Looking for Input on Grind Geometry

[Rick Marchand]

Hello all,
I have been toying around with a new blade geometry and REALLY like it. It's got a bit of Japanese/Tribal influence to it. It looks cool but the design is based on function rather than style. I was trying to make a light knife with more rigidity and resistance to flex. Please be honest and tell me what you think.

My attempt at addressing the "strength vs thickness vs cutting ability" dilema.

Rick

I hope you can read the pics.....

The prototype... that you may have seen before...

As forged.... cleaning up the bevels...

A similar blade showing grind lines...

 

[tychoseven]

Rick, I see a lot of thought behind that deceptively simple design. When you first posted pictures I noticed some things, like your off-center ridgeline, and now I know why you've done it that way. Truly a "thinking man's" tool.

As for decreasing flex, the only suggestion I can offer is to add a fuller somewhere, like between the spine and ridgeline. That would keep your blade lively and light, but add the rigidity you're seeking.

 

[Rick Marchand]

Rick, I see a lot of thought behind that design. When you first posted pictures I noticed some things, like your off-center ridgeline, and now I know why you've done it that way.

As for decreasing flex, the only suggestion I can offer is to add a fuller somewhere, like between the spine and ridgeline. That should keep your blade lively and light, but add the rigidity you're seeking.

Thanks Tyco,
A fuller will reduce wieght but does not add rigidity. You cannot add that to an object by removing stock. A fuller is a great way to lighten a blade while retaining a fair amount of rigidity.

 

[d_filgate]

Rick,
That is an amazing looking blade. It was hard to tell from the diagrams, but the pictures
of the actual blade make it really clear.
I can see how that could be a very functional knife on many levels.
Good looking blade!

 

[J. Doyle]

Rick, I think that's a well thought out design. As I see it, you've pretty much achieved what you described. You still should have plenty of strength in both the spine and the edge.

I like the edge geometry. Especially the fact that you described the main grind as being 'shallow convex'. I think that's key there. If you get those too convex, they really start to sacrifice slicing ability, IMHO. The micro bevel is perfect. I think the cutting edge and edge spine of your design are just about as strong as they can be and balance weight, strength and efficiency.

In fact when I do a full heigth flat grind, after HT, I convex the bottom third of the blade down to almost sharp then apply a micro bevel. A similar concept to what you've done.

All said, I like it. Nice work.

 

[chopchop]

When you say add rigidity, to which direction are you referring? Are you trying to stiffen up the knife against torsion for twist-popping out sections of wood? Or against bending from side to side like a fillet knife?

I'm not a knife maker, but it seems like a second ridge line, or maybe a wider ridge... so that you have more of a hexagonal cross section than a diamond/rhomboid cross section... would do the latter. To reduce torsion, it seems like you'd need more of a plus shaped cross section, b/c the longer the lever arm (ridge to edge), the more torque there would be.

I think there are some traditional Scandinavian designs with a rhomboid cross section (Tapio Wirkkala maybe?), but without the intentional convexing on the cutting grind.

...and your work is amazing, btw. That's a beautiful blade!

 

[OwenM]

Interesting idea, and looks awesome, but I think it would come into its own on a much larger and wider blade.
On this knife, it's still a low sabre grind. I don't see the lost cutting ability vs. a wider blade with full height convex grind being outweighed by a small mechanical advantage in rocking the blade out when it's wedged. For that matter, I don't see a narrow grind like that getting wedged all that much. Looks like it would be pretty efficient at splitting and cutting materials that would grip on a thinner flat grind.
That knife is gorgeous, either way, though.

 

[Joezilla]

Rick, some hand made Thai-eneps have that slight variation at the point that I've seen. If are going for edge flexion, watch that micro bevel's angle too so it doesn't roll on hard stuff. What i would be interested to see is if it had any effect on shock absorption on the bigger stuff!

 

[Joezilla]

Thanks Tyco,
A fuller will reduce wieght but does not add rigidity. You cannot add that to an object by removing stock. A fuller is a great way to lighten a blade while retaining a fair amount of rigidity.

+2 on that. I asked the wise elder machete engineers about their fullers, and referenced I-beams. They said it was impossible to add rigidity that way, they just put it in for aesthetics.

Rick, does it have a full distal taper?

 

[TheGame]

In my opinion, fullers would make it look funny. However, that is only my opinion.

Rick, I like the template that you have laid out. It makes it easy to understand, and couple with the knife show very well what you mean. Overall I think it is a well thought out process :thumbup:

(but the knife looks messed up, so if you will, just send it to me... )

 

[tychoseven]

Thanks Tyco,
A fuller will reduce wieght but does not add rigidity. You cannot add that to an object by removing stock. A fuller is a great way to lighten a blade while retaining a fair amount of rigidity.

Ah, my bad. Rigidity remains about the same while weight goes down. I see. Is this still the case if you forge the fuller instead of grinding/scraping?


In that case I have nothing to offer but my admiration of your work!

 

[Big Mike]

Rick, I really like the look of the blade. :thumbup: :thumbup:


I doubt the blade will be much stronger (laterally) then a blade of the same thickness with a full height grind.


You do gain extra support to the edge by having a shorter primary bevel, the trade off being the blade gets thicker quicker (always a concern when slicing thick material, but as you state the convex primary bevel does help part the sliced material).

Also, your design does lend itself to a stonger point.

+2 on that. I asked the wise elder machete engineers about their fullers, and referenced I-beams. They said it was impossible to add rigidity that way, they just put it in for aesthetics.

Here's the deal on fullers.

For a blade of a given weight, if it is made with fullers it can be thicker then a blade without fullers; the thicker blade provides the extra strength, not the fullers; the fullers only helps in weight reduction, and do not add any strength.

On Ricks design, the tapered top section of the blade provides weight reduction, much as adding fullers would.




Engineering school did teach me a few things (other the partying).



Big Mike

 

[CID25]

Interesting idea, that prototype looks really nice

 

[Shotgun]

Instead of doing a flat grind on the back maybe do a slight hollow grind. That way you would have more of a bite on a ferro rod.

 

[stingray4540]

I really like it!

I agree with Shotgun though, a hollow grind would not only allow for better bite on a ferro rod, but also reduce weight even more.

Personally, I would like to see the secondary bevel removed and leave it as a full, slight convex. I also think the edge should come up to the ridge line, so the ridge line ends at the point, giving you a super strong diamond shaped point. It would also look better too, IMO.
Just some of my thoughts, so take them for what they are worth, i.e. not much, lol.

I have a question too, what is the thickness at the ridge?

 

[PayetteRucker]

it looks ideal to me, except why not turn that microbevel V into a full scandi?

 

[pitdog]

When I first saw it I thought it was a bit of an odd duck but after reading your explaination it now makes a lot of sense !
I'd maybe move the ridge line up just a touch higher so it more closely resembles your top drawing, this would be purely for aesthetic reasons though !

 

[kgd]

I can tell you guys that Rick's leaf blade feels awesome in the hand. Great balance and it really does feel like a thin knife. I started looking around for something to cut and Rick managed to pluck the blade out of my grasp figuring I'd probably hurt myself with it

 

[crossada]

this is a traditional tommi knife with a similiar grind with the taper off the ridge line. it cuts great despite being over 1/4" thick.

 

[Mack]

It brings to mind some of the Loveless designs. At least to my eye.
I can't imagine that would be a bad thing.

It is a beauty, that's for certain.