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The best Western and Japanese handsaws are quite thin yet in competent hands won’t kink in a cut, and the spring steel they are made from is tempered to allow sharpening with files. They are usually taper ground in two dimensions, so the blade’s cutting edge is thicker than the back, and both the back and the cutting edge taper from the saw’s heel to the saw’s toe. The thinner the cutting edge, the greater the taper, and the higher the polish, the higher the saw’s quality, as taper results in less set required for the teeth, aided by the steel’s polish that inhibits binding in the cut. All these features allow for a narrower kerf requiring less sawing effort.
There are two fundamental choices in manufacturing a thin saw that won’t kink. The least expensive choice is to make the saw stiff by using hard steel and disposable blades, because such saws can’t be economically resharpened. The second choice is to temper the saw so that it can be filed, and to stiffen it by tensioning the blade using hammer and anvil.
When a thin blade is struck on an anvil by a convex-faced round hammer, a dimple is created; often so small it can’t be seen by the eye. Steel from the area around the dimple is pulled inwards toward the point of impact, making the steel in the circular area radiating from the dimple stiffer, or “tensioned” on its surface. Hundreds of such hammer blows applied in certain patterns equally to both sides of a handsaw blade can make it stiffer, can true a warped circular sawblade, or can dish a large bandsaw blade to conform to its wheels while at the same time tensioning the cutting edge. Truing sawblades are not low-order skills, and the major saw factories and filing shacks of logging camps and commercial sawmills was where you found them. Today it’s largely done on computerized machines, except for hand saws. Here you either find an old, retired saw doctor who worked for a big mill, a Japanese saw maker still tensioning by hand, or are on your own because there are few references. I’m not going to make a saw doctor out of you today. But I can get you started with some basics to practice with on old sawblades.
This old saw has a 3/8” kink in the area marked in chalk, and before I do anything else to rehabilitate the saw, I’ll remove this kink and true the cutting edge.
The first step is to remove the handle and bend the blade using your hands in as complete a circle as possible….in both directions. This relieves any recent stress put in the saw, and sometimes makes the existing kink worse or reveals additional problems like bow or twist.
The tools I’ll use to remove the kink are a steel anvil and two hammers, both heavy and light, both with slightly convex faces. I’ll mark the areas to be struck with chalk and using and oily rag, keep all steel surfaces clean and oiled to prevent marking the blade.
Removing a kink or bow requires stretching the steel surface on the concave side of the kink, and compressing the surface on the convex side. Before doing either, the saw’s tension at the cutting edge needs to removed or my attempt may make the kink worse. I accomplish this on the concave side by striking along a line running an inch or slightly less upwards from the tooth gullets. Each “X” represents two light hammer hits. I made identical chalk marks on the opposite side of the saw, but I don’t attempt to strike them yet.
On the identical marks on the convex side of the kink, I’ll accomplish two tasks simultaneously using light hits with the heavy hammer. The heavier hammer strikes will both remove the tension from this side of the saw and straighten out the kink by reversing the conditions that caused it, compressing the near side and stretching the far side of the blade.
I sight down the cutting edge to insure I removed the kink and repeat the previous steps if necessary. Once the kink is removed, I tension the cutting edge using identical light hammer strikes on both sides of the saw in turn, around ¼” to 3/8” above the gullets, insuring I don’t strike the gullets or teeth.
When tensioning is complete, the saw should flex in either direction as I did at the beginning, and return to dead straight.
Continued….
Edited 8/15/2007 11:37 pm by BobSmalser
Replies
Only after the blade is straight and tensioned do I continue with rehabilitation. This saw was habitually filed without jointing, and instead of straight or crown-breasted, the cutting edge resembles the hooked nose of the Wicked Witch of the West. Accordingly, I must stamp in new teeth. And guess what? 7 new teeth per inch on a 26” cutting edge require 182 strikes of the stamping dies, and a major retoothing usually bows the blade. So as soon as the blade comes out of the carrier, I again bend it both ways and strike 182 blows on the convex side just above the gullets with the light hammer. View Image
Edited 8/11/2007 12:17 pm by BobSmalser
Excellent article, Bob. Thanks very much.Folks may also be interested to know that basically the same techniques of tensioning are applied to circular saw plates especially those of diameters 12 inches and more.
Large diameter break down saw blades in the order of 60inches plus in diameter become quite exciting when tension is upset due to overheating, for example....Philip Marcou
This just a small trial balloon to see if I can satisfactorily explain something significantly more complicated than tuning a block plane. Hammering circular sawblades is more complicated still. This will eventually be a magazine article on advanced saw filing to go a step beyond all the good basic filing primers out there.A good filer can crown or change the crown of the cutting edge, make the teeth taller and the gullets deeper to clear damp sawdust better, and even change the fleam or cutting edge bevel at the heel to make the saw start easier. These are features than can only be done by hand.Filing with a 60-degree triangular file used at a 22 to 45-degree slope from vertical instead of straight across like the filing machines do produces taller teeth with longer cutting edges along with deeper gullets to better clear sawdust.A crown-breasted cutting edge:View Image12-pt crosscut sloped gullets with no set, for hardwoods:View Image8-pt crosscut sloped gullets with light set, for softwoods:View Image5-pt rip sloped gullets with full set complete with raindrop, which is why I often phosphate blue the blades:View ImageMy focus is on boatbuilders who as you can see have no choice about hand saws because of odd angles and 500lb workpieces.
View Image“When we build, let us think that we build forever. Let it not be for present delight nor for present use alone. Let it be such work as our descendants will thank us for; and let us think...that a time is to come when those (heirlooms) will be held sacred because our hands have touched them, and that men will say, as they look upon the labor and wrought substance of them, ‘See! This our father did for us.’ “ --John Ruskin.
Bob, I think you can more than "satisfactorily explain".I for one would be chuffed to see a further article from you about doctoring large diameter circular saws.
In fact, I beleive the moderators ought to have a section where this type of article is permanently displayed . This is what I have seen at "Practical Machinist" forum. The section would have selected articles of interest and suitable for reference purposes for all woodworms.
I wander if this idea has come up in the past?Philip Marcou
Philip
I agree that a seperate location on this site for articles like this would be a welcomed and valuable resource addition to the Knots. Woodcentral has this available, and I've enjoyed Bob's articles over there for years. He has an entire page of topics there, (without counting, over 30) and they are all excellent.
Perhaps we could even be enthralled with a nice article or two regarding modern plane making from this really fantastic planemaking friend of mine.....
Jeff
Edited 8/14/2007 9:46 am ET by JeffHeath
Knots should consider creating a "best of" section like Craigslist (a message board site for those who don't know). Craigslist has a "best of" feature in which readers can nominate a post for "best of" status. If the moderator/s agree, the post is listed permanently in a separate "best of" section.
The same idea could be used on knots. All of Bob's tutorials would undoubtedly make their way into the best of section. Imagine being able to browse and re-browse a section containing all of the very best tutorials and posts from knots!
FWW already has an extensive on-line articles section, where I also have some.
The magazine pays the authors for the articles and in turn, charges for their use. I've no arguments with that, the competition between WW magazines is fierce and remembering back when FWW began there were no other periodicals featuring high-end work, only Popular Mechanics. Taunton broke new ground. Moreover, for those of us making 400 bucks a month back then, subscribing to FWW was an inexpensive alternative to buying the few WW books there were, and I still appreciate that. I owe Taunton, and like seeing them still in business at the top of the heap.
The first 10 years of issues still sit in a complete but dogeared set about 10 feet from me.
A piece from me on selection, use and advanced filing will get there eventually. I just have a lot more work to do on tensioning before its ready for prime time.
“When we build, let us think that we build forever. Let it not be for present delight nor for present use alone. Let it be such work as our descendants will thank us for; and let us think...that a time is to come when those (heirlooms) will be held sacred because our hands have touched them, and that men will say, as they look upon the labor and wrought substance of them, ‘See! This our father did for us.’ “ --John Ruskin.
Edited 8/14/2007 8:27 pm by BobSmalser
I am aware of FWW's extensive online database of articles. What I was thinking of, however, is a collection of particularly helpful knots posts -- a "best of knots" section. For example, I recall a post by Rob Millard in which he described in great detail his lime-water finishing process for mahogany. Rob's technique could be made into a FWW article, but for whatever reason it hasn't. Similarly helpful, article-quality posts should be preserved and collected into a database. Posts like Rob's have been incredibly helpful to my self-taught education. In fact, having the ability to interact directly with the author is generally more helpful (for me at least) than readng an article or a book. Fortunately, Bob, your tutorials are preserved on various sites. But there are equally helpful posts that have not been made accessible to later viewers. That's why a "best of" section would be helpful.
So, how about it FWW? A "best of knots" database containing article-quality posts that for one reason or another do not make it into the printed publication?
WoW! That's art!Thanks for a beautifully described primer.Frosty"I sometimes think we consider the good fortune of the early bird and overlook the bad fortune of the early worm." FDR - 1922
Wow, thanks for that tutorial.
That was at the grad school level and I am almost embarrassed to ask my first grade questions that are certain to have been asked and answered before. In fact I had a site bookmarked beofre my most recent computer crash and read an article that mostly addressed my questions, but that was a long time ago and before I had any old saws in hand, or real interest for that matter. I just don't remember the exact details.
I have recently bought a couple of vintage Disston D-8's, tuned up, sharpened and ready to cut. In the process the bug got me in it's grasp and I've bought several other old saws that need a little TLC. I remember you can wedge a split handle apart to reglue and that you must take care in removing the split nuts and medallions.
I can't remember how to clean up the blade. Do you recommend sandpaper, steel wool, a scraper, synthetic material, or some combination. How aggessive can one be, etc? I have done a little sharpening on an old back saw, and have found several links to help in that area. Any help you, or anyone, cna give on cleaning, derusting, and generally preparing an old saw to sharpen will be greatly appreciated.
Bob, many thanks for the excellent tutorial. It was fascinating!
Lump and Cup Removal
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On saws that have been kinked repeatedly or severely, it’s common to achieve a straight cutting edge by hammering and tensioning as I described in the previous installment, but still not have a saw that will cut smoothly. This Disston #16’s cutting edge was hammered straight, but you can see a small bend remaining in the saw’s back and what appears to be a cup or lump remaining that will bind in the kerf during sawing and cause the saw to wander.
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A short straightedge run down the blade allows chalking the lump’s outline on the concave side. Turn the saw over and transfer the marks to the convex side of the lump.
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Any tension in the concavity is removed using a small, convex-faced hammer, hammering on the marks from the outside of the circle inwards. Each mark represents two light hammer strikes.
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Flipping the blade to the convex side, the lump is hammered out using the large hammer in exactly the same sequence and locations as in the previous step.
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The blade is checked again using the straightedge and while there are still lumps and hollows, they are smaller. Rub out the old chalk marks and use the straightedge to make new ones, then repeat the same marking and hammering sequence of using the light hammer on the concave side and the heavy hammer on the convex side. Stop when the straightedge makes full contact with the blade.
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Then tension the saw as I did in the first installment using the small hammer. Strikes near the edges provide tension to the edges, strikes near the center flatten the saw. If strikes are not made equally in force, location and number on both sides of the saw, the saw will bow or cup, and this is the basic principle used to both tension the blade and hammer out defects.
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Cupped toes can be difficult and often not worth the effort, so I’ll shorten the saw instead.
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Sawblade steel grinds to the line easily on the coarse wheel with an occasional water dip to keep it cool.
Continued....
Edited 8/15/2007 11:39 pm by BobSmalser
View ImageAnd the grinding marks easily cleaned up by drawfiling.“When we build, let us think that we build forever. Let it not be for present delight nor for present use alone. Let it be such work as our descendants will thank us for; and let us think...that a time is to come when those (heirlooms) will be held sacred because our hands have touched them, and that men will say, as they look upon the labor and wrought substance of them, ‘See! This our father did for us.’ “ --John Ruskin.
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