Can I Put a Convex Edge on a Benchmade 806D2?

J

JDMSMBACPA

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May 21, 2003
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I have an old style (drilled for tip up only) Benchmade 806D2. I've already voided the warranty by removing the BT2 from the blade. Given all the convex grind buzz around here lately, I've been thinking about further modifying my 806D2.

At a minimum, I'd like to put a convex edge on it.

Ideally, I'd like to convert the original saber grind to a full-convex grind. I know that would mean removing a lot of hardened D2 and therefore a lot of work, but the result would be a pretty radical modification.

I think I have the tools, time and patience. Anyone have any suggestions on how to proceed?
 
You can put a convex edge on just about anything.

I would recommend getting a variety of quality wet/dry sandpaper and a nice thick telephone book. That and several hours should be all that you will need.

You may also wish to try just putting a convex edge on the knife rather than putting a full convex grind on it. I generally just do the edge, as it seems to perform as well as a full convex grind and takes much less time to put on a knife that did not come convex from the factory.
 
The full convex grind is a MUCH larger job than you want to take on. I'd go for the convex edge. Just order up some adhesive backed Hand American wet/dry paper, and stick the pieces to an old mouse pad. I'd start around 300 grit, and work my way up to at least 1200 grit. The job should take a few hours. The higher the convex runs from the edge, the better the knife should cut.

A full convex grind, using this method, would take only a few months. Hehehe.

If you have a problem with getting the edge nice and sharp when you're done, just give the blade a couple strokes on a Sharpmaker. A couple strokes won't mess up the convex edge too badly.
 
I agree with Buzz. The convex edge is way more feasible than trying to take the heat treated D2 blade and changing it to a convex profile.

A convex edge with hollow or flat ground blades is used by some custom knifemakers and Chris Reeve knives on the Sebenza (IIRC).
 
I believe that only disassembly and obvious gross abuse are what voids Benchmade's warranty. Even then, they won't give you too many problems if the knife is intact when you send it in.

Regarding the convex edge, if you use a Sharpmaker, reprofile the edge to 30 degrees, apply a microbevel at 40 and then sandpaper sharpen. It will cut a lot of time off of the sandpaper sharpening (just ignore the extra time trying to sharpen D2 on a Sharpmaker :D ).
 
If you have a belt sander then it won't take too long. I have taken a custom D2 blad to a full convex profile removing the secondary edge bevel. If you have to do it by hand prepare for a long time.

Your best bet in such a case is to make a set of pseudo-files by gluing sandpaper to wood and really lean into the cutting, creating a multi-bevel approximation to a convex profile.

Once you have this shape roughed out then you can go to a full convex profile in a short while with sanding on a soft medium to give shape to the curve.

However you should realize that the performance benefit from going from a full convex profile, to just adding a convex relief to the edge isn't a big one and you are not likely to notice the difference.

In fact, just adding a flat relief grind to the edge will give a massive benefit in performance, as thombrogan describes. You can then smooth out this dual profile by convexing it freehand with sandpaper on a soft backing.

JJ of Razor Edge was one of the first to promote extensive double beveling, or the use of a relief grind. Joe Talmadge made a number of comparisons of performance before and after to illustrate the huge change in performance (many times to one on slicing).

-Cliff
 
Thanks for the information, everyone. My 806D2 is already sharpened at 30* (using a Sharpmaker--it wasn't that difficult ;) ). It would be easy to add the 40* microbevel thombrogan mentioned. Then I could finish the job with the mouse pad.

If I understand Cliff correctly, the performance gains from going further (to a full convex profile) would not justify the additional work. Ihappen to own a belt sander, however, and it would still be pretty cool to have the only fully convex ground 806D2, though :cool:

P.S. Buzzbait, your convex edge page is what got me going.

P.P.S. I just got an e-mail from Benchmade. I specifically told them I had removed the blade, removed the BT2 and replaced the blade. Angie said they would install bronze washers for $1 each and $5 return shipping. :cool:
 
With a belt sander, it isn't a lot of time. Just a few minutes with a coarse belt will shape the profile as its only a small knife.

If you fully convex the profile, and don't steepen the edge significantly (push it hard into the slack region) the edge will be ~10 degrees per side. This will greatly enhance the cutting ability, but may induce durablity issues.

You can fix this with a secondary edge bevel, but this then begs the question as to why apply the full bevel in the first place. If you like the look of it - of course go ahead.

-Cliff
 
I put a convex edge on a rather obtuse edge of an early Benchmade Axis 710 (I could have sworn it was ATS-34).

Anyway since the blade was so "blunt" from the factory (a very common complaint of the 710 back then - I think Joe Talmadge had the same) -
I faced either radically re-sharpening it or sending it back.

I chose the former since for me it was relatively easy.

First because I did not want to marr the finish of my brand new knife - I taped the blade face exposing only about 1/4" edge.

Using a fine Diamond hone (EZE Lap 6") I concentrated in grinding away the shoulder between the blade face and the edge bevel. It was tedious but not that hard work - I used both forward and backward strokes - this was not exactly delicate type work.

As the shoulder started to merge with the face and bevel I started to use more of a rolling motion to literally "merge" the face to the bevel - ie: trying to get a zero bevel - continuous edge - again sounds harder than it actually is to do. At this stage I did more cutting forward as if I was trying to slice the face off the hone type strokes - but doing more of a rolling motion (like a shallow dishing scooping action) - again trying to merge the edge into the face.

The hardest part which probably doesn't apply here or to most other cases, was I had to grind a primary edge bevel angle on the 710 - that was more actute than the blunt factory angle - but like I said this probably will not be the case here.

So the final strokes on the diamond hone (without the problem of getting rid of a blunt primary edge) would be to roll the stroke from the final edge angle to blend the edge into the face.

I would then finish the edge by stropping to polish the now convexed edge (zero-)bevel - then finish off with a very few light strokes on fine (white) crock-sticks (I would examine the edge under about 20-30x magnification to be sure the crock-sticks did cut in a separate final bevel - otherwise the convexed edge bevel is not acute enough at the edge - and a bit more work is required)
 
I've been practicing on my Gerber Yari, which had a rather thick edge. I had some 360 and 400 wet-dry paper lying around in the garage. I've worked on it for an hour or two using the paper, a mouse pad and the information here and on Buzz's convex page. It's already getting a nice convex edge. I'll finish it this weekend. If I am satisfied with the results, then I will start working on the edge of my 806D2 (which, I'm sure, will be more work).

I think I'll satisfy my desire for a knife with a full convex grind by buying a Bark River Knife & Tool Gameskeeper

gameskeeper-green.jpg


Thanks for the info :)

P.S. I'd already removed the black coating from my Yari, so I didn't have to worry about scratching it.
 
I'd try 50 grit sandpaper before buying another knife. It will cut aggressively and take maybe a a little time off of your initial sharpening (be done in 9 hours instead of 9.25!). Then, after the knife exhibits an almost mirrored satin finish (by working up from 50 grit to 9,000 grit/.3 micron sharpening film) and a DNA-popping edge, then you buy the Gameskeeper because you're too sick of looking at the other knife. :)
 
I'm not touching that :p

I'm really pleased with the results I'm getting on my Yari. It sure seems to cut better than it did with the 40* primary and 30* secondary bevel applied with a Sharpmaker--especially in wood.
 
Well I started working on the 806D2, It is going quick--maybe because I had already put a 30* back bevel on with my SharpMaker. I'll post a review and, if possible, picures when I am done.
 
Forget how to do it. Convince me that convex is better in all applications than a good hollow grind.
There goes Buzz starting a controversy again. Debate to continue.

(Yes, Buzz, we have met on another forum,)
 
Originally posted by csbjr
Convince me that convex is better in all applications than a good hollow grind.
Click to expand...

No can do :) First, I don not like convex grinds. I prefer full flat, convex, saber or Scandinavian ground blades for a variety reason (and I'll admit a big one is cosmetic--beauty is in the eye of the beholder and I've never liked the looks of hollow-ground knives). Second, I'm only worried about my applications. If the convex edge doesn't work better for me then it should be easy enough to put a traditional edge back on the knife. All I will have lost is some steel. Third, I am a novice knife knut, but one willing to learn from others or by trial-and-error. What I have read about convex edges makes sense to me in theory. Now I will try it to see how it works in practice. The difference between theory and practice is that in theory there is none and in practice there is :D

I will tell you this--my convex edge Yari sure seems to cut better now in every media I have tried than it did before I put a convex edge on it.
 
Originally posted by JDMSMBACPA

I will tell you this--my convex edge Yari sure seems to cut better now in every media I have tried than it did before I put a convex edge on it.
Click to expand...

Yep, that has been my experience with all the knives that I have put a convex edge on. The difference is like night and day.

Perhaps csbjr should give it a try before he knocks it.
 
First, lets clarify our terms. A convex edge (which could be done to a hollow or flat grind), is just a rounding at the edge bevel. How height of the rounding, and the angle of rounding, will affect cutting performance vs durability. If you have a hollow or flat grind, I see absolutely ZERO downside to convexing the edge, if you merely round the edge bevel. I don't think I've ever run into an instance where a convex edge, when properly done, would hurt performance, and many instances where a convex edge would greatly help cutting performance and/or edge durability.

A full convex grind is an actual rounding of the entire blade, right down the edge. A convex grind generally has more steel to it than a flat or hollow grind, so you’d have to have an extra thick blade if wanted to change it to a full convex grind, and still maintain good edge durability. A full convex grind is nothing like a hollow grind, and much different from a flat grind in performance. The convex grind excels in many areas, but there are some drawbacks. You have to weigh what you're cutting, how you make your cuts, and your idea of aesthetics, against the type of grind you use. There are occasions, such as working with wood, where a convex grind may be of great help. Then there are times when a convex grind may be too heavy or thick for a particular application. I personally prefer convex grinds for outdoor work and some other general utility chores, but hollow grinds and flat grinds are better for some other cuts. There is no perfect grind for every application.

Is a full convex grind more versatile than other grinds? I don't think so. I think that a flat grind with a convex edge bevel is the most versatile, when we're talking about small to medium sized knives, not designed for a specialty purpose. Not to say that means that a flat grind with a convex edge bevel is the best grind for all occasions, but it is seldom outmatched for general utility chores.
 
Buzz,
I agree with many of the points you make. I'm just not convinced that convex is anywhere near the top of the list for general utility work. Yes, woodworking tasks in general are probably best served by a convexed EDGE. A full convex profile is my choice for splitting bone (GB mini). I sure hope however, that the convex grind Folding Hunter I have on order from Dozier makes me a believer. If it cuts better than the other Doziers I use, it will be absolutely phenominal.
 
JDMSMBACPA :

my convex edge Yari sure seems to cut better now in every media I have tried than it did before I put a convex edge on it.
Click to expand...

Is the bevel wider than it was before, if so then cutting advantage is due to the creation of a relief, this effect could also have been seen with a flat bevel, or a hollow one, the ability for more extreme performance would follow in that order.

Buzzbait.

A convex grind generally has more steel to it than a flat or hollow grind
Click to expand...

In general, convex grinds -> flat grinds -> hollow grinds are in that order in ability to remove metal and minimize profile. However in application this optomization is rarely carried out and thus that order can be ignored.

Usually the nature of the bevel doesn't imply anything about its obtuseness. For example hollow grinds are commonly used on cheap knives, shallow and narrow primaries which produce knives that cut poorly and take long to sharpen. This isn't due to the hollow nature of the grind.

The convex bevels used by most ABS guys are very thin, producing very high cutting ability, easily double to one, and sometimes more than the thicker flat ground v-bevels on most knives, especially the tactical ones. This again isn't due to the convex nature bevels.

You can take any flat bevel and convex it to make it thinner, which is in general what people are doing when they are reporting cutting advantages to convexing a knife. However you can also convex the bevel and make it much more obtuse and thus it will now cut a lot worse.

The only inherent advantage of convex edge bevels used in such a manner is a slight gain is smoothness of cut due to a more flowing profile - but this is a fairly small effect and easily swamped out by small changes in geometry. Anything else can easily be duplicated with multiple v-bevels, usually two is enough as was described by JJ of Razor Edge.

Now convex primary grinds are a bit different. For long blades which can take very heavy impacts, convex grinds are in general more suitable as they can handle shock better. This is mainly due to the fact that the impact will tend to "roll" around the profile instead of concentrating all the force at one spot.

You also see this effect with the edge, which is one of the reasons why durability can be significantly enhanced by the addition of a very small additional microbevel.

-Cliff
 
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