Thread: Hardening of sawplates

I pulled out a few more Disston saws and picked up a few new-to-me saws and have included their hardness data here.

Contest: I'll give two sets of new split nut saw screws, your choice of sizes, to the person that can identify the data points that correspond to the No. 12 and the Acme 120. Yes, they're in there.

Historical hardness survey of Disston saws 092416a.jpg

Ahem..

Rob I think your nuts are relatively safe.

I am guessing that both the No.12 and the ACME 120 show no appreciable difference to other saws or may even not be as hard as other saws. The reason I say this is that allegedly the saw plates were hand selected, presumeably by an "expert", which probably meant the oldest person in the plant, and was not a result of any scientific process back around WW1 and before that.

It really is anybody's guess as to the criteria they used for selection. I would suggest that one of the few things that consistently set these saws apart is their taper grinding, which is significant. I don't have any 120s, but the few No.12s I have always have a delightful tone to them when struck (without the handle on).

Regards
Paul

Alright, I'll up the ante: Ten screws mix and match your choice.

Remembered a few more saws to include. Now it is even more clear why the Golden Age, the points within the yellow box, was so highly regarded - the saws were attractively formed and finished, the screws were finally robust enough to tolerate years of use and the quality control of the steel was the best that it would ever be. Now 28 saws, one per green dot.

Historical hardness survey of Disston saws 092516b.jpg

Ok Rob I'll take a punt. The lure of those saw nuts calls .

Both saws followed a very similar timeline so that limits the period from 1876 to 1924 (1927 in the case of the No.12). Without further information I will go with the first two saws from 1906 (in the first graph you posted in #242).

I think those points correspond to RC 52.5 and 50. I'll say the former is the 120 ACME and the latter the No.12. There, I've probably just done any credibility I may have had until this moment .

Regards
Paul

Paul,

You're correct that the Acme 120 is no harder on average than the other saws from the time it was produced, nor are the two Pre-77 taper ground backsaws. Amazing that nobody has seen fit in the century that has passed since this saw was produced to test the hardness of one of them.

These data show clearly that the marketing claims Disston made need to be examined with skepticism. Woodworkers and carpenters seem to be easily sold on the claims, no matter how implausible, of recognized manufacturers.

I'll let the challenge sit a while and then publish the tabulated results.

Regards,
Rob

I agree Rob that many of the claims may be fanciful at best and outrageously untruthful at worst. I think a lot of the perceived value was to do with aesthetics as much as performance.

It really does beg the question as to exactly what you were paying for. If I go to the Simonds brand, there is negligible difference between the bottom end of the Simonds range and the secondary Bay State line. In fact they are the same price.

It is only when we look at their "third level" saws that there may be some difference. The most notable is the absence of taper grinding and to a lesser extent fewer saw screws fasten the handles. The sawplates do not have the same level of polish and the saws may not have the same degree of tension in them. I have a few of these but at this stage have not got around to re finishing and sharpening them so I can't offer any more observations than that.

What all this may mean is that there are millions of Warranted Superior saws out there still at bargain basement prices and all good performers.

Regards
Paul

Hi Rob.
I dunno why it took so much time for my brain to wake up enough to figure out why I was squinting at the graphs.
I think we should be looking at a scatter plot, given the differing time intervals and repeated measurements.
This is only estimated from your graph, and rounded-off to whole values ...
The linear regression is pretty much flat, and the variability looks arguably pretty even.
Cheers,
Paul

hrc wwf.png

Paul,

I agree. I'm planning to post the data set after giving a chance for guessers. I was thinking of asking a friend of ours, a statistician, to have a look. He could probably extract some interesting insights.

Cheers,
Rob

HRC of Disston saws vs. decad of manufacture 092616a.jpg

I'm not a statistician, but in a related field. I couldn't glean much from that chart in terms of determining what's the acme vs. what's the 12.

The sample size would need to be a lot larger for me to guess at whether quality control and consistency was a problem in any of those years (or worse or better). It'd be easy to make the standard comment that it appears that wartime quality wasn't quite so consistent, etc.

I'm kind of surprised to not see the acme saw being at the top end of file hardness (55 or so), and presume the high dot at 54 is a different saw since it's been in the chart for a while. Overall, with what's shown, I'd say the reputation of disston for not making many duds is well earned. All of those saws should file and hold their teeth just fine - the one that's 54 might be a bit hard on files, though.

(I'm also at a bit of a weakness in terms of guessing at these things because I don't know that much about disston's production methods and I sort of get a saw and file it and judge it by how well it works, whether it has decent stiffness, etc).

I do think it'd be neat to get a hundred or two hundred disston saws, do this, and then do the same thing with simonds and atkins. I've had a fair number of atkins saws, but the only one I ever really liked is the rip saw I sent to Mr. McGee through ebay, admittedly I didn't even loosen the set a little bit, but it wasn't as floppy as the other atkins saws I have, including one that was quite expensive for my tastes.

Rob, what are you thinking? You're closest to the data and most apt to have a thought about whether you're seeing anything discernible.

I've made a few comments scattered throughout my posts but here's a summary.

1) From the earliest saws to the latest there's a trend to increased hardness. HRC ~49 in the early days to ~50/1 around WW2.

2) Variability in hardness in each saw appears to decrease from the earliest saws until the Golden era. The variability increases during the WW2 period and later. Some of these saws, Post-28's, have some areas of anomalously high hardness. Some of these anomalous readings are due to bulges/bumps in the plates, but some aren't. I don't know what is going on with these saws. The variability in hardness appears to decrease during the WW2 period and then it increases again.

3) The Acme 120 is no harder than the other saws or significantly different from the overall average. The particularly hard saw that you point out is not the Acme. The taper ground backsaws that I think may be predecessors of the No.77 backsaw line introduced in the 1870's are also no harder than their contemporaries.

I've decided that the detailed analysis of the trends in the data is best evaluated by our statistician. He can give us a pretty reliable idea of the importance and significance of the trends and power of this series of measurements.

It's also important to remember that the rated variability in the type of tester I'm using is ~ +/- 0.5 units.

Here's the latest calibration data.

HRC tester calibration data and curve 092716a_Page_1.jpg

HRC tester calibration data and curve 092716a_Page_2.jpg

This may help illustrate the trends I refer to above.

This plot shows the changes in hardness of the saws I tested across time.

Variations in Hardness and Standard Deviation of Hardness of Disston Saws 092716c_Page_1.jpg

This figure shows the average of the standard deviations in each time window.

Variations in Hardness and Standard Deviation of Hardness of Disston Saws 092716c_Page_2.jpg

The black lines are cubic trendlines.