Noobish grinding question

[phil000]

Hi guys, I am looking at all sorts of different knives and a lot of them have different types of ground...flat ground, hollow-ground and others I have already forgotten...WHAT DOES THIS MEAN? And is there any BEST one for utility-ish work?


Thanks I get smarter each night I read this forum...

Phil

 

[phil000]

...or is this just too vague/stupid a question to ask?

 

[kel_aa]

Most knives start start as a flat rectangular piece of steel. The grind deals with how you make it "sharp". You can just file at an angle until they meet (like your common $5 machete). However, that sort of knife is unsuitable for many uses from a cutting efficiency and sharpening effort perspective. Hence you want to to reduced the profile blade and turn it into a more triangular instead of rectangular shape. We call that effort a primary grind. The primary grinds (blue) illustrated in the first three frames are flat, hollow, convex (quite descriptive). The fourth frame is a saber grind, which basically means a grind that only goes up a portion of the height of the stock. Specifcally, it is a flat saber grind (it can also be hollow (see Cold Steel Voyagers for instance) or convex). Sometimes the descriptor "full" is used to relate the height of the grind. The first frame might be called a full flat grind, the second a full hollow grind.

We call the actual edge the secondary grind (red). The edge can take as well all of the above geometric shapes (hollow is rare though unless you grind it on a wheel). What is commonly refered to as the Scandi grind is similar to frame four, a flat saber grind without a transition between the primary grind and the edge.

We also sometimes remove some material in between the primary grind and secondary grind in an effort to thin the edge. We call that a relief grind. So now you know what everything refers to, it's just a matter of stringing the descriptors together, for example: a full flat blade with a hollow relief and convexed edge.

Funtionally, I like full flat blades, but they tend to be more expensive (it's easy to see why machining something with the profile of frame one will cost more than that of frame four simply due to the amount of material that needs to be removed, plus you should ideally start with a thicker stock). Saber grinds are commonly done due to cost and asethetic issues. The same is of true of the Scandi grind, although there is also some cultural connection as well as misplaced belief in their superiority.

 

[phil000]

Alright thank you very much, that clears a lot of things up for me...thanks for your time and for explaining it to me

 

[Cliff Stamp]

..... as the Scandi grind is similar to frame four, a flat saber grind without a transition between the primary grind and the edge.

These are actually often hollow, all the cheap ones are. It is why a lot of people think the edged are weak and they need to be "convexed". The grind from shoulder to edge is usually a 9-11 degree taper, but due to the hollow the actual edge can be under five degrees per side. Thus it doesn't take much in the way of a knot of small piece of hardwood to turn it.

When it is sharpened you can clearly see this hollow as the middle of the bevel won't get hit by the stone. Once the edge is resharpened to the primary flat angle of 9-11 degrees is is much more resistant to bending, about ten times as much. The hollow doesn't need to be fully removed, it isn't a bad thing, you just don't want it right to the edge on a hard wood working knife. On the more expensive scandinavian knives the bevels are usually flat. The cheaper ones also often run secondary bevels.

-Cliff

 

[kel_aa]

The cheaper ones also often run secondary bevels.

Which ones do you refer to? How much cheaper does it get?

My Frosts Moras did have a hollow. You can still see some reminant of it as the white part of the edge near the handle. But when you sharpen it'll work itself out of most the edge anyways. I think that is relatively minor compared to general issue of the difference between a Scandi grind and a flat grind. It's much easier to go from flat to "Scandi" than from Scandi to flat (I tried here).

 

[Cliff Stamp]

Which ones do you refer to?

I don't think it is brand dependent, Jim Aston and Ragnar have mentioned it for several. I would assume it depends on the person who sharpened them. I have seen Opinels as well for example with significant secondary bevels and some which run basically full convex. It can cause some issues for the first sharpening if you just take the flat to the stone and nothing happens to the edge for awhile because you basically have to grind off that secondary bevel before the knife will sharpen.

I think that is relatively minor compared to general issue of the difference between a Scandi grind and a flat grind.

Yes, as long as you realize that many initial edge damage problems are caused by a hollow. As you noted it takes care of itself with regular sharpening.

It's much easier to go from flat to "Scandi" than from Scandi to flat (I tried here).

Yes, in fact it is a known consequence of sharpening secondary edge bevels that eventually the edges will thicken to the point the cutting ability will be reduced and ease of sharpening is scuttled because the edge has climbed too high on the primary grind.

This has in fact transformed it into a scandinavian type blade. The solution is to regrind the primary. Unless you are a really heavy user, this is something done really infrequently, as in far less than yearly.

-Cliff

 

[phil000]

does benchmade's life sharp include regrinding the primary?

 

[DGG]

Benchmades are made of great steel and it is the rare occasion that they will need to be "profiled" or "reprofiled", two words, same meaning. However if needed I'm sure they will do it.

You can easily do it yourself and not have to chase to the post office, burning $3/gal gas, standing in line, buying postage, waiting 6 weeks for your knife to come back. Who need this grief?

Sharpening isn't rocket science although it can be challenging sometimes.

http://forums.egullet.com/index.php?showtopic=26036

 

[kel_aa]

Benchmades are made of great steel and it is the rare occasion that they will need to be "profiled"

If by quality of steel you mean they don't have to be sharpened as much therefore the edge thickens less over a given period of time, then I agree.

Phil, regrinding the primary is not something most production companies will do you. That kind of service is only something you would expect from custom makers and small-scale, high-service production shops (Chris Reeve, Strider?). What knife are you looking at? When I sent in my 800 for an handle repair, they sharpened my knife, but did a horrible job of it by grinding away a lot of the edge and putting a 20> angle on it. I have since pulled it down to 15, but the edge is way to thick as it is and the primary needs to be worked (or a hollow relief added). But it's a pretty knife and touching the primary is not something I really want to do. Compared to a Spyderco with a factory edge at 12 degrees (Notice the difference in edge width even though the Benchmade is more obtuse):