Advanced Knife Machining WIP, Pointy Fighter

[Nathan the Machinist]

This will be a somewhat technical WIP covering machining techniques that I frequently use in my shop, as applied to knifemaking. As more advanced machine tools become more common in many of our shops I believe that some these techniques might become more prevalent in other maker’s shops. I plan on going over side milling bevels (edge up), cutting bevels with a face mill (edge flat), fixturing and zeroing challenges for bevel milling, machining strategies for fine surface finish and long tool life, milling complex 3D scales, the use of vacuum hold down in scales production, and dry machining with the use of coated carbide. I might do some CNC grinding in a VMC too, depending on how well I can tweak the surface finish from a face mill.

I can almost guarantee that my approach to knifemaking is different than yours. I’m not proclaiming that “my way is better” or that everyone should work the way that I do. Sometimes it is useful to look at things a different way, so I’m showing you my different way.

I’ll be documenting the project from design inception through production and discuss things like the design process (prototyping and optimization, weight and balance compromises and ergonomics), design for manufacturing and details of the setup and machining.

This is mostly a “real time” WIP, and it will be taking place in my busy shop while there is other work going on at the same time. This means there will be lulls and delays while I tend other jobs and it will likely get interrupted a few times. Also, since this is a new pattern for me you’ll see the hiccups and tweaks as they occur.

I’m going to start this with a discussion of the design process. Those of you wanting to see metal chips should check back in later, just design talk here.

This is the knife that I plan on making:

I know that discussion of my design process is not why folks are here, y’all want to see metal chips. However, to me, a discussion of why we make something a certain way is as important as how, and I don’t think we discuss that enough. So, y’all wanting to see steel cut, come back later, I’m starting this with some thoughts about design.

 

[Nathan the Machinist]

I’m gonna try and make this a fun project. I’m making a big, extra stabby fighter here that will be made almost completely on a milling machine. It is a goal of mine to eventually do a completely milled knife, but I don’t think I’m quite ready to give up my 2X72 knife grinder just yet. But I’m getting close.

For this project, I’m building a relatively large hard use fighter/utility tool/stabbing weapon for people in uniform and feral hog hunters etc. My goal is a durable, well balanced machined weapon. I’ll be starting with relatively stout stock and achieving weight reduction and mass distribution utilizing distal taper, deep fullers, swedge grind and a skeletonized tang. The ergonomic goals include the use of a standard "forward" grip, a fencing (or saber) grip and a reverse grip (upside down, edge out) for an average to large hand.


My design process starts with hand drawings and is initially based upon intuition and experience where I figure out what I think I want on paper and then scan that into the computer for further development. I’m almost always wrong about something at this point in the process. In this case I got the handle all wrong.


I’m tracing it with NURBS geometry where I make further refinements. When I started it looked like this:

The blade is designed as a stout stabbing weapon similar to a WWII era bayonet with a beefy point and deep fullers. There is a thumb ramp (in the wrong place initially) and a substantial finger coil behind the guard for safety, and the proximal end is also shaped for thumb placement when held in a reverse grip.

I cut out the preliminary design in cardboard and immediately found problems with the grip. I don’t like how it “points” in the hand (when gripped it kicks out to the side at an angle), the grip is too tall in the meaty part of the palm and too long for a solid reverse grip because the thumb has too far to reach. I make a couple tweaks to get in the ball park and then move on to playdough models.

There is a point here I’d like to make. Too many knives are made with handles that just look cool, or are easy to make, or are simply laid out to use a convenient bar of steel without enough work being done to optimize the shape of the handle for the tasks to be done and for the human hand. Sometimes the grip becomes an oversight.

Handle some of the knives made by folks like Bob Loveless and a lot of the ABS guys and you will find there is a reason they don’t look like broom handles. And I have a cool trick for you so you can back into that design very easily with just cardboard and modeling clay. Seriously, you need to try this.

It is an iterative process. First you cutout your preliminary design in cardboard and layer the grip with clay. Pass it back and forth between your two hands, squeezing on it as you do so. It will eventually start to take on an idealized shape, and it will reveal where your tang profile is wrong because the material will be pulled away from the tang where you have tang where it shouldn’t be, or built up in places where you need to add material. For a knife of this nature requiring three specific grips there are some compromises to be made in the geometry, but you can get something that is pretty dang good in all three, and all you have to do is look at the playdough. These are some of my work in progress models:

Once I had the handle right I modeled it in CAD.

First as a relatively faithful copy, then as a somewhat simplified version that captured all of the significant dimensions and geometry but looking a little less like a constipated cat turd:

With the scales modeled I was able to calculate my weight and balance in the CAD system and start working on skeletonizing the tang and moving some meat around to balance the knife.

 

[Frank Niro]

I certainly enjoy your styling and will be looking forward how a knife can be made differently than the way I would do it. Thanks for this, Nathan. Frank

 

[Bailey Knives]

I want to see chips flying! Just kidding, your insight on design and your clay ideas are worth trying. Cant wait for the next installment

 

[Dan Pierson]

Thanks a lot Nathan. This is going to be an excellent read.

 

[Holmesmade]

If you don't have or want to buy clay, wet paper towels can accomplish very much the same thing. It takes a little more squeeze to shape the paper towels, though.

 

[fumbler]

This aught to be a cool WIP. It's neat seeing how people do things differently but this one will be waaaay different.

Thanks for doing it.

 

[Nathan the Machinist]

Balance and weight:

It is possible to have two knives of identical length, weight and center of gravity that behave very differently in the hand based upon mass distribution. As the mass moves out towards the extremities of the knife it resists changes in rotation. Also, because one end can not rotate around a center without the other end also moving around that center, a weight such as a pommel on one end resists movement at the other. Through this mechanism, a pommel doesn’t just balance a long or heavy blade, it resists deflection and adds power to a cut through the conservation of momentum. This little blade I’m making doesn’t really need a real pommel, but the tang certainly doesn’t need to be overly skeletonized down on that end either. This blade would be an extremely poor candidate for a tapered tang unless I were attaching some form of counterweight to compensate.

The handling of a fighter benefits from a light tip, however taken to an extreme this is at odds with the tip strength needs of a modern tactical knife. I’ve chosen to start with a .250 blade thickness and I’m carving away unnecessary weight with deep fullers and a swedge that creates distal taper past the fuller. The blade that I have come up with is .180” at one inch back from the tip and has a pronounced diamond shaped cross section.

I’m skeletonizing much of the tang but leaving it solid at the very end for balance.

According to my calculations the end result once the scales and hardware are figured in is a total weight of 12 ounces and balance across the “guard” in a package just under 13” total length and .250” thick at the ricassio. In my opinion this is very good so I’m done with the design and ready to start building it. It will be interesting to compare the final results with these calculated values.

I’m not telling you all this just to impress you with my awesome knife balancing-fu. Nothing I’m doing here is at all novel. Most experienced knifemakers do this, either through intuition, experience or trial and error, but it doesn’t usually just happen by itself, some thought has to go into it.

So to sum up, I’m making every effort that I can to make this a tough tactical knife that is still reasonably light and lively. I’ll end this part of the discussion here because I know I’m going on a bit about an esoteric topic, but I felt this particular topic needs more discussion around here so that’s my .02. Moving on to the good stuff, the next post (in a few days) will be cutting chips. I’ll talk about speeds and feeds and stuff…

 

[Huntsman Knife Co. LLC.]

Awesome thread Nathan! I will definitely be following this one.

 

[BenR.T.]

My Mill comes today, great timing Nathan! Thanks for doing this, the whole process should be very informative.

 

[PaMtnBkr]

I don't have a mill or any maching tools but I am enjoying the process you are using to explain the mindset behind your reason for direction. The use of clay to figure out your ergonomics of the handle is simple but genius! I'll be watching this one! Thank you Nathan!

 

[Salem Straub]

Thanks, Nathan!

 

[jawilder]

Subscribed

 

[Patrice Lemée]

Thanks for sharing Nathan! This will be very interesting, even if I don't understand half of it.

Now Salem, pass the popcorn!

 

[Nathan the Machinist]

Thanks for sharing Nathan! This will be very interesting, even if I don't understand half of it.

Now Salem, pass the popcorn!

Hey Pat, I was reading your WIP the other day and was inspired to do this one. You're inspirational bro. :thumbup:

 

[AVigil]

Now you got us all excited.

Looking forward to it

 

[JCoutts]

I'm definitely subscribing to this one, I think this is going to be one amazing WIP! I can't wait to see everything that you have to show Nathan!

 

[Salem Straub]

I don't know Pat... if I passed the popcorn to you, you'd probably do something weird like put brown gravy on it, ya Canuck!

 

[NickWheeler]

Nathan- Please be forewarned, Angi is probably going to kick you. I have spent very LITTLE time on the forums lately, but you just started something that I won't be able to leave alone.

Thanks for sharing!

Salem... the gif with Gus actually made me laugh... like out loud and stuff. :foot:

 

[Erin Burke]

Nathan,
What process did you use to get your cat turd model into CAD?
Erin