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Boron Carbide stones

Posted by Eli 
Eli
Boron Carbide stones
April 23, 2015 09:56PM
Chinese vendors offer boron carbide stones in grits from 400 to 1500. I am not aware of equivalent western stones (3M offers loose grit for blasting). Looking the properties up boron carbide is an tiny bit harder than silicon carbide. Are there other differences with regards to sharpening?
Re: Boron Carbide stones
April 24, 2015 05:03AM
Eli, I bought 3 sets ( pairs ) of those boron carbide stones. 2 sets of square slabs 150x20x5mm in 400 and 800 grit and one pair of triangle stones ( fit for Sharpmaker ) in 400 grit.

In mine stones the grit is almost equivalent to same number sandpaper grit. In other words the 400 is a bit coarser than spyderco 600 and 800 is almost like the ceramic in Fallkniven DC4.

The stones are very hard with performance similar to SiC; they practically don't absorb water and show very little wear ( none in practical terms ) with steels like S30V and D2. But like other hard stones they get clogged with steel; I remove the steel with rubber eraser ( used by kids in school ). They are basically used to do micro bevels; in some cases I use them to do a relief with 10 DPS before the true micro bevel.

2 sets came perfect, with no voids and true flat. One of the triangle stone came with little imperfection in one tip but this is no problem since this portion goes in the support slot. I'm very pleased with these stones.
Re: Boron Carbide stones
April 24, 2015 05:52AM
Here a photo of the 3 sets of boron carbide stones and the mount, copy of sharpmaker base slot. The fixed mount with the aluminium slab and boron carbide stone ( fixed with 3M double side tape ) is about 19 DPS for quicly repair of damage micro bevel before aplying new one at 20 DPS ( now I use much shallow angles in majority of my knives ).

Eli
Re: Boron Carbide stones
April 27, 2015 09:29AM
cabraljr, this is a very nice setup that you have built. It sounds like you are happy with the quality and performance of the stones, which is good to know. My question is maybe a bit higher level. Considering the economy of scale (and hence price advantage) of silicon carbide, what motivates Chinese makers to produce boron carbide stones? Maybe they are just experimenting and these stones are going to disappear soon, replaced by cheaper alternatives. Or maybe there are subtle qualities that are going to make them stay as an alternative to their aluminum oxide, diamond and silicon carbide siblings?
Eli
Re: Boron Carbide stones
May 10, 2015 11:41PM
Excerpt from Lapping and Polishing Basics for material properties in loose form and not directly applicable to hard stones.



There are four basic types of abrasives that are used in lapping and polishing processes: silicon carbide (SiC),
aluminum oxide or alumina (Al2O3), boron carbide (B4C), and diamond (C). All of these abrasives have distinct
properties and are used for different materials and applications.
  • SiC: SiC is hard and generally has a needle or blocky structure. SiC is used in many applications where
    rough lapping is required. It seldom is used for polishing or applications that require smooth surface
    finishes.
  • Al2O3: Al2O3 is relatively hard and has a sharp, angular structure. Alumina is commonly used where fine
    surface finishes are required as it breaks down over time and gives excellent surfaces during lapping
    and polishing. Alumina is also relatively inexpensive.
  • B4C: B4C is harder than most other abrasives (excluding diamond) and has a blocky crystal structure. B4C
    provides excellent removal rates and is typically used when fast removal with moderate surface quality
    is needed.
  • Diamond: Diamond is the hardest material known and has a sharp, angular structure. Diamond is extremely
    useful in lapping and polishing due to it’s removal rates and surface finishing qualities. Diamond can
    produce excellent surface finishes combined with high removal rates.
MATERIAL ............................ HARDNESS (KNOOP 100) ... DENSITY ... STRUCTURE
SILICON CARBIDE (SIC) ...... 2450 ............................................. 3.22 ....... BLOCKY, SOLID, SHARP
ALUMINA (AL2O3) ................. 2000 ............................................. 3.97 ....... BLOCKY, SOLID, ANGULAR
BORON CARBIDE (B4C) ...... 3000 ............................................. 2.51 ....... BLOCKY, SOLID, SHARP
DIAMOND ( C ) ........................ 6000 ............................................. 3.51 ....... SHARP, ANGULAR, SOLID
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