Scratching up the blade!! Help

[Joshua]

Hey guys, new to the wicked edge and to the group. I sharpened about a dozen knives now and have had a few issues, but worked through most of them. However… not sure about this one.

I jsut got done sharpening my SBD evo typhoon, and noticed that I had some pretty decent scratching up the blade from the bevel on both sides, but more on the left. When I noticed this, I tried to slowly walk through the motion that I was using to learn from my mistake, but couldn’t see how the stone would have been able to touch the blade… I’m kind of at a loss. Some assistance would be greatly appreciate. I’m using the Pro 3 system and reprofiled to about 19 degrees (from 18 on left and 20 on the right).

Was this just me being careless with the cleaning of the blade while sharpening, or has anyone else ever experienced this? Thanks all!

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[Marc H]

Welcome to the Forum:

Scratches are commonly seen with new systems.  Several issues can contribute to them. First, newer stones just getting broken in tend to shed loose abrasives with use.  New stones can be messy and will get better in short order.  As your working the edge the loose stones can be dragged across the knife side steel.  The loose abrasives can may get picked up on your finger tips too..

A real common source of the knife blade scratches are by allowing the top edge of the stone to slide below the bevel before lifting the stone off and away from steel contact.  It’s easy to get a good rhythm going when muscle memory kicks in and over run your sharpening strokes.  To avoid or prevent this many of use stone stops.  The term is used generically for any thing placed on the guide rods below the stones to stop the downward motion before the stone stop slides below the bevel.

Forum member “airscapes” makes and sells a fully adjustable stone stop with a cushion bumper.  His stops work great. They can let you set the stone side range to match each knife you clamp then you lock them tight.  Here’s the link for accessories.  I use both upper and lower stone stops, above and below the sliding range I need to use, to limit my sliding motion, both up and down, to keep my stones centered on the knife edge.  They allow me to use as much of the stone’s surface as possible without going off the edge, both up off and down below.

My last suggestion is to protect knives your sharpening,  especially when they’re special knives, by applying blue painters tape just below the bevel along the full length.  This helps protect the steel from any unintended contacts.

Your vertical-like scratches suggest you may have brought the stone edge, with some loose abrasives, below the bevel. Cleaning the blade while sharpening can scratch it if loose diamonds are caught in the cleaning material, but I’d expect those scratches to be more horizontal like a wiping stroke, not up and down, like a sharpening stroke.

Here’s another thread on this issue.

 

Marc
(MarcH's Rack-Its)

[Joshua]

Thanks Marc, I appreciate the thorough reply. The blade is not very long, and when “recreating the incident,” it doesn’t look like the stone caused it by direct contact, because the tried to twist it around ad I couldn’t get it to touch that part of the blade even when I tried. If I had to guess, it may have been that when I was using the newer, low grit stones (100 to reprofile), their may have been some loose abrasive that came off and when I wiped it down with the paper towel, it dragged the abrasive. I believe the tip needed a little more reprofiling, so I’ll bet thats what happened. Dang… lessons learned.

I will definitely be investing in some stops just for good measure though, thanks for the heads up on that!

Follow-up question then. If it was the abrasives coming off and me dragging them that scratched it, what method is best for removing loose shavings between stones? I was just using a dry paper towel or cloth. Is there a better way to avoid this?

Thanks again Marc, I appreciate you sir!

 

Josh

[Marc H]

For loose abrasives that haven’t come free yet, I’d use a dry nylon scrub brush and a shop vac or compressed air.  The pronounced shedding will stop soon as the stones get better broken in.

Marc
(MarcH's Rack-Its)

[tcmeyer]

I don’t believe in the loose abrasive theory.  The scratches are too uniform for that.  What are the chances of catching a piece of loose grit and wiping it down the side of the blade so as to cause such a scratch?  And then repeat it almost exactly?  And exactly what was it that wiped the side of the blade in such a manner.  If it wasn’t the stone it must be a finger.  Nope, I’ll opine that the scratches are a result of interrupted or misdirected strokes which dragged a corner of the stone down the side of the blade – oops!  I’ve done it any number of times and it’s always been my fault.

I have a neurological deficit which reduces my hand-eye coordination, so I use a trick to give me better control of the stone’s position throughout the stroke.  When using “down and away” strokes (my preferred method) I eyeball the top edge of the stone and line it up with a point just above the far end of the blade and I move the stone along that line watching it throughout the stroke.  This effectively gives me “closed-loop” control of the stone as opposed to “open loop control”  where I tell the stone to follow a pre-planned path and then hope that it does so.

For “down and toward me” strokes, I can’t use the same method, but I still eyeball the point at which I first touch the stone  to the tip of the blade.  With moderate speed strokes, I can still begin my strokes within a quarter-inch or so of the intended point on the stone face.  As the strokes ends very near to my body, the accuracy of this end of the stroke is less of a problem than when my arms are waggling out in space.

[Joshua]

Thanks TC, that’s a valid point. The problem that I have is trying to recreate the incident. I have put the knife back into the clamp at the exact same spot and no matter how I angle the stone on the rod, I cannot get it to touch the blade where the scratches are… I use up-away strokes, but maybe something was off when I was initially trying to reprofile towards the tip.

Regardless, thanks for the advice. I have heard a lot of people talking about a downward stoke, and I think that I am going to have to try it. maybe I’ll get better results.

[tcmeyer]

There’s a couple of good reasons to use downward (edge leading) strokes.  The major advantage is it reduces the chance of breaking away fragile bits of the edge.  Imagine a tool machining a groove across span of steel.  When it reaches the far edge of the span, it will tend to break away any particles of steel which might not be held solidly in the steel matrix.  In strokes going the opposite direction, the tool enters the span, engaging the steel where it has solid backing to support it, hence less chance of edge breakage.  Clay Allison has done some testing where high magnification photos have supported this theory.

The other major advantage of edge-leading strokes is the fact that your fingers spend almost all of the time below the level of the edge.  Think blood.

I think that the edge breakage issue is less important at higher grits, but I adhere to it with all grits (except w/ strops and DLF, of course) as a matter of good practice.

The following photo is an extreme-case example, where a 200-grit stone with a not-yet-broken-in cluster of diamonds ripped a chunk out of an edge.  You can see that the damage to the edge is way bigger than the groove approaching it:

• This reply was modified 2 years, 9 months ago by tcmeyer.

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