Japanese chisels.

[mtt.tr]

Sorry for starting yet another jap related issue but why cant you dry grind them i haven't but want to know why i cant.

 

[PeterSk]

Because pennies to pounds says that you'll overheat the edge and draw the temper of the steel

 

[mtt.tr]

Because pennies to pounds says that you'll overheat the edge and draw the temper of the steel

Why are they more likely to over heat?

 

[PeterSk]

Because they're made from carbon steel, not the HSS stuff which some tools are made from.Without delving into a whole bunch of chemistry theory, the hardness that is exhibited by the metal in tools is due to how all the atoms arrange in a nice uniform pattern. If you heat the metal up too much, those atoms move about and the metal becomes soft as the structure is lost. The temperature which counts as "too hot" varies dependent on the type of metal involved and how it's made and tempered.

A drystone grinder will remove a lot of metal from whatever you apply it to very quickly, which generates heat extremely fast. The thinner the metal at the ground edge, the faster it will heat up, so you cannot sensibly sharpen carbon steel tools on a drystone grinder as it will heat up the tool faster than you can control

 

[studders]

I thought it was because they need a flat bevel?

 

[mtt.tr]

I assume then is i keep plunging there shouldn't be an issue?

 

[studders]

Do you mean plunging in water when grinding?
Grinding will give a hollow bevel which is undesirable on Japanese chisels as far as I remember.

 

[Blister]

This may help

http://www.finewoodworking.com/ToolGuid ... x?id=28816

 

[Derek Cohen (Perth Oz)]

I would disagree with those that assert the blades of a Japanese chisel are too brittle to chop into hard wood, or that you should never hollow grind one for fear of removing the backing to the hard steel.

My Japanese chisels are there expressely for hard woods. They are my go-to chisel for chopping. (As an aside, many may point to the fact that their bench and dovetail chisels have steel hoops, so therefore they are for chopping. In my mind this is really more about the way in which Japanese chisels are used - tapped with a gennou - and that this aids precision, per se).

I also hollow grind all my Japanese chisels (as I believe another DC does), and will do so to even the Kiyohisa set that is expected to arrive in the next couple of days (there is my drive-by! ). I do use a Tormek, however, which has a 10" wheel and this (a) leaves only a shallow hollow, and (b) is unlikely to heat up the thin hard steel edge. I would not recommend a high speed grinder for most, since these may just prove to create too much heat - however, I have ground Japanese chisels in this way and not affected the temper.

Regards from Perth

Derek

 

[woodbloke]

I also hollow grind all my Japanese chisels ...
Regards from Perth

Derek

I seem to recollect Derek, in a previous conversation, that you mentioned that Jap paring chisels should have a single flat bevel at 25deg. This is so they can register from both sides (which is very useful btw) In any event, I don't grind my Jap chisels but use the full range of 3M papers from Matthew to hone a single bevel on my bench (30deg) and parers (25deg) chisels.

It doesn't take long either and like Derek I use mine on hardwood with no chipping of the hardened edge - Rob

 

[Derek Cohen (Perth Oz)]

I seem to recollect Derek, in a previous conversation, that you mentioned that Jap paring chisels should have a single flat bevel at 25deg. This is so they can register from both sides (which is very useful btw)

Hi Rob

That is substantially correct. My argument is that chisels have a coplanar face. That is, they are not sharpened with a secondary bevel. The presence of a secondary bevel makes it impossible for the chisel to register and be used bevel down (as one does when either paring in a close area or when attempting to limit the cutting action). A hollow grind offers the same registration advantages as a flat bevel as long as the microbevel is honed on the bevel face, that is, at the same angle as the hollow. Of course a hollow grind has advantages over a flat grind when it comes to sharpening.

25 degrees for paring chisels
30 degrees for chopping chisels

Regards from Perth

Derek

 

[woodbloke]

I seem to recollect Derek, in a previous conversation, that you mentioned that Jap paring chisels should have a single flat bevel at 25deg. This is so they can register from both sides (which is very useful btw)

Hi Rob

That is substantially correct. My argument is that chisels have a coplanar face. That is, they are not sharpened with a secondary bevel. The presence of a secondary bevel makes it impossible for the chisel to register and be used bevel down (as one does when either paring in a close area or when attempting to limit the cutting action). A hollow grind offers the same registration advantages as a flat bevel as long as the microbevel is honed on the bevel face, that is, at the same angle as the hollow. Of course a hollow grind has advantages over a flat grind when it comes to sharpening.

25 degrees for paring chisels
30 degrees for chopping chisels

Regards from Perth

Derek

Agreed Derek... that makes sense. Doing it that way would make the honing process faster but I find that single flat bevel doesn't take too long to hone either. As ever, horses for wotsits :lol: - Rob

 

[yetloh]

I agree that there is no problem with hollow grinding which I do on a Creusen water bath grinder but I do this only if I get a significant knick in an edge. Otherwise, I agree with Rob that there is really little point in the hollow grind; in the time taken to set it up you could have flat sharpened it.

Jim

 

[woodbloke]

Some of Matthew's 100g paper on a bit of 10mm glass removes metal fairly smartly as well :shock:..you need a decent guide to do it accurately though - Rob

 

[mtt.tr]

So if im careful on a dry high speed grinder i shouldn't have an issue same as my other tools

 

[GazPal]

So if im careful on a dry high speed grinder i shouldn't have an issue same as my other tools

Just be sure to keep quenching the blades to keep them cool and all should be well. Or you could invest in a wet stone grinder.

 

[mtt.tr]

So if im careful on a dry high speed grinder i shouldn't have an issue same as my other tools

Just be sure to keep quenching the blades to keep them cool and all should be well. Or you could invest in a wet stone grinder.

I just work out why i can grind all my other chisels but not these well im sure all will be fine

 

[GazPal]

So if im careful on a dry high speed grinder i shouldn't have an issue same as my other tools

Just be sure to keep quenching the blades to keep them cool and all should be well. Or you could invest in a wet stone grinder.

I just work out why i can grind all my other chisels but not these well im sure all will be fine

Overheat any chisel or hardened edge and you run the risk of drawing the temper or softening the edge. Treat them all the same way by keeping the edge cool during grinding there'll be no problems. :wink:

 

[studders]

Now that I've thought about it, and despite what I've read, it does make sense to hollow grind Japanese Chisels.
I can't see the point of the backs being hollow ground otherwise. If that's done to reduce the amount of removal for a flat back then doing the opposite on the bevel would negate the advantage.
Also, once honed, the edge of the bevel would be as strong as a flat grind surely? (providing the honing produced enough of a flat)

 

[dh7892]

In Toshio Odate's book, he advises against a hollow grind because of the removal of softer iron backing that supports the harder steel.


Derek has offered some credible and eloquent evidence against this and I tend to agree with him. However, the second reason that Toshio advises against the hollow grind is the re-forming the Ura is made more difficult because of the removal of the support for the steel. I have no practical experience of this so I can't comment on whether it's true or not.

I agree with Rob that paper on glass works pretty well.