Thread: Hardening of sawplates

As I mentioned over here (https://www.woodworkforums.com/f275/9...24-26-a-213028) at post #9, No. 12 handsaws from the Golden Era are significantly more consistent in hardness than are other Golden Era saws.

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Just a brief update.

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Seems that the various makers of handsaws operating at around the time of 1896-1917 Golden Era had somewhat different ideas as to the best hardness for their products.

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I picked up a new-to-me Ames 4-4 portable hardness tester today.

Ames 4-4 portable hardness tester.JPG


This will complement my existing testers allowing me to make measurements on the 150kgf HRC scale in the shop. It also provides a useful backup/check to my existing instruments.

This is my HR 150A.

HR150A hardness tester.JPG


Chinese made and consequently only finely finished where it really needs it - rough everywhere else. With proper adjustment these are very fine instruments. Problem is that it isn't at all portable and it really doesn't take well to being moved.

Both of these testers can do measurements on the HRB (with carbide ball indenter) and HRC (with diamond indenter) scales with loadings of 50, 100 and 150kg. Unfortunately these loadings are too high for thin materials like saw blades when the thickness gets below 0.032" or so.

This is the Ames 2-S 'superficial' hardness tester. As with the above two instruments there are two indenters corresponding to the Rockwell N and T scales. For hard materials like saw blades the N scales with loadings of 15, 30 and 45 kg are used.

Ames 2-S superficial hardness tester.JPG


While checking the function of my new find I thought to compare each of the testers on the same set of hardness calibration blocks.

Historical hardness survey of Disston saws 050917a_Page_49.jpgHistorical hardness survey of Disston saws 050917a_Page_50.jpg
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Surprisingly the linearity of all three testers was virtually the same. I expected that the Ames testers would fall down compared to the HR150A.

Here are the corrected, and in the case of the 2-S HRN45 -> HRC converted, measurements.Historical hardness survey of Disston saws 050917a_Page_47.jpg



As you can see, the HR150A shows a much lower variability from measurement to measurement. I attribute a lot of the variability observed with the Ames testers to the relatively poor resolution of their read-outs.

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When properly set up and calibrated the HR150A beats the portable testers hands-down. These testers are available used starting at about $300US. Shipping will be expensive but for about $500 all-up you can save yourself the kind of trouble I discuss in this thread (The importance of testing.).

Chinese copies of the Ames testers are selling right now in the ~$800 range. Used Ames testers come up all of the time on eBay for less.

With tools like these you can actually know what you're doing when you heat or hammer on a saw blade, no guessing or judging colors needed.

Immediately after posting the above I was browsing eBay and happened on this.

New Abe MRBR-DI tester.jpg

This is a New Age Instruments MRBR-DI multirange hardness tester. This is an apparently obsolete line as I couldn't easily find it on the website. It has two advantages for me - first the design allows me to measure things that I can't easily measure with my other testers such as anvil faces and second it offers the alternative of Brinell scale measurements.

As above I tested it with the following results.

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Excellent linearity and precision is comparable to the other instruments. Accuracy is easy to correct using Excel.

There are a number of these available at prices that undercut the Ames testers and are much cheaper to ship than the HR150A type instruments. Highly recommended.

The latest data. 116 Disston saws included here.

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Some descriptive statistics.

Historical hardness survey of Disston saws 082117a_Page_19.jpg

The dataset is up to near 90 pages now so I won't tire you with additional details but Disston Golden Era saws are the most consistent in hardness and are more consistent than the saws of any of their major North American competitors.

This is how Disston Golden Era saws compare to the contemporary competitors.

Historical hardness survey of Disston saws 082117a_Page_54.jpg

The average Disston isn't the hardest, Richardson was a little harder. Disston No. 12's however were harder, in the statistical sense but practically only about 5%.

Where was the thread about tensioning saws?

I had a need to hammer a saw to stiffen it today. I was given a woodrough and mcparlin saw (didn't check spelling there), and it had a brown cake of rust (uniform patina-ish, but thick. Not flakey).

I also got a scotch brite wheel a couple of weeks ago and decided to remove the gunk and blue it. When I did that, I must've taken all of the stiffness out of it - it flopped with a clank, a lot like a cheap saw.

I hammered the tooth line straight (it lost its straightness), but still floppy, so I hammered a few hundred strikes on each side from top to bottom (i recognize that some accounts describe the rollers working nearer the tooth line), and end to end and got a large fraction of the stiffness back. Out of sheer luck, still straight after the strikes, but fixing that would've been no issue.

This is the first time I've had the opportunity to take a saw that had really lost its stiffness and hammer some back into it and see the difference in use.

David,

Here's the thread on tensioning: Saw blade tensioning for panel and hand saws

I've found that the key to tensioning handsaw blades is to apply a lot of lighter blows.

My thinking on the subject has evolved since I started these investigations and I am now of the opinion that tensioning, as it applies to unsupported handsaw blades, is more a matter of adjusting the tension rather than instilling it. Interesting that you've found your saw is stiffer in response.

Confusing the matter is that the word 'tensioning' is used in at least five distinct senses in the realm of saws generally. The tensioning of handsaws, circular saws and bandsaws all involve hammering the blades on an anvil. Bandsaw blades are also tensioned in another sense between the rollers/pulley's. Backsaw blade tensioning is accomplished by moving the back relative to the blade in such a way as to straighten the toothline.

Yeah, I give up on the word "Tensioning", I don't know what it's called. At the ground level, it's useful for a rank and file user to be able to add stiffness to a saw when it needs it. I was just about out of mental stamina last night when I posted that, and I also failed to take a decent picture of the saw (but that doesn't matter). It's just got even hammering all over the surface.

I have never removed nearly so much material from a saw, but this one was given to me, so I felt like it was a good one to experiment on. To set it aside and not use it would've not been in the spirit that it was given to me. It's not like I removed a couple of thousandths or anything, just the surface, which is where the stiffness apparently was.

I wouldn't suggest the average person use a deburring wheel to remove rust from a good handsaw, though, leaving the rust in situ and covering it with wax is probably a better idea. the sensation with this saw after removing the rust was that it was loose, but it had critical points or something where it would feel loose and then almost "clank" once it got to a certain amount of flex.

I'm no longer buying saws, but if I do going forward, and one is floppy, I'll hammer it. Not sure if the same thing could be done to a cheap impulse hardened tooth department store saw, but I may try that sometime. There's no reason to suspect anyone else would be interested in that (I'm not really , more just curious).

Ditto on the lighter blows, though. I never hit any of my saws that hard. Probably about as hard as one would nail a finishing nail, but with a short stroke. Small blows keep any variances in straightness in check.

Another way to adjust the tension in a handsaw blade is to grind the surface. If you're inclined try grinding one side of an old blade and, if you cut down into the steel enough, you'll see that the blade tends to become concave on the ground side.

I bounce the hammer on the blade, only giving enough additional impulse to keep the head bouncing with the same amplitude, a lot like dribbling a basketball. The handle is used mostly to guide the the head around the saw, not to power it into the steel.

What hammer weight are you using? I'm only using a 24 ounce hammer, so it needs a little, but in the end, the force is probably about the same. My saw has scuffs all over it (on both sides, hardened metal anvil under it), but the scuffs pretty much disappear with an application of oxpho blue.

One of the most useful things I ever learned in converting tools in disrepair to usable was hammering, and it's one of those things that if you can observe results at all, you can come up with something workable without knowing too much other than that both surfaces contacting the saw need to be burr free and that you can't or shouldn't "whack the crap out of" the saw.

Without the desire to hammer, this saw would've been undesirable with the cake of "patina", and unusable once it was removed without the extreme care that is necessary when using a saw that is slack (and that's no fun at all).

Hard saw, though (the macparlins). Did you test any of those? I always tell people that you can get by fine with mexican nicholsons, but I had two files from the transfer point when nicholson went to mexico, and they couldn't handle this saw. A quick tooth reprofile and then application of fleam made three files very shiny despite being careful to file outward and taking extra time to do that.

I still hold disston in the highest regard. Not too hard on files, good durability in the wood, stiffness more consistent than anything else I've gotten. The McParlins when they're clean are also very good, and very stiff, but the hardness is not a gain in practicality - it is a file killer instead. I don't think it's by accident that disston got the market share.

Never tested a Woodruff & McParlin branded saw. Of all of the saws I've tested the hardest individuals were Disstons. I have a WW2 period D-8 that has some very hard spots of HRC 55 or so but overall it really isn't exceptionally hard on average. The hardest of all is an Acme 120 with an average hardness of HRC 57.25.

For handsaws in the 0.030" to 0.035" range I find a hammer of about 2 pounds works best. A lighter hammer just bounces around a lot without making much progress and using a heavier one, such as a 2.75-3.25 pounder carries the liabilities of denting or over working the blade.