Advancing between grits

Cox Workshop

Cox Workshop

Joined
May 8, 2014
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So I've got what is probably a very newbie question. When I advance through the grits say from 60 to 120 I have a hard time telling if I have removed all the 60 grit scratch lines. I'm doing this on 2x72 grinder. With hand sanding I can change the direction of my sanding to make it easier to see when I've removed the lower grit. Is there a trick on the belt grinder? Or is this just one of those things when I have a bit more experience I'll know when to move to the next grit. After I move to say a 220 the 60 grit scratch lines become really apparent and I have to move back to 120.

The issue might be exacerbated by the fact that I'm definitely using belts too long. "Use them like the are free" would be easier if I was selling my knifes :) Hopefully someday!
 
Keep in mind that I'm pretty much a noob, but you can grind at different angles between grits, so that the scratch lines face different directions as you go from one belt to the next...
 
Twist and turn the knife in bright light from all angles. You should be able to see a difference.
That being said, if you are using worn out belts, a worn out 120 may be more like a 240, and a worn out 60 may be more like a 120.
So if you are using a old 60 and a new 120, you may not see a whole lot of difference.

And why aren't you selling some knives!!! At least sell a few to some buddies for cost or a little less. That will allow you to at least break even and get some new belts.
Try to make one knife and make it perfect, or as prefect as you can get. Then you can sell it, get a bit of cash and get some belts to make 2 the next time. Sell 2 get belts, make 4, etc, etc.

Best of luck, and post some pics of your work. Would love to see.
 
As was just mentioned, you can grind at an angle, but that can easily mess up your grind if your blade isn't long enough. It works fine on an 8" chef knife but not so much on a 3" skinner.

For me, I only grind my blades to 60 pre heat-treat and then start with 120 after heat treat. You can tell if all the deep marks are gone if they are all black. Another trick if you don't want to do that is to use a sharpie, dykem, or an acid etch to paint the blade between grits. Grind until all the darkened scratches are gone.
 
Thanks for the advice everyone!

Hawk - What you mentioned makes me thing maybe I need to upgrade the lighting in my shop a bit. I picked up some gooseneck lamps at a yard sale a week ago. I'll get them setup and then retry the twisting and turning method. I do plan on selling some soon. I've got a few decent ones that should be worth at least the cost of materials.

Jason - I really like that dykem idea. I'll give that a shot. Seems like that will give me a good feel for what is going on when I grind.
 
Coating the blade with an industrial sharpie inbetween the lower grit belts helps me pick out the trouble areas.
 
For me dykem and sharpie ink etc. don't seem to help that much when trying to tell whether or not you've ground down the previous grit scratches since it seems to just rub off quite easily when it comes in contact with even a pretty dull, fast moving belt (for me at least). Like Jason mentioned, give the blade a quick etch in some acid (Ferric Chloride or vinegar etc.) and that seems to stay on a lot better, some guys even use the very light rust that forms when dunking their plain high carbon steel blades in water as an indicator.

Also, SHARP belts WILL help A LOT. Try to save some of the bevel grinding (something like 1/4" from desired height should be enough) for post heat treat also. Just grind up about 1/8" after HT with the coarsest grit (60), then a littler more with the medium grit (120), and just grind the final tad using the a "sharp" finer grit (220).

Another way that you yourself mentioned is to give the blade a quick pass over a higher grit like 400 and that with show you pretty quickly if you need to grind a bit more with the grit your using. Just my $0.02 :)

~Paul
My YT Channel Lsubslimed
 
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DyKem, sharpie, etc will al work....but a quick dip in the FC tank will work as good or better. It will show where the grind is going and any deep scratches.
 
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