J tool questions

[Vincent Tai]

Kuro Ura - ura finishes in general; Preferences? I really like a Kuro finish anything personally. A perfect unblemished Kuro ura makes me very happy. I do see a lot of the older plane blades (by reputable smiths) where the clay mixture wasn't as fine tuned and as a little flakes off in the fire the Kuro finish turns mottled. I quite like this but is this at all acceptable these days? A rougher sen scraped version you see in a few of the older blades where some lines are deeper and the ura is untouched by abrasives ( Abrasives knock off the ridges in sen lines and serve to blend/polish the lines) also really catches my eye these days. I am perfectly happy with the grindstone and scotchbrite finish on most blades. Very clean and logical and decently pretty. A polished sen finish I like more on Nomi. Lots of options in this category but any sort of musings would be very much appreciated.

For those with genuine wrought iron backed stuff, how much softer is it? any problems with cracks or stuff? Cracks as in the variability in the material, those striations and some lines where the material isn’t fused to itself.

Nomi neck to ferrule area; does any have a major preference for how much the neck matches up the the ferrule or how off it is? I see that most are a little off, and some smiths grind to blend that area. I don't like the look of the latter. For those with the higher end chisels, how matched up is that area? Any Kuro-finished necks that matched up very well or perfectly with the ferrule? Jessica if you see this; the Ichihiros you used, do you remember what finish they had? The Kuro-oxide or the super refined and polished steel? Do you remember at all how well the necks blended into the ferrules? I always think that Ichihiro's must have some of the most perfectly mating neck to ferrule examples possible; for the file and polished finished versions that is.

These questions are a bit odd but I have my reasons for them.

Thanks,

Vincent

[Brian Holcombe]

Unless I’m misunderstanding your question; I prefer zero sori. I want the perimeter (uraba and ashi) flat as possible. If there is sori I tap out until their is none.

Personally I like the kuro ura best, Kunikei does these amazing black ura that really are attractive.

Filed neck but not necessarily a filed ferrule.

[Vincent Tai]

Hi Brian, I meant Sori the other way. Most Japanese planes I’ve encountered if you put a straightedge on the Ashi you can see there is a small curve, it is dished slightly. The smiths have the blades curved a little to counteract the bending towards jigane side during hardening and usually a little is retained. In older blades sometimes the blades get relaxed and then start going back to the curve that the smith originally created. I have a couple NOS from Takeo Nakano and Shoichiro Tanaka where I see this prominently.
And I agree about zero sori, that would be perfect. But I haven't met a blade with that yet, though I know you have from the images of your Kanna in your write up about ura-dashi! I need to buy some newer blades.... The reason I asked such a weird question is it seems to me that many many many blades are slightly curved and I just wanted to get a gist on people's thoughts. Also I want to make kannas. I had the wild thoughts of advantageous Sori late last night. Combine that with me accustomed to old blades with quite a bit of curve....

I had quenched a Kanna I made last night and it was my first time heat treating one. I was quite nervous since I could only guess at how much curve I should've put in to compensate for the movement towards jigane. I had thought I would end up with a bit of curve left but I've just checked and amazingly its near dead on flat. unfortunately the clay mixture I used wasn't very well tuned and the ura is not a smooth Kuro-oxide but a patchy and lighter one. To rub it in there is quite a velvety and nice Kuro-oxide that formed above the hagane.

Also I wrote this quite late and the question of preferences of sori is faulty in the end. Sorry. I'll delete it.

By the way Brian I'm not directing this deluge of info at you particularly but I thought I would give plenty of context for others.

In another forum's thread: Chris Hall; "The curvature along the ura length provides a certain amount of pre-tension to the blade when it is in position to cut. While I am not entirely sure of the reasons, my thinking goes like this:

1) since the edge of the blade is subject to forces from the wood trying to deflect the blade edge back, this pre-tensioning puts the blade in a slightly stretched/tensioned condition, so it will be more resistant to deflecting. Kind of like an arm-wrestler getting into a pre-tensed position as he/she takes the grip with an opponent. How's that for a creative analogy?

2) similarly, the subblade is crowned along its length too, and is put under tension against the main blade as it wedges between the main blade and the pin. The curvature/camber in the main blade helps resist the push from the sub blade.

3) I suspect the curve along the length helps hold the blade in place, esp. when going without the sub-blade. "

In yet another forum's thread:

So (back in the good old days when he had time to use a forum): "Check how much the steel is bent with the small rule. If the steel is miraculously not bent at all, then you don’t need to read this. Just do uraoshi as usual. But it is usually bent because of the difference in tension between the iron and the steel. The older the blade the more bent."
He goes on to expand on using a Kanna ban to gain a small flat area which can be used on the stones.

The topic of the sori pops up soon after;

Q2: So when we refit an old blade into an old dai, how much of the curvature should be removed before refitting the dai? In your drawings it only looks like you tried to remove a portion of the curvature. For some blades the curvature is small enough (only .002inch/.05mm or so) that removing it all is no problem - or it's so small that it should just be left alone. However on other blades the curvature is large enough (0.5 - 1mm) that removing all of the curvature at once would significantly alter the ura-suki, could make the hagane very thin at the edge, and noticeably change the taper of the blade so it may become loose in the dai, perhaps requiring a new dai. What would you suggest?

So: "Yes, this is a good "helping question" for further understanding my above article. Thank you!

The intention of uraoshi is not to make the ura flat in order to match the dai, but to gain enough flat surface so that you can maintain the flat contact between the steel and the stone. (Someone help me out with the English here!!) If there is only 5mm of flat area, it is very difficult to keep it apressed onto the stone flat, so you'd need about at least 2cm. The amount depends on how curved the steel is."

DBurnard; It does sound as though you (like me) don't think the hagane curvature is left/put there on purpose to aid in securing the the blade in the dai -
So: "No, it is definitely not intentional. This is not my opinion but a fact. Many of the most expensive sugu-zukai planes have absolutely flat back. The block maker spends hours making it flat and grinding the hollow again, if it is lost too much. So you can see why kuro-ura (the back that has the oxide film intact) which is flat is so special."

Okay lots of info here; So is dead on here. Chris's thoughts were what sparked my musings of advantages of sori last night when I remembered that thread. I had forgotten about So's words until this morning. I still think Chris could be onto a few things but that the ideal is still zero sori.
I guess to rephrase; outside of the perfect world of zero sori; what is your preference? The problem with this question is it becomes apparent quite quickly (if you aren't slow like me) that the less curve the better. I got caught up in thinking about the advantages of sori when my head wasn't on straight I guess. Sorry to waste anyone's time. The other fit and finish preference questions are still reasonable though.

[Brian Holcombe]

Given the choice between a sori situation in which the edge of the blade is up away from the flat surface (not contacting) and one in which it is first contact, I would take the one in which it is contacting. It's easier to manage, but has some disadvantages.

If the edge is not contacting than the ura-dashi is what will place it in contact, very careful ura-dashi work will make for a very fine uraba. I do the majority of this work using a granite plate and checking solution so that the actual sharpening only takes place using a 13k stone on the ura-side. This makes for a neat ura and how neat it is entirely depends on how careful the ura-dashi work is done.

The alternate scenario where the uraba contacts first along the extreme edge is easy to setup and maintain but is not so visually appealing because the back does not become entirely flat until it has worn to the point where contact can be made all the way around. It has no negative effect on performance.

I can't speak from experience with respect to applied tension, that makes good sense to me and I want to say that it's probably happening in my planes more often than not but I've not been able to setup a situation in which I can compare with and without in order to know the effects result.

[Vincent Tai]

Thanks Brian, Very helpful as always.

Vince.