Recommendation? Bevel vs Flat disc grinder

N.W. Gean

N.W. Gean

Joined
Oct 10, 2018
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462
Hello all. After researching on the forums here about their merits and seeing that I can get a disc from USA knifemaker for ~100 bucks, I am ready to pull the trigger on a disc grinder build.

But the million dollar question is, do I need a beveled disc or a flat disc? I want to make finishing the flats of my fixed blade hunting knives easier and higher quality than using my flat platen (leaves scratches on edges that I can't get out because of belt curl). The blades are about 4.5" long with a roughly 5" tang. I am also interested in tapering tangs on my belt grinder and flattening on the disc, as I have been unsatisfied with the flatness of the tang coming off the belt. If it factors in to the choice, I do not foresee myself making folding knives.

Thanks everyone for your consideration.
 
Well more knowledgeable people will come along. But till then I went through this exact same thing when I built mine. If you want a flat grind then buy a flat disc. Imagine a beveled disc looking like a funnel without the spout (exaggerated for sure). Now I know tons of people prefer one or the other. But I love my flat disc grinder.
 
Well, too late now. I decided that the bevel would be worth trying first. I don't want to get my work caught. It sounds like the hollow just isn't perceptible over such a small area.
 
N.W. Gean said:
Well, too late now. I decided that the bevel would be worth trying first. I don't want to get my work caught. It sounds like the hollow just isn't perceptible over such a small area.
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I'll suggest seeing if you can change your order. The hollow is noticeable, at least on my thin chef's knives. I wish I hadn't ordered my bevel discs, anyone want to buy one?
 
I think It depends on what you're trying to do. If you're trying to create flat mating surfaces between—lets say—a handle scale and a bolster, then you'd probably want the flat disc. But if you're trying to create a "flat" primary bevel on a long knife, then the bevel might be useful.

I think that for knifemakers, disk grinders fall somewhere between a flat platen and a mill/surface-grinder for flattering.
 
weo said:
I'll suggest seeing if you can change your order. The hollow is noticeable, at least on my thin chef's knives. I wish I hadn't ordered my bevel discs, anyone want to buy one?
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I knew I would pick the wrong one :confused:

I'm not sure I can change my order, but per Tracey Mickley of USA Knifemaker:
"The second question is: "Doesn't that bevel leave sort of a hollow? It's not flat, it's a bevel after all." The answer is that it is as flat as the human hand can managed to grind anyway. There is an insanely small hollow ground affect. It calculates out to around 0.0005" across a 1.5" blade. Less than 1/2 of a thousand inch. A mere human can't hand grind something to that tolerance. It's flat enough. Look at the seams on any of my knives at www.mickleyknives.com . I use my beveled disc on all of those. It gets flat."

I am in the unknown territory of having used neither, unless you count a mediocre 6" disc on a 4x36 sander (not sure that one is super flat).
 
N.W. Gean said:
It's flat enough.
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Not trying to question Tracey's knowledge and experience, but I make almost exclusively damascus kitchen knives and when going to hand sanding before etching, the hollow is most definitely noticeable and I find it takes longer for me to hand sand that flat than when I come straight off the 2x72.
But I will also admit that I've really only used my disc grinder a few times because of this. And I also realize that changing the angle of the knife on the disc should mitigate this problem, I've just decided to stick with the devil I know for right now.
 
weo said:
I make almost exclusively damascus kitchen knives and when going to hand sanding before etching, the hollow is most definitely noticeable and I find it takes longer for me to hand sand that flat than when I come straight off the 2x72.
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You would know more about it than I do, but I think I'm gonna have to roll with it for now. It very much appears to be a matter of preference. Who knows? Maybe after a while of using a beveled disc, by the time I get ahold of a flat disc, I might not like it.
 
N.W. Gean said:
You would know more about it than I do, but I think I'm gonna have to roll with it for now. It very much appears to be a matter of preference.
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And Dave Lisch, MS knows a lot more than I do and he's the one who suggested I get a beveled disc. I figure it's just a matter of learning how to use the tool and I just haven't taken the time yet to learn this one.
 
Sam Salvati said:
How to grind long blades across a flat disc then?
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I've seen and heard of 2 explanations. 1) make sure your finger pressure is only on whatever part of the blade is in contact with the part of the disc you want to be working, and/or 2) angle the blade on the disc so that it's not going to be contacting the up and down portions at the same time.
We shouldn't forget that the inside of the disc is moving a lot slower than the perimeter, so some sort of adjustment has to be made, so I can see either one (or a combination of both) being viable options.
Untitled.jpg
 
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I can also see that with a beveled disc, as long as the blade is being ground on any radius line of the disc, then there should be no hollowing that happens. But like I said earlier, I just haven't taken the time to master that yet (if ever).
 
I guess I don’t understand why a beveled disk isn’t also flat. My understanding is that were you to put a square on the hub of the disk, the face of the disc would move away from the square at a 1° arc. Meaning, at the edge of the disc, it is 1° away from the square. But the face of that disc from the hub to the edge is flat. So if you only grind between the hub and the edge, isn’t it going to grind flat?
 
Blackdirt cowboy said:
I guess I don’t understand why a beveled disk isn’t also flat.
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It is. It's a flat plane from center outward.

My take on the 1° bevel is so that you can grind your bevel on one half of the disk. If the blade is longer than half the disk, then the extra length doesn't hit the other side of the disk.

Then to grind the other side of the bevel, you switch sides of the grinder and put it in reverse, so the sparks don't get in your face.
 
A.McPherson said:
It is. It's a flat plane from center outward.
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Yes, but only on each radius line. Because we've got a disc, and each bevel point starts from the center, you have a cone.
Here's what we'd have if we cut the disc in half:
Untitled1.jpg
 
weo said:
Yes, but only on each radius line. Because we've got a disc, and each bevel point starts from the center, you have a cone.
Here's what we'd have if we cut the disc in half:
View attachment 1507763
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Yep.
I see what you are saying, about the hollow grinding effect too... Although I think if you moved the blade around at all while grinding it'd be pretty easy to mitigate.
 
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I use both, but like the 1° bevel disc. It isn't "grabby" on a blade with a length over 5".
I think people are overthinking the arc thing. On a 2" wide blade with a 1° arc angle, the hollow is .005". And that is assuming you hold the knife at an exact center to edge orientation. If holding the knife at 45° to the edge-center line the hollow is less than 1/1000 of an inch.
 
I’ve had both, I have a steel flat one now and that’s what I prefer

but I don’t really use it on bevels anymore
 
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