I think I know my own answer but am looking for validation.
Currently I have the original SG-250 but have seen good videos of the SB-250
My understanding is that the SB-250 may work better on really hard steels (are any kitchen knives in that range?) and is also a bit more aggressive/fast than the SG-250. But if time to sharpen a knife is not critical (I am retired and only sharpen a few knives for friends and family) then the SG-250 is perfectly fine.
Basically I am looking for a reason to buy the SB-250 in cases where the SG-250 is inadequate
Quote from: eckorsberg on April 27, 2025, 11:15:56 PMreason
The key is in the chemical used in the respective wheels. The SG us aluminium oxide which is suitable for carbon steels which is most knives and hand tools. The SB wheel is silicon carbide which is harder than aluminium oxide and so is better at sharpening alloy steels which are too hard for aluminium oxide. I am talking abut scratch hardness are used in mineralogy. What you are using to sharpen has to be able to scratch the tool or knife being sharpened.
If you have hard alloy steel knives such as Japanese knives that are glazing your SG wheel then you will need to use something harder to sharpen those knives. Either buy the SB, ur hand sharpen using a silicon carbide stone or diamond hone.
Quote from: John Hancock Sr on Yesterday at 12:31:54 AMQuote from: eckorsberg on April 27, 2025, 11:15:56 PMreason
The key is in the chemical used in the respective wheels. The SG us aluminium oxide which is suitable for carbon steels which is most knives and hand tools. The SB wheel is silicon carbide which is harder than aluminium oxide and so is better at sharpening alloy steels which are too hard for aluminium oxide. I am talking abut scratch hardness are used in mineralogy. What you are using to sharpen has to be able to scratch the tool or knife being sharpened.
If you have hard alloy steel knives such as Japanese knives that are glazing your SG wheel then you will need to use something harder to sharpen those knives. Either buy the SB, ur hand sharpen using a silicon carbide stone or diamond hone.
Thank you for that clarification but I guess that leads into a follow up question. How would we know what (Rockwell C) hardness a knife may be? It is possible that we could look up the manufacturer data sheet to get this information but I think I most cases we are presented with a knife with the request "can you sharpen this?" but otherwise know nothing about the technical details of how it was manufactured.
Quote from: eckorsberg on Yesterday at 01:28:34 AMHow would we know what (Rockwell C) hardness a knife may be?
Rockwell hardness is not what we are interested in. Mohs hardness is what determines which griding material we should be using. Rockwell hardness is testing the deformation (ductility) of the material. Mohs hardness is testing its resistance to scratching. If you can scratch the knife with aluminium oxide then you are good to go. But if aluminium oxide does not scratch it you need something harder, say silicon carbide (SB) or diamond or CBN.
Can you tell us what brand of knives you have?