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  #1  
Old 01-28-2017, 07:34 PM
gkyle840 gkyle840 is offline
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Slightly darker streak during grinding

I am doing doimg some finish grinding on my most recent knife on the grinder. I am currently at a 220 grit belt. It is a brand new gator belt. I have a dark streak in the tang that I cannot seem to get out. I was just curious what would cause this line and how to remove it. It is about 1/8" wide and 1 1/2" long. I couldnt get it to show up in a picture so the best I can do right now is describe it.
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Old 01-28-2017, 08:08 PM
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Ray Rogers Ray Rogers is offline
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I don't know what it is but I'm pretty sure the only way to get rid of it is to remove some metal. That may be a few thousandths or it might turn out to be half the handle. If you want it gone that's what you'll have to do.

But, maybe you can hide it. If you're using 1084 or a similar carbon steel you may be able to etch the tang (and the blade, of course). If the etch matches the discoloration you have now then it will all blend in. Part of that will depend on what you use to etch. FeCl can etch dark, vinegar usually is lighter.

That is assuming that the discoloration is on the edge of a full tang. If its on the side then just put the scales over it ...


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Old 01-28-2017, 08:20 PM
gkyle840 gkyle840 is offline
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I have a feeling it is something I have done while grinding? I have had it happen on other blades as well. I will try and get a pic of it.I have tried a few different belts and sometimes it gets lighter but always returns.
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Old 01-28-2017, 08:26 PM
gkyle840 gkyle840 is offline
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https://drive.google.com/file/d/0Bxh...w?usp=drivesdk

Here is a pic. There are two visible dark lines. Its driving me crazy.
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Old 01-28-2017, 08:55 PM
gkyle840 gkyle840 is offline
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I have used a lot of new belts on this knife :/
If I have the dark marks on a 120 grit and I move to a 220 it will remove them and look good. If I hit it again with the 220 trying to get one last scratch out, they start coming back. It seems only the first 5 seconds of a brand new belt will get rid of them. Why is this and any idea what they are?
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Old 01-28-2017, 09:27 PM
jimmontg jimmontg is offline
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Looks like the belt is causing it when it shouldn't. They look like marks made with a worn out belt. You say it's a gator belt? Something is contaminating your belts if they start making those marks after only 5 seconds. You have a high speed Grizzly right? Are the belts coming into contact with any painted surfaces? A high surface speed with 220 grit needs a light touch, but the 120 shouldn't make those marks unless worn out. Those marks look like you ground some wood or micarta first and then ground the steel. You said the belt was new though. I presume you know you're not supposed to mix belts for handles and metal, but that looks like a bad belt. Does the heavier grits make those marks too?
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Old 01-28-2017, 09:42 PM
gkyle840 gkyle840 is offline
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The front of the belt isnt contacting anything but the knife. I pretty much got them out and sanded down to 400 grit. It took me a total of 2 new 220 belts and 2 new 400 grit belts. Those 4 were norton and 3m belts. I wasnt getting another new gator belt out. I think its due to the belt getting metal on it from the knife but that is awful quick isnt it? I have a stick to clean the belts but I think once I use that they wouldnt be any good for finish work as ot leaves a residue on the for a short while.
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  #8  
Old 01-28-2017, 10:05 PM
gkyle840 gkyle840 is offline
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Here is what it looks like now. Not sure why it looks brownish at a certain angle.
https://drive.google.com/file/d/0Bxh...w?usp=drivesdk
https://drive.google.com/file/d/0Bxh...w?usp=drivesdk
https://drive.google.com/file/d/0Bxh...w?usp=drivesdk
https://drive.google.com/file/d/0Bxh...w?usp=drivesdk
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Old 01-28-2017, 10:35 PM
Doug Lester Doug Lester is offline
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It sort of looks like you are building up an oxide layer on the surface of the knife. Are you grinding with gloves on? Are you cooling regularly in water? Try grinding with bare hands hands so that you feel the steel get hot and then cool in water every few passes.

Doug


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Old 01-28-2017, 11:35 PM
gkyle840 gkyle840 is offline
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I just use my bare hands while grinding. With the finish sanding I dont let the blade heat up much to my knowledge however I do not dunk the blade in water as it rusts really quick and on the last grit or two I was hoping to avoid this. What would cause the oxide layer?
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Old 01-29-2017, 06:48 AM
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Crex Crex is offline
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Studying the pics, it looks like you are trying to jump to the 400 grit too soon. There are a lot of deep scratches in the surface that the 220 grit should have removed completely. Running at Griz speed you may need to add in a 320 grit step to get rid of the scratches if they are from the 220 belts. If they are from a coarser belt, say 120, then you are not through with the 220 before going to 400.
Think about it - if you didn't get them out with the 220.....400 hasn't got a chance.

Belts are either "clogged" or dulled to the point that the steel is getting too hot and oxidizing to a discoloration level. Try using a sanding block and fresh paper, it will take a little elbow grease but should remove the discoloration. Griz's run real fast and it doesn't take much pressure/run to dull a belt.
Are you using a magnet to hold the blade to the belt? If so you may not be feeling the heat build up before it's too late. Don't wait until it burns your fingers to dunk/cool it.


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Old 01-29-2017, 08:51 AM
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Ray Rogers Ray Rogers is offline
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You said Gator belts and you said Norton and 3M. Are the Norton and the 3M also structured abrasive belts?

Gator belts are designed for final finishing work. That means they aren't meant to remove much metal. Trying to use them to remove scratches could have about the same result as using a dull belt. So, if you are using mostly structured abrasive belts try switching to regular belts meant for moving metal and your results should improve a lot ...


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Old 01-29-2017, 09:37 AM
gkyle840 gkyle840 is offline
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I think your right about the belts getting clogged. The dark areas are smoother and shinier than the light areas so I would assume the dark areas are where the belt is clogged. Is there a good way to unclog and sharpen the belts without leaving a residue?
I think I am going to try Scotchbrite nylon mesh sanding pads as I have had a lot of trouble with hand sanding so far and keepimg the lines in the bevel crisp.
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Old 01-29-2017, 10:07 AM
damon damon is offline
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Quote:
Originally Posted by gkyle840 View Post
I think your right about the belts getting clogged. The dark areas are smoother and shinier than the light areas so I would assume the dark areas are where the belt is clogged. Is there a good way to unclog and sharpen the belts without leaving a residue?
I think I am going to try Scotchbrite nylon mesh sanding pads as I have had a lot of trouble with hand sanding so far and keepimg the lines in the bevel crisp.
wrap sand paper around a block of wood if you want to keep your lines crisp.
those soft pads will round off edges/corners.
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Old 01-29-2017, 10:31 AM
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You can't really sharpen a belt but you can unclog them - to some degree - with a belt cleaner. A belt cleaner looks like a gigantic rubber eraser. Tru-Grit has them.

However, a belt cleaner won't do you much good on a structured abrasive belt...


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