how high to take cobblers knife

[wbusby1]

Hi all,

Just told a cobbler friend of mine I'd sharpen his cobblers knives. They're primarily for cutting leather... should I keep them pretty coarse? I have a 600 grit stone, 1000, 2000 and on up from there but I'm thinking the 600 might be the best finish for leather. Thoughts?

 

[no_one_just_Roy]

I don't know about western knives, but Japanese kawa-bocho (leather knives) need both cutting power and precision so they need to be VERY sharp and most people finish them with around 5000-10000 grit stones, which are finer than ones for average kitchen knives (usually 1000-3000 grit for home use and 3000-8000 for pro use - you should note that people in this forum are obvious exceptions )

A kawa-bocho is almost always a single bevel, carbon steel knife. How about your friend's blade?

 

[lancep]

Is he a cordwainer (shoemaker) or a cobbler (shoe repairman)? Shoemakers use different knives for different tasks -- there is cutting the heavy leather for insoles and outsoles, there is thinning the upper leather for overlapping seams (skiving), there is trimming of the edges of the outsole, there is skiving of heavy leather for toe puffs and heel counters, there is cutting of a channel for the the outsole stitch. Most folks in the trade generally don't take their knives to a high stone, simply because time is money and for many of the tasks something like 1000 is adequate. However, for something like fine skiving of upper leather, a very fine stone could be great.

Many shoemakers make a four sided sharpening paddle, with 3 grades of garnet paper and a side of leather for final stropping. Also, many use grinding wheels and/or leather/paper wheels which allow them to sharpen and/or hone quickly.

 

[wbusby1]

Well, this a single bevel and could be carbon. Although I'm guessing it's cheaper soft carbon if it is and that I shouldn't take it real high because it won't hold that edge for long but I guess I could try and find out. Maybe I'll just stop at 2,000 anyway. No, this guy has never used these knives because they come dull and he has doesn't know how to sharpen at all.

 

[Davidl]

I work with leather and can say 1000 japanese grit knife is sharp. I may attempt to go 6k to 8k, so there may be improvement on high carbon steels.

If you want to know what the purpose of this knife is Im guessing (key term) it is to slice into the leather to open up a channel/slice for stitches, add glue to the channel and smooth the leather to create a hidden stitch in shoe soles.

It may be for cutting roughly pieces of leather.

 

[lancep]

That knife, called a lip knife, is generally used to trim the edge of the sole/welt and the heel. It has a 'safety' tip which is bent at 90 degrees to the blade so that the sharpened edge of the knife won't contact and cut the upper.

 

[wbusby1]

Yeah, I got to watch him use it for just that (cutting the sole) after I sharpened it. I stopped at 2,000 grit but it was far from a perfect edge, I had a helluva time with that steel and that curve and with a stop on either side. I was using the sides of stones and since I was doing it for free I just called it good. He was pleased with the results even if I wasn't.