Mirror polish failure...

L

Legendary_Jarl

Joined
Feb 8, 2010
Messages
1,114
Hello,

I got a nice collector's knife that unfortunately came with the blade all scratched up. I have spent several hours trying to bring it back to mirror finish(by hand) and I just keep failing.

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I start with 320 sanding paper and then go 400, 600, 800, 1000, 2000. Then I apply simichrome and remove with cloth. No luck. I have tried this process twice and twice I have failed miserably to get rid of the scratches or bring the blade back to mirror finish.

Is it that I need to get even lower grit? 250?

Is there a tool I could get to make my life easier?

Thank you for any feedback!
 
You won't like the truth. Those are deep scratches.
You need to clamp the blade securely to a raised board such as a 2x4, in a clean area. You need good sand paper such as Rhynowet red starting at 120 grit. Use a hard backing like a block of micarta or even steel. After sanding thoroughly at 120 and completely removing any sign of the scratches, you need to clean the area and move on to 240. The time at 120 will be the longest. I then go 320, 400, 800, 1200, 1500, 2000. Clean up and get fresh microfiber cloths after every few grits, you can't afford low grit debris around. Then switch to pink 4000 grit 3M polishing sheets. For the last couple grits and the polishing sheet you soften the backing slightly by adding a layer of duct tape to the backer.
That will produce mirror. However, the fuller has grooves or scratches in it also. I would have liked to see the entire knife to better assess whether it's worth attempting all this.
It might help to watch the Nick Wheeler hand sanding YouTube video.
 
Legendary_Jarl said:
What's a good example of a professional?
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A lot of the knifemakers or craftsmen on this forum. I was going to suggest posting in the maintenance and tinkering area, but it appears that your thread has been magically teleported there already.
 
i have "hundreds" of hours experience in perfect mirror polishing, down to 0.25micron but realized that especially flats larger than 2cm²

The easiest item to do so is a geometrical object which makes only point (or line) contact with your backed sandpaper, e.g. a wire pocket clip or convex 3D surfaces like a wrist watch.

Anyway.. the nearer you try to reach perfection, the bigger the problem \phenomenon of micropitting (and of burnishing) becomes. PhD doctorates have written doctor thesis on this topic and they
 
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You'd have to remove a significant amount of steel to make those scratches/gouges disappear. I'd say forget sanding, it would require a re-grind of the entire blade.

If you only focused on the areas with the scratches/gouges, and removed enough steel to make them disappear, you would end up with a very uneven, wavy surface. And if only one side were re-ground, then the blade would not be symmetrical.

I think the only two choices are either a complete re-grind or living with it the way it is.

Makes me wonder what the previous owner was doing with it. Stabbing it through the hood of a car?
 
Do you know what type of steel the knife is made of? Are you attached to having a mirror finish? Or just a nice even finish? I ask because if it is carbon steel it might be possible to have it sandblasted and parkerized to give the blade a nice dark military look that will also act as a rust inhibitor.
 
eric brinkerhoff said:
Do you know what type of steel the knife is made of? Are you attached to having a mirror finish? Or just a nice even finish? I ask because if it is carbon steel it might be possible to have it sandblasted and parkerized to give the blade a nice dark military look that will also act as a rust inhibitor.
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I believe it is AUS8. I'm not married to a mirror finish I just want to get it to look nice for display, that's all.
 
fishface5 said:
Maybe go for a satin finish instead and polish the fuller?
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This might be your best bet since you aren’t married to the mirror polish. Pretty simple to make straight scratches, but I also just found some YouTube videos describing the process. Good luck!
 
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Hand rub satin finish with a buff to bring out the edges.

I'd stop at about 320 grit then with a loose sheet of 2000 give everything a light buff with a little extra on the edges/high points. From here buff with cotton wheel or hand rub with polish.
 
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