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63868 | Louis Michaud <louis_michaud@U...> | 1999‑06‑11 | Some Rockwell C hardness numbers |
GG, This is not a scientific study (low sampling number, etc), but I was supervised by an engineer and the machine is accurate to ±1 Hardness Rockwell C. Just for the heck of it... The numbers stated are from the average of 3 readings. If other Galoots have data for legendary outperforming tools, for other time periods, please send them in for comparison. Or, you could always send me your infill for testing... ;-) Plane irons HRC Record #7 T14 Tungsten steel, laminated 63.2 Stanley #4 SW laminated 62.6 Stanley #5 SW laminated 62.3 (Rev. Hock says 62 for his blades) (LN states 60-62) Saws No.7 Disston Philada 48.5 D8 Disston Philada 44.0 No.12 Disston Philada 48.5 #4 Backsaw Disston Philada 48.9 Bow saw blade, no mark, 24 x 1 in. 52.0 (3 for $1.50, drive by...) (LN Ind. dovetail saw suppose to be 52) Chisels Marple Blue Chip 58.8 TH Witherby Warranted bevel edge 62.4 Stanley #720 60.8 #66 beader blades orig. Stanley reeding 54.5 LN router blade 62.0 #45 blades 62.1-63.2 #46 blades 63.5-63.7 EC Atkins No.5 scraper blade 51.4 When I told him the age of some blades we were testing, the engineer was impressed at the hardness attained. He was also surprised that the teeth of the saws could be bend with out breaking when the metal had a hardness of 48-52, I didn't know better... Louis Michaud |
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64154 | eugene@t... | 1999‑06‑17 | Re: Some Rockwell C hardness numbers |
At 09:33 AM 6/11/99 -0400, Louis Michaud wrote: Good things about Rockwell C readings, mostly snipped out now. GG's I haven't seen any comments on that post, but I have some questions. Way back (quite a fur piece), I yacked about a Disston 12 I found broken cleanly in half, no hint of bending first. It also had several missing teeth. From the condition of the handle I guessed it had seen very little use. Wanting to make scrapers out of the blade, I was surprised how difficult it was to cut up. So I had it tested. I don't know the calibrated accuracy of the machine being used, but it was in the QC lab of a tap and tool manufacturer. On that one we got 52 repeatedly (I would have guessed it was even harder). Now, I'm sure hardness must have varied a lot over the production years or batch to batch with limited QC specs and methods. But if many of Disstons saws performed like this one, the complaint dept must have recieved a lot of nasty e-mail. >This is not a scientific study (low sampling number, etc), ... >The numbers stated are from the average of 3 readings. ... Gotta ask: three whacks at one sample or tests on three samples? Also, I think I remember both Rev. Hock and the Leachmeister doing larger sample testing of old stuff and beta-testing . Has anyone who might want to comment checked anything? Does it sort of fit in with Louis' results? >the engineer... >He was also surprised that the teeth of the saws could >be bend with out breaking when the metal had a hardness >of 48-52, ... ... I couldn't alter the set of any tooth in that #12 blade without hearing that sickening little *snap* sound. Gene |
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64159 | Ron Hock <ron@h...> | 1999‑06‑17 | Re: Some Rockwell C hardness numbers |
I have a good, old, Wilson, WWII vintage, accurately calibrated hardness tester and would be happy to test anything that comes this way (as long as you some green for the return UPS... ) Flat, parallel surfaces will yield the most accurate results and the item must be thick enough for the test to work. Also, we'll get poor results from things surface hardened, plated, or otherwise surface treated. I did some tests some while ago of old Satanley blades, etc. but I had the problem of the laminated blades. In order to test the hard "bit", I would have had to put the little test dimple in the back of the blade and I didn't want to do that. Be advised and if needed recommend a suitable test location on the piece. Also, please note that hardness alone does not a good tool make. There are several other constituents that can make or break (literally) a tool. Alloy, hardening process, hardness, sharpness all have to be right for the thing to work. (There's a joke or two in all this hardness talk.) The Never-Wrong Reverend Ron > Also, I think I remember both Rev. Hock and the Leachmeister doing larger > sample testing of old stuff and beta-testing . Has anyone who might want > to comment checked anything? Does it sort of fit in with Louis' results? > |
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64163 | "George Langford, Sc.D." <amenex@a...> | 1999‑06‑18 | Re: Some Rockwell C hardness numbers |
Hi Gene & even-tempered Galoots ! Gene remarked on the brittleness of a Disston saw whose hardness was in the neighborhood of Rc52. Small wonder. Except for the shock-resisting tool steels (the S series) one should never harden & temper a tool steel in the temperature range that gives a Rockwell C hardness in the mid-fifties. That's because the steel will have its worst possible combination of hardness and ductility. In other words, it will be brittle. Therefore, tools which have to end up in the mid fifty Rockwell C range must be made from S series tool steels, or they must be lower in carbon so that they end up in that range after tempering at lower temperatures. The so-called temper-embrittlement range is around 500 degrees Fahrenheit. The S series tool steels don't drop to the mid-fifties in hardness unless they're tempered considerably hotter than that, so they don't get brittle. Saw steel will therefore perform better if tempered into the mid forties on the Rockwell C scale. Galoots whose saws become brittle after electrolysis can prevent that by baking the saws around 300 F for several hours immediately after the electrolysis to drive off the hydrogen that causes the embrittlement (actually, delayed cracking due to residual stress). A saw whose teeth have already cracked due to omission of the post-electrolysis baking step will have to have all those teeth "pulled" and replaced with new ones filed from the solid. Without seeing the broken teeth first-hand, I can't say which malady did in that Disston, so I've given both of the sad explanations. Best regards, George Langford amenex@a... |
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64173 | Louis Michaud <louis_michaud@U...> | 1999‑06‑18 | Re: Some Rockwell C hardness numbers |
Gene, Rev. Ron and Galoots, >Gotta ask: three whacks at one sample or tests on three samples? 3 whacks at 1 spot on 1 sample. Average the 3 tests and that's 1 reading. Then we took other readings on different areas of the sample. Eliminated highest and lowest, averaged the rest and that is the number given on the list. For the thin saw material, we did a Superficial N test. It still uses a diamond point but loads to 15 kg instead of 150. I gives the hardness only at the surface. A chart converts the N numbers to HRC. On thick saw blades (7, D8) there is no difference between HRC and N. On the thinner material HRC tends to be inconsistent. On the laminated plane blades, the readings were consistent over the lenght of the hardened steel. Elsewhere it fell to 15 HRC (or lower) which is considered unreliable and off the scale. The saws had an even hardness. 3 tests on one spot done on 4 different areas of the same sample. The average of the 3 tests varied only by 0.3 HRC from one area to the other. The D8 had higher variance but I don't have the numbers here. Hardness on the chisels usually went down to 50 HRC about 1 3/4 in. from the tip and then even lower. >be bend with out breaking when the metal had a hardness of 48-52... >I couldn't alter the set of any tooth in that #12 blade without >hearing that sickening little *snap* sound. I took out some set on the bow saw blades at 52 HRC by pressing the blades in a steel vise. It responded well without any snaps. After sharpening, the resulting set was sufficient. I'll see when I have to set the teeth again... >Also, please note that hardness alone does not a good tool make. There >are several other constituents that can make or break (literally) a >tool. Alloy, hardening process, hardness, sharpness all have to be right >for the thing to work. > >The Never-Wrong Reverend Ron I did these tests only to get a general idea of the hardness for different tools/application. I don't consider an HRC number to indicate a quality scale. Hardness is only -1- parameter. I also hoped to get feedback on the variability just for the fun of comparing. Bon rabotage, Louis Michaud |
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64198 | eugene@t... | 1999‑06‑18 | Re: Some Rockwell C hardness numbers |
Thankyou to George Langford & Rev.Ron for adding to the info being absorbed by this sponge-brain. Even tho the blade I was talking about had never been zapped, with lots of Galoots now dumping saws into zap-tanks, one of George's comments bears repeating: >Galoots whose saws become brittle after electrolysis >can prevent that by baking the saws around 300 F for >several hours immediately after the electrolysis to >drive off the hydrogen that causes the embrittlement >(actually, delayed cracking due to residual stress). Sometimes things didn't work out just right at the factories, but we are more fortunate than they were, having Ron and George and others willing to help. Gene (Disston would have paid them for their help dontcha think?) :>) |
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64216 | Douglas S Caprette <dscaprette@j...> | 1999‑06‑20 | Re: Some Rockwell C hardness numbers |
On Fri, 18 Jun 1999 19:51:06 eugene@t... writes: >Thankyou to George Langford & Rev.Ron for adding to the info being >>Galoots whose saws become brittle after electrolysis >>can prevent that by baking the saws around 300 F for >>several hours immediately after the electrolysis to >>drive off the hydrogen that causes the embrittlement >>(actually, delayed cracking due to residual stress). > Oh yeah, that reminds me of a question I forgot to ask: Does this mean that just letting the saw sit around for a week or so before using, or setting it in the sun al say will be inadequate to prevent cracking? |
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