Ken LeVan - Posted - 03/01/2018:  18:06:14

Does anyone know of a conversion factor that will convert Janka values to shore D values?

link-o-sausages - Posted - 03/01/2018:  23:59:36

That would be tricky as janka and shore are measured in similar yet functionally different ways. I would assume that the pore structure of wood wouldent give you very accurate shore values, Hence the janka method.
Why do you need this kind of data?

Ken LeVan - Posted - 03/02/2018:  05:06:30

I make two things that require the wood to be hard: fingerboards, and now wooden tone rings. each for a different reason - the fingerboards have to resist being scratched and hold the frets, which softer wood wouldn't do as well. In the case of the tonerings, we know that wood is "squishy" compared to metal and to get a good head bearing, we want a hard material.

The Janka scale was developed by the flooring industry and has to do with making a dent in the wood with a steel ball - one kind of "hardness-spike heels on the nice new floor: - this is important for floorboards, but not for banjo fingerboards and tone rings.

The Shore D scale is used to measure the hardness of synthetic materials like hard hats, tires and bowling balls.  We all know that there are a number of new fingerboard materials because the use of ebony and rosewood is becoming more and more ecologically indefensible every passing day - Dalbergia of any species is already verboten. How do they measure the hardness of various "ebonite" materials?

In my own practice, I have been working on impregnated wood for fingerboards and tonerings. I showed this on a thread I did about fretless banjos - my "FretNaught" which has an impregnated fingerboard and tone ring.  I know that my materials can have Shore D values ranging from the 80s to 95 and are basically scratch proof with fingernails (which would be measured on the Mohs scale - yet another "hardness scale).

Ongoing, it would be handy for me to know where. let's say rosewood would fall on the Shore scale, or where various thermosetting resins would fall on the Janka scale -just for my own development.

I also make nuts from a matrix composed of bone dust and a very hard stamping die resin, which is probably harder than pure bone, certainly harder than Corian, but I'm curious.

I can buy a Shore D durometer, and that may be the best approach, even though, apparently the ones I can afford are not as accurate as the industrial ones, but at least I would get an apples to apples comparison and could make my own chart.  My reason for this thread was to find out if anyone else has done that.

Edited by - Ken LeVan on 03/02/2018 05:07:19

sculliganman - Posted - 03/02/2018:  09:26:20

Found this on google: " mandolincafe.com/forum/showthr...-hardness ".

mikehalloran - Posted - 03/02/2018:  09:48:59

"How do they measure the hardness of various "ebonite" materials?"

There's Rockwell: how high a diamond bounces and MOHs: resistance to scratching

Although MOHs is important with nuts and frets, I wonder how relevant it is with fretboards aside from giving an indication of the material's resistance to fingernail wear.

Ken LeVan - Posted - 03/02/2018:  11:04:06

I read the Mandolin Café thing a few days ago when I started to search -they bought a durometer, which I may wind up doing, and yes - what I am interested in is fingerboards wearing through by fingernails, which is what happens to them. There is a reason why fingerboards are not normally made from walnut or cherry.  It's not the strings that do the damage, as is normally thought, but the fingernails of the players. strings wear out the frets, fingernails make divots in the fingerboard.  With fretless banjos, it's a different story, and abrasion resistance to strings themselves becomes important.  So many scales, so many ways to express hardness - Janka, Brinell, Shore, Mohs, etc.

In the case of the hardness of the fingerboard, it's only the surface down one mm or the depth of the fret tang that's important.

I will figure this out, and I only asked the question because I thought someone out there might have gone through the same exercise.

rmcdow - Posted - 03/02/2018:  16:00:54

Hi Ken,

I think what you want to know is not going to be measurable by either Shore D or Janka hardness, as it looks more like you are concerned about would be described more accurately as wear hardness. Janka was made to measure wear as well as hardness, but I never quite understood how this could work, as it is only a dent test.
Mohs is a hardness scale that assesses this in one way, but still not what you want, as it is a scale of the scratch hardness of materials as compared to each other. I believe what you want is a scale that measures abrasion resistance.

Here is a pdf that outlines an abrasive wear resistance test that I think is closer to what you are looking for. I've used this type of test to test the thickness of gold plating, using 400 grit sandpaper rather than 80 grit, and it can be done with consistent results.

academicjournals.org/article/a...20Pdf.pdf

Ken LeVan - Posted - 03/02/2018:  16:42:18

quote:

---

Originally posted by rmcdow

Hi Ken,



I think what you want to know is not going to be measurable by either Shore D or Janka hardness, as it looks more like you are concerned about would be described more accurately as wear hardness. Janka was made to measure wear as well as hardness, but I never quite understood how this could work, as it is only a dent test.

Mohs is a hardness scale that assesses this in one way, but still not what you want, as it is a scale of the scratch hardness of materials as compared to each other. I believe what you want is a scale that measures abrasion resistance.



Here is a pdf that outlines an abrasive wear resistance test that I think is closer to what you are looking for. I've used this type of test to test the thickness of gold plating, using 400 grit sandpaper rather than 80 grit, and it can be done with consistent results.



academicjournals.org/article/a...20Pdf.pdf

---

Thanks Rives!!

This follows what I have been thinking, which is that density, as in the Janka scale is not necessarily the best measure of suitability for flooring or a fingerboard, and density does not necessarily correlate with "hardness" or abrasion resistance.  also, woods that have certain substances in their structure (the ones that dull tools) are more abrasion resistant. and that the abrasion resistance / hardness of woods that are not naturally the densest / hardest can be enhanced and made to be as abrasion resistant as the densest ones.

rmcdow - Posted - 03/02/2018:  21:56:47

The study is interesting in that it does demonstrate that quartersawn wood is going to wear better on a fretboard, which is intuitive, but good to see it proven. I don't know what their setup was for the abrasion testing, but it seems like a flap sander against the face of the wood for a set period of time and exact distance from the wood, before and afterwards weighing the wood, might give some results that could be useful.