decided on the angles to forge each blade. My pessimistic guess is that the blacksmith probably didn’t really know any better. Maybe the Blacksmith forged the blades at the same angle as the desired cut without thinking about the effects. I could also be completely missing something. I am far from an expert on ha-ganna and my experience is still limited, so take all this with a grain of salt.
In any case, hopefully this doesn’t come as disappointing news to those who bought blades from the same shop as me. I think these blades will probably work quite well with more tolerant woods, like basswood. But for really soft woods the edge geometry starts to become a problem. I’d be interested to hear from anyone else who has started to play around with ha-ganna, and curious what your experience has been like.
~Jon
Very interesting! I remember a similar idea about sharpening carving V chisels about nosed (right?) vs. winged (left) profiles. It makes sense to me that the nosed shape would tend lift and tear grain, while the winged would slice nicely before scooping. I saw this noted on the reference from Don’s post from part 1 on slide 82/83.
All of the irons from my set are noticeably winged, but not near as much as your re-profiled iron.
Thanks again for deep diving and posting about these. Hope all is well there!
Thanks Martin,
It’s really interesting to hear that your blades have a similar “winged” profile. I’m guessing your blades are probably forged at tighter angles than their intended cutting angle.
As for the nosed vs winged profiles, I think your totally right about the nosed profile tending to lift and tear the grain. I can’t really see much benefit to ever sharpening a ha-ganna blade or gouge with that kind of profile.
Appreciate the comment,
Hope you all is well for you too!
Re: sharpening v-gouges. The other thing in the article I referenced, is the shaping of the bevel to wrap around the outside of the ‘v’, which forms a conical shape. Then, the conical shape is reduced to become what is called a keel. On a v-gouge that shaping reduces the ‘drag’ during a cut. As I wrote before, I really like when someone else tries out my ideas before me. 😎
What supplier did your friend use for his blades? Thanks
I believe he special ordered them through a tool dealer that doesn’t regularly stock ha-ganna. I will have to ask for more details.
Thanks,
Jon
Thanks
Jon i also would be interested as to were to procure those irons
Great post! Thanks for the details.
Returning to confirm your findings. I was very fortunate to only be able to afford the 60° and 120° forged blades when I began my Ha-ganna journey. (So I never bought the 150° forged blade intended to make 15 degree cuts.) I later bought a 90° and 2 weeks ago completed my set with a 44°
The 44° is ground to cut 60° grooves; the 60°, 90° grooves; the 90°, 120°; and the 120°, 150° grooves.
Conclusions? A blade forged 30° narrower than intended groove angle is heaven!! Until I can see a master’s setup to convince me otherwise, I’m sold on this.
The 44° ground for 60° is a HUGE improvement over the initial attempt (like yours) of a 63° forged for s 60° cut. Yet, there remains an issue: at a 40° bedding angle, the “keel” of my 44° blade is just barely level (as opposed to the other blades, on which the leading cutting edge hangs lower than the trailing edge.)
A “tail dragging” level blade offers significant resistance through the cut, AND as the bevel increases from 20-25°, the “hips” of the keel begin to be wider than the material removed. This causes resistance AND lifts the blade out of the groove.
I either have to increase my bedding angle on a new dai, or grind away the fat hips to allow the blade to pass cleanly through the cut.
Thanks for sharing your insights Rob. I’ve come to the conclusion as well that the more acute angle blades for 60° grooves and above are definitely more troublesome to setup properly. It’s interesting that you’ve discovered a new issue regarding the limitation of the standard bedding angle for the 60° groove blade. I imagine increasing the bedding angle may be the only way forward but that must come with tradeoffs as well in terms of edge durability, clealiness of cut, etc. Keep us updated on your progress.
I am still dreaming of going to visit a kumiko craftsperson to get some more clarity on these questions/issues.
Id like to add my thanks to this blog. I myself am crazy in love with Japanese furniture and kumiko design. I got my self some ha-ganna planes to speed up my proces. And immediately had problems understanding the way these planes are suppose to be maintained. This is truly the one and only good information on the internet available on this topic. Only thing better world be to hop on a plain to Japan and vind a kumiko artist that speaks English. Thank you! i love your design. And i strive to be as good as you in the future.