Japanese blade "tapping out" disaster

[David Wong]

To conclude this thread...

While grinding the plane blade down, I uncovered a defect (or two) in the blade. As I ground the blade down near my scribe line, I noticed a black smudge on the ground part of the blade. I assumed it was just metal filings and water, as I just quenched the blade. I made another pass and found the black spots still there. On closer inspection, they are voids in the hard layer of steel. I am making the assumption that these voids right at the base of the crack line, caused the fracture.



I was able to recover the blade and tap out the ura. This blade was very difficult to tap, and I had to hammer dangerously low on the soft layer of the bevel to eek out barely 1mm of flat. I somewhat forced the process by excessive flattening of the back, so the ura is not very attractive. In future, I will switch to a more pointed hammer, as Wilbur suggested.

[jamie shard]

Very interesting, thanks for posting those images!

[george wilson]

Just goes to show that metal can be defective even on expensive tools. Especially if they are forge welded. Heating high carbon steel up to sparkling white hot,very near the melting point to get it to weld is tricky business. The higher the carbon,the trickier as it burns up worse. It is hard to get high carbon to weld to low carbon(or wrought iron). Their welding temps are different. We have expert smiths in Williamsburg. They don't like to forge weld steel over 1080. Your blade is much higher carbon.

I have had to repair laminated blades on good American made antique chisels at the museum. One such was not even hardened,and the cutting edge curled back like a fish hook,seen from the side view. Another just plain came loose from the iron body of the chisel. I forget how many "high quality" old tools I had to repair or harden,etc.

I honestly cannot recommend tapping any tool with a hard lamination on a rusty,irregular surface. That is just asking for trouble. And I do not have to be a user of Japanese tools to know that.

Any way you can get a refund on that defective iron?

[Winton Applegate]

For any one interested in the process of hand forging high quality steel blades (including making the steel from iron and carbon in an authentic duplication of an ancient furnace) (and modern laboratory authentication of the quality of the steel ) be sure to check out the Nova episode here.
Maybe overly dramatic . . . maybe not. I enjoyed the show.

[Winton Applegate]

For what it's worth, using the end grain of a wood block for an "anvil" is a little more forgiving. Probably takes longer, but the "shock" seems less dangerous.

Toshio Odate in the book I posted photos of agrees with you. That was his practice and recommendation as well.

[Wilbur Pan]

To conclude this thread...

While grinding the plane blade down, I uncovered a defect (or two) in the blade. As I ground the blade down near my scribe line, I noticed a black smudge on the ground part of the blade. I assumed it was just metal filings and water, as I just quenched the blade. I made another pass and found the black spots still there. On closer inspection, they are voids in the hard layer of steel. I am making the assumption that these voids right at the base of the crack line, caused the fracture.

Hi David,

Where did you get your plane?

[David Wong]

Hi Wilber,

I got it from a shop in Japan.

http://www2.odn.ne.jp/mandaraya/kashin.html

[Greg Portland]

For any one interested in the process of hand forging high quality steel blades (including making the steel from iron and carbon in an authentic duplication of an ancient furnace) (and modern laboratory authentication of the quality of the steel ) be sure to check out the Nova episode here.
Maybe overly dramatic . . . maybe not. I enjoyed the show.

It's now available on Netflix for those who subscribe...

[jamie shard]

Toshio Odate in the book I posted photos of agrees with you. That was his practice and recommendation as well.

Thanks, I've been trying to convince him for a while. I'm glad he approves.

note: this statement in no way implies any actual conversation has occurred between the Mr. Shard and Mr. Odate. Further, no japanese plane blades were harmed in the writing of this post.

[george wilson]

I had thought that the Viking sword maker was doing everything the right way,always only forging at a red hot temperature. That,and very high carbon steel was the secret of the ancient Wootz(Damascus) steel. When Europeans forged,they heated their steel to a much higher temperature,causing their carbides to melt and re form as large crystals. Forging at red heat caused the unmelted carbides to be crushed into tiny crystals,but was nearly as hard as forging cold steel for the blacksmith. It is these very small carbides in a soft matrix that give Wootz steel its ability to take a sharp edge and still be tough. Then,he heated the sword white hot to weld in his lettering(which did not really appear to be truly up to welding temp,as it was not sparkling hot),and would have ruined the carbide structure.

Then,the quench was way too small. The oil was boiling,and he took the blade out while it was still really hot. The quench should be large enough to not heat appreciably when an object is quenched. I am not sure how he imparted a spring temper into the sword,unless the hot withdrawal from the too small quench was supposed to automatically make a spring temper. It is not the usual way to go about hardening and tempering.

I am not sure the original sword had inlaid letters. They looked just chiseled out and left that way. If the Vikings had inlaid letters made of lower carbon steel,or wrought iron,they would not have corroded away as fast as the blade itself,and would still have been seen in the blade.

I don't know. Maybe there are things that are standard practice in sword making that are not employed in ordinary work.

[Pat Barry]

To conclude this thread...
While grinding the plane blade down, I uncovered a defect (or two) in the blade. As I ground the blade down near my scribe line, I noticed a black smudge on the ground part of the blade. I assumed it was just metal filings and water, as I just quenched the blade. I made another pass and found the black spots still there. On closer inspection, they are voids in the hard layer of steel. I am making the assumption that these voids right at the base of the crack line, caused the fracture.

I would say this is a chicken and egg situation. My thought is the defect you found when grinding the blade is most likely due to the crack caused by hammering. Highly doubt that the steel just happened to have voids there before hand. My 2 cents obviously.

[Wilbur Pan]

Hi Wilber,

I got it from a shop in Japan.

http://www2.odn.ne.jp/mandaraya/kashin.html

Did/do they ship to the U.S?

I would say this is a chicken and egg situation. My thought is the defect you found when grinding the blade is most likely due to the crack caused by hammering. Highly doubt that the steel just happened to have voids there before hand. My 2 cents obviously.

That is a good point. I’ve cracked one blade when tapping it out, to the point where I popped the chip completely out. I remember it leaving a jagged surface much like in David’s picture above.

Also, if those inclusions were there, by the location in the photo some sort of defect should be noticeable on the back of the plane blade.

[Wilbur Pan]

For any one interested in the process of hand forging high quality steel blades (including making the steel from iron and carbon in an authentic duplication of an ancient furnace) (and modern laboratory authentication of the quality of the steel ) be sure to check out the Nova episode here.

Another Nova episode worth watching is here: http://www.pbs.org/wgbh/nova/ancient...rai-sword.html

[David Wong]

Did/do they ship to the U.S?



That is a good point. I’ve cracked one blade when tapping it out, to the point where I popped the chip completely out. I remember it leaving a jagged surface much like in David’s picture above.

Also, if those inclusions were there, by the location in the photo some sort of defect should be noticeable on the back of the plane blade.

The shop will ship to the US using EMS.

I tend to think the voids were present in the blade before my cracking it. You can see that the walls of the voids are black oxidized. I do not recall whether they were visible on the back of the blade.

[Stanley Covington]

Everyone makes this mistake. From your picture, clearly the problem is improper support.

The important thing to keep in mind is that the purpose of the hammer strikes is not to bend the blade, but rather to deform the jigane (softer, low carbon steel layer). Each individual hammer strike deforms a little area of the jigane. After many blows, the accumulated deformation causes the jigane to expand. But at the same time, the high-carbon steel layer refuses to deform and expand, and the resulting stresses cause the blade to curve.

To effectively deform the jigane without cracking the HC steel layer, the specific spot on the bevel your hammer strikes each time must be supported on your rounded metal anvil surface and aligned PRECISELY where the hammer would strike the anvil if the blade was not there. This is absolutely critical. The commercial jig shown in the previous post ensures this precise alignment. Remember, you don't want to support the blade across its width on the anvil, but only where the hammer blow will fall. I imagine tapping a ball bearing welded to the anvil with my hammer. Some practice is helpful.

Make a hardwood practice piece approximately the same dimensions as your plane blade, including a bevel. Hold it lightly between thumb and forefinger, and rest it against the anvil, indexing against your forefinger so that the spot you intend to strike is in full contact, and not offset. If you have aligned the practice piece properly, and swing your hammer precisely, the hammer strike will not cause the piece to flip, or twist, or dance a jig, but it will just sit there while all the hammer's force goes directly through the wood, crushes some fibers on its way, and then flows into the anvil. It's a very stable feeling.

Use a rounded metal anvil surface. The corner of a vise rounded over with a file works well, but I have used a 5lb sledge as an anvil in a pinch. A bit of paper glued to the anvil makes for a softer surface that might help your control. Use a lightweight hammer with a smallish face: A tack hammer, or sawset hammer works well. A domed-face hammer won't.

I don't have time to talk about the strike pattern, other than to say most of your strikes should be focused on the center two thirds of the bevel, and well away from the HC steel cutting edge. Also, there is no point in striking either end of the bevel's width. It helps to draw an oval "strike zone" on the bevel using a marking pen to help focus your hammer strikes.

Get right on top of the anvil, and orient your wrist against your body to help maintain the length of the hammer's arc in perfect alignment with the strike point on the anvil so you don't inadvertently extend the hammer too far and chip a big piece out of the blade. Strike with the bottom edge of the hammer making little crescent indentations. Move the blade a little with every strike. Remember, you want the stresses distributed fairly evenly, so your strikes must be distributed in a regular pattern. Don't try to develop a rhythm yet: Make every strike precisely and deliberately, pausing between strikes. Speed will come with lots of practice. Check your progress frequently.

I hope this helps.

Stan