dealing with a really bad burr

[Cliff Stamp]

Yesterday, I sharpened a very old carbon steel knife of this pattern :

It ground very easily on the belt sander. I was using a worn 80 grit belt and it removed steel faster than using a fresh belt on most modern cutlery steel. It also produced a large burr which was visible by eye.

I did a few passes on a 600 grit DMT hone to apply a microbevel at 10 (primary was 5) and it just pushed it from side to side. Very high angles (45 degrees) did nothing.

To remove the burr I had to hone right into the Spyderco medium which just squashed the burr flat then alternate very high angles on the DMT 600 and repeat twice.

I finshed by going back to 10 degrees on the DMT and then refining on the Spyderco medium.It was a wonderful example of how a knife can have excellent grindability and be horrible to sharpen.

-Cliff

 

[gunmike1]

This weekend I'm about to jump into some old knives I inherited from my grandfather. This will be my first chance to break in my DMT X coarse that should arrive tomorrow. Considering the looks of some of the knives I think I will be frustrating the hell out of myself with some burr experiences similar to that. On the plus side there are some decent looking Forschner kitchen knives among that group, though they just appear to have never been sharpened.

 

[Dog of War]

Cliff - were you sharpening edge leading on the belt sander?

I've never experienced a blade having such extreme problem with burr formation like you describe .... so I'd like to ask, is a blade with this behavior really worth sharpening? (assuming it's not a case of it being the only tool available)

As I work with more knives and have become more critical and consistent in the way I judge performance, I'm coming to think it's generally true that stubborn burr formation is a good predictor of poor edge retention and less than optimal heat treat. I realize on machetes and similar some might feel there's a working advantage to running the blades soft, although IMO better steel selection could make a significant improvement over what you usually see with these. Similar situation with these Dexter Russells I would guess, aimed at the meat worker who still uses a steel.

 

[Cliff Stamp]

The big problem with the carbon ones is that the patina often goes into the edge and it keeps falling apart until you get all that rust ground off. Your best bet is to grind them sharp, and then if an excessive burr forms, grind right into the stone and then reform it. The steel grinds so readily that reforming the edge is almost instant. You might want to pick up a large bastard file as well because some of those knives can be filed and that is way faster than a stone.

-Cliff

 

[Cliff Stamp]

Cliff - were you sharpening edge leading on the belt sander?

Yes.

I've never experienced a blade having such extreme problem with burr formation like you describe ...

It is pretty common on some of the softer blades, especially the stainless ones. It tends to be really common on the heavily used blades, I wonder if it isn't actually fatigue damage.

I'm coming to think it's generally true that stubborn burr formation is a good predictor of poor edge retention and less than optimal heat treat.

Yes and yes.

I realize on machetes and similar some might feel there's a working advantage to running the blades soft, although IMO better steel selection could make a significant improvement over what you usually see with these. Similar situation with these Dexter Russells I would guess, aimed at the meat worker who still uses a steel.

There is cost. It would be obvious that if you used a shock steel on a machete and made a blade which was 54-58 HRC (depends on the steel, peak the toughness). You would get a much better blade in all respects than the mystery alloys which are often really soft. However you can't expect this for $5. In the machetes they are likely just air cooling with a single temper with no cold treatment.

-Cliff

 

[STR]

Those are the kind of knives I usually use a butchers sharpening steel on Cliff. I rarely use a steel otherwise but on those older ones or ones that I refer to as "grandma's butcher knife steel" I've found they just seem to do the job better than anything else I've tried out. Can't say why. Maybe you can figure it out and tell us.

STR

 

[Cliff Stamp]

Those are the kind of knives I usually use a butchers sharpening steel on ...

The ones I get though are massively rusted/worn, the bevels don't intersect so they need a lot of steel removal. I don't even know how they were used. I had one before this which was so rusted you could see through the blade above the edge, the blade actually turns serrated as you sharpen it and the edge intersects the holes. Nice point about the butcher steel though, I'll make a note to try a file the next time. This was always the way they were sharpened here, I don't think I have ever seen a stone used in the kitchen or on the wharf.

-Cliff

 

[Dog of War]

Thanks for the reply, Cliff. I wonder if years of having been steeled and never otherwised sharpened could have contributed to the extreme burring.

 

[Lucky Bob]

I don't think I have ever seen a stone used in the kitchen

It depends on the kitchen... I worked in a fairly upscale restaurant for a summer, and there was a fairly high-grit japanese waterstone soaking under the counter that all the cooks with with japanese style knives would use before their shift. As for european style knives, I think everybody used ellipsoid diamond "steels".

 

[Cliff Stamp]

It depends on the kitchen...

Yes, I meant locally.

I wonder if years of having been steeled and never otherwised sharpened could have contributed to the extreme burring.

It seems likely to me because that is how you would expect fatigue to effect the blade and I see the same thing on a smaller scale if I let a large chopping blade blunt extensively (won't slice paper) before I sharpen it. It would be fairly easy to check, just see if the effects stabilize over time.

-Cliff

 

[Cliff Stamp]

I cleaned up a few cheap utility kitchen knives and they exhibited the same behavior. I cut them on an 80 grit belt which formed a huge visible burr, 1 mm+ wide. An attempt to remove it with a 600 DMT rod just pushed it around. Even using a 200 silicon carbide waterstone just pushed it around which was unusual with that waterstone so again the knives were cut into the stone and then the edge reformed with the waterstone, then actually polished with a 4000 and microbeveled with a 600 DMT. Normally jumping from 200 to 4000 isn't productive but this was really soft stainless and it ground extremely easy. Blades easily sliced paper towel though likely not for very long.

-Cliff

 

[db]

Very good way to remove a bad burr, Ben at EdgePro suggests the same method.
http://www.knifeforums.com/forums/showpost.php?post/723328/

 

[knifetester]

Use new belts on these knives. That may help, or it might not.

 

[thombrogan]

Use new belts on these knives. That may help, or it might not.

Welcome back, KT! For honing, worn belts can do well. For removing lots of steel without messing with the temper, new, sharp belts (or well-cleaned old, sharp belts) are the ticket by my fool reckonings.

 

[Cliff Stamp]

Use new belts on these knives. That may help, or it might not.

I general it always helps to minimize burr formation if the abrasive is of higher quality. I use really cheap belts, but mainly I consider the belt sander just a shaping tool.

-Cliff

 

[knifetester]

Yeah, I use my belt sander for hogging off metal mostly. It is also the only method I use on machetes other than a file or grooved steel in the field. I never worry about fatigued metal that way!!

Thom-
thanks for the welcome back, I don't know for how long, as my family and career keep me prety tied up most of the time.

The BM705 and 730 you sold me (both M2 CF handles) are often carried, especially the 705. On trips to urban areas the 730 is my primary carry. The 730 still has the same edge you applied, just a light stroke on a ceramic rod now and then to keep it honed like a razor.