Is a Disston D12 really superior?

[Kees Heiden]

It certainly looks like you are on to something!

And yes you can file 56 HRC. Once I tried to file sawnotches inthe edge of cheap hardware store chisel. I don't know it's exact hardness of course, but it is a usable chisel. It worked but it was damned hard on the file!


BTW, I wish I could find Rob Steepers messages about this on the Australian forum again. At the end he got some very usefull information. With a raster, covering the entire surface of sawplates he could see a pattern that looked remarkably like a hammer tensioning pattern.

[Patrick Chase]

I calibrated the tester as I always do, using the N30 superficial scale. The result of the measurement was exactly 74 N30, which roughly translates to 61 on the Rockwell C Scale. That is as hard as most chisels, but yet was made to file. In flexing the blade, it doesn't seem any stiffer or prone to fracture than any other of their saws. If you accept the premise that using spring steel to cut iron was a pretty demanding application, then the measurement I took on the #12 of 56C is not at all surprising. Attached is a picture of the saw, major load removed to allow the reading. The superficial scales use the outer green ring.

Where are you getting those superficial to C-scale conversions?

The normative tables in the ASTM E18 spec equate 74 N30 to an approximate hardness of Rc56, not Rc61 as you state. See table 9 in ASTM E18-03. Ditto for the tables here and here.

If your conversions were consistently off by that much then everything would make sense IMO.

[Pete Taran]

Typo Patrick. I wrote 74 but as you can see from the photo it is 78 which is 61 C (approx). I'll correct the original typo for posterity.

[Patrick Chase]

Typo Patrick. I wrote 74 but as you can see from the photo it is 78 which is 61 C (approx). I'll correct the original typo for posterity.

Thanks for the correction. I confess to having read the text and not looked at the picture (and also not extended enough benefit of the doubt). Sorry about that!

I'll defer to your greater experience on this one. As you know files have to have a certain amount of hardness "margin" to cut for any nontrivial length of time, and in my experience Rc56 (to say nothing of Rc61) is pretty iffy with anything but a very hard chromed file like a Valtitan. The fact that we work very small cross-sectional areas (single gullets or the tops of teeth) with saws undoubtedly helps to start the file cut cutting, so this isn't comparable to trying to file an Rc60-ish chisel or something like that.

It may be that my technique is less than ideal, or it may be that we have different notions of acceptable file life. It seems to me that it's also possible that the sawplates in question might be somewhat face-hardened for one reason or another (the N30 -> Rc conversions assume uniform hardness, obviously).

Thank you for a very educational thread. I really enjoy this stuff, as you may have noticed.

[Kees Heiden]

Face hardening certainly is a possibility. Those plates are hammered. But I also have not nearly enough experience and knowledge in this field to comment any further.

[Kees Heiden]

Finally, I found the thread on the Australina Woodworkforums. I don't know if I can add a link here, but when you open the Handmade saws forum, which is under Home made tools and jigs, and when you look for the thread about saw plate hardening, you'll find a huge discussion. It gets really interesting towards the end where Rob Streeper presents a bunch of data on a whole lot of saws. I don't know how statistically relevant his data set is, but it is more then I've ever seen somewhere else.

[Pete Taran]

Nice theory, but it doesn't hold up to Disston's own stated process by which they blank, harden, temper, tension, grind, polish and straighten in that order. If there was any work hardening, it would be removed in the grind and polish phases. Plus, I don't think there is a lot of hammering at the edges of the plate, and 2 of the 3 measurements I take are at the edges of the plate. There is no pattern I've seen where the edge values are lower than middle which would support the work hardening theory. And even if it were, I average the three values to get a composite reading for the saw, so it would be the same relative to all other values.

I don't know why some marvel that old time saw makers made some really hard steel. They obviously didn't have the kind of statistical control they did today. Some were harder than others, some softer than others. Such is the way of random variation present in all manufacturing processes. To the 56 C that I mentioned, remember that someone in the Disston plant had to file it the first time and deem it worthy of the Disston name. If it were too hard to file it would have never made it out of production. But yet it did which tells me it was within their accepted norms for that model. I don't think Disston had any fancy chrome plated files in 1900, so whatever they made in the plant is what they used.

[Pete Taran]

I browsed over the thread that Rob was working on. I'm not a member so I didn't look at his data, but it looks like his findings are consistent with mine. The premium saws as a group are harder and with less variation than other saws. The only thing that gives me pause is his use of a junky chinese tester and not a Wilson which in the analog world is the coin of the realm. Having said that, while his readings may not be accurate, they are probably precise.

[lowell holmes]

If I did not already have a 12. I would be on this in a heart beat.

[Kees Heiden]

Not everything from China is bad.

The discussion on woodworkforums is a bit of a train wreck, so it is hard to find what he did exactly. But he has more then one hardness tester and made quite an effort to calibrate them using hardness testblocks. He has a live long career in measurement technology, so I suppose he knows what he is doing.

Otherwise I agree. Outliers with very high hardness sure do exist. 56 HRc made me pause for a while, but sure, why not?

[lowell holmes]

My D-12 is restored with a new curly maple handle, new saw nuts,and cuts like a dream. It is 12 tpi.

[Charles Guest]

I recently went on a saw buying binge. I ended up with four new saws. I acquired a 8tpi panel saw with the notch. I also got a D7 10 tpi, a D8 10 tpi, and a D12 10 tpi.
They are all cross cut saws.

For the life of me, the D7 seems equal to the D12 except for maybe the wood in the handle.
The handle in the 8tpi panel saw is the superior handle with the lamb's tounge. It is most comfortable to hold and the handle is eased on the edges more.

Except for the D12, these saws were inexpensive. The D12 was a $70 saw.



My worn down D23 10tpi is a better cutting saw than any of them, but the recently acquired saws need sharpening and the set needs to be made smaller. They seem to rock in the kerf.

I look forward to messing with them.

I didn't notice much difference. Sold the 12 and made a few bucks on it. It was an old one that I bought from a very reputable expert, so it was in good fettle. It was a rip saw. Couldn't tell much difference between it and a 7 rip of the same length and tpi. Lot of hype with the 12s if you ask me.

[Kory Cassel]

It's all in the sharpening and geometry. If the D-12 has a thinner plate, less set, and the same geometry as the no 7, it should cut faster if they are both sharp. That is the only thing that makes one bit of difference. Fancy steel is marketing hype for hand saws IMO. The most logical contention is that the no 12 and D-12 need that fancy steel in order to be ground so thin. I don't personally buy it, but many just straight up fanatical saw guys do. If the 7 is sharpened better than the 12, it will cut better even with it's 'inferior' steel.

[Pete Taran]

Kory,

I know the reason why "many straight up fanatical saw guys do" think that there is a difference in the steel. It's because as fanatics, we collect, observe, measure, study and make informed decisions about what's real and what's not. Opinion and conjecture is just that, opinion and conjecture. You should come on board the reality train and leave arm chair observations behind. It's a fantastic journey!

Happy Sawing,

Pete

[lowell holmes]

The reason I have a saw vice, saw set, and a wallet of saw files is so I can experiment with and sharpen my hand saws.

It is nice to put a board on my saw bench, strike a cut line with a tri-square, and cut a board without having to get the "skill saw" out.