Thread: Saw File Hardness Measurements

calibration mark saw file hardness imanging.JPG

I've been distracted & not following this thread, but would like to throw in a few cents at this point.

As Rob has suggested, I think that hardness of files per se, is not usually the issue. I have struck a few files that have worn far more quickly than average, but by far the most serious problem I have is because the files are simply too brittle & shed teeth like a broken-down old ewe eating gravel.

I accept that a file is working awfully hard to remove metal from saw plate, I know it's not a linear scale, but they aren't all that far apart on the hardness scale compared to filing mild or bright steel, for eg, so one has to expect & accept pretty rapid wear on a saw file. Just how rapidly they should wear is up for discussion, I guess. It's those fracturing teeth that cause me all the bother, though, you cannot get consistency with a file that catches and sheds another tooth or two on every stroke! Is it because of faulty heat treatment, poor contol of alloy composition, or what? I don't know the answer, so if you can shed some light on this it will be a very good start. I do know that we didn't have to put up with anything like this 25 years ago, with files made by companies like Nicholson & Wiltshire. As FF often points out, brand names mean diddly squat, these days.....

OK, watching what unfolds...

Cheers,

Well, back in town and catching up with fora discussions. Rob yet again puts in the hard yards. We can conclude that there is a suitable range of hardness, and the subject files are within it (files not included in the testing, China, perhaps N*n, may not be). So what causes the brittle teeth? Is it the poor grinding/honing of the steel blank? Is it the poor cutting of the teeth? Or both in combination?

Do we have any data on the differences between top quality steel (Sweden, Japan, perhaps some US) and lesser quality (India, China, Latin America), and the size/cost of those differences? I suspect the cost of steel does not vary much on a per file basis. Where do the Swiss source their steel?

Cheers
Peter

Originally Posted by Heavansabove

Well, back in town and catching up with fora discussions. Rob yet again puts in the hard yards. We can conclude that there is a suitable range of hardness, and the subject files are within it (files not included in the testing, China, perhaps N*n, may not be). So what causes the brittle teeth? Is it the poor grinding/honing of the steel blank? Is it the poor cutting of the teeth? Or both in combination?

Do we have any data on the differences between top quality steel (Sweden, Japan, perhaps some US) and lesser quality (India, China, Latin America), and the size/cost of those differences? I suspect the cost of steel does not vary much on a per file basis. Where do the Swiss source their steel?

Cheers
Peter

Hi Peter,

My conclusion from the present study is that hardness is a necessary but not sufficient condition for user acceptance. If the file is adequately hard then other factors dominate. I suspect that roughness, i.e. uniformity of the toothed file surface is a big determinant but we need more work. I have four additional files, all new, that I plan to work to death using my Foley filer. Lately however I've been overloaded with other tasks. When I get my current batch of dovetail saws made up I may have time to get back to this study.

Interestingly I have been working my way through a box of new 5.5" Nicholson XXS files. Very inconsistent. I had one wear visibly to the degree that it had a bit of a sway back from simply sharpening one saw - no toothing just the first shaping of the teeth. The other files in the box that I've used so far have lost teeth (2), worn okay and done an acceptable job (2) plus the one that is soft as putty.

Relying mostly on my stock of older and better files has prevented me from encountering this issue until now. I now see very clearly what everybody is upset about.

Cheers,
Rob

Originally Posted by rob streeper

.....Interestingly I have been working my way through a box of new 5.5" Nicholson XXS files. Very inconsistent. I had one wear visibly to the degree that it had a bit of a sway back from simply sharpening one saw - no toothing just the first shaping of the teeth. The other files in the box that I've used so far have lost teeth (2), worn okay and done an acceptable job (2) plus the one that is soft as putty......

Yes, I think it's the inconsistency that bugs me the most! Like getting a box of files of a certain brand (brand painted on, which is immediately suspect!), which were barely tolerable, then another batch about 9 months later, ostensibly the same files, that were absolute rubbish - took two files to tooth in a 12" tpi saw, and the results were far from perfect!

Been thinking about the implications of your hardness testing, Rob. One problem I see is the need to grind off the teeth to get a smooth testing surface. As I understand it, the teeth are upset on a soft blank, then the file is hardened & tempered. It seems to me that the teeth are going to take up/give off heat at a very different rate from the body of the file, and so it's possible they end up at a different hardness. Body hardness may not truly reflect the tooth hardness, and this might be one explanation why user perception doesn't quite match your hardness results ????

Just a thought.....
Cheers,

Originally Posted by IanW

As I understand it, the teeth are upset on a soft blank, then the file is hardened & tempered. It seems to me that the teeth are going to take up/give off heat at a very different rate from the body of the file, and so it's possible they end up at a different hardness. Body hardness may not truly reflect the tooth hardness, and this might be one explanation why user perception doesn't quite match your hardness results ????

That's a very astute observation Ian, and I totally see the logic.

Yes they are punched up, which is why they are higher than the blank, unlike a milled file where the top of the teeth are the same height as the blank - because the teeth are milled (funnily enough). That would no doubt mean they've been work hardened too, but I guess that affect disappears completely with the subsequent heat treatment.

It would be kinda like very shallow case hardening, and may be all wiped off by the grinding. You may also have unearthed some inkling as to why the teeth are so brittle. If they are quenched incorrectly (too fast) then the teeth would suffer the most by far, and may even be well up over 60Rc compared to what lies beneath (and it ain't the prize in this case )

Originally Posted by IanW

.... a box of files of a certain brand (brand painted on, which is immediately suspect!)

Ah, I see the power of repeating that ad infinitum is paying off......

So, just once more for emphasis:
If the brand is printed on - be afraid - be very afraid.

Originally Posted by IanW

Yes, I think it's the inconsistency that bugs me the most! Like getting a box of files of a certain brand (brand painted on, which is immediately suspect!), which were barely tolerable, then another batch about 9 months later, ostensibly the same files, that were absolute rubbish - took two files to tooth in a 12" tpi saw, and the results were far from perfect!

Been thinking about the implications of your hardness testing, Rob. One problem I see is the need to grind off the teeth to get a smooth testing surface. As I understand it, the teeth are upset on a soft blank, then the file is hardened & tempered. It seems to me that the teeth are going to take up/give off heat at a very different rate from the body of the file, and so it's possible they end up at a different hardness. Body hardness may not truly reflect the tooth hardness, and this might be one explanation why user perception doesn't quite match your hardness results ????

Just a thought.....
Cheers,

I haven't been able to track any definitive information down on the alloy(s) used for making files beyond some discussion of W-1. W-1 is a so-called 'shallow' hardening tool steel. I looked further into what is meant by shallow and in this case it implies that the depth of hardness induced by water-quenching (W-1) is about 8 mm, suggesting that the files are hard all of the way through given their dimensions. It is also possible that the files have been over-heated during processing resulting in irreversible damage to the steel.
Though the results will be of limited in generalizability I'm going to do microscopic, manual usability and machine wear and hardness testing of the remaining four files from this batch to see if I can detect any issues. I'll put in a couple of the Nicholson's from the box I discussed above.

I've acquired some files from a source new to me - Corradi. These files are apparently marketed both by Pferd and Corradi, though there are some discrepancies between the literature offered regarding the product specifications. Looking into the individual companies I don't see any direct connection. Pferd being a marketing name of August Ruggeberg GmbH & Co. est. 1799 and Corradi is a 5th generation family owned company est. 1910. Perhaps they collaborate on the Corinox line?

I've been watching with interest their Corinox files for some time now. I recently became aware that they're manufacturing Corinox needle files in three cuts, 00, 0 and 2. These correspond to 51, 64 and 97 teeth per inch respectively (PFERD - Literature).

These files, according to the manufacturer, have hardness in the range of HRC ~70 and are marketed for use on hard materials. Intrigued, I decided to spring for a box of #2 cut files. I also purchased a box each of 4" (66 tpi) and 4.5" XX slim (64 tpi) taper sharpening files marketed under their Iridium brand. The files arrived via express courier yesterday morning.

My initial impression is that the files are very nicely finished. Uniformity on visual inspection is very good.
Further I did a couple of hardness measurements using the HRN45 scale of my Ames hardness tester on both the XXS 4" files and the Corinox needle files. The 4" sharpening files have an average HRC 64 and the Corinox files are, as the manuracturer claimed, very hard at HRC 70.

I did a little sharpening with both the 4" and Corinox needle file and the cutting action of both files is excellent.
Using a hand glass I examined the edges of the files that I tested after use and found that the 4" XXS file showed very minimal signs of having been used. The Corinox file looked as-new.

Sounds like the best news since the Industrial Revolution....

You've got my attention with one word, Rob - 'consistency'. I like to use a new side or fresh file for a final light 'polishing' stroke across each tooth. Given the files we get these days, it's not easy - you're lucky if the corners on the same file are a reasonable match, let alone the next one out of the box! If we can have consistency and an appropriate degree of hardness as well, who could ask for more? ....

Cheers,

Corradi have come up before in discussion. I remember commenting that they call Saw Files "3 Square" incorrectly.

Here's the shop:
Three Square Saw Files Extra Slim Taper - Corradi Shop, High quality files and rasps

They only ship to USA/Canada (no big deal for someone with a Shipito address or similar).

Prices are in Euros, which is a bit weird for a USA shop. Actually reasonably smart from a merchant's point of view because they can then adjust the price according to the current exchange rate. Pricing of imported goods must be one of the trickiest things to do, but this way solves the problem.

Rob, what's the taper like? Worthwhile as a taper or just lip service?

Yes, it's starting to come back now. I remember being a little sceptical (at the time, 2 years ago, in the big thread). They say on the Home page "All our products are made in Italy", but then in the Needle files section "these are made for us in Italy". Nothing really wrong with that at face value (but the only other Italian manufacturer that I know of is Stella Bianca and I very much doubt they could make a decent Needle judging by the Taper files - you have them in your possession Ian), BUT the Needles sure look like a rebranded Vallorbe/Glardon Needle which would mean that they are made in Switzerland (nothing wrong with that either, but it ain't Italy). We know that V/G do extensive rebranding for many other companies such as F.Dick.

O'course at the end of the day, if the files work - who cares where they are made.......

Immm
I'm following this one for sure

Yep, gotta take more measurements. Results will be reported on this thread. Hopefully I can get some done tomorrow to address the dimensions of the files. Overall, the 4" Iridium sharpening files look a lot, profile wise, like the Logier file included with the package from Brett.

These are some closeups of one of the Corinox needle files that I've used. A new file is included in each frame for comparison (upper) and the used file (lower).

Corinox needle files new above used below 1.jpg

Here with different light.

Corinox needle files new above used below 2.jpg

The lower file was used to sharpen three saws. First a 14" 14ppi rip tenon saw on a 0.025" plate, then a 19" 10 ppi crosscut half back saw on a 0.032" plate (yes, I know it's the wrong size file) and finally on an 8" 15 ppi rip dovetail saw on a 0.015" plate. The file shows no visible evidence of having been used. Amazing.

The scale divisions = 0.1mm/line.