Grind Marks appearing during Hand Sand Finish

J

J Lensmire

Knifemaker / Craftsman / Service Provider
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Oct 30, 2021
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Noob, here. I use 80 then 120 grit ceramic belts when initially grinding my blades. Once that is done, I finish pre-heat treat grind with 120 then 220 Aluminum Oxide belt.
After heat treat, start with 120 Aluminum Oxide to remove scale and if needed, bring blade thickness close to final. I then transition thru 220/440 Silicon Carbide.
I finish all my blades with hand sanding. My question is, after all this, how can I still have what appears to be 80/120 grit marks on blade that appear during hand finish?
this occurs on both A2 and CPM154, currently the two steels I am using.
 
I start with 36 grit, so I'm quite familiar with what you are seeing. If you run through a progression of grits, unless you remove a significant amount of material and truly get beneath the low grit scratches, then they will be hiding. Grinding in the same direction, the bevel will look more polished, but the scratches can be hidden. Once you switch to hand sanding along the length of the blade, they quickly jump out. I hand sand at 120 until none remain under different angles and lighting. Then a progression of higher grits goes more quickly and shouldn't yield any more surprises. You will find that a truly clean 220 hand sanded looks a lot better than 220 off the belt if you had low grit scratches hidden.
 
Richard338 said:
I start with 36 grit, so I'm quite familiar with what you are seeing. If you run through a progression of grits, unless you remove a significant amount of material and truly get beneath the low grit scratches, then they will be hiding. Grinding in the same direction, the bevel will look more polished, but the scratches can be hidden. Once you switch to hand sanding along the length of the blade, they quickly jump out. I hand sand at 120 until none remain under different angles and lighting. Then a progression of higher grits goes more quickly and shouldn't yield any more surprises. You will find that a truly clean 220 hand sanded looks a lot better than 220 off the belt if you had low grit scratches hidden.
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Richard,

Thats what I thought. I guess I just need to purchase stock in 120 grit paper. Do you buy rolls for hand sanding, or packs of sheets? I haven't worked out cost difference yet. I'm trying to get things worked out now, so when I retire from my current job and attempt to consistently sell some blades, the kinks are worked out and I'm proud of the product I'm putting out. Still see all the imperfections that non-knife friends don't pick out. Thanks for the info.
 
I recently stocked up on Rhynowet red paper from Pop's Knife Supply. They sell 50 packs at a good price. I got 120, 220, 400, 800, 1200, and 2000. I might have a few others as well. Depending on what you are doing you might not need any high grits. 120 is a staple.
 
As Richard said they are just low spots/deeper grinding marks. They are hidden by the fact your lines are going vertical. Most will have an intermediary phase between rough grinding and finish sanding to identify the low spots.

You can often identify the bigger low spots just by running to fingers along the bevels softly pinching. Is surprising how much you can feel/pickup this way.

In knives with a blended plunge like kitchen knives I just tilt the blade 30 degrees on The platen when I hit 240 grit. This quickly shows the stubborn spots and I can flatten them before moving on to 400 then hand sanding.

On knives with plunges I use the disk sander, again the contrasting scratch patterns help quickly identify the low spots from rough grinding. I do this process even on machine finished blades

The same thing can be achieved by going to hand sanding at a lower grit, but I try to avoid hand sanding as much as humanly possible so prefer a little powered help. I've also found that as I get better on the grinder, my blades are coming off the grinder flatter and cleaner and I end up with much less in the way of stubborn spots to grind/sand out
 
I drop back one grit level post-HT. If I went to 120 pre-HT, I start at 80-100 post-HT.
 
Lots of good tips already, but I've also learned to just stop using 36 grit belts. They just create too much of a headache with the occasional really deep scratch. I start at 60 grit and go up from there. But I also do almost exclusively thin kitchen blades post-HT, so YMMV on big thick knives before HT.
 
Michael Black said:
Lots of good tips already, but I've also learned to just stop using 36 grit belts. They just create too much of a headache with the occasional really deep scratch. I start at 60 grit and go up from there. But I also do almost exclusively thin kitchen blades post-HT, so YMMV on big thick knives before HT.
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Decades ago, I started with 400 grit belt on bevels from precision ground bar stock.

It was to try and slow grinding down on my full speed grinder.



Now I see posts by Ed Caffrey has also tried it just to avoid all the belt changes and missed scratches.
 
12345678910 said:
Decades ago, I started with 400 grit belt on bevels from precision ground bar stock.

It was to try and slow grinding down on my full speed grinder.



Now I see posts by Ed Caffrey has also tried it just to avoid all the belt changes and missed scratches.
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Yikes, that must have taken an age
 
Nick-D said:
Yikes, that must have taken an age
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Full speed, 400 grit and really well spheroid annealed - no mill scale, flat, butter soft.

Thin blades, no crowbars.

It did slow things down, but that was the point. grind look, grind look.

It slowed things down, but I had no variable speed.
no chasing scratches, no belt changes, just grinding.
 
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