The Durometer and the Knifemaker

The Durometer and the Knifemaker.

Now the reason for this post you will find out shortly but it is hardness, you understand correctly, hardness but in particular the hardness achieved of the blade you have just hardened.

Surely the hardening and the consequent hardness achieved is one of the fundamental characteristics of a knife and a failed temper results in a low quality knife.

Often we hear about the hardships reached after the hardening but I see few makers certify this hardness through a document that certifies it.

It is not enough to follow the procedure of the tables to achieve the typical hardness of that particular material.

For this reason it is essential to use this tool if it is present in your laboratory as a knife maker or have your test done through a tool that takes on an important role, the hard meter.

Tempering blades in houses

Today many makers temper their blades “at home”, others rely on specialized companies that certify the work done by providing the necessary data but also doing many operations such as turning off and finding with professional equipment.

And that’s why those who temper the blades in their laboratory with more home-made equipment must pay attention to the final result to have a very high level result also as mechanical features of the blade or blades.

Clearly having a certified hardmeter in your laboratory is a huge advantage because it allows you to check but also experiment with the different steel and mode the hardness obtained of your blades.

The durameter is a measuring tool intended to measure the hardness of materials.

There are many types of hardmeters, each intended for a specific application and equipped with its own measurement scale.

To measure the hardness of a material, the hardmeter penetrates it, leaving a fingerprint (called a witness) on the tested point.

On the knife is made on the part of the blade that is covered by the handle to clearly avoid having the sign of the test in an exposed area.

The test can be called a non-destructive test,as the knife maintains its integrity and functionality.

The hard meter still leaves an imprint, so it must be used, either in areas where the witness does not bother, or on special specimens made with the same material to be tested but clearly that is fine when you do tests but certification must be done on the blade.

It is important to note that the test cannot be repeated in the same position (or even in the vicinity of other witnesses): in fact, the surface near a witness is geometrically and structurally modified, and the repetition of the test would result in major measurement errors.

How the hard meter works

The principle of operation of the hardmeters is almost identical for the various types: a tip (called a penetrator) of varied shape, is pushed with a force known against the material to be tested, depending on the hardness of the material and directly proportional to it, this will penetrate for a certain depth.

Measuring the depth of penetration or the size of the footprint indicates the hardness of the material.

Methodologies and scales

With the development of metallurgical engineering, the need to objectively verify the hardness of the alloys was immediately born.

The first engineers independently studied methodologies and realized their instruments.

The methodologies, although practical and functional, were not standardized, and there was no need to tie the scales to the reference metrological systems.

As a result, engineering scales multiplied, linked to the test methodology and instrumentation used.

Only recently, international bodies have been working on the standardization of instruments, scales and created an objective link between the hardness scales and the International Measurement System.

However, even today, several scales of measurement for hardness are in use, each of which refers to its own specific methodology.

Some examples of hardness measurement scales:

• Shore;
• Brinell;
• Rockwell;
• Vickers;
• Knoop, New10014

For a knife maker the scale used and the Rockwell, although sometimes especially when you hear about contact wheels we also talk about Shore which is designed to test the hardness of elastomers or plastomers, for example rubber or plastic, characterized by reversible deformations.

Rockwell Scales

The Rockwell scales are designed to test the hardness of metals.

The unit of measurement is a conventional scale drawn directly from the depth that reached the penetrator, when it is pushed with some force into the material to be tested.

Although two types of scales are essentially used, there are many more, such as the scales A D E F G R R NT W Y.

Each scale corresponds to a preload and a distinct penalty:

• • B scale, used for example on soft metals, with a penetrator consisting of a hardened steel sphere 1/16 inch in diameter;
  • C scale, used for example for thermally treated metals then hardened, with a penetrator consisting of a conical pointy diamond and beamed with an opening of 120 degrees.

This methodology is very practical because, the durometer, in addition to generating the footprint, measures its depth, immediately presenting its measurement in the engineering scale.

Method C is the method we use on knives.

The 5 stages of the Rockwell trial where you:

1. 1. applies for 1-2 seconds, without impact, an initial load of 98 N or 29.40 N;
   2. wait 1-2 seconds and reset the dial to 100 or 130 depending on the test method;
   3. adds to the initial load of 98 N or 29.40 N another final load, for example 1373 N, expect 3-6 seconds;
   4. eliminates the second load to return to the initial preload of 98 N or 29.40 N, then wait 1-2 seconds.
   5. it reads on the dial, with the penetrator always solicited by the initial load of 98 N or 29.40 N.

Once the blade is hardened

This part of the post is a delicate part but you need to talk about, providing you with some tips that I received thanks to some good makers and that it is important to be careful.

I purposely wrote at the end of the post this consideration for those who had the calm and patience of the real maker to take one step at a time to get to the bottom of this post.

The knife once hardened still receives several other operations always performed with the singer tape, abrasive paper, polishing, etc. etc.

Now as you can imagine the part of the blade more delicate is where the thicknesses become more and more fine, then towards what will become the thread of the knife (the sharp part).

The seding tape

A tape that flows quickly on a low-thickness part of the blade overheats it and this can affect the hardness of the blade wire because it can ruin the hardening process that you have performed especially on certain types of steel.

So it is important in the final stage of making the knife to use new abrasive ribbons , this to avoid passing the tape hundreds of times by heating the metal and without taking away material given the poor abrasive capacity lost to wear.

So it is important to use new ribbons and to be very careful not to limestone too much and to overheat the blade and “burn” the metal.

Portable digital durometer models

Over time, technology has created digital hard meters that have very good reliability.

That’s why I want to show you a model that you can find on the Ceroni Knife Shop website and which I’ll put the link of the durometer I’m talking about.

A comparative test was also performed between this digital hard meter model and a traditional hardmeter on the same block to check the reliability of the tool that proved to be quick and accurate.

It works very well! The durometer was compared to the same sample with a galileo certifying hardmeter.

Portable impact hardwood

A fundamental tool to verify and certify the success of the temper and that can not be missing in the ideal laboratory of a knife maker.

Surely this hard meter has the advantage of:

• be very compact,
• a low price compared to laboratory hardmeters,
• you can carry it with you and do some measurement for your friend maker,
• ease of use.

For more information, please contact info@ceroniknives.it

Conclusions

The hardness test, the resilience test, the traction test are the classic mechanical tests performed on samples built with standard dimensions to have comparative data based on different materials.

Clearly for knives making specific tests is crucial and must be built according to the characteristics that a knife must have.

But I’ll make you a specific post about that.

Clearly even doing knife tests is a cost and clearly means building knives that will be basically destroyed.

Rockwell hardness is a fundamental test to certify the knife but it is not destructive.

A knife must have a basic certification that you cannot fail to provide as documentation delivered with your knife if you want to be a level knife maker.

Are You Experience?

Andrea

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