Advanced Knife Machining WIP, Pointy Fighter

So, I'm still making these largely the same way, but with a few refinements.

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I've started milling a chamfer onto what will be some of the edges

One of the most important changes I've made to my process is turning the vises at an angle so the motion in the Y axis is of a similar magnitude as the X axis when milling the bevels

While it's pretty easy to zero on a square vise it's not so simple at an angle, so I've added a bored hole to the soft jaw to zero off. So I calculate the angle with a couple measurements with a touch probe and compensate in the CAM system. Then I just zero off the locating hole.

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The end result is a smoother cleaner milled bevel than I was getting before.

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After the profile is trimmed out the chamfer added earlier make more sense

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so, after some refinements in the machining process, the finished as-machined blade is pretty clean:

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I'm pretty proud of how well these little details have all turned out. I hope you'll pardon me for displaying some finished work.


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This is machined and tumbled but not yet sharpened. The chamfers are a new detail for me. Getting them to terminate cleanly at the scales (go up to, but taper out to not go under) how I wanted was a new technique for me.

Cutter life hasn't been great but the finish is the best I've done yet for milled finish.

I've changed to 3V so I'm taking it a little thinner. The thickness was milled down to .235 compared to .250 for the original pattern. The primary "grinds" and the clip are a little thinner and the fuller is deeper. This allowed me to take some weight from the back as well. It balances the same but the finished assembled weight is down a little over an oz.

I appreciate everyone's interest in my work. I hope some of y'all get something of value from all this.



edit, got a good shot of some actual finished work:

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Thanks Nathan , a great presentation ! When I was learning the machining stuff It was immediately obvious that vibration can be a large problem .Poor finish , short tool life and other problems .Your photos picked up that nicely.. But the practical -- the popcorn stuffed the turkey , it's ready . will your knife take out the turkey ?
 
Nathan, that is beautiful work. But knowing how it was made makes it even more impressive to me. Awesome!
 
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Totally awesome stuff my friend. :eek: :cool:

As I was scrolling down through the new pics, I was thinking... "that chamfer is nuts, but it would be tricky to get it to taper off just right where it meets the scale..." Of course I knew you'd have all that figured out and dialed in. :cool:

Kick ass in so many ways Nathan. :thumbup:
 
So, to ask dumb questions.

A. What is the final blade only length?

B. Is the method allowing some cost savings due to "mass" production.

I only ask as I have a limited budget and LOVE your blades. Heck, I would even buy a blade only to get costs down a little so I could afford one someday.

Again, total respect to your work.

Larry
Tinkerer
 
Greetings,
Maybe I am the only one whom does not understand why you angle the vise(s). Nathan, can explain in layman terms the advantage?

Again, Thanks.

Dennis
 
Dennis Paish said:
Greetings,
Maybe I am the only one whom does not understand why you angle the vise(s). Nathan, can explain in layman terms the advantage?

Again, Thanks.

Dennis
Click to expand...

It's a three axis simultaneous interpolated motion. When the vise is set parallel to the table there is a large motion in X with very small motions in Z and Y. The motions in Z don't really effect the surface finish because Z is perpendicular to the edge because the soft jaws have the blade angled. But the small motions in Y are very small compared to X causing some small unintentional artifacts. Angling the vise cured this. It was the no-so-obvious solution to a no-so-obvious problem. Solved, the milled bevel is almost as perfect as ground which has been a goal of mine for years.
 
Nathan - you're the Master!!! I'm so impressed with all that machine work - even the gcode to create that is impressive!

Ken H>
 
wow, what a pleasure to read/see/watch. Really appreciate the effort put into making your project visible to us at BF. Good on you!
 
Nathan the Machinist said:
I promised a technical WIP, so I'm going to go into some detail about vacuum fixturing for those of you who are interested. Most of you will probably want to skip to the next post, but to anybody interested in trying it, this is an important post.



I am machining micarta scales. There are a number of different ways of approaching this depending on the design of the scale and the material, but in my shop it usually starts with a sheet held down to a vacuum table. A lot of us have vacuum pumps for wood stabilization that might consider using this on a mill or router for part fixturing. A vacuum is capable of generating over 4,000 pounds of hold down force across a 12X24 sheet.

This is my vacuum hold down table.

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It is canvas micarta.

It is 12 X 24 X 2”. It has a big aluminum “chunk” attached to the bottom of it so it can be clamped into a pair of matched vises. I used to run it off a subplate but out of vises is a lot faster to setup.

This is not how it usually looks. It usually has a bunch of gasket traces carved into it from previous jobs that have been filled in with epoxy and milled flat. It was getting a little Swiss cheesy so I went ahead and mowed the whole top of it down so previous traces wouldn’t show for this WIP.

This is how you make and use a vacuum table for parts like this:

1. You need a vacuum pump. Most manufacturers use some form of a rotary vane for this and that’s not a bad choice. However, your hold down force is a function of your surface area and the depth of the vacuum. Some good rotary vane pumps get down pretty low, but many do not. Since I frequently machine relatively small parts I use a multi stage positive displacement vacuum pump that pulls a high vacuum to maximize my holding force on smaller parts.

Commercial CNC wood routers that use vacuum for part fixturing in furniture manufacturing are typically 200-600 CFM, but they're holding multiple sheets of wood against an MDF spoil board without gasketing so it takes a lot. For this small table I'm using an old 30 CFM “Absolute 1200” pump which is an unusual pump for this but it's working. You could probably achieve good results with just 1 CFM if you use a vacuum reserve tank and good gasketing and are careful. One advantage to a larger pump is you can run two lines from a manifold at the pump and have two vacuum zones that can hold a part in more than one location in case your vacuum becomes compromised you don't throw a part.

2. You need a vacuum table. Industry frequently uses an aluminum waffle table capped with an MDF spoil board that you can pull vacuum through or add foam rubber gasketing. For the small parts we’re making we want to maximize our surface area, so a precut grid of gasket channels is often no good because they don’t ever fit the profile of the part perfectly so I like something I can mill a channel in directly like phenolic. This channel can be filled with epoxy when you’re done and the table surface gets resurfaced every time you put it in the machine. You could use aluminum, but a 2” slab of micarta weighs the same as a 1” plate of aluminum, and is stiffer (stiffness increases by thickness to the 3rd power, so despite having a lower flex mod the 2” phenolic table is actually stiffer than 1” aluminum would be, and weighs the same).

You obviously can’t use an MDF spoil board with coolant, and I don’t like cutting this kind of stuff dry. Coolant keeps the dust and the fumes down.

3. You have to plumb the table to the pump with somewhat flexible tubing that won’t collapse under a vacuum. I’m using ½” LDPE tubing and push-to-connect fittings. The tube is relatively flexible and can pivot freely in the fitting. I have air water separator filters at the actual vacuum pump to catch any random drip of coolant or trash that may make it through. Take note that these units are installed backwards from how you’d normally install them on an air system, which makes sense when you consider the direction of air flow. You want ball valves at your table so you can turn the vacuum supply on and off at the table. It is good to have the line go up to the ceiling then back down to your pump. That way any little bit of coolant that leaks into your table has to go uphill to make it to your pump. The less stuff your pump ingests the better.

4. You need to distribute the vacuum in your table and to your part. I’m running two air lines (there is a good reason for this if anybody is curious) but you only need one. I drilled a hole into the edge of the table and drilled a hole down into it from the table surface. From this you need to cut a small air channel out into your part and (usually) out into the perimeter gasket. This helps distribute the vacuum all over the part. Otherwise you can have one section of your part pull down directly over your vacuum hole and can sort of seal off with the vacuum never making it all the way across the part. A lot of CFM makes obtaining the initial seal a lot easier. You either want a 2-3 HP pump, or a reserve tank to give you the CFM you need to obtain the initial seal. After that a small pump can maintain vacuum if your gaskets are good.

5. You need to gasket around the inside profile of your part and you need to cut little o-ring grooves everywhere you have a drilled hole in your part that would violate your vacuum zone. I cut my profile gasket channel with an 1/8” cutter along a path centered an 1/8” from the edge of the part. I program it this way, but you can also cheat with your offset compensation values and get the same result. I’m using a 1/16” o-ring cord stock (60 duro buna-n), which is actually .070”, so my channels are .057 deep giving me .013” o-ring compression. Too much compression and your part won’t sit flat against the fixture, and too little and it becomes difficult to obtain the initial seal.

I glue the ends of the cord stock together with super glue and I also glue the gasketing down into the groove with a few drops of super glue in strategic spots. I like the crappy consumer grade glues you can get at Lowes for this because it has a good reliable low bond strength and poor adhesion which makes it easy to get back out of your fixture later.

In use, you turn your vacuum on (with your ball valve) then you turn the vacuum back off (at the ball valve) and the part should remain unmovable. This confirms you have a good seal. Then you open your vacuum valve again before commencing machining. This seal retention makes removing the part tricky when you're done. I just pull my push-to-connect fitting to release the vacuum or if the part has holes in it I take a rubber tipped air nozzle and press it into a hole and use air pressure to blow the part loose from the table. You could use a three way ball valve and vent to atmosphere, but I don't think it's worth the trouble.

I think that sums up the use of vacuum for part fixturing.





I kinda doubt anybody actually read much of that, but I promised to go into technical detail and to anyone trying to figure this out on their own for the first time this ^ is gold.

The next post will be 3D CNC machining complex contoured knife scales. It'll be a little less dry. I'll try to get it up tonight or tomorrow.
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nice work on the vacuum setup.

When our shop was doing some G10 scales for a folder in production, we tried the vacuum setup but to no avail.
We tried and put many hours into the vacuum trials, in the end we went back to screws in the pivot hole and lanyard hole for each individual scale. As you have detailed, clearly there are a number of detailed parameters that are required to make this work.
 
Hi Nathan,
i stumbled on this thread because someone was selling one of these knives. the seller said their was an awesome video on the knife and i watched it. Jean Claude Van damme Nathan. That video was impressive to say the least and then i arrived here.

Yes, i'm leading up to asking this. How long a blade are you capable of doing actually. I'm thinking/talking in the neighborhood of 31-36 inches approx. Yes, what i have seen you outlined seems like a different way to make a sword imho. Specifically a chinese jian/gim sometimes mistakenly called a Tai Chi sword.

the toughness that you showed in that video was screaming sword to me . only thing is the sword is sharpened at different levels.
top 1/3 from the tip is very very sharp, then the next portion slightly more than a 1/3 is just nice and sharp meant for more heavier tasks like cutting off an arm , the last section is sharp , but not so much, this section is used for parrying/blocking .

This thread made me freak out in my mind thinking of the possibilities Nathan
 
This is what happens when you put evil genius to GOOD use! I really admire you're skill and ingenuity, not to mention the generosity of sharing the information.
 
knife dragon said:
Hi Nathan,
i stumbled on this thread because someone was selling one of these knives. the seller said their was an awesome video on the knife and i watched it. Jean Claude Van damme Nathan. That video was impressive to say the least and then i arrived here.

Yes, i'm leading up to asking this. How long a blade are you capable of doing actually. I'm thinking/talking in the neighborhood of 31-36 inches approx. Yes, what i have seen you outlined seems like a different way to make a sword imho. Specifically a chinese jian/gim sometimes mistakenly called a Tai Chi sword.

the toughness that you showed in that video was screaming sword to me . only thing is the sword is sharpened at different levels.
top 1/3 from the tip is very very sharp, then the next portion slightly more than a 1/3 is just nice and sharp meant for more heavier tasks like cutting off an arm , the last section is sharp , but not so much, this section is used for parrying/blocking .

This thread made me freak out in my mind thinking of the possibilities Nathan
Click to expand...

There is more to a sword than making a big knife.

Look to Dr. Dan Keffeler for 3V swords. He is the man (and the world cutting champion). He and I are of the same mind on 3V and heat treat, and he understands the geometry of a cutting sword. The man can cut down a proper tree in two whacks.
 
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