M2 vs M42

[John Keeton]

What an amazing wealth of information you folks are. I've been eyeing up those d-way and Thompson tools, I'm going to add them 1 at a time as the need arises.

John, the flute profiles Doug uses are different than D-away and one or the other may suit you better. I started with a Thompson V bowl gouge and wore it out over a few years. I am on my second one, but now prefer the D-Way profile. For spindles I prefer Thompson. I agree with Reed on sharpness. I sharpen on a 600 grit CBN and can’t tell a difference in the edge. On durability IMO it depends on the wood. It it has a lot of silica I think the 10V does a bit better, but that is pretty subjective on my part. They are both excellent tools and it really comes down to what works best for you. I have several of both!

[Neil Strong]

I don't agree with his call on edge sharpness and the V10. The sharpening discussion comes up regularly, and the consensus seems to be that edge sharpness is pretty much the same for all metals that we use, but some are easier to get to that point than others.

Sharpness is to some extent a subjective measure. My subjective judgement has been that M42 takes a finer edge and keeps it for longer than V10 when used for light fine finishing cuts.

I confirmed this when I undertook some controlled tests in which I compared several steels, including M42 and V10. Here are my results...

Light finishing shear cuts .png

But, V10 holds its edge for longer compared to M42 when used for heavy cuts...

Push cuts in hard redgum.png

The Tt is the results is for Tantung, which outperformed both V10 and M42 on the heavy cuts, but didn't do so well on the fine finishing cuts.

The metallurgy explains these differences, but how a tool is used also effects the result, thus the difference between the light finishing cut performance compared to the results from the heavy push cuts.

These side by side test were all done on very hard Australian woods using traditional bowl gouges that were all ground on the same grit wheel (#360) to a 55* bevel angle. As John Keeton points out, flute profiles can make a difference in performance. All of the test gouges used in the above tests had parabolic flutes other than the M42, which had a V flute profile. I attempted as best as I could to control for any difference in flute profile.

[David Walser]

These debates are always fun and interesting. However, on the question of whether M2, M4, V10, or any of the other common high-speed steels used in making turning tools, can be sharpened as keenly as the others, this has been answered in the lab. One of the ways to reliably testing the sharpness of an edge is to use an instrument that measures the force necessary to cut through a standardized, calibrated medium. The less force this takes, the sharper the edge. (See, for example, the Edge-On-Up Edge Tester. There are other brands that use, more or less, this same method.) There are other types of instruments that measure the sharpness of an edge. My point is only that there are instruments that measure an edge's sharpness, and it has been demonstrated through the use of those instruments that all of these tools can be sharpened to same degree of fineness. That is, any differences in sharpness can be accounted for by the variability of one sample from another sample of the same metal, or any differences fall within resolution of the test instrument.

So, why do so many of us believe that one of these steels can be sharpened more finely than the others? I think two things are going on. First, each of us is a sample of one. Our experiences are unique to us. Your M2 gouge is different from mine, even if they were made in the same factory. Each piece of wood that you turn is different from the wood that I turn, even if it is the same species. Heck, each piece of wood that you turn is different from the next piece that you'll turn. Given all this variability, is it any wonder that we might have different impressions of how sharp an M2 gouge might be compared to one made from M42 or some other steel?

The second reason is really a subset of the first. It is that some of these steels are harder to sharpen than the others. When I started turning, a lot of experienced turners used high-carbon steel tools for making their finishing cuts. The claim was that high-carbon steel tools could be sharpened to a finer edge than the (then) new M2 tools. Well, that wasn't true. M2 tools could be sharpened to just as fine an edge. What was true was that the methods these turners used to sharpen their high-carbon steel tools didn't work as well with the newer M2 tools. So, it wasn't that the M2 tools couldn't be sharpened, it was that the turners couldn't sharpen them. I think, but don't know, that something similar is going on today.

[Neil Strong]

So, why do so many of us believe that one of these steels can be sharpened more finely than the others?

~:~

Because we know from experience that they can be sharpened more finely and, more importantly, that some steels hold a fine edge for longer. Not perhaps as much of a difference as some tool makers would want us to believe, but there are differences, otherwise why would anyone bother with any of the alternatives, regardless of any differences in the effort or cost to make them sharp?

What the cutting test like the CATRA cutting test do for knives is standardised the conditions (eg % of silica in test material) under which a knife is tested for the durability of its cutting edge when used in a slicing action.


But, such devices in themselves don't tell in a single test run result is the more complex interplay between edge geometry, carbide size and tool presentation that we deploy in wood turning.

For those that might be interested in such things, the following article goes into some of those complexities...

https://knifesteelnerds.com/2018/06/...dge-retention/


Going back to the results from my light fine finishing cut test that I included in my post #17, and repeated here again...

Light finishing shear cuts .png

... the protocol that I used to measure the durability of the fine cuts was the continuous length of the fine shavings coming off the gouge. A steel was knocked out when the fine shavings coming off it fell below 1" in length, which is the point at which I considered the gouge had become too blunt for this cut and tear out likely to happen. Here is what I was measuring...

Shavings off finishing wing cuts.jpg

The bevel angle on all of the gouges in that test run were ground to 55°, so that was a controlled variable. My interpretation of the results is that the finer carbides in M42 allowed the acute wing edge to cut fine shavings for longer than the V10. It took and kept its fine cutting edge for longer. On that test with that particular cut the M42 was definitely sharper than the V10 if the CATRA criteria of “How long will the sharpness last?” is used.

[PJ Seiber]

Thanks guys, this has been interesting to say the least. Very informative. Like I said I'm kind of a noob and as I invest in tools I want to get the best bang for my buck. I'm looking at more for durability and sharpness. A BIG THANKS AGAIN.

[John Keeton]

One other factor to consider - an edge is created by bringing together two surfaces. With most other woodworking tools, both surfaces are honed to an equal grit to produce a fine edge. In woodturning, typically our gouges are ground only on the outside surface. There are exceptions like the skew. If one of those surfaces has visible mill marks that are not honed away there is an inherent barrier to obtaining a fine edge. The flute of a D-Way gouge has been polished. Many or most other brands have not.

I haven’t reviewed this thread recently, but I don’t recall that being mentioned.

[George Yetka]

Metallurgy, is quite frustrating it would be nice if there was 1 steel to rule them all. Something that had strength, edge retention, antirusting, ease of putting an edge , etc etc. I find you have to pick your favorite 1 or 2 attributes for a blade and suffer on the rest

[Neil Strong]

One other factor to consider - an edge is created by bringing together two surfaces. With most other woodworking tools, both surfaces are honed to an equal grit to produce a fine edge. In woodturning, typically our gouges are ground only on the outside surface. There are exceptions like the skew. If one of those surfaces has visible mill marks that are not honed away there is an inherent barrier to obtaining a fine edge. The flute of a D-Way gouge has been polished. Many or most other brands have not.

John makes an important point here. It is well worth the effort to put a fine polish on the working end of the flute if it doesn't come with that. I can't see an existing thread on methods for doing that, so I'll add that to my to-do-list.

The other tool that we use that benefits from a polish on its working face is the scraper.

I've been making some bowl gouges recently and at the end of that process I take the grind/polish on the flutes down to a finer finish than I will grind the bevels to. An inch of polished flute will suffice for as many re-sharpenings of the bevel that most of us will need if we are grinding with CBN wheels.

Here is the latest one I have been working on, which has been made from tungsten carbide...

10X flute after polishing.jpg

Needless to say, when I'm doing side by side test runs of the different tool steels I bring the flute polish up on all of them to the same level of finish and grind the bevels on the same grit wheel.