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Doug Sanders

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I have a ryoba (Japanese style saw with two sides of cutting teeth- for the uninitiated) which has gotten dull over the past few years. Wanting to resharpen it, I was told by a helpful customer service person at a mail-order tool company that, judging from the price I paid for it, it was made from impulse-hardened metal and could not be resharpened.

 

What is impulse hardening? Why can't it be resharpened? Should I buy a new replacement blade or invest in a saw with better metal? I enjoy tool upkeep as a relaxing aspect of my overall craft and work, so filing a saw sharp seems rewarding.

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can I sharpen it with one of those Japanese files for Japanese saws? Apparently there is a 'beginner' file and an 'advanced file' (in the Lee Valley catalog. Japan Woodworker just sells one sort although they have a few lengths depending on the length of the saw).

 

:) need more info- sorry... :)

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I would check the hardness with a file you have on hand first. If it is too hard, it will ruin your expensive file and skate right across the steel. I doubt this is the case, but better safe than sorry. A fresh file should just bite into the steel, but not cut it easily.

 

I picked up a really cheap version of this type of saw at Home Depot recently and it works well for what I am doing. I could check the teeth on my saw for comparison.

 

The Japanese file would be a nice tool to own.

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can I sharpen it with one of those Japanese files for Japanese saws?  Apparently there is a 'beginner' file and an 'advanced file' (in the Lee Valley catalog.  Japan Woodworker just sells one sort  although they have a few lengths depending on the length of the saw).

 

:) need more info- sorry... :)

 

I doubt you can do much with a normal file. Impulse hardening basically does a flash heating by electric current and very fast cooling of the teeth -- resulting in a very hard surface (basically the maximum untempered hardness reachable by the steel used). However the hardened region normally penetrates somewhat less than half the thickness of the metal (for toughness - otherwise the teeth would be very brittle). The steel of the body of the saw is likely to be fairly soft - usually no more than a mild spring temper.

 

Unfortunately, most diamond hones I've seen that would be suitable would cost as much or more than the saw.

 

-- Dwight

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You are right about the impulse hardening, another throw away tool. I check the Marples I got at Home Depot and it is defnitely not impulse hardened. I think the saw cost $20 and was too cheap to pass up. So far it has held up well.

 

Highland Hardware sells a thin diamond file, but again it would be cheaper to buy a new saw.

 

Save up for one of the Japanese saws and then get the file. I have a video of a Japanese custom saw maker. Incredible work. The blade is scraped by hand and the teeth are cut and set by hand.

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I think I'm beginning to get it. Impulse hardening is harder than 'traditional' forging. Therefore a file is needed of sufficient type to file hard metal. Japanese files good for traditional Japanese saws.

 

Although my saw is of a Japanese make (Kagokoro is brand, I think) it's mass produced. I think I'll save pennies and buy a better quality one, along with a Japanese file.

 

I have a Dozuki also, much better quality, and it cuts like a charm.

 

Interestingly, the cheap Ryoba I have has actually had teeth chip and break when cutting very hard woods (boxwood, pink ivory wood)- especially when I've been aggressive with it :) . Seems to confirm what has been said about brittle teeth.

 

-Doug

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  • 9 months later...

Late in the day, I wanted to add a couple of things to this issue.

 

With Japanese saws (ryobas or otherwise) there are two general flavours:

the machine made, mass produced variety, and the handmade variety.

I'll make an attempt to describe the differences between the two, in terms of benefits and shortcomings.

 

PRICE

The machine-made (MM) ones are cheap. VERY cheap. Normally a replacement blade for them costs around $15-25 and lasta good while.

The handmade (HM) ones are a good deal more expensive. I would expect to pay at least $100 for an entry level handmade saw.

 

LIFESPAN

Both MM and HM ones will last a while before they require attention. In the case of MM, 'attention' means throwing away the blade and getting a replacement. This adds to the the cost, but in the longrun the MM will probably cost you less than a good HM. The reason for this is that the HM ones will require sharpening every once in a while. This will, of course depend on the amount of use they get, but i expect anything between 50-80 hrs of sawing. If you are a carpenter that is not a lot but for most people that's plenty for a few years :) My HM saws have yet to dull and I have had them for a year now I believe. In that time, I have gone through one replaceable blade, though admittedly, my MM saw gets a lot more action; it's my workhorse while the HM ones are for finishing and accurate cuts. Which brings us to:

 

PHYSICAL CHARACTERISTICS

A wee difficult to explain in detail without more visual aids, but generally speaking the blade of a Japanese saw (nokogiri) consists of three parts. The tang, which is the part of the blade that goes in the handle, the teeth and the middle part or body. In this pic these are red, green and uncoloured, respectively. This is where all the differences are more evident. A MM nokogiri is stamped from a sheet of steel. Simple, easy, fast, and cheap. This is unhardened steel. The teeth and only the teeth are then impulse hardened. As others have described, this means hardened by electric pulses (which can be seen as a series of little lines running along the length of the blade close to the teeth. You want to harden the teeth, whilst keeping the blade (and especially the tang) more flexible to take in the forces. HM blades are made of two pieces generally (a welding line is usually visible and desirable with HM blades)... One piece for the tang and one for the rest of the blade (which is hardened). After a series of treatments whereby the blade-maker scrapes the metal and gives it its shape. This is a time consuming process requiring a lot of training and skill, hence the higher cost. All worth it in my opinion, BUT for certain things and certain places. OK, I'll try to be more brief... The two processes result in a significantly different blade anatomy in a few ways:

The MM nokogiri are of uniform thickness. The HM ones are thinner in the middle part of the blade and wider in the teeth section. The latter is more desirable and results in smoother cuts, less binding, a more flexible blade and a much thinner kerf (because the MM ones have to be a certain thickness for the machines to work properly). The teeth in HM nokogiri are cut and filed by hand a VERY skilled process called metate (also the name of the person that perfroms it). The ones in MM are stamped.

 

Now, all these things being said, the MM ones are great for most reasons. Like I said before, they make great workhorses, are manufactured very well and used with care will last a long time for a miniature carver. Choose one with the thinnest blade (0.4 mm is good I think). Be aware of its performance and change the blade whenever you start noticing a decline.

 

MAINTENANCE

With the MM saws, maintenance invloves a trip to the garbage can for your old blade and a trip to the store for you. The maintenance of a HM nokogiri is very different. Their teeth can be reset and resharpened by a trained metate. The saw usually comes back so nefreshed it takes you by surprise. The process isn't cheap, but it really brings the saw to its full potential. I know a lot of woodworkers that send their newly-bought HM saws for the appropriate tensioning and tuning. I must stress this is a difficult process and not one for the beginner. It takes years to learn properly and needs a keen eye. As a beginner the best thing you can hope for is a slight improvement of a dull blade and the more usual one is the damaging of it. I don't mean to be discouraging, but it takes practice to learn and if you can afford to practice on expensive saws then it CAN be learned. I depend on my saws too much to abuse them by personally sharpening :D

 

Now, based on all this, my personal attitude towards choosing between HM and MM nokogiri is as follows: they are not the same thing, I use them for different reasons and I like them both. My MM saw is what I pick up by habit. If I need something cut, my hand goes there directly. It's always available and handy, it cuts well and fast and I make sure I don't abuse it by dropping it or hitting it or bending the teeth or the blade. When I am making precision joinery I will consider using my thinner HM nokogiri, but even then not always. A HM saw means I am generally in a different mindset. Calmer, more focused, more precise... More tuned. The energy you receive from a well-made HM nokogiri is unparalleled.

 

OK OK, I am almost done (I am trying to avoid work, that's why this is so long :o ). My advice in brief is: Use the MM saws for everyday tasks. Replace the blade (thinnest possible and designated for hardwoods) often and you'll have a trusty companion. Buy a HM one as a treat and experience the difference. If so inclined, buy a feather file and play with filing some teeth. Hard to say which ones are more expendable, that's up to you. Setting can be done with a very small hammer and the special tool for setting nokogiri teeth (quite cheap I think). I can send you more links with resources if you need. Alternatively, buy a HM saw, use it for most things (with care) and once a year (or less often depending on use) send it to a metate for tuning. It WILL come back better :) .

 

Here's my 2.36 Yen. I hope I didn't bore you and you found some of this helpful. A very nice page is: http://www.daikudojo.org/ShopTalk/index.htm. The articles describe the saws in more detail and the metate (Grable is the only metate I know of in the US and he is very good).

 

Ouch... did I start 2 hours ago? B)

Back to saving the world.

 

-t

post-126-1131138093.jpg

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Thanks for the explanation. Much better understood now. In the end (that last email of mine was almost a year ago) I purchased a machine-made blade and am using it less aggressively. I noticed that the saw pretty much cuts at the same rate whether or not you're leaning into it B) or not.

 

May your kerf always be in line...

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May your kerf always be in line...

 

hehe, I seem to remember seeing that before.

It's a Japanese saying isn't it?

 

As for leaning, you're right, it's a lot better all around NOT to lean on the blade.

Let the teeth do their thing. Loosely push and pull on the handle for the smoothest cut. I also tend to count my strokes. It helps my pesky mind from overthinking the process and let's my hands and saw do the job. B)

 

-t

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