WIP, Machined knife

Nathan

This is way cool, and as I have one of your great "pig stickers", I am enjoying this WIP even more :D. I do have a question -


Since you did the profiling "dry", is there a reason you did the bevels with coolant?

Thanks

Bill Flynn
 
Nathan the Machinist said:
This is why I take this approach:


19.jpg~original


20.jpg~original



The plunge is perfectly symmetric, the edge is perfectly straight and centered and exactly the thickness I intended. Don't get me wrong, I'm not saying that my way is better or that I think I'm a better knifemaker because of it. I'm saying that, for my goals and priorities, there is literally no better way to do this.
Click to expand...

Can't argue with results like that.
 
billf said:
Nathan

This is way cool, and as I have one of your great "pig stickers", I am enjoying this WIP even more :D. I do have a question -


Since you did the profiling "dry", is there a reason you did the bevels with coolant?

Thanks

Bill Flynn
Click to expand...

Oh yeah man, that's a really good question. To explain that I need to explain why one would even want to cut dry when conventional machining has been done wet for forever.

In a nut shell, the reason to run dry is improved cutter life using modern cutters in certain kinds of cuts. The coating, AlTiN (aluminum titanium nitride), forms a very thin coating of highly abrasion resistant aluminum oxide that replenishes itself in use while hot. So the cutter wears better when it's hot so long as it isn't glowing red. The carbide chips less when it's warm and tends to crack when you spray coolant on it while being run at speeds appropriate to carbide. Run it too slow and you get BUE (built up edge) which wears out carbide pretty fast. So there are a lot of good reasons to run fast hot and dry when you can.

But, nothing wrecks a cutter faster than re cutting chips. This is particularly true when cutting materials such as Elmax that form really nasty hard and abrasive chips.

It may not be obvious, but the art and science of machining revolves a lot around chip load per tooth. There is a window for a particular material and cutter combination where you have an optional chip thickness for a given cutter diameter. This changes (often favorably) when there is less than half of the cutter engaged, due to radial chip thinning. But, in a nutshell, your feed rate is a function of that optimum chip load and your RPM. So, when you're able to take a cut where you can feed hard enough and spin fast enough that your speeds and feeds fall within a favorable window that includes a heavy chip and a high spindle speed you can then safely throw your chips out of the cut without risking recutting them. So, when your fixture and part are conducive to machining without a lot of chip accumulation and when you can run a pass that is throwing chips well, you can then safely run dry. When running dry you can also run higher SFM because there is no thermal shock from coolant. This leads to a happy combination of high material removal rates and long cutter life. This is high speed machining. Ask any machinist, cutting a difficult material like Elmax at 41 IPM and getting good cutter life is not trivial.

But, there are times when you need to turn the coolant on. This machining center (loving known in my shop as "The Old Grey Pig") is a heavy boxway mill. Moves like a fish, steers like a cow. So I have to slow it way down for accurate cuts, otherwise it can't get out of its own way and it clips corners. When fed slow, the RPM needs to come down too in order to stay in that chip load window. Fall out of that window in these materials and things rub instead of cut, (with ~15% vanadium carbide by volume = wear, and with 18% chrome = bad work hardening) so things are going too slow to throw the chip. And at slower SFM BUE becomes a problem. However thermal shock is less of a concern and the coolant has EP additives to reduce BUE. So, for slow finishing cuts like that, even if you're using an air blast you probably want to go ahead and turn on the coolant.

So, to sum up, you run dry when you can, and wet when you need to. There is a lot of gray area in there too.
 
If your not bleeding and sweating when finished, your doing it wrong. It is amazing that there are so many different ways to arrive at that end point. Is there are right way or a wrong way? Not in my opinion, just different ways. Thanks for showing us your way!
 
Nathan

Great explanation - thanks ! Even a non-machinist can understand that !

Of course, it looks like even your "old grey pig" is a pretty nice machine :p

Bill
 
Great stuff Nathan. I'm eagerly waiting for more. I like machining in my own fumbling way, but this is like magic to me.
 
I'm in school to be a machinist, so this thread is awesome!

I've been working how to cut bevels in my head for quite a while (knife nut in a machine shop...what do you expect lol), it is awesome to see how someone else does it.
 
Nathan, what do you do with the cutter once it's worn out after half a day's work? Does it get resharpened? new carbide teeth? recycled?
Love the thread, btw.

-Daizee
 
Excellent thread by one of the most talented, knowledgeable "Hack Machinists" I've ever had the pleasure of knowing. Your work is inspirational in every way - and second to none !

In regards to milling the bevels standing up as you've done on this piece vs. laying it down, and milling one side at a time with support on the back or bottom side, as was done with your Dagger. Or was it the Hunters that were milled one side at a time ?

Whatever the case, what kind of tool or workpiece deflection do you encounter in this type set-up ? Your excellent video shows one pass. Was that literally, a one pass per side operation, or did you need to make numerous passes to remove material that remained due to deflection ?

Again, excellent work Nathan ! Excellent !

:thumbup:
 
crazyengineer said:
I'm in school to be a machinist, so this thread is awesome!

I've been working how to cut bevels in my head for quite a while (knife nut in a machine shop...what do you expect lol), it is awesome to see how someone else does it.
Click to expand...

Yeah man, there are lots of ways. Something they all have in common is it is much better to leave the stock square so you have something to hold onto until you've got your bevels.

In fact, even for people who are hand grinding, if you'll leave some/all of the meat behind the bevel your tips tend to come out cleaner without that roll you get grinding on an unsupported point.
 
daizee said:
Nathan, what do you do with the cutter once it's worn out after half a day's work? Does it get resharpened? new carbide teeth? recycled?
Love the thread, btw.

-Daizee
Click to expand...
It depends on the cutter and the cut. In this case the cutter in the video is just taking a spring pass and all the work has been done with a rougher. Once the finisher starts to leave a bit of a burr I move it down into the rougher's slot and put in a new finisher. At that point it is just getting broken in and it will perform well as a rougher in this application (endmills chatter less and are more durable once the very edge has been slightly worn). After that it gets put onto the shelf to be used as a rougher for profiling. When used as a rougher for profiling I keep the point down and out of the cut so once it is dull in that application it can still be used as a rougher for regular endmilling. After that it goes into the scrap carbide pile. The geometry of the cutter and the coating make it perform extremely well and consistently from cutter to cutter and you just don't get that kind of performance and consistency with regrinds. If it were a larger cutter I might send it out for sharpening but I'll frequently use inserted cutter bodies for larger cuts.
 
David Wesner said:
Excellent thread by one of the most talented, knowledgeable "Hack Machinists" I've ever had the pleasure of knowing. Your work is inspirational in every way - and second to none !

In regards to milling the bevels standing up as you've done on this piece vs. laying it down, and milling one side at a time with support on the back or bottom side, as was done with your Dagger. Or was it the Hunters that were milled one side at a time ?

Whatever the case, what kind of tool or workpiece deflection do you encounter in this type set-up ? Your excellent video shows one pass. Was that literally, a one pass per side operation, or did you need to make numerous passes to remove material that remained due to deflection ?

Again, excellent work Nathan ! Excellent !

:thumbup:
Click to expand...

Dave! Where ya been man?

The hunters and dagger were surface milled. Surface milling is slow and leaves a messy finish but you can get any crazy geometry you want without any constraints. I take that approach when I'm trying to do something weird like wrap a hollow grind around a deep belly and keep the grind perpendicular to the edge or in the case of that dagger manipulating the grind to keep the point stout rather than a function of the width of the blade. The dagger was laying down, the skinners were edge up so I could do both sides at the same time.

I'm sure there is some workpiece deflection but due to limitations measuring a tapered work piece, there isn't any that I can measure. That video is short to show folks what it looks like. In reality there are roughing passes and a tool change to the finisher. There are three steps down, two trajectory passes and then that finish pass with a fresh cutter. I experimented with milling in the conventional direction rather than climb milling to reduce deflection but found it made no difference in this application.
 
Nathan the Machinist said:
Dave! Where ya been man?

The hunters and dagger were surface milled. Surface milling is slow and leaves a messy finish but you can get any crazy geometry you want without any constraints. I take that approach when I'm trying to do something weird like wrap a hollow grind around a deep belly and keep the grind perpendicular to the edge or in the case of that dagger manipulating the grind to keep the point stout rather than a function of the width of the blade. The dagger was laying down, the skinners were edge up so I could do both sides at the same time.

I'm sure there is some workpiece deflection but due to limitations measuring a tapered work piece, there isn't any that I can measure. That video is short to show folks what it looks like. In reality there are roughing passes and a tool change to the finisher. There are three steps down, two trajectory passes and then that finish pass with a fresh cutter. I experimented with milling in the conventional direction rather than climb milling to reduce deflection but found it made no difference in this application.
Click to expand...

Thanks for taking the time to write the detailed response Nathan :thumbup: I thought the video might be, as you stated - "short to show folks what it looks like". I was at first amazed that you completed the material removal in one pass. Then it dawned on me you were most likely just giving us a taste of the process.

Again - I can't over state the incredible skills you posses working with machine tools Nathan. I'm excited to see the end result which, there is no doubt in my mind, will turn out as perfect as perfect can be.
Thanks again for giving us a glimpse into your world and the humble nature with which you do it. We're lucky to have you here, taking the time out to document and clearly explain your process, procedure and theory, in regards to how it should be done when using machine tools to reach your end result.

:thumbup::thumbup:
 
Machining is becoming a lost art. The trade schools in CT. have dropped it from their curriculum. CT. was the place to go during and after the war for a job in the defense industry when machinist were in demand.
What a shame. Thanks for your post.
 
The thing that I so admire about Nathan's WIPs is the deep artistic sense shown in his understanding of the modern machining process. Even a Neanderthal like myself has to be delighted to see the flow of design, thought, process, and elegant approach in these threads.

Besides, watching those videos is like seeing an F-15 on a low approach. (and a knife comes out the other end!)

I hope exposure to the machining approach will help us all understand that it's the "maker" who puts the art in the knife, regardless of the method or tradition in which the work is done.

Go Nathan,


John
 
I agree with what John has stated about Nathan's style and superlative machining skills....there's 'machining' and then there's Nathan's approach to machining.

For those that have never had the utmost pleasure to handle one of his knives, they are amazing....PERFECTLY balanced, finished and sharpened.

Mathematics at their finest....

Not only can he 'machine', he's a Master when it comes to metallurgy and heat-treat. :)
 
Hello!

I completely agree with the last statement! I am lucky enough to own one of the 8" fighters and it's an amazing beast! (hopefully, I will add another one soon! ;) )

Best regards,
Alex
 
I'm also in agreement with John, Dawkind, and A.L.E.X.
I've got one of Nathan's knives, a smaller user, and I love it, as well as most people that handle it.
Dozier
 
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