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Richard Gillespie
07-27-2010, 10:43 AM
Tried to do a favor for my son and sharpen some of his hand saws. He works as a restoration contractor and is very busy. Busted my you know what trying to sharpen the first one of his saws I picked up. Re-read my notes on sharpening and set to work. Though it has been several years since I last sharpened a hand saw, I didn't remember it being that hard to do. 2 Hours later and 4 ruined files I quit. Took the saw out in the sunshine and immediately realized that the teeth were fire hardened by their discoloration.

Are there files on the market that will handle them? Or is this intended to be either a disposable saw or one that requires being sent out to have new teeth cut?

David Weaver
07-27-2010, 10:49 AM
Induction hardened, intended to be disposable.

Diamond feather files will cut them, but diamond files don't usually have crisp very delicate profiles to do it. I'm still waiting to shed laziness and try a diamond feather file on a disposable saw (I have dull disposables and some diamond feather files), but I haven't done so yet so I can't comment on practicality.

I'm not aware of widely available cheap (like where the price makes sense against a disposable saw or saw blade) and good feather files, either, especially not something that matches saw taper (though if you have a saw that has disposable blades, the induction hardened teeth are probably a pattern that would warrant a very delicate feather profile, anyway.

Schtoo? Schtoo does have some reasonably priced diamond feather files if you want to try. I haven't seen them anywhere else, though maybe some of the importers here are starting to pick them up?

General recommendation would be to pitch it, though, and replace it with a sharpenable saw if you want one that you can sharpen.

george wilson
07-27-2010, 10:52 AM
A thin saw blade will probably tear the diamonds off of a diamond file. It would be better if you could rig up a jig to accurately grind a very small amount of metal from each tooth of the saw.

If you do try a diamond file,file only with very light pressure to avoid tearing the diamonds out of their matrix.

Could you use an India slipstone? That would cut the steel,and not get worn out.

Bob Strawn
07-27-2010, 3:21 PM
As far as hardness goes, diamonds are to the hardest steel, as the hardest steel is to sheet rock.

You can use pressure and burnish diamonds into steel. This will make a diamond sharpener. So if you have a knife with a single bevel, you can rub fine diamond grit into the blade like you would flatten the back of a plane blade. Then you can use the knife as a file to sharpen with. This will sharpen disposable Japanese saw blades, carbide table saw blades, whatever.
I use 0 to 0.25 micron diamond grit for this purpose.

Taking dings out or straightening a Disposable Japanese Saw Blade is another thing entirely, I have not had anything like consistent success with those operations. I have gotten close to success only to totally mess it up before I finished.

Bob

george wilson
07-27-2010, 3:46 PM
You can't easily press diamonds into HARDENED steel,or soft steel too easily. The best thing to use is copper if you want a lap. Spread your diamond dust on a hardened steel surface. Lay the lap over the oiled dust,and gently hammer the lap into the diamond dust. Just impress the 1 side of the lap with diamond dust.

I doubt that a lap would cut enough to sharpen a saw very effectively,though.

The best thing to do is just rig up a way to grind the tips of the teeth(Japanese type saw,I take it?). You don't have to grind much off at all,and shouldn't.

Personally,I think Japanese type teeth are the most trouble of any type teeth to maintain. You've got 2 angles to mess with,the gullets and the tips. Sharpening the tips soon makes the teeth short.

Also,those tall,thin teeth seem like they would be more easily broken off than Western teeth. I have seen Japanese toothed saws with a few broken off teeth,too.

David Weaver
07-27-2010, 4:03 PM
bob, how did you attempt to sharpen them? My assumption would be that you'd work on the secondary facet of the japanese teeth maybe once or twice and then still throw the saw away.

I haven't tried it on an impulse hardened blade yet, but I'm curious as to whether or not it will work. Obviously, teeth aren't going to be like a perfect jointed height, but that probably won't matter because they hardly have any set and they should be deadly sharp - and whatever gets removed isn't going to be enough to make teeth like show up on a saw that's been sharpened 10 times without jointing.

Dave Burnard
07-27-2010, 6:23 PM
If the teeth are dull enough to require resharpening or replacement, rather than disposing of the blade, you can retemper the hardness of the teeth down to a range where they are resharpenable. The blades are usually a simple carbon steel like 1095 so a dark blue temper color (around 550F though, so you can't use a regular oven) should get you down to about RC58-59. Pale blue, around 600F would drop it to RC57 or so.

Dave

Richard Gillespie
07-27-2010, 9:56 PM
If the teeth are dull enough to require resharpening or replacement, rather than disposing of the blade, you can retemper the hardness of the teeth down to a range where they are resharpenable. The blades are usually a simple carbon steel like 1095 so a dark blue temper color (around 550F though, so you can't use a regular oven) should get you down to about RC58-59. Pale blue, around 600F would drop it to RC57 or so.

Dave

Thanks Dave for the suggestion. If I'm able to figure out how to rig an oven that will achieve 550 degrees how long must it hold it and do I then allow the blade and oven to cool as one?

george wilson
07-27-2010, 10:36 PM
You may very well warp your blade beyond hope heating it. Best grind a little off each tip.

Bob Strawn
07-28-2010, 3:07 AM
You can't easily press diamonds into HARDENED steel,or soft steel too easily. The best thing to use is copper if you want a lap. Spread your diamond dust on a hardened steel surface. Lay the lap over the oiled dust,and gently hammer the lap into the diamond dust. Just impress the 1 side of the lap with diamond dust.

I regularly use diamond bedded in steel for sharpening.

http://battlering.com/woodworking/images/Sharpening/Sized/Sharpening%20Setup%20used%202.jpg

Copper works better for larger grits, but I prefer steel for the finer grits. As far a bedding goes, if you put fresh monocrystalline diamond grit on a steel plate and then polish the back of a chisel on that plate, you will in fact bed the diamonds into both the soft metal plate and the hardened tool steel chisel.


bob, how did you attempt to sharpen them? My assumption would be that you'd work on the secondary facet of the japanese teeth maybe once or twice and then still throw the saw away.


The first time I worked on a Japanese Saw, I was fixing drift on it. I lay a sheet of paper so it half way covered a sharpening stone, and then I lay the body of the saw on the paper with the teeth extending on the stone. Then I stoned the saw. This used a normal, but inexpensive stone, and it did a wonderful job on the impulse hardened teeth. It did however damage the surface of the stone.

Later when my favorite, a Razorsaw 650 was loosing it's bite, I decided before replacing the blade with one of the spares I got for it, I would try touching up the edge. I put it in a saw vise. I lay my honing surface flat against the surface until I was confident I was flat on the surface. Then I drew the hone towards me. There are several facets on a Japanese saw, and a lot of teeth, but this process takes less time than you think it would. The results were well worth the effort. That blade now has several teeth missing, and I am still using it. I love, absolutely love the Razorsaw 650.

I doubt I will be happy with the blade after I sharpen it much more. It is not so much that I am changing the angles or mangling the form, since I am not removing all that much steel. Instead as the saw wears deeper it will probably be beyond my meger skills to fix it. I have five spare blades for it, because I never want to be without one.

Bob

Dave Burnard
07-28-2010, 3:37 PM
You may very well warp your blade beyond hope heating it. Best grind a little off each tip.

That's a reasonable alternative, essentially jointing the blade with a grinder. May have to experiment with how much needs to be removed to reach/soften the body of the teeth enough to cut them with a file.

I haven't seen warping when I've retempered, but it certainly could happen, especially with uneven heat. If warping does occur, then you'll then have a timely opportunity to learn the art of saw straightening and to acquire a few more tools: saw anvil, straightening hammers, tensioning hammers, etc. ;)

If the blade is otherwise headed to the dustbin, there isn't much to lose in trying various approaches. If it's a typical japanese made replaceable blade pullsaw, the bodies of the blades are supposed to be in the mid-low RC50's which would make a decent saw as is.

How long to temper - doesn't really need much soak time considering the thinness of saw blades. Uniform heat is more important, but that's hard to come by in this temperature range without dedicated oven-like equipment.

Richard Gillespie
07-29-2010, 6:41 AM
That's a reasonable alternative, essentially jointing the blade with a grinder. May have to experiment with how much needs to be removed to reach/soften the body of the teeth enough to cut them with a file.

I haven't seen warping when I've retempered, but it certainly could happen, especially with uneven heat. If warping does occur, then you'll then have a timely opportunity to learn the art of saw straightening and to acquire a few more tools: saw anvil, straightening hammers, tensioning hammers, etc. ;)

If the blade is otherwise headed to the dustbin, there isn't much to lose in trying various approaches. If it's a typical japanese made replaceable blade pullsaw, the bodies of the blades are supposed to be in the mid-low RC50's which would make a decent saw as is.

How long to temper - doesn't really need much soak time considering the thinness of saw blades. Uniform heat is more important, but that's hard to come by in this temperature range without dedicated oven-like equipment.
The saw involved is a traditional western style with wood handle. It appears that only the teeth were induction heated. Worse case for me is to grind off the teeth and cut new ones. That in itself is a daunting prospect. I've got too much other work to do and that would have to take a back seat.

I'll return the saw to my son and he can do with it what he wants. At present, it is somewhat sharper then when I started.

David Weaver
07-29-2010, 7:38 AM
I regularly use diamond bedded in steel for sharpening.

http://battlering.com/woodworking/images/Sharpening/Sized/Sharpening%20Setup%20used%202.jpg

Copper works better for larger grits, but I prefer steel for the finer grits. As far a bedding goes, if you put fresh monocrystalline diamond grit on a steel plate and then polish the back of a chisel on that plate, you will in fact bed the diamonds into both the soft metal plate and the hardened tool steel chisel.



The first time I worked on a Japanese Saw, I was fixing drift on it. I lay a sheet of paper so it half way covered a sharpening stone, and then I lay the body of the saw on the paper with the teeth extending on the stone. Then I stoned the saw. This used a normal, but inexpensive stone, and it did a wonderful job on the impulse hardened teeth. It did however damage the surface of the stone.

Later when my favorite, a Razorsaw 650 was loosing it's bite, I decided before replacing the blade with one of the spares I got for it, I would try touching up the edge. I put it in a saw vise. I lay my honing surface flat against the surface until I was confident I was flat on the surface. Then I drew the hone towards me. There are several facets on a Japanese saw, and a lot of teeth, but this process takes less time than you think it would. The results were well worth the effort. That blade now has several teeth missing, and I am still using it. I love, absolutely love the Razorsaw 650.

I doubt I will be happy with the blade after I sharpen it much more. It is not so much that I am changing the angles or mangling the form, since I am not removing all that much steel. Instead as the saw wears deeper it will probably be beyond my meger skills to fix it. I have five spare blades for it, because I never want to be without one.

Bob

Bob - I have stoned most of my finer-work saws, too, just as you have mentioned, with either a diamond hone or a ceramic stone. I, too, have been very pleased with the "cheap" saws. They leave an amazingly nice surface for the price. I haven't sharpened any saws but the ones without induction hardened teeth, though, but thanks for attesting that it works fine.

As to the OP's statement of taking the teeth off and filing the plate, I would be kind of surprised to find that the plate could be filed into decent teeth - it's probably too soft. Better off giving the saw back to the mentioned son, and letting him know he should find an older saw for cheap (atkins or something that doesn't get the same press as the disston saws in nice shape) and file that.

Bob Strawn
07-29-2010, 2:16 PM
As to the OP's statement of taking the teeth off and filing the plate, I would be kind of surprised to find that the plate could be filed into decent teeth - it's probably too soft. Better off giving the saw back to the mentioned son, and letting him know he should find an older saw for cheap (atkins or something that doesn't get the same press as the disston saws in nice shape) and file that.

Oddly, while I too think this has a reasonable chance of failure, I would still try it. Stainless steel, saw steel and spring steel often can make great scrapers. A top quality scraper requires the ability to work harden to produce a good burr. If the base material is able to work harden by burnishing, then it has the classic characteristics of a good saw material and the teeth are likely to harden during the process of filing.

Since the steel being used as a base has been chosen for it's ability to impulse harden in combination with some rust resistance and good spring qualities, there is no motive for the companies to select an alloy or temper that will work harden. As a general quality however most of these saw bodies make great scrapers. This in turn means that they will make great saws. The edge will not last as long as the impulse hardened edge, but that will just mean you get more practice sharpening saws. Our end of the world needs more good metates anyway.

Bob