A scratch pattern question

[Aaron Rosenthal]

I don't want to kick a hornet's nest, so please forgive me .........
I know some have displayed an unhappiness about the granularity of the DMT Extra Extra Fine diamond plate. Everyone has their preferences and I don't want arguments. That's not my question.
When I sharpen going through the gradients to the above plate, then using a leather strop charged with green Chromium Oxide, I still have minute scratches on the face of the blade, whether chisel or plane. The back is flattened.
I use PMV-11 blades in my newer planes; regular bevel down blades in the Baileys, and I've no idea on the chisels.
My question is, how much is my smoothing, cutting, chopping, etc. is degraded by the remaining noticeable scratches on the mating surfaces of my irons?

[Jim Matthews]

Precious little.

The magic happens right at the cutting edge.

[Scott Winners]

I have noticed a couple users here have jewler's loupes to check their edges when sharpening. I have been thinking about grabbing a cheap loupe since I spend a fair bit of time looking over the top of my bifocals at my edges.

At the end of the day, if the finished surface of the wood meets your approval, then your tool is sharp enough. If your tool is a pelasure to use, it is sharp enough.

M2c

[Jack Dover]

If you can see the scratches then they're probably from coarser stones, unless your eyesight is so sharp you can see ±3 microns with a naked eye. Diamond plates are indeed vary in granularity, I think DMT has specs for tolerances on their website somewhere, and since diamonds are hard-wearing, there's always going to be scratches. You, however, can alleviate it a bit by reducing pressure on a tool when sharpening, but you won't probably get a perfect mirror polish like oilstones\waterstones can produce.

Getting back to your primary question: you should rather be looking at surfaces left by a blade, not on a blade. If the surface is smooth then your cutting edge is good enough. Speaking from personal experience using DMT plates for quite a bit I can tell you that scratches were never a problem (other things were though) or even a remotely noticeable factor in tools performance.

[ken hatch]

Aaron,

Sharp is sharp but, there's that damn but that is always there. Mostly what the type of scratches and the pattern affect is the surface of the wood and the life of the edge. Diamond plates and synthetic stones have "grit" and will leave deeper and sharper sided scratches vs. natural stones. Those sharp sided scratches can produce a shine that will seem to blind you but when looked at under magnification show up as deep (relative) scratches. I haven't tried all synthetic water stones but that is the case with the ones I have tried such as Shapton stones and diamond plates. Most natural stones will not produce as shinny a surface as a synthetic stone but when the cutting edge is looked at under magnification it is much smoother.

All that is getting pretty deep into the sharpening weeds but if you want the best and longest lasting cutting edge use either Ark stones or JNATs.

ken

[Andrew Pitonyak]

On the back, no difference. At the cutting edge, well, that depends on a few things.

It MIGHT leave a scratch on the surface if it is at the cutting edge. Is your final surface, then it might not matter.

I believe, not sure why, that scratches at the cutting edge may promote other edge failures in the vicinity of the scratch.

I usually use a loop, I like them. Sometimes I use this, a USB microscope that I can connect directly to my phone or computer.

https://www.amazon.com/gp/product/B07DRGR6LX

I usually use this type where the focus is at the base and the base is clear to let light in.

https://www.amazon.com/gp/product/B009NVEM6U

I also have this type, well, I have this one actually as well, that folds into a case

https://www.amazon.com/gp/product/B00EXPWU8S