Hard brittle handsaw teeth

[William Flather]

I just took several handsaws to a local handsaw sharpening shop here in central PA. We had a discussion about the fact that the teeth on some saws seem to get very hard and brittle, ruining files and possibly breaking off if you try to re-set them. He seemed to think my saws may be OK, but I have run into this problem in the past.
Is there any way to correct this problem on such older saws? These saws are older Diston, along with one Fulton backsaw.

[george wilson]

some saws are made to not be re sharpenable,but I don';t know how far back this goes.

The only cure for hard teeth would be to heat them to a spring blue color. But,without special ovens,this might be impossible without warping the blades and ruining them.

If it was do or die,I'd take a narrow grinding wheel and rig up a jig to hold the saw at the correct angles and grind the teeth. But that would be very complex,and still no way to SET the teeth.

[Jim Koepke]

Howdy William and welcome to the Creek. Without a location in your profile old fogies like me will likely forget your are in Central PA.

There have been a couple of discussions here about some, mostly older, saws having varying hardness to the point of being very hard on files.

I have no source to verify this, but sometimes I think pitting on the plate can also play into this problem of teeth snapping off when setting.

It is possible to find honing stones in different abrasive material. I have had success using an India stone on bandsaw teeth. It is slow and tedious, but with the difficulty in finding decent saw files these days it might be an option to try. Not sure a saw sharpener for hire would want to do this.

jtk

[William Flather]

Updated my profile.
Yes, the saws, except the backsaw, have some rust, no major pitting near the teeth. Many of my saws (and other tools) went through a flood years ago, somehow the handsaws were overlooked for a couple days before I got them washed and dried. I was heartbroken.

Heating in an oven: George, I do seem to recall while looking for pertinent threads on this your discussing temps you would need to reach to bring the blades up to spring blue, I think you were looking for 650 - 750 deg?
I'm wondering if this could be done in a regular oven if I use a remote thermometer.

Local handsaw sharpening services are becoming more limited in this area as the old-timers retire or pass away.

This guy is Amish and has a sharpening business that serves a wide area, and I am pretty sure will be using a Grizzly narrow belt sanding rig to sharpen the teeth. He did seem to know his way around handsaws, but I am pretty sure trying to change the temper in the blades is a mystery to him. So until next Thursday I am keeping my fingers crossed and am anxiously waiting to see the results for myself. His electric tools are driven from a generator powering a motor driving a belt shaft for all his rotary tools. Typical for this area. I asked him if he would be calling me to let me know when the work was done. He smiled and said no. :D

[george wilson]

Heating your blade to blue is going to be very risky about warping it. Spring temper can vary depending on the hardening temp they put the saw through. Back in the old days they did not have accurate means of determining oven temps,which causes variations in the quality of antique tools. Normally the temp for spring blue would be about 750º. BUT,kitchen ovens heat differently in different places inside. AND_AND_AND there can be as much as 75º difference in the TRUE temperature you have set vs. what the oven actually heats to.

The best thing to really do is cut your blade up for making scrapers and buy another old Disston saw. Even I would not want to try heating a large,thin saw in my pyrometer controlled PROPER heat treating furnace,for fear of a permanently warped,twisted,or convex surface on the treated blade.

I think Disston might have made some specially hardened saws that were for sawing reclaimed lumber with possible stray nails in them. They were not re sharpenable. Anyone recall anything on that? I'm forgetting things at my age.

Do the Amish have phones? I thought they did not want wires connecting them to the outside World. Or even radio waves.

[Mel Fulks]

I don't sharpen saws. Fortunate to always have had good sharpener around. Common for just a few teeth to break and the rest be ok, but probably hard on files. In real bad cases some got re toothed but no attempts at heat retreating.

[William Flather]

OK, I'll abandon the thought of messing with saw blade temper.
Amish (and Old Order Mennonite) and phones: I think this largely depends on the church they belong to. Some will have a phone, housed in a shed away from the house and barn, often down near the road. If they are really progressive, it will have an answering machine with it. This guy apparently is not a member of such a congregation.
Adoption of technology varies very widely. Around here you can find barns electrified, but not the house; electricity in the barn would be used to refrigerate milk and light the milking stalls. It is OK here since it is not a luxury. You can also find horse drawn wagons that have gas or diesel motor driven bailing machines mounted on them. No tractors, horses. Others may have tractors, but no rubber wheels; steel wheels. Very hard on roads they are.

[Doug McKay]

William,

Disston made a very hard,famous and valuable cabinet makers saw called the ACME 120. It had a VERY hard blade and was filed to run with no set, the teeth can snap if you try to set them. If you have one suggest you send it to Matt Cianci, an expert on these. When I hand filed mine the blade was almost as hard as the file!

[William Flather]

Doug, I don't think I have an Acme 120, but i'll check.

[Mike Siemsen]

The chart I looked at said 560 degrees F for High carbon for spring steel dark blue. Try it on a junker first. Let it cool off in the even so it cools slow.

[Jim Davis]

Disston never advertised the Acme 120 as being harder than their other saws. The model 40 was a handsaw for metals, but the teeth were very fine, as one would expect.

I have come across both No. 7 and D-8s that had some hard teeth that broke when I tried to set them.

As far as heating and warping, there will be no warping if the whole plate is heated evenly and cooled evenly. Evenly is more important than slow cooling, though it's hard to do the first without doing the second.

I tried to retemper a D-8 plate but couldn't get it hot enough in the kitchen oven. No warping though.

Jim

[george wilson]

Charts vary widely about tempering temperatures. It also depends upon the alloy of the steel you are tempering. One size does not fit all.

As I mentioned,kitchen ovens do not heat evenly. (That is the problem,at least partially) Not even for normal baking of foods. On the "British Baking Show",which I watch with my wife,the contestants are always moving biscuits,muffins and other small baked goods around,re arranging them on the baking sheet. Some are getting browner than others while some aren't baking fast enough. This happens all the time when they bake small items.

I tried to fire blue a pistol barrel many years ago. Could not get the whole barrel to evenly blue. In my Paragon 22" deep knife maker's electric furnace with pyrometer control,I have no problem getting items of different mass within themselves(I.E.,a flintlock pistol barrel that has a much thicker breech and a thinner muzzle) blue all over. I still would not want to blue a thin saw blade in it because it will get stresses released and will warp.

[Doug McKay]

Disston never advertised the Acme 120 as being harder than their other saws. The model 40 was a handsaw for metals, but the teeth were very fine, as one would expect.

I have come across both No. 7 and D-8s that had some hard teeth that broke when I tried to set them.

As far as heating and warping, there will be no warping if the whole plate is heated evenly and cooled evenly. Evenly is more important than slow cooling, though it's hard to do the first without doing the second.

I tried to retemper a D-8 plate but couldn't get it hot enough in the kitchen oven. No warping though.

Jim

?????

From Disstonian institute "The Disston 120 or "Acme" saw was a special model made from 1876-1924. It features an ultra-tapered and hardened blade, filing with tall, narrow gullets, and no tooth set."

From Disston 1924 catalog
"The Disston No. 120 Acme Saw is not an ordinary type of hand saw and should not be used for ordinary work. It is designed for sawing dry, seasoned lumber only, and cannot be used successfully for general work. It is a fast, smooth-cutting saw for fine cabinet work, sawing mitres, etc. It will cut a joint sufficiently smooth to glue without planing, and is very popular with those doing extremely accurate sawing. It must be kept properly sharpened and should not be set. The Disston six-inch cant safe-back File is made expressly for filing this saw. The No. 120 Saw is very high in temper. The blade is specially ground for clearance and the teeth require no set."

[Mike Siemsen]

I agree with you on all points George. If someone wanted to try this I thought the lower temperature, if it worked, would be a better bet as the home oven can't get up to 700 degrees and you can always do a higher heat later. It is far and away easier to find another saw, but there are experimenters in the mix. A convection oven would help as well.

[Jim Davis]

?????

From Disstonian institute "The Disston 120 or "Acme" saw was a special model made from 1876-1924. It features an ultra-tapered and hardened blade, filing with tall, narrow gullets, and no tooth set."

From Disston 1924 catalog
"The Disston No. 120 Acme Saw is not an ordinary type of hand saw and should not be used for ordinary work. It is designed for sawing dry, seasoned lumber only, and cannot be used successfully for general work. It is a fast, smooth-cutting saw for fine cabinet work, sawing mitres, etc. It will cut a joint sufficiently smooth to glue without planing, and is very popular with those doing extremely accurate sawing. It must be kept properly sharpened and should not be set. The Disston six-inch cant safe-back File is made expressly for filing this saw. The No. 120 Saw is very high in temper. The blade is specially ground for clearance and the teeth require no set."

"High in temper" does not mean "hard." In fact, it means nothing specific. Temper is the amount a piece of steel is softened after hardening. "High temper" was just an advertising term to present the idea of very high quality.

[Mike Allen1010]

[QUOTE=george wilson;2479714]Heating your blade to blue is going to be very risky about warping it. Spring temper can vary depending on the hardening temp they put the saw through. Back in the old days they did not have accurate means of determining oven temps,which causes variations in the quality of antique tools.

The best thing to really do is cut your blade up for making scrapers and buy another old Disston saw. Even I would not want to try heating a large,thin saw in my pyrometer controlled PROPER heat treating furnace,for fear of a permanently warped,twisted,or convex surface on the treated blade.

As usual, excellent advice from George. I've sharpen literally hundreds of vintage saws and probably run across no more than a dozen that were too hard to file and set without snapping off teeth. My advice would be to find another saw.

It's not uncommon that a saw might have a couple "hard spots" with teeth that are difficult to file and prone to breaking when setting – especially if you inadvertently attempt to set it opposite of how it was originally set. Probably a result of the variability in steel making and hardening that George mentioned. Often, you can identify these saws in the wild because their missing several teeth adjacent to each other.

Depending on the pitch of the saw (# of teeth per inch)and what you want to use it for, a few individual missing teeth scattered along the tooth line won't really affect performance, unless the teeth are really big (4-6 PPI). Fortunately quality vintage saws are are still fairly broadly available. Unless an old saw is rare or has sentimental value, it's a lot less work to tuneup and sharpen one with a fairly consistent tooth line. Restoring old saws with a irregularly shaped/spaced teeth or a real uneven tooth linetakes a long time, goes through a lot of files and and is much more difficult to achieve a good result.

Just my two cents, YMMV.

Cheers, Mike

[Daryl Weir]

323993

Having filed a few of these Acme 120's, I can attest to the fact that overall they are harder than Disstons regular line of saws. OK, there can be some hardness variation between samples but once you get in the 55 Rc range, a few points variation either way can be the difference between the file cutting and not cutting at all. To me, they are equal to the hardness of the metal cutting saws. My Bahco files also know the difference in the fact that the blade is just flat out hard on them. Don't poo poo the Bahcos as they will outlast the old vintage Nicholson's on these Acme 120's.

While the very early Acme's that I have don't have that secondary etch, which by the way varied over time, they also filed harder than a regular Disston saw.

Most of the Acmes I've purchase have had broken teeth from unknowing people trying to set them, which indicates a harder more brittle blade.

Take care,
Daryl

[Jim Davis]

Daryl, I am sure your experience is as you say. I have to ask--have you filed a No. 12? They are famous for wearing out files. In fact, all the old Disstons are harder than most of the other brands of the time, or after. Doesn't mean they were meant to cut metal. These pictured, from 1918 Disston literature, were made for cutting metal. Also, the No. 10 and other "plumbers'" saws were advertised as hardened to be able to cut through nails encountered in cutting openings in existing structures.324002

[george wilson]

Notice in the catalog picture just above,Disston recommends use of their SUPERFINE file. This is,because as I have said many times here,a fine cut file will file harder steel than a coarser cut file.

[Doug McKay]

[QUOTE=Jim Davis;2482879]Daryl, I am sure your experience is as you say. I have to ask--have you filed a No. 12? /QUOTE]

Jim, Daryl is the top, or top 2, hand saw filers in this hemisphere........ I believe the answer is YES.

https://www.youtube.com/watch?v=ug78FQEPvvI

https://www.youtube.com/watch?v=ar5hoQiVjIY

[Daryl Weir]

Daryl, I am sure your experience is as you say. I have to ask--have you filed a No. 12? They are famous for wearing out files. In fact, all the old Disstons are harder than most of the other brands of the time, or after. Doesn't mean they were meant to cut metal. These pictured, from 1918 Disston literature, were made for cutting metal. Also, the No. 10 and other "plumbers'" saws were advertised as hardened to be able to cut through nails encountered in cutting openings in existing structures.324002

Hey Jim,

I've filed more No.12's than I care to admit. They are still my favorite saw that isn't in the no-set category. The No.12 is a little harder than most but still not as hard as an Acme 120. All of the saws in my till are Disston No.12's.

For comparisons sake, I will use on the order of 1 1/2 edges to 2 corners on a Bahco file to file all new teeth in and bevel file a No.12 cross cut but will usually go through a whole file just to file new teeth in on an Acme 120 and that's no bevel, which I use a regular cant saw file for.

http://i279.photobucket.com/albums/kk132/daryl_weir/saw%20storage/till_front.jpg



Sorry for the confusion, I wasn't insinuating that the Disston Acme 120 was a metal cutting saw, only referencing the hardness similarity. However I believe it could be, if filed the same as a metal cutter.

I've filed a few of the metal cutters and they are in the same hardness category as the Acme.

Take care,
Daryl

[Stanley Covington]

Try heating the individual teeth with a soldering iron or even a candle flame. There is no need to heat them hot enough to change blue, as you only need to chase a little bit of carbon out of the crystal lattices, thereby softening the metal of the teeth locally, and not re-temper the entire sawblade. Having relatively less mass than the blade proper, the teeth will heat up quickly, lose carbon, and soften, while the hardness of the body of the blade will remain unchanged.

There are those with limited experience and "a little knowledge" that say that steel must be heated to 650 degrees or whatever to soften it, but this opinion is not supported by tradition, practical experience, or science in the case of localized partial annealing.

Start at the extreme tip or extreme heel of the saw (where the teeth see less use) and soften two or three teeth this way at a time, timing how many seconds the heat is applied. Do not quench the teeth but allow them to cool naturally. Then test the hardness of these few teeth with a file. Repeat, either reducing or lengthening the time until the hardness is just a tad less than what it was before you began the process.

Repeat for the rest of the saw.

Also keep in mind that many saws have been abused in the past by giving the teeth too much set. The mechanized commercial saw sharpeners regularly bent the teeth too far, or too sharply (vs a bend with a greater radius) causing work hardening and stress fracturing to develop at the base of the tooth weakening it greatly. Sadly, there is no way to solve this common problem other than filing the sawblade to remove the damaged metal, since heat treating alone will not mend stress fractures.

Stan

[Kees Heiden]

Are you sure Stanley? I am certainly not a metallurgist, but I play around a little with steel. As far as I know, burning out carbon is something which happens above hardening temperatures. You can soak a piece of high carbon steel for a pretty long time at 1400 to 1500 degree Fahrenheit without much loss of carbon. raise the temperature only a little and it goes quickly, especially in an oxidising atmosphere.

At such low temperatures as a soldering iron, I don't think carbon will be lost. If that would be true, then normal tempering would also lead to carbon loss. Knifemakers often recommend to temper two or even three times, to reduce stress as much as possible, without losing hardness. If carbon would dissapear in meaningfull quantities at such low temperatures, then tempering three times would also lead to significant carbon loss. Heck, give it enough time and even at room temperature carbon would dissapear if it was so volatile. All the antique chisels would be soft as butter if that was true...

But I don't dispute your experience. When I look at the tempering graph for 1095 steel (a very simple high carbon steel, similar to what was used in the old saws) I see that HRc values between 55 and 49 are reached from 600 to 700 degree Fahrenheit. That is exactly the temperature of a normal soldering iron. And indeed a sawtooth is pretty small and steel a poor heat conductor. So, if you manage to get the heat from the soldering iron into the saw tooth, then you are just retempering it, not burning out carbon.

[Stanley Covington]

Yes, I am sure. And partially annealing (softening) steel does not require much carbon to leave the steel and be "lost," if I can borrow your terminology. All it requires is for some of the carbon to migrate out of the martensite crystals. This happens on a comprehensive scale when tempering, as you know, but can happen locally at lower temperatures, in smaller amounts, in standard high-carbon steel. It will not work in high-speed steels, of course, which are formulated to resist relatively high temperatures unchanged.

As you wrote, tempering 3 times can lead to carbon loss, which is the goal. The best blacksmiths know their material and can get it right in one try.

Everytime steel is heated high enough to allow carbon to flow out of the martensite crystal lattices, the amount of martensite in the mass is decreased, and the steel becomes somewhat softer, if even just locally.

Heat the steel too many times, at high temperature, and the carbon will migrate to the surface of the mass and appear as black scale. Repeat this enough times, or overheat the steel (burn it, as the blacksmiths say) and there will not be enough carbon left in the steel to make a decent chisel.

If you have a chisel that tends to chip easily because it was not properly tempered, then the method I described can be used to make the steel a bit softer, but tougher. Give it a try.

[Kees Heiden]

Something new for me to study. Thanks for bringing it up.

[Stewie Simpson]

Hi Stanley. Within your discussion on partially annealing, I assume you avoid quenching.

regards Stewie;

[Stanley Covington]

Hi Stanley. Within your discussion on partially annealing, I assume you avoid quenching.

regards Stewie;

Hi Stewie,

Yes, quenching would be counter-productive.

Blacksmiths often quench when tempering to stop the annealing process, or to keep it from going too far. But, as you know, tempering can be accomplished without heating in a forge or quenching. For instance, soaking an initially heat treated and hard blade in molten lead, or in automatic transmission fluid at the right temperature, will do the job too.

Not suited to partially annealing sawteeth, I suspect

Cheers.

[Stewie Simpson]

Stanley; thank you for your feedback . Its a fascinating subject.

regards Stewie;

[Kees Heiden]

In this post I am not going to give any answers, only more questions.

First question. Why do some old saws have areas with a few hard and brittle teeth? Som ideas:
-Carbon content is higher in those areas. I don't know how likely that is.
- Impurities? Often those lead to lower hardness levels instead of higher.
- Work hardening? The saw blades were tensioned with a hammer after heat treatment. This leads to spots with higher hardness. But they didn't do that in the toothline... This can only be cured with a normalising cycle and new hardening.
- Unequal tempering. This could be something. Just below the spring temper temperature we find a brittle tempering temperature. Most simple steels have this effect that the steel is more brittle when tempered around 550-600 Fahrenheit then when it is tempered at a lower or higher temperature. It is best to avoid this point, but it could easilly happen when trying to heat up a large sawblade all at once to a spring temper. A small area accidentilly being tempered at this brittle temp could explain this phenomenon.
- Any other effects?

The second question. Does a new tempering cycle, at a lower temperature then the original, change anything in the steel? Apart from the temperature you also have the time effect, a longer tempering cycle does more then a shorter one, but this effect is much smaller then a change in temperature. But it is kind of hard to imagine what happens when you heat the steel again to a much lower temperature.

Tempering is a rather complex subject. Steel as quenched is made up of martensite. This contains steel crystals with more carbon atoms then there is room for them, thus putting the crystals under a lot of tension and thus making the steel very hard and brittle. The tempering moves carbon out of the martensite crystals and forms small FeC carbides. The carbon isn't lost from the steel, it can be regrouped again at normalising and hardening temperatures. But this short explanation doesn't really solve the question. Maybe when the tempering wasn't completed on the first try, a new tempering cycle, even at lower temperatures, continues the process.

[Stanley Covington]

Kees:

I will take your questions at face value, instead of the bait with which you are wont to chum the waters of Sawmill Creek.

I think the period of time during which the sawblade was made, the country, and even the manufacturer are important factors to consider when looking at quality. The best manufacturers of yesteryear made better quality saws with fewer defects than others. But manufacturers in all ages did produce (and still do produce) sawblades with serious defects. I think modern sawblades are cheaper, exhibit fewer defects than those made during the Golden Age, and are more homogenous in quality, but at the cost of mediocre technique, materials, and ultimately, performance.

The history of the handsaw industry is fascinating, and indeed important. Let me give one example. Although Henry Disston advertised his products as being made with London Spring Steel, in fact, he created the first commercial steel mill of importance on the American continent, and for decades, was the largest producer and consumer of high quality steel outside of Europe. This was long before the railroad boom. The reasons for his claiming to use British steel, but instead making his own (which was every bit as good if not superior to the Sheffield product), were based on war (he never made weapons, BTW), and public perception. Disston was the world's largest, most skillful, and most respected manufacturer of handsaws in the world for many decades, but British steel had a better reputation. Worth looking into.

Carbon Content: It wasn't until recently that mankind has been able to measure carbon content accurately. Indeed, experience was the key to getting carbon content right, and is one reason blacksmiths had been credited with magical powers in ancient times. So it was not only difficult to get the carbon content right, it was even more difficult to get the right carbon content distributed evenly throughout a sawblade. The same principle applies to swords, cutlery, shears, scythes, etc..

Impurities: Absolutely. Especially silica and phosphorus. Hard to get out and keep out of the steel making process. Try doing it without a modern metallurgical lab.

Work hardening: I doubt hammer tensioning was the main culprit, but the process of setting sawteeth definitely causes localized work hardening at a critical location.

Unequal Tempering: Of course. Heat treatment skills and mysteries aside, this is unavoidable if the carbon content is unevenly distributed.

Others: I suggest you consider work hardening, stress accumulation, and stress cracks due to abuse. Kinks can be worked out of a sawblade, or may not even be readily apparent, but once steel has been bent past the plastic limit, it is never the same again.

Without a doubt, saws are the most difficult tool a blacksmith can attempt to make. QA is a bitch.

With few exceptions, the skills required to make a Disston No.12 are gone. One cannot buy a modern, production handsaw that compares in quality and performance with a top of the line handsaw made in the 1920's and 30's by any of the famous makers. For those who disagree, I strongly suggest you do some research into what makes a truly world-class handsaw.

We are lucky to be able to obtain these old jewels at relatively low prices, certainly cheaper than they could be replicated today. Enjoy them while you can.

Stan