Straightening Bent Handsaw Blades

[Bob Smalser]

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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 were 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.

http://pic20.picturetrail.com/VOL12/1104763/17430481/270960317.jpg

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.

http://pic20.picturetrail.com/VOL12/1104763/17430481/270960325.jpg

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.

http://pic20.picturetrail.com/VOL12/1104763/17430481/270960327.jpg

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.

http://pic20.picturetrail.com/VOL12/1104763/17430481/270960322.jpg

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.

http://pic20.picturetrail.com/VOL12/1104763/17430481/270960320.jpg

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.

http://pic20.picturetrail.com/VOL12/1104763/17430481/270960404.jpg

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.

http://pic20.picturetrail.com/VOL12/1104763/17430481/270960403.jpg

When tensioning is complete, the saw should flex in either direction as I did at the beginning, and return to dead straight.

Continued....

[Bob Smalser]

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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. ;)

[Greg Crawford]

That's great, Bob. Timing is right on, too. I saw an old D-23 in an antique store this week that was shaped like a Z. It was in bad shape overall, and they wanted $22, so I wouldn't even get it as a trainer, but it's still amazing timing. Thanks for all the time you spend helping us learn.

Greg

[Michael Schwartz]

I have a real old fine toothed diston that is overall pretty good, but is kinked at the verry end. I will have to give this a try.

[Zahid Naqvi]

Bob, as usual very educational as it turns out I need to work on a saw these days. I have a diston cross cut that is giving me trouble. Visually it looks straight but when I pull it back, and if I am moving a little fast, it starts wobbling. I have checked it several times and looks true but the wobble it still there. Although it may have something to do with my faulty technique.

[Bob Smalser]

I have a diston cross cut that is giving me trouble. Visually it looks straight but when I pull it back, and if I am moving a little fast, it starts wobbling. I have checked it several times and looks true but the wobble it still there.

This little piece is a trial balloon to see if I can satisfactorily explain something significantly more complicated than tuning a block plane.

http://www.vintagesaws.com//othermakers/offer.JPG

It could be technique. Set yourself up to saw exactly like the old timer above from Pete Taran's site. The sawing arm moves in one arc directly in line with the kerf, not two or more that are created by poor body position. And hold the saw very lightly to let the teeth and gravity do more work than your muscles.

It could also be the saw's tension. Usually if there's a tension problem, the blade is bowed. But not always, and on some saws that look straight, you can stone one side of the teeth to oblivion and the blade still won't track straight in the kerf.

On yours after bending it back and forth, I'd check to make sure it was still straight. If it was, I'd retension it with 6oz hammer strikes immediately above each gullet on one side and measure the bow I just created by standing the saw on its edge over a length of butcher paper and scribing the bow with a pencil. The side you hit will be the concave side of the bow.

Then I'd hammer it identically on the other side and see if the bow fully straightened out. If it didn't, the saw needed additional hammering on the convex side.

If it still didn't cut straight, I'd repeat the procedure on the other side of the saw, using my scribed line as a reference. Each side should bow identically, and if they don't, the side with the deeper bow needs some additional hammering on the convex side.

[Mike K Wenzloff]

To add to Bob's excellent advice re body position and straight arm movement (which is an arc), twisting the hand while withdrawing the saw is a natural tendency and will also cause the saw to vibrate on the back stroke.

Typically a slight amount of hand rotation also happens on the forward stroke, but the tension created by the teeth being engaged makes it negligable in its effect--but should be consciously avoided as well as it can make it more difficult to stay on line.

With the back stroke, the lack of tension (no teeth engaged in cutting per se) the rotation can show up by the teeth rattling against the cut and the top of the blade hitting the slight roughness in the kerf.

Take care, Mike

[Gary Herrmann]

Excellent article, Bob.

[Charles McKinley]

Thank you again Bob!

[Bob Smalser]

Here's a comment from another site that relates to Zahid's question here.


I have yet to hear of a good reason, other than decorative, for the "horns" at each end of the saw handles.

These protrubances do severely limit the size of the hand that fits comfortably, unless one is fond of blisters on the sensitive skin between thumb and index finger.

I have yet to get hold of a handsaw with a truly comfortable handle. Surely, these tools are meant for work and not just for admiring their intricate finish.

So, anybody knows the reason for the long "horns"/


It's all in the manner you were trained to hold and use the saw. Previous generations certainly liked them, or they wouldn't be there.

The giant sawmakers from 1860 to 1940... Disston, Atkins, Simonds, Bishop, Spear and Jackson....were in hard competition with each other making the type and style of saws that were demanded by the professional tradesmen who bought them, not the other way around. And just like with all the other makers of professional-grade hand tools sold during the era of some of the finest craftsmanship in furniture, homes and yachts our countries have ever seen. They competed with each other to meet the demand, not determine it.

http://www.vintagesaws.com//othermakers/offer.JPG

Here's why this handle style was demanded. What I often see today is a hard, 4-fingered grip more suited for a framing hammer than a handsaw. This picture from the Vintage Saws website of a mature carpenter who likely used handsaws every working day of his life reveals all the features of efficient sawing:

1) His body position both takes advantage of gravity and allows his sawing arm to swing in a single arc directly in line with the kerf, instead of two or more arcs both up and down and sideways that cause the saw to wobble. A death grip on the saw handle alone will result in multiple sawing arcs, and a wobbly sawblade.

2) His grip on the saw is three-fingered and very light, using his index finger to aid alignment of his forearm with the kerf. Here you can see the benefit of the handle's horns for kerf alignment in combination with a soft grip. The web and heel of the hand unconsciously feel the horns and use them to aid keeping the saw plumb with the kerf.

3) In efficient use of his body after decades of daily practice, you can see he's letting the saw's teeth and gravity do more work than his forearm and shoulder muscles.

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4) Cuts in boatbuilding are usually more difficult because neither the workpiece nor the worker standing on a scaffold are plumb and level like our carpenter cutting on sawhorses. That's why youngsters in that trade were assigned thick saws building shelves to master the saw there before tackling more difficult cuts with more fragile and expensive saws.

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http://www.fhwa.dot.gov/Environment/fspubs/77712508/fig13.gif

Saw handles without a top horn were either flooring saws designed for surface penetration or larger saws used to fall or buck 25 or more inches of green log where two hands were required, gravity wasn't always in the user's favor, precision was less important and the muscles did as much or more work as the saw's teeth. Sandvik and other continental European sawmakers also made handsaws without horned handles, although the tradition there was largely frame saws, and there's no shortage of Disstons and others with the top horn cut off, which is easy enough to do if you don't like them.

[Michael Fross]

Thank you very much Bob. I'm just starting to do some rehabs of 2 old Disston saws I found in my fathers garage. I also want to attempt my hand at making a dovetail saw per the Norse Woodsmith's site (and if any of you have not checked that out, all I can say is wow! LINK (http://www.norsewoodsmith.com/ww/dovetail/bs-index.htm))

Much appreciated.

Michael

[Brett Baldwin]

Thanks for making these fading skills available for those of us who are interested in them even though they aren't a necessary part of our livelyhood Bob. Even if we aren't saw doctors, at least we can save a few saws that would otherwise be decoration.

[Bob Smalser]

Much appreciated.


This just a small trial balloon to see if I can satisfactorily explain something significantly more complicated than tuning a block plane. This will eventually be a major 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:

http://pic20.picturetrail.com/VOL12/1104763/9131162/238005847.jpg

12-pt crosscut sloped gullets with no set, for hardwoods:

http://pic20.picturetrail.com/VOL12/1104763/9131162/269216839.jpg

8-pt crosscut sloped gullets with light set, for softwoods:

http://pic20.picturetrail.com/VOL12/1104763/9131162/238005849.jpg

5-pt rip sloped gullets with full set complete with raindrop, which is why I often phosphate blue the blades:

http://pic20.picturetrail.com/VOL12/1104763/9131162/266424129.jpg

My focus is on boatbuilders who as you can see have no choice about hand saws because of odd angles and 500lb workpieces.

[Bob Glenn]

http://www.vintagesaws.com//othermakers/offer.JPG


How many of you guys out there still using hand saws, work in a button down dress shirt and tie! :eek:

[Greg Crawford]

Thanks for the generosity with your knowledge, Bob. As I've looked more into hand saws and read about horns, I've developed a question. Do the horns help with the proper technique? The saws at the Norse Woodsmith's site had handles with horns that looked longer than usual. You mentioned that some types of saws didn't have horns on top or at all. Does the type of saw, back saw, rip, panel, etc., have anything to do with the size and/or style of horns?

Just got my curiosity up. Thanks.

[Bob Smalser]

All the horns do is help you keep the saw plumb. Length I believe was more about cool-looking designs that attracted the eye. The handle notches mean something, however:



Is one of the saw handles in your original message handed or is there a finger groove on the other side too, to cater for R&L hands?
Klaus

Many long rip saws have thumbhole handles to facilitate using two hands on long, tiring cuts:

http://pic20.picturetrail.com/VOL12/1104763/9131162/271870223.jpg

There are times and places for the finest thin saws, and roughcutting long, straight rips isn't one of them. The heavy D-8 shown is perfect for such grunt work; it has more weight for gravity and when you get tired and muscle through anyway, a mistake is less likely to kink the blade.

Today these 28-30" thumbhole rips when refiled also make good crosscut saws for beams and other heavy airdried stock, because it's hard to find a crosscut saw with coarse teeth and the length and handle help.

Older saws had handles designed for how the sawmaker intended you to use the saw.

http://pic20.picturetrail.com/VOL12/1104763/9131162/271873428.jpg

On top is a Disston #12 cabinetmaker's saw and the bottom an Atkins #53 combination saw for rough framing.

http://pic20.picturetrail.com/VOL12/1104763/9131162/271870227.jpg

The Atkins' handle has a large notch designed to fit the web of your second hand for two-handed work. The #12 purposely does not so you won't muscle through using two hands and kink the thin blade.

Later as power tools grew in importance, sawmakers dropped these features and used mostly the larger notch because it was cheaper to make and later generations no longer bought fine saws.

[Greg Crawford]

I knew about the thumb hole on the rip saws and I've also read that the notch was for a cord to hold the saw in a holster, but that's even more in depth than I thought. So much of the woodworking craft has been tossed aside, it's a real shame. The more I work with various aspects, the more I learn that some tasks are much better accomplished with hand tools. I've given up on edge sanding and turn to a plane now. You can get a whole bunch of planes for the price of one oscilating edge sander, and they're easier to control so the results are better. You also can't cut two different width and length pieces from a single piece of stock on a table saw or miter saw nearly as easy as hand sawing. Now I just need to get a couple more hand saws.

Thanks again Bob

[Bob Smalser]

Part II
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.

http://pic20.picturetrail.com/VOL12/1104763/17481462/271961830.jpg

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.

http://pic20.picturetrail.com/VOL12/1104763/17481462/271961828.jpg

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.

http://pic20.picturetrail.com/VOL12/1104763/17481462/271961826.jpg

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.

http://pic20.picturetrail.com/VOL12/1104763/17481462/271961825.jpg

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.

http://pic20.picturetrail.com/VOL12/1104763/17481462/271962015.jpg

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 tension or stiffen the blade and hammer out defects.

http://pic20.picturetrail.com/VOL12/1104763/17481462/271962013.jpg

Cupped toes can be difficult and often not worth the effort, so I’ll shorten the saw instead.

http://pic20.picturetrail.com/VOL12/1104763/17481462/271962012.jpg

Sawblade steel grinds to the line easily on the coarse wheel with an occasional water dip to keep it cool.

Continued….

[Bob Smalser]

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And the grinding marks easily cleaned up by drawfiling.

[Steve Thomas]

This is great!
Bob, thank you for sharing your knowledge.

[Marc Gélinas]

This is the definition of getting the answer before asking the question,

Thank you Mr. Smalser

[Don C Peterson]

How do you know if you've got the saw retentioned correctly? I've followed your advice and straightened several saw blades. After the straightening, jointing, filing, and setting they all seem to cut great. One part of me says that should be good enough, but then the other part says "what if it could be better?"

[Bob Smalser]

How do you know if you've got the saw retentioned correctly? I've followed your advice and straightened several saw blades. After the straightening, jointing, filing, and setting they all seem to cut great. One part of me says that should be good enough, but then the other part says "what if it could be better?"

More isn't better, and a light touch is required. Hit that thin tool steel too hard or too much and it will crush and permanently distort. I'm even clearer about that in the next installment:

Advanced Saw Filing and Reconditioning
http://www.sawmillcreek.org/showthread.php?t=66090&highlight=life

[Bill Brehme]

Don, I'd go with the school of thought... 'perception is reality'...

If it CUTS great, it IS great...

By the same token, I can also relate to wanting to be absolutely sure!

Ugh, the sicknesssss....

[Don C Peterson]

Bob,

that's pretty much what I thought. Most of all, I didn't want to damage the saw so I went as lightly as I could and still get the blades straight. I was just wondering in the retentioning process how you know you are done?

Bill,

to me it's kind of like when I started using planes. I didn't know whether the plane was well tuned or not because I'd never used a well tuned plane. With saws I have no reference point to judge. So even though the saws cut fine by MY estimation, I'm pretty sure that's not definitive.

[Bob Smalser]

I was just wondering in the retentioning process how you know you are done?


Look at my first test. Bend the blade into a circle in both directions back and forth. If the blade returns to straight, the tension is correct.

That's also the first evaluation of a used saw before you buy. You catch the hacks who straightened the saw over their knee and are palming it off as perfect.

[Don C Peterson]

Thanks Bob, as usual your advice and willingness to share your knowledge is much apppreciated.

[Glen Evans]

Hi all,

On my ongoing quest to learn about saw straightening I have read and re-read this article. I have also spent about 10 hours in the shop over the last couple of months whacking away on a number of saws. Without alot to show for it!

Currently, I'm working on a gently bowed D12, no kinks, just about a 3/4" bow along the length. I've removed the tension on the concave side an inch down from the teeth, then I've worked the convex side with the larger hammer.

I have never been able to straighten this saw. I've tried removing the tension on both the tooth edge and the back edge of the concave side and worked both edges on the convex side with the large hammer--nothing. I've even used the small hammer and re-tensioned the edges from the convex side (1/4" in from the gullets and the back). The bow just won't come out!

I've probably hit below each gullet 30 times now and I'm not making headway. I've lightly pounded the snot out of the convex side with the large hammer and the bow just won't come out.

Is anybody else having this problem?? Am I the only one? How many times do you have to strike the plate to make a change??

(I have had some success heating the saw plate and bending and then re-tensioning--but the hammering method escapes me.)

I need some help

Thanks
Glen

[Jim Koepke]

Wish I could be of help, but there has not been any reason for me to start beating on my saws with a hammer. Knock on wood.

jim

[Bob Smalser]

Currently, I'm working on a gently bowed D12.....The bow just won't come out!



Some blades simply can't be successfully straightened because somebody before you tried to and permanently distorted the steel.

All these blades were originally tensioned with a hammer at the factory, and as the method relies on dimpling one side of the blade and then the other to counterbalance....

- There is a limit to how hard you can hit the blade above and beyond what the factory already did without permanently distorting it.

- There is a limit to how many times the saw can be hit before it no longer responds.

- The thinner the blade, the more easily it can be permanently distorted. #12's and #16's are a third thinner than #7's, which are in turn thinner than Warranted Superior plate saws. Practice on the Warranted Superiors instead of the #12's.

If there is any one common fault I've seen in hammering saws, it's hitting the steel too hard.

[Glen Evans]

Thanks for the help Bob, I suspect that I've inadvertently work hardened the blade?? I also wondered if the small anvil I was using had too small a surface area, (4" x 6").

Either way, its disappointing to think I ruined the D12--that was the nicest flea market Disston I have found:(. Good info on the blade thickness comparison--I noticed that the blade was thinner than my D-8's but I didn't how much thinner the D12 was--particularly in comparison to the Warranted Superiors, (just my luck the two that I have are straight!)

I've learned a ton from these articles and appreciate your insights very much. I keep a printed copy of your filing and restoration articles with my sharpening files and jigs for quick access. They have helped me resurrect several old gems!

Again thanks
Glen

[Bob Easton]

Wonderful advice Bob. THANKS for being so generous with your knowledge!!!

I recently made a frame saw for resawing some cedar boat lumber. The first blade I used did a passable, but laborious job. Following your rehab instructions, I cut down a D-8 blade and tuned it up. (removed a kink, tempered the edge, jointed, refiled all teeth to 90*, tuned the set) That blade evolved from fairly good to wicked sharp. It works very well at resawing boards 10-11 inches wide, although that's a lot of work.

For regular ripping, such as removing the sapwood from a 4/4 flitch, the weight of the saw does ALL of the work.

Resawing boat lumber: http://www.bob-easton.com/blog/?p=346

[george wilson]

Glen,do not entirely give up on your ruined saw until you try what we had talked about.Clamping it between steel plates and baking. I guess you haven't tried this yet,but it just might work. My only doubt is that we can afford the temperature to stress relieve the saw(can't get it red hot!) but, do try it anyway. Let me know how it turns out.