How do I get a small knife edge?

[Pietje]

Working with the T8, I usually get an edge of 3-4mm. Now I like to get an edge with less 1mm wide. What technic do I have to use to get this result?

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Pietje

[Dutchman]

The width of the edge is determined by the sharpening angle and the thickness of the blade. So take a thinner knife or sharpen it more bluntly.
Or am I not understanding the question correctly?

[tgbto]

Pietje,

The width e of the bevel is a function of three things (as seen on the attached picture):
- The pink blade angle beta (in dps here)
- The red bevel angle alpha (dps)
- The blue distance between the tip of the original thinned blade and the actual tip (d)

The relationship between e, beta, alpha and d can be worked out with a bit of trigonometry, but to make a long story short and get back to your problem, if you want a small e you either have to :
- increase the bevel angle alpha, as shown by the green bevel compared to the orange bevel. This will however only take you so far because you won't be able to get the bevel any thinner than half the blade thickness at that point. Moreover, increasing alpha will make the blade less sharp AND worsen the edge retention. You will only gain in toughness. Plus this will leave part of the current wide bevel visible.
- decrease the distance d. To do so, you have to thin the blade as shown by the dotted line. You can do that over the entire height of the blade, and you will most likely need a belt sander AND a lot of skill. You can also thin the blade more locally, that is grind a primary bevel at a much higher angle than alpha, THEN grind your secondary bevel at alpha. However I'm afraid this defeats your initial purpose of having a very thin bevel.

Keep in mind that the reason blades come out of the factory with a very thin edge is because they are sharpened very close to the original tip of the blade, i.e. with a very short distance d. As you use and sharpen your blade, you will quickly get to a point where the bevel height is significant, especially if you don't feel the burr early on in the process. A new blade will require very little grinding to raise a burr.

I'm afraid once the edge is wide there is not much to be done apart from thinning the blade...

Cheers,

Nick.

[Pietje]

Thanks both of you for the explanaition.
Pietje

[Pietje]

But how can I put a microfase on the edge?
I´m often reading about 18° GrindingAngel and than adding a microfase with 14° on it.
When parameters like thickness of the blade or distance between jig and edge are absolut items, I can only imagine that an indrustrial plane grinding machine and a sinus machine vise.
Is there an alternate method?

[tgbto]

Pietje,

I'm not sure what you are referring to by microfase. In case you are referring to the microbevel, that is a short bevel at the very tip of the edge, it can only be made at a HIGHER angle than the main bevel angle.

So you can first grind for 14dps, then increase the angle and grind only a short bevel at 18dps. It is perfectly doable on a Tormek, I'd recommend using a fine grit stone (SG just recently graded fine, SJ or DE-2x0) in order to not grind too much.

sorry if I didn't understand you correctly.

[van]

Pietje,

I'm not sure what you are referring to by microfase. In case you are referring to the microbevel, that is a short bevel at the very tip of the edge, it can only be made at a HIGHER angle than the main bevel angle.

So you can first grind for 14dps, then increase the angle and grind only a short bevel at 18dps. It is perfectly doable on a Tormek, I'd recommend using a fine grit stone (SG just recently graded fine, SJ or DE-2x0) in order to not grind too much.

sorry if I didn't understand you correctly.

Maybe it should do it in reverse, first at 18 ° dps and then at 14 ° dps to create a small bevel.
Or am I wrong to interpret the question?

[Pietje]

Hello!
Both of you have the right intension to my question. I was wrong using "microfase". Microbevel seems to be correct.

[tgbto]

Maybe it should do it in reverse, first at 18 ° dps and then at 14 ° dps to create a small bevel.
Or am I wrong to interpret the question?

If you do it first @18dps then @14dps, you will be working on the edge first, then on the shoulders. It will be very hard to be consistent in doing so, as you'll have to be doing heavy grinding of the shoulders while at the same time making sure you keep a hair-thin 18dps bevel along the edge.

Doing it 14dps first, then a few light strokes @18dps ensures that the edge is ground @18 but not too wide.