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Turning #2: Tool Steel Wear Resistance

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Blog entry by OSU55 posted 03-12-2017 12:17 AM 1604 reads 0 times favorited 7 comments Add to Favorites Watch
« Part 1: Segmented Bowl Process Part 2 of Turning series no next part

As an engineer I’m always curious about claims of big improvements. When it comes to turning tool steel, there are a lot of marketing claims that some of the newer tool steels can get 3x to 10x more cutting time vs standard M2 HSS between sharpenings. There’s also plenty of users claiming the same type of extended life. Thing is, none of the claims by users or companies are supported by factual, objective data. Before I spent my hard earned $ on tools costing 2-5x more than common M2 HSS, I wanted something more than claims.

James T, Staley, Adjunct Prof. in the Dept. of Materials Science and Engineering at North Carolina State
University, Raleigh, conducted a scientific test of tool steels found in today’s turning tools. His findings confirm the claims of extended wear life. However, they also confirm gross exaggeration. The report is “Ranking Wear Resistance of Tool Steels for Woodturning”. A copy of the complete report can be found here (there are some other sites as well):

http://nmwoodturners.org/files/ZerbySharpening/Tool%20Wear%20Testing%20by%20Jim%20Staley.pdf

Below is his final summary chart, showing predicted relative comparative wear of the different tool steels:

His study conclusions:

> Relative wear resistance of tool steels when turning hard, dry wood rank similarly using
either measurements of corner wear or average current of a motor driving the tool into the
wood at a constant rate.

>These measures of resistance to wear increase linearly as the product of Vickers hardness
and the ratio of the volume fraction of carbides to volume fraction of the steel matrix
increases.

> Using this criterion, wear resistance of any tool steel can be calculated if these values are
known.

> All of the steels advertised as being more wear resistant than M2 are truly more resistant.
However, the relative wear resistance is less than claimed.

> Cryotreatment applied to triple tempered tool steel has no effect on wear resistance.

The report contains the methodology and test data utilized to support the conclusions. This is the only objective test I have been able to locate regarding the subject. It’s not surprising that companies make unsubstantiated claims, and it’s not surprising users support the company claims. For the companies, it’s simply called marketing. For the users, it’s called confirmation bias, which is the opposite of buyer’s remorse. In psychology and cognitive science, confirmation bias is a tendency to search for or interpret information in a way that confirms one’s preconceptions. It suggests that we don’t perceive circumstances objectively. We pick out those bits of data that make us feel good because they confirm our prejudices. We spend our hard earned $’s on something that is 5x better, and by golly, it is 5x better!



7 comments so far

View Tomoose's profile

Tomoose

422 posts in 3788 days


#1 posted 03-12-2017 04:05 AM

Thanks for the informative writeup. I agree that it is easy for marketing departments to stretch or manipulate the truth. Being one with a degree in marketing, I would say your analysis of buyer psychology is spot on.

Cheers,
Tom

-- “I am always doing that which I cannot do, in order that I may learn how to do it.” Pablo Picasso

View Woodknack's profile

Woodknack

12842 posts in 2795 days


#2 posted 03-12-2017 07:08 AM

Good info. I’ll have to digest it later.

-- Rick M, http://thewoodknack.blogspot.com/

View Redoak49's profile

Redoak49

4029 posts in 2403 days


#3 posted 03-12-2017 02:36 PM

This is an interesting study on machining wood with tool steels. However, there are a couple of comments that I would like to offer.
1. The type of machining here was a plunge cut and the results of the study are only valid for that type of cut. With this type of cut, the tool and tool tip will heat up significantly because it is contained in a groove. In addition, the chips are also somewhat trapped in the groove and will contribute to the wear on the tool.

2. With other types of wood turning such as with a gouge on the surface, these parameters are different and are likely to contribute to a different tool wear parameters. The cutting tip profile is different than that used on other types of tools like a gouge and will contribute to different forces, wear patterns and heat buildup.

3. The comment on the effect of cryo treatment is likely valid for this experiment. However, there are well documented papers showing the cryo treatment on tool steels enhances cutting on steel. Does this make a difference in turning wood? In some cases, as in this experiment…No. But with steel it does make a big difference.

I am glad to see this type of study and hope that there will be more with different types of tools as it helps develop better tools and an understanding of the process.

(Some may wonder what my background is concerning machinability. I worked as a metallurgical enginer long time in the steel industry making steel with a large part of it in the development of steels designed to enhance machining characteristics. I was involved in the production and testing of these grades and have patents for steelmaking process. Many of these grades had additions of such things as lead, bismuth, tellurium, sulfur, phosphorus and others to make the steel machine more easily with less tool wear. The testing involved various types of tools including plunge cut, drilling, and others and at times what worked for one type of tool did not work as well for others.)

View OSU55's profile

OSU55

2355 posts in 2404 days


#4 posted 03-12-2017 03:39 PM

Thanks for the comments. I believe the relative comparison of wear remains valid for a plunge cut vs a gouge, as well as various tip profiles. As discussed in the paper, failure begins at the grain structure level and the grain structure determines when and how fast it propagates. Just as the test values/#’s would be different for different wood species, different tip profiles/edge profiles would effect the values, and I’m sure there would be some variance. A particular steel may perform better at a particular bevel angle. Also, I do not believe the temperatures reached (not scorching the wood) are a significant factor, unlike machining steels. So, the graph posted could shift a little this way or that – no argument there. At the end of the day, I think the testing debunks the myth of 5-10x greater tool life, which to me is the real value of it. Making a purchasing decision based on a 25% improvement in tool life vs the claimed xxx improvement certainly changed some of my decisions. This does not include different tool design aspects, such as V or U groove bowl gouges, etc. I would love to have the resources to test some of these things out.

View Wildwood's profile

Wildwood

2670 posts in 2549 days


#5 posted 03-13-2017 08:49 PM

I have posted that link here or another message board before. Yes wear resistance manufacturer’s state not always real world due comments already made and my personal experience. Another point not covered in the article is chemical composition of M2 HSS can and does vary. Also what country is producing the HSS tool you are buying. Yes some companies in Sheffield England or U.S.’s count cutting steel to length and putting bevels and handles on them manufacturing!

Think most important thing to know about any turning tool is the actual usable length of that tool. Bottom line all tools need sharpening when dull regardless of steel use to make them!

-- Bill

View Redoak49's profile

Redoak49

4029 posts in 2403 days


#6 posted 03-13-2017 10:27 PM

Wildwood….you are absolutely correct. The carbon alone can vary from 0.78 – 1.05% and with the variations in other elements can leave to a wide range of properties. I know that some producers are going to go to the lowest amount of alloys Mo, W and V to reduce costs. In addition, there are wide variations in as produced properties.

View Wildwood's profile

Wildwood

2670 posts in 2549 days


#7 posted 03-14-2017 03:03 PM

Here is another article like to post although not really complete list of tool brands but good read anyway. Most of the best known tool providers are absent, (Crown, Henry Taylor, etc.).

http://woodturninglearn.net/articles/ToolSteel.pdf

-- Bill

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