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I was given a batch of old router bits. some have blackened tips....solid carbide, some HSS. Does the fact that they were once 'burned' cause them to be trash? I want to send some out to be sharpened, but don't want to waste money.
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03-30-2018, 07:20 PM
(This post was last modified: 03-30-2018, 07:22 PM by R Clark.)
Why don't you try a cleaning of one first, and give it a shot? How well does it cut after cleaning?
I doubt very seriously that any reasonable use of the bit destroyed the carbide. The HSS could be a different story, but I'd still clean one first.
Then, if there's a bunch of them and you're still not sure, get a couple professionally sharpened and see how they do.
I get mine sharpened locally, so I don't pay shipping. Recently had 14 bits sharpened for somewhat under $100. There's no way I could replace them for that.
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+1 on the clean them up
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(03-30-2018, 06:20 PM)AlanS Wrote: I was given a batch of old router bits. some have blackened tips....solid carbide, some HSS. Does the fact that they were once 'burned' cause them to be trash? I want to send some out to be sharpened, but don't want to waste money. .................
I would give them a soak in lacquer thinner overnight to dissolve the resin adhering to them, and then buff them with a green scrubby or fine steel wool to see if they clean up... You can also use a wire brush on them., Then you can use a thin diamond "card" and "touch up" the bit by rubbing just the FLAT face of the carbide on the diamond hone. You would be surprised how much sharper the bit will be if vigorously done. And you can also use the same procedure on High Speed Steel bits.
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High speed steel bits, no problem. Carbide bits, Black is probably trash.
Carbide it not a metal like steel. It is a matrix of carbide particles bonded in metal, typically tungsten. (Tungsten Carbide)
Carbide cutting edges are rarely worn out, they are almost always overheated first. The excess heat softens the tungsten matrix, which allows the carbide particles to fly off.
Of course this happens first at the cutting tip. That is where the heat is produced, and the razor edge is the most susceptible to heating up because of the little mass available to absorb the heat.
You have nothing to lose by cleaning the bits and testing the edge on cheap stock, but my experience tells me the Carbide is toast, literally!
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I'm with Ralph and would also look into what you have as well. If it's an MLCS or 1/4" diameter spiral, then I probably wouldn't bother. If it's a $75 bit and the cleanup seems successful, they that's a different story.
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I burned up a high speed steel bit some 40 years ago on plywood. Apparently the glue heated up. Even if you sharpened it, it would be worthless. The steel probably got hot enough to anneal at the burn marks and is no longer as hard as it had been.
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On a carbide blade the blackness is a burnt "varnish" that can be cleaned and the blade will feel sharp again. A shout out for the blade/bit cleaning solution from Rockler. Non-toxic and works really well. I just used some at work on about 20 bits and I'm using the same batch on saw blades still.
RD
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(04-14-2018, 05:18 PM)Richard D. Wrote: On a carbide blade the blackness is a burnt "varnish" that can be cleaned and the blade will feel sharp again. A shout out for the blade/bit cleaning solution from Rockler. Non-toxic and works really well. I just used some at work on about 20 bits and I'm using the same batch on saw blades still. That is not universally true, in point of fact, I have virtually never found this to be true. The blackness is discoloration of the Tungsten or HSS in virtually every case.
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04-15-2018, 02:41 PM
(This post was last modified: 04-15-2018, 03:41 PM by sailor 56.)
(03-31-2018, 04:05 PM)handi Wrote: High speed steel bits, no problem. Carbide bits, Black is probably trash.
Carbide it not a metal like steel. It is a matrix of carbide particles bonded in metal, typically tungsten. (Tungsten Carbide)
Carbide cutting edges are rarely worn out, they are almost always overheated first. The excess heat softens the tungsten matrix, which allows the carbide particles to fly off.
Of course this happens first at the cutting tip. That is where the heat is produced, and the razor edge is the most susceptible to heating up because of the little mass available to absorb the heat.
You have nothing to lose by cleaning the bits and testing the edge on cheap stock, but my experience tells me the Carbide is toast, literally!
That is not quite right.
Carbide cutting bits are typically a combination of particles of tungsten carbide (produced by carburizing fine tungsten particles) and a base material that is usually either particles of cobalt or nickel alloys. These particles are then hot pressed and heated (sintered) to form a solid product. This is generally refereed to as powder metallurgy.
The resulting product is not only stronger than HSS, but should withstand high temperatures better than HSS.
There are no carbon particles, the carbon atoms are joined to the tungsten atoms.
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