Dark spots from belt sanding

D

Dewnmoutain

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Aug 26, 2021
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https://imgur.com/a/egn2hZ5



Im currently sanding up some knife scales using my belt sander. When i changed to 120 grit to start smoothing, i ended up getting a couple of dark spots appear on the sanded wood. Ive tried sanding the spots off but it just makes it worse, or at best, it removes just a little of the dark spots.

Whats causing this? Id look this up myself, but i keep getting results for sanding the floor and uneven staining.
 
You are burning the wood with the powered sanding.
If you clamp the blade and hand sand, you will be able to remove the discolored parts.
I like to shape my handles on the belt grinder with a light touch and a coarse grit. Once you have it to shape you can switch to hand sanding with finer grits.
 
Looks to me like your burning the wood. I know this sounds simple and silly but how old is the sanding belt you are using? what kind of belt is it? How hard are you pressing on the belt when you are sanding?

Also what kind of wood is that? If its a very dense/hard wood you need to be using fresh aluminum oxide belts and let the abrasives do the work of ripping away material. This goes with pretty much with any type of scale material you are working with.
 
Open coat aluminum oxide belts on high speed .............20 m/s
 
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Diego_B said:
Looks to me like your burning the wood. I know this sounds simple and silly but how old is the sanding belt you are using? what kind of belt is it? How hard are you pressing on the belt when you are sanding?

Also what kind of wood is that? If its a very dense/hard wood you need to be using fresh aluminum oxide belts and let the abrasives do the work of ripping away material. This goes with pretty much with any type of scale material you are working with.
Click to expand...
...its an old belt. And black walnut.
 
Diego_B said:
Looks to me like your burning the wood. I know this sounds simple and silly but how old is the sanding belt you are using? what kind of belt is it? How hard are you pressing on the belt when you are sanding?

Also what kind of wood is that? If its a very dense/hard wood you need to be using fresh aluminum oxide belts and let the abrasives do the work of ripping away material. This goes with pretty much with any type of scale material you are working with.
Click to expand...
Its an old belt. Couple years old. Used it for other projects, but since it kept sanding well i just kept it, and kept using it.
Its an alum oxide belt.
Was using mostly medium pressure.

But thanks for the advice. I'll get new belts tomorrow
 
Also get a rubber belt eraser/conditioner/dresser or whatever it's supposed to be called. They are remove material from open coat belts when you press them against the moving belt, as though you are grinding the rubber. You will see it almost instantly remove loaded material. If you used hard pressure when grinding, or overused a loaded portion of the belt, you have probably ruined that part of the belt's ability to cut. If so, it's time for new belts, because the time it will take you to get a good result with worn belts is an order of magnitude above the time it takes with fresh and properly maintained belts.
 
Slow the grinder down a lot on the endgrain
Use a new belt, preferably open coat aluminum oxide made for wood sanding
Don't press hard or linger on the endgrain
Do endgrain and handle butts on the slack belt
Clean belt often
Hand sand to finish
 
I notice burnt spots on micarta and wood when I use worn or very fine grit worn belts. When I use low grit fresh belt it takes off the burn. But hand sanding with low grit sand paper or sand blocks or scotch bright and files works too.
Hope this helps as it helped me.
 
Plus walnut likes to burn. I'd say more than ironwood even but not as much as osage orange.
 
To put some numbers to this, I have taken to shaping my handles with a 60 grit belt, low speed. VERY light touch, but very reduced risk of burning. When subsequently moving up the grits, I am not shaping, just refining the surface, and doing very small shape refinement. I thus go to a slack belt and scalloped edges at 120 and above. Hand sanding and rasps at that point would work, but I guess I am not that patient…
 
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