Irritating little scratches on a mirror finish?

S

spencer

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Hi everyone,
I don't post here very often because I usually get what I need from searching the various forums, and Ive researched this topic for years now; normally getting the same info repeated over and over again, but I'm having a problem, and was hoping someone on here could help. Before I ask my question, let me say thanks to everyone that has contributed to these forums; you've made my life a lot easier. I make knives full time now, and Ill be the first to say that I have been lucky to have the sales I do, mostly through groups and people that I'm associated with. I have predominately made tactical, wilderness survival, and fighting knives, so I never had much need or use for a mirror finish; I just did satin finishes, or coated them. Every once in a while I would get a request for a mirror finish, and they always came out pretty good. In the past year or so I have started to make some hunting knives and other designs that really need a mirror finish and are expected to have one. So here is my question: How the hell do I get rid of the ultra fine scratches every time I do a mirror finish? I have tried so many different belts and polishing compounds in the past year, I should own stock in the companies! What I'm talking about is the irritating little scratches that keep showing up after polishing. My normal process is to grind up to a 220 (AO) before HT, then after HT I clean up with a 220 (AO), 400 (AO), 600 (AO), 1000 3M Trizact, 15 micron 3M, 9 micron 3M, then buff on sewn muslin wheel with Matchless green, then loose muslin wheel with matchless white. I don't know at what part in the process I'm getting these scratches but I get them every time. They are very fine, kinda like 600 grit or so. I'm fairly positive I'm removing all the scratches from the previous belts as I progress (not saying it cant be me, but Ive been doing this for about 12 years now, and I really don't think its because I'm missing them as I progress). When I finish, I have a very deep mirror, and you cant even tell there are scratches at all , if you hold it at the right angle. Just like everyone else, I'm just trying to get better. I don't know what else to do. All of the knives this is happening to are made from O-1, A-2, and D-2; I had read somewhere that tools steels don't take a mirror finish as well as the stainless. Is this true? Any suggestions or help would be greatly appreciated. I haven't had anyone complain about this, but it bugs me that I cant correct it. Thanks in advance.
 
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Spencer, I know exactly the frustration you're having. I do know the more chromium a blade has, the better mirror polish you can get. I'm sure you're doing this already, but just to clarify......are you alternating your sanding direction when you change grits? If you do, and the scratches that ruin your mirror finish run edge to spine, you know the problem doesn't lie with the grits you sanded horizontally. My guess is this.....you're doing everything you need to do correctly, but DUST, or some other fine partiulate is getting in your way at some point. Can you see the scratches before you take the knife to your buffer, or only after? Mirror finishes are very difficult to perfect!
 
I am by no means an expert, and this is probably obvious, but cross contamination of grit may be an issue. Clean all surfaces completely before moving on to the next grit or compound size. Make sure your hands and all tools are clean and strops/pads of a certain grit are stored/kept away from each other.

I did some sample prep in college and we did a lot of lapping and polishing. Cross contamination of media sizes was probably the biggest source of scratches.
 
Thanks for posting samuraistuart. I'm not hand sanding at all, I'm hollow grinding, so no I'm not alternating directions. I had thought about going to hand sanding, but I was afraid of getting uneven scratches in the hollow. I can see the scratches kind of when I get into the micron belts, but not as much as after I buff. It seems like Im missing some step between 600/800 grit and 1000. I don't know.
 
I thought about the cross contamination thing, but this has been going on forever now, exactly the same way every time. I'm pretty sure its something I'm doing, or a step Im overlooking.
 
Another thing you can do, to pinpoint the problem, is paint your blade all over with a black chisel tip marker between each grit step. This should aid you in seeing at what point it is you are not removing all scratches from the previous grit. This can also be done by etching lightly in ferric chloride, or wiping the blade on and off with naval jelly. Anything to blacken the deepest scratches so you can see when they come out.

Also, having a couple different shades of strong light, and looking at the blade carefully from all directions between grits my bring the issue to light.
 
Thanks for that tip, Salem!

Loveless' book and video on knifemaking has some interesting tips on mirror finishes- my impression is that he depended heavily on the green rouge, and would really lean into it to "smear" and blend any imperfections. He didn't go that fine on belts, but let the "green chrome" do a lot of the work for him.
When I was doing a lot of silver work, we regularly rotated (ha ha) the buff wheels, adding new ones for white rouge and demoting each one to a coarser compound, rather than using one with just one compound for its entire life. That way you kind of end-run some of the contamination issues.
 
I would suggest the buffing wheels. They can easily attract dust and contaminates that will scratch your blade.
 
I do think it has something to do more with the buffing end of it. On the Loveless legend video he says he is using a roughing wheel on the buffer, and your right Elementfe, he does rely on the buffer , and lean into it. I have no idea what a roughing wheel is though, and I have to say, a lot of makers go way beyond the 600 or 800 grit Bob Loveless used. Does anybody on here use some real stiff buffing wheels with a heavier compound to remove fine scratches? If so, what are you using? Again, the scratches look to be 600 or 800 grit. they don't show up till I'm into the micron belts. I keep going back to 400, and sometimes 220, starting over, trying to remove them; then every time I get done, there they are. by the way, I like the idea of demoting the used wheels, that's great!
 
I went through a similar problem and I buffed the blade after each grit to get a clear picture of where the scratches were, turns out they were from the belts and I was just not seeing them after the next grit. Without varying the angle it is really tough to know if you have the previous grit scratches out. Buffing, expecially after 600 grit is usually a eye opener, some of the scratches left look like canyons, once you get rid of these then the other grits go really quick. I buff then mark the larger scratches with a marker, go to the next grit, buff and mark. really helps see if you are really getting these out or just hiding.
 
Until recently the Loveless Shop/Jim Merritt would grind to 15 Micron, coarse grey compound then green. 15 Micron is around P1200 in the European grading system. I started using two new felt backed film belts from TruGrit and Jim has started doing the same. They come in a 1200P and 2000P. With the felt backing you eliminate the joint bump (can cause scratches) that most finer film belts have. With the tiny bit of cushion they also have a bit better life.

I do add in a 2000 and 2500 grit hand sanding then buff with green and lastly pink scratchless. I only do the hand sanding to make sure I minimize time on the buffer and maintain crisp lines. I also keep a hardened piece of steel next to the buffer and I constantly strip the buffs and add fresh compound. As a reminder to reload the buffs break a small piece of compound off the bar and keep it in your hand while buffing. Let the compound work for you not the buff.
 
I have recently tried black emery on a sisal wheel leaned into it and created a whole new set of canyons very aggressive.
Not sure where in the grit progression the black should fall.
I haven't achieved a good mirror yet. But have been doing the same as Patrick to ID scratches between grits.
 
I believe your problem is as Patrick stated. You have not removed the scratches from the belt grinder. I do almost 100% hollow grinding. I find I must go with at least a 400 and 600 hand sanding procedure. If you see scratches, back up to your belt grinder. You can after that go first to the black rouge and then the green or white but using different buffs of course.
 
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Thank you David; exactly what I was looking for! Thanks so much everyone for the suggestions.
 
Well Im not sure how far it is from you but I would take a trip up to RW Wilsons in Weirton W. Virgina he has got a super simple method to get a very nice mirror polish and would be happy to show you.

Brett
 
You can go to Ron Wilson's web site by simply typing in his name. He has an article there on how he does his mirror polish. Sorry but for me it would mean creating more of a problem than helping with anything. Frank
 
Thanks guys. I just read Ron Wilson's article on polishing. Thanks for suggesting it Brett. After talking to a few people today I think I'm gonna try a 120 belt after HT , an add a grey buffing compound to the process. I tried a piece of 1" x 1" square stock, fixed against a brace on my work rest, and went through the same process I do with the knives, just to rule out the missing scratches, going from one belt to the next. Now, I didn't HT it, but still had the same scratches! I have to admit, there were slightly less scratches, but still there. I am convinced I need another belt in between somewhere, or another buffing compound. A lot of makers only go to a 400, or 600 grit finish before cut and color on the buffer, Ive always gone higher. I'm not disregarding any suggestions though; thanks for all the input. I'm anal about this stuff as is, I need to fix this. Seriously, I appreciate it.:D
 
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