paulgatx

Mirror finish help needed

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Hello, newbie here working on my second knife.  The first was a practice knife made from a file, and I left the finish rougher as I wanted to retain the file lines.  This one is a wedding gift for a friend of my mother's, and while it will likely be a heavily used knife, I wanted to deliver it with a nicer finish since it's a gift.

It's a Baby Bowie made from 5160 leaf spring steel.  It's mostly done (hardened, edged, handle attached and shaped), but I still have to polish the blade and sand and finish the handle.

I hoped to get it there on my belt grinder, but I realize now that I hadn't done the proper research yet.  Now I'm trying to figure out how shiny I should be able to get it on my grinder and then how to finish it.

I have a 1x42 Kalamazoo grinder with cheapy AO belts from 40-400 grit and then nicer ceramic (mod edit Silicon Carbide) 1000 grit belts.  The finish in the picture, if you can see it properly, is the best I can get with stepping up from 120-240-400-1000.  The scratches in the middle of the blade seem to have been caused by the 1000 belt when I put it against the platten.  I can get it shinier around the edges of the flats on the slack part of the belt, but the platen grinding seems to not work as well.  I don't know if this is me (pressure, technique), the belt, or the platten.

So is that the best I should expect on a grinder?  I have automotive wet/dry paper in grits 400-600-800-1000-1500-2000-2500-3000.  Is it best to just use those now with a backer and alternating direction polishing?  I've also seen videos using a sanding wheel, but I don't have one, and haven't purchased one yet.

Thanks for any and all advice.

IMG_20180707_150218499.jpg

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Are you planning to buff it and can you do so SAFELY!   Buffers are one of the most dangerous tools in a knifemaker's shop!

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It appears to me that the blade is pretty wedgey to begin with.  I don't think those scratches are from the 1,000 but that you are not removing the previous grit marks completely when stepping up in grit. When we reblued guns we only went to 230 grit and they came out smoother than that.

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Thomas, I wasn't planning on buffing since I don't have a grinding wheel or sanding/polishing wheel.  Just hoping to do it with the belt grinder and hand sanding, unless you guys tell me it won't be possible.  In that case I'm willing to add new toys to my shop.

DOCTOR, I wish I had taken some pictures as I progressed.  I swear I had a finer finish after the 400 grit, which is why I was surprised to see the deep scratches after the 1000 on the platen.  But perhaps you are correct in that the 1000 only highlighted the scratches from the previous grits.

So would you recommend going back to the grinder?  I can't really go perpendicular on my grinder because it doesn't have a usable flat surface wheel, just the platen and slack area as shown in the picture.

IMG_20180708_162435727.jpg

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I haven't seen 1000 grit ceramic belts anywhere, so that part has me a little bit confused.  If they are out there I'd like to know as I might be interested in getting some myself.  I'm with BGD on this one.  You don't have to do a full 90 degree change when switching grits either.  It just needs to be enough of a different direction so that you can tell when you have completely erased the traces of the previous grit.   After finishing up with the grinder I frequently use about 45 degrees from the grinder marks in one direction and then 45 degrees the opposite direction before returning to the orientation of the grinder.  IMHO if you want to get a mirror finish without a buffer you will need to go to 3000 grit at least.   A word of caution though:  Mirror finishes will make tiny blemishes/mistakes as plain as day.  Also if the knife will be used much at all that mirror finish probably won't last long.  I've only done a couple blades with mirror finishes and my general take is it's not worth the effort on a blade that will be used much. 

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Buzzkill, my bad, it's silicon carbide not ceramic.

Sounds like I'll go back to the grinder with some 45deg passes to see what I can do.  Then maybe I'll take a crack with the wet paper up to 2000 or so.  Maybe not go for mirror but at least get the big scatches out.

Thanks for the tips.  So far I have found finishing to be the most difficult part of knife making, but it's also the area I had no training in previously since my classes used 1800s equipment.

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Let us know how it works out for you.  I do recommend that on your final grit selection you sand in line with the length of the blade though.  To me it seems that my eyes don't pick up the sanding direction as much that way.

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Those scratches are from the coarser grits. You dont notice them until the 1000 grit starts to make it shine. Get a magnifying glass and you will be able to see the 1000 grit marks. Polishing hardened steel by hand is an excercise in patience.

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Trugrit.com has norton belts tgat go up to 3000 grit after that you can go to a cork belt in lew of a buffer provided you remove all privous scratches along tge way

a piece of scrap silk and some jewlers ruge work well after this ....... if you are a masochist

 

enjoy

 

du

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Thanks everyone, this makes sense now.  I've got my plan of attack now, but no, I am not a masochist.

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Had to go back to 600 with a sanding block perpendicular, then back to the 1000 belt grinder to finish.  Not perfect, but much better.  I need to be more careful when stepping up my grits next time.

IMG_20180713_204647357.jpg

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Yeah, it's a pain to get every last scratch from the previous grit sanded out.  If you can still see the marks from the previous grit and sanding direction with a magnifying glass those will become quite noticeable when you get to mirror finish, or close to it.  For me, no matter how fine I go on the grit using the belt grinder, it always looks better to do the final grit by hand and in line with the length of the blade. For the few blades I've done in mirror finish I had about as much time hand sanding as I did for everything else combined to that point.

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When I was crazy and wanted mirror finishes, I used the belts DuEulear was talking about.  Norton NORax, down to x5, which is around 4000 grit, then buffed them. Like Buzzkill says it's hard to get the scratches from each previous belt totally gone.  Other tips; keep the work area super clean.  When you step to another belt, put it in a bag or somewhere where grit and debris are not going to get on it, and air chuck the grinder and your area.  One small piece of grit from a previous belt or dirt could have you going back and working through the grits again.  I think with the right application of elbow grease you could skip the buffer and do the final polish by hand.

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Thanks for the additional tips, guys.  I called this one done and finished the handle.  I definitely spent more time finished this one than I did forging it, so that's an area for improvement.  Also found a nice sheath on eBay that fits it perfectly.  I think he'll appreciate it, since he knows I only just started this craft.  On to my next knife ... A camp knife for my buddy that supplied me all of the spring steel and handle wood.

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