Anyone look into the inside of folding knives on the construction?

[tkdroamer]

I too found my ultimate passion in EE. I was a musician until I was 25, my degree was BioChemistry. Then I found my ultimate passion in electronics. I started from the bottom, promoted to EE, became manager of EE before I retired. Since retirement, I still study and worked on electronics at home. I went back to music electronics designing guitar amps and extreme high end hifi power amps.

I am very involved in mechanical design also because the kind of instruments we design, the mechanical design is every bit affecting the electronics design about the placement, location of all the stuffs.

I find no education, theory is good enough unless one has a good dose of common sense with I found a lot of people don't have even with high education. When I hire engineers or techncians, I really don't put too much in what school they came from or even what experience they had. I gave them a test I made up, mostly simple stuffs that you can do it if you have a good dose of common sense and truly understand the stuffs. In the analog part test, a lot is straight from a book I studied in the first class of analog circuit in a technical school called Heald College. Those are for technicians. You would think and EE should be able to answer that.............WRONG!!! Anyone failed the test, I just cut the interview short and sent them away politely.

My most favorite part of electronics is RF/microwave and electromagnetics. That I can see and predict how the signal move and all that. Even after I retired in 2005, I still spent a few years studying electrromagnetics and antenna until I realize I memory is really going down, that I forget stuffs I studied. I kept very good notes, a lot of times I read back my notes I wrote a few weeks ago, it's like I never seen it before. But then after I follow my notes step by step, I realized I really UNDERSTOOD it!!! And it's like I have no memory of it anymore!!!! It's a scary feeling. I kind of stop studying since and just more to design amplifiers which was what got me into electronics and quit playing music.

Funny the company I worked for before called me back in 2015 to design the next phase of the instrument and I worked as a contractor for a year and half before I really call it a quit. The tax was really bad and because of my income, it hurts my wife's medicare payment, not only paying a lot of tax, it increased the medicare payment!!!! So I really retired since as my wife really want me to quit.

Nice.
To be clear my EE is electrical engineer, not electronics. I know they are associated but an EE degree can go in many directions much like an ME. I gravitated into control & automation.
Way back in the day one place I worked at had a ton of Seimen's controllers and I/O. We had a steady load of board level repairs that we could do ourselves. When Seimen's came out with the next generation of hardware, the boards were so compact we could no longer do repairs ourselves, effectively making the I/O cards throw away units.

 

[Rich Parsons]

As always, that depends. I doubt a background in, say, biomolecular engineering would help much in this discussion...

Certainly. I was more talking about the problem-solving and analysis engineering education seems to focus on. It’s useful well beyond the scope of their discipline.

Yes, a good engineer that learns in college about systems and how the parts make something complete or larger parts, and how they connect can have discussions in lots of areas by asking the right questions.

If they only think about the specific minimized project then no they will not be able to join the conversation productively.

 

[Alan0354]

I have followed the thread. Yes, disassembled there is a thin cross section. But assembled, it is carrying little to none of the load. You don't seem to understand engineered design.
Yes, there could be issues if the knife assembly were to somehow get loose causing undue loading on the thin cross section.


I have followed the thread.
Yes, disassembled there is a thin cross section. But assembled, little to none of the load would be on the hole section. You do not seem to understand engineered design.
Yes, if the knife assembly were to somehow get loose, it could load the hole's cross section. But that would be akin to operator error wouldn't it?

I disagree, the ball bearings make it a pin point pressure on the thin part BUT there is no support right next to the pressure point where there are NO thick part of the blade to hold it together. Below is the example.

Both cases, we apply the same weight onto a thin plank, but the top one apply evenly along the plank. In the lower drawing, the pressure is only in the middle, there is no support next to it, it's a long distance from the pressure point to the support on each side. Which one you think it will hold up better?

Please do NOT assume I don't know engineering. I have been EE and manager of EE for 30 years and deeply involved in mechanical design. I own 3 US patents and published 2 papers in American Institute of Physics, Review of Scientific Instruments solely on my idea and I got the phase II SBIR funding on the idea of the second paper.

I worked for Seimens Medical division designing the front end of their first generation Ultra Sound medical scanner with color doppler from 1985 to 1988. I don't like Seimens, too stuffy and slow. I like small starter companies where I do everything.

We all called EE, electronics or electrical.

 

[Alan0354]

OK, let me try another way to describe more closely. This is to ASSUME that there is no slack and the circle of ball bearings apply pressure evenly around the whole circle.

I drew the blade with the milled out thin part and the hole in the middle for the pivot screw. I drew the path of the BALL BEARINGS in RED.

On the top drawing, it's typical of the ball bearings that the path is about mid-way between the edge of the pivot hole and the junction where the blade goes back to the THICK part.

I labelled in GREEN the critical distance. If the distance is large, the thick part of the blade is NOT going to help the thin part where the path of the ball bearings run.

On the LOWER drawing, IF the path of ball bearings is closer to the edge where the thin part transition to thick part. Then you can count on the thick part can help strengthen it as the path of the ball bearings are very close to the thick part of the blade.


Now, this is assume like what you said that there is NO SLACK and all the balls are in contact. If there is any slack, it becomes a pin point pressure and that will be bad.

Every knife I open that with ball bearings, they are all like the TOP drawing.

 

[Gerry Seymour]

OK, this is just talking only about theory. This is what I drew out:

View attachment 29247

A) I was thinking about what you said. I would agree with you if the support is a FLAT WASHER as shown in Fig. 1. You can see the whole thin section of the blade(RED) is supported by the flat washer (GREEN). Even the blade is thin at that point, it is still very well supported.

B) But look at Fig.2. If it is supported by ball bearings as show in (GREEN) balls. The pressure right a the tip of the ball bearings pointed by (RED) arrow. You see, there is NO SUPPORT in the rest of the area that is very thin. This will not give good support and the pressure is on the thin part of the blade.

See what do you think.


I have to agree, there doesn't seems to be an issue in real life. There is enough knives that has very thin part in that area. It would be better known if it is a common problem. maybe people don't use the knife for prying and all purpose. But to me, I want it to be all-in-one that if heaven forbid I have to cut myself out of a car accident, I might have to pry metal to get out and that's ALL I HAVE. That's why I am not even looking for the best steel blade that has best edge retention, just have to survive one time, but it has to be tough enough to survive that ONE TIME!!!

I think I found my knife already, just talking out of curiosity.




As for argument about putting a pry bar in the glove box, what if I am driving, I cannot reach it. Worst is if I am a passenger at the back seat?!!! It has to be ON ME all the time.

So a couple of thoughts on this.

Firstly, I suspect (but do not know) two reasons why more expensive/robust knives tend not to use ball bearings. 1) ball bearings present an additional potential point of failure. 2) that can be mitigated by using tight tolerances and better surfaces with a washer, which is more expensive. Others with better understanding of materials might be able to point out if/where I'm mistaken in this.

Secondly, you're still looking at a cross-section as if it were the entire structure. There is a small area that is thinner than the rest, and how it is supported. Since that thin area is such a small portion of the structure, what you should be looking at is how the section around it is supported. Again, the materials attached to it likely add structure, and are adding it to the stronger portion (where it can do more good than it can at that thinnest bit).

Here's an analogy for the way I'm looking at this. Look at your car door. What's the weakest bit? Probably that glass. If you assessed the door's ability to withstand a side impact based upon the weakest bit, you'd miss the structure, entirely. The majority of the door is sheet metal (or less), but there's also a beam inside the door that braces against structural members when closed. So in assessing the door for this, you should ignore the glass and focus on what will be bearing that load: the side-impact beam and how it braces.

 

[tkdroamer]

Ball bearings are not the weak link here, We are talking about the thin flat part of the blade that is the weak part. Look at Fig.2 of post #61, The balls only contact to the surface of the metal at a PIN POINT as indicate. The pressure is at a pin point where the ball contact the flat surface, there is no support on the surrounding surface. It is very different from the case drawn in Fig.1 with a flat washer where the force is distribute evenly on the surface of the thin part....which is surrounded by the thick part of the blade.

If that is the case, it would be a Thrust bearing, not a case bearing. But the effects are the same. IF the knife is assembled correctly, the load is distributed across all the ball bearings, not just two points of contact like post #61 shows.
For certain, a thrust washer can handle more direct load, but it is a huge tradeoff when the part has to move frequently. The drag coefficient of a thrust washer is very high.

 

[tkdroamer]

OK, let me try another way to describe more closely. This is to ASSUME that there is no slack and the circle of ball bearings apply pressure evenly around the whole circle.
View attachment 29262

I drew the blade with the milled out thin part and the hole in the middle for the pivot screw. I drew the path of the BALL BEARINGS in RED.

On the top drawing, it's typical of the ball bearings that the path is about mid-way between the edge of the pivot hole and the junction where the blade goes back to the THICK part.

I labelled in GREEN the critical distance. If the distance is large, the thick part of the blade is NOT going to help the thin part where the path of the ball bearings run.

On the LOWER drawing, IF the path of ball bearings is closer to the edge where the thin part transition to thick part. Then you can count on the thick part can help strengthen it as the path of the ball bearings are very close to the thick part of the blade.


Now, this is assume like what you said that there is NO SLACK and all the balls are in contact. If there is any slack, it becomes a pin point pressure and that will be bad.

Every knife I open that with ball bearings, they are all like the TOP drawing.

You are making my point about the knife being properly assembled. Remember, all bearing surfaces, whether bearings or washers are used, have to be flat and parallel. So, the thick part/thin part you mention would have to be machined to the same thickness, wouldn't it?

 

[tkdroamer]

I disagree, the ball bearings make it a pin point pressure on the thin part BUT there is no support right next to the pressure point where there are NO thick part of the blade to hold it together. Below is the example.

View attachment 29261
Both cases, we apply the same weight onto a thin plank, but the top one apply evenly along the plank. In the lower drawing, the pressure is only in the middle, there is no support next to it, it's a long distance from the pressure point to the support on each side. Which one you think it will hold up better?

Please do NOT assume I don't know engineering. I have been EE and manager of EE for 30 years and deeply involved in mechanical design. I own 3 US patents and published 2 papers in American Institute of Physics, Review of Scientific Instruments solely on my idea and I got the phase II SBIR funding on the idea of the second paper.

I worked for Seimens Medical division designing the front end of their first generation Ultra Sound medical scanner with color doppler from 1985 to 1988. I don't like Seimens, too stuffy and slow. I like small starter companies where I do everything.

We all called EE, electronics or electrical.

You are describing spanning and distributed weight. This has zero to do with the knife.

 

[Rich Parsons]

Alan,

I get where you trying to go with your discussion.
I have seen this for transmissions and does one use a ball bearing , a cylinder bearing, or ...
Each has advantages, from cost and serviceability, and functionality to address the loads.

What I would like to understand is what load / force are you trying argue is the issue for a specific design?
Once I understand this then I can comment on the design quality from my limited experience.

 

[Dirty Dog]

Yes, a good engineer that learns in college about systems and how the parts make something complete or larger parts, and how they connect can have discussions in lots of areas by asking the right questions.

That's not a feature of being an engineer. It's a feature of being educated.

 

[Rich Parsons]

That's not a feature of being an engineer. It's a feature of being educated.

I was speaking of Good Engineers.
Because some / many I know cannot see the forest for the trees, nor the cliff past the existing tree.

And yes a good education can bring the idea of a system. I did not mean to imply at all that it was limited to any one area of study

 

[Alan0354]

So a couple of thoughts on this.

Firstly, I suspect (but do not know) two reasons why more expensive/robust knives tend not to use ball bearings. 1) ball bearings present an additional potential point of failure. 2) that can be mitigated by using tight tolerances and better surfaces with a washer, which is more expensive. Others with better understanding of materials might be able to point out if/where I'm mistaken in this.

Secondly, you're still looking at a cross-section as if it were the entire structure. There is a small area that is thinner than the rest, and how it is supported. Since that thin area is such a small portion of the structure, what you should be looking at is how the section around it is supported. Again, the materials attached to it likely add structure, and are adding it to the stronger portion (where it can do more good than it can at that thinnest bit).

Here's an analogy for the way I'm looking at this. Look at your car door. What's the weakest bit? Probably that glass. If you assessed the door's ability to withstand a side impact based upon the weakest bit, you'd miss the structure, entirely. The majority of the door is sheet metal (or less), but there's also a beam inside the door that braces against structural members when closed. So in assessing the door for this, you should ignore the glass and focus on what will be bearing that load: the side-impact beam and how it braces.

This is completely different. The glass can be broken on the car door, but the metal still keep the passenger safe. The metal of the door can collapse, but as long as it is still serve as a barrier between the passenger and the outside, it still serve it's purpose.


THIS is very DIFFERENT from the folding knife. If the thin part crack, YES, the blade is still going to be held in place by the pivot screw onto the handle. BUT it will wobble. If you look at the structure of the folding knife, the blade is held open by a THIN frame(in frame lock) or a small hook. If the blade start flopping, it likely will not be held secure. The next time you thrust, the blade might collapse onto the fingers.............EVEN though it still held together in one piece.

You have to look at the situation. It is very critical the blade do NOT have free play and wobble EVEN THOUGHT it is held together no matter what. Those folding knife has to be more precision than people give them credit. That's one thing I have to work on a lot of the knives to make sure the line lock moves deeper under the blade. A lot of them came with the liner only like half way under the blade, any shock might make the liner slip and let the blade collapse onto the hand of the user. It's very critical. You cannot allow the blade to be wobble at all>

 

[Alan0354]

You are making my point about the knife being properly assembled. Remember, all bearing surfaces, whether bearings or washers are used, have to be flat and parallel. So, the thick part/thin part you mention would have to be machined to the same thickness, wouldn't it?

No.
This example is ASSUMING it is properly assembled and the circle of bearings are pressing on the red circle evenly.

Still it depends on the CRITICAL distance indicated by the GREEN. If it is farther away, the thick part doesn't help as much.

 

[Alan0354]

That's not a feature of being an engineer. It's a feature of being educated.

From my experience, good engineer must have a good dose of COMMON SENSE and a good INSTINCT. Ability to think out of the box, open to other's ideas and think about it. Never dismiss other people ideas.

Saw many engineers that never get out of the books and theories, that they never can move on and adapt to the real world. I worked with a software engineer from UC Berkley and a ME from Stanford. If I were their manager, I'll FIRED both of them first day. they only know how to talk theory, why this doesn't work, why that doesn't work. I DON'T care why it doesn't work, give me something that works!!!

I was working for 10 years in an environment 50% were PhDs. Nobody ask people what degree and all that. We only care whether it works or not.

 

[Gerry Seymour]

If that is the case, it would be a Thrust bearing, not a case bearing. But the effects are the same. IF the knife is assembled correctly, the load is distributed across all the ball bearings, not just two points of contact like post #61 shows.
For certain, a thrust washer can handle more direct load, but it is a huge tradeoff when the part has to move frequently. The drag coefficient of a thrust washer is very high.

Out of curiosity, would you be able to keep the connection tighter (more force holding it closed) with a bearing than a washer? I'd assume the rolling ball would move much more readily under those conditions than a flat washer. And if that's true, would the difference in force need to be significant?

I'm having trouble picturing all the moving parts of this.

 

[Gerry Seymour]

That's not a feature of being an engineer. It's a feature of being educated.

I think it's part of what's needed in certain curricula (engineering being a great example) just to survive. While liberal arts educations can give a great path to basic logic, there's not much problem-solving focus in most degree programs.

 

[Gerry Seymour]

This is completely different. The glass can be broken on the car door, but the metal still keep the passenger safe. The metal of the door can collapse, but as long as it is still serve as a barrier between the passenger and the outside, it still serve it's purpose.


THIS is very DIFFERENT from the folding knife. If the thin part crack, YES, the blade is still going to be held in place by the pivot screw onto the handle. BUT it will wobble. If you look at the structure of the folding knife, the blade is held open by a THIN frame(in frame lock) or a small hook. If the blade start flopping, it likely will not be held secure. The next time you thrust, the blade might collapse onto the fingers.............EVEN though it still held together in one piece.

You have to look at the situation. It is very critical the blade do NOT have free play and wobble EVEN THOUGHT it is held together no matter what. Those folding knife has to be more precision than people give them credit. That's one thing I have to work on a lot of the knives to make sure the line lock moves deeper under the blade. A lot of them came with the liner only like half way under the blade, any shock might make the liner slip and let the blade collapse onto the hand of the user. It's very critical. You cannot allow the blade to be wobble at all>

It's only different because you're looking at what happens if it fails. Look, instead, at whether it's important to the structure under the load in question. You could replace the glass with 1/4" steel, and it wouldn't make that much difference in most side-impact crashes, as far as what happens to the structure of the door.

Analogously, it's also possible that replacing the thin section with something 3x as thick would have little impact on the overall structure of the knife.

 

[Alan0354]

It's only different because you're looking at what happens if it fails. Look, instead, at whether it's important to the structure under the load in question. You could replace the glass with 1/4" steel, and it wouldn't make that much difference in most side-impact crashes, as far as what happens to the structure of the door.

Analogously, it's also possible that replacing the thin section with something 3x as thick would have little impact on the overall structure of the knife.

As I said, it's different. This is a picture of the typical knife with ball bearings.

Let's try this way. Look at the picture. This is a typical knife with ball bearings. You can see the DAYLIGHT between the frame on both sides to the blade. The only part that hold the blade tight is the two ball bearings (labeled BB) on each side of the blade. There is NOTHING else supporting the blade. It is only until the thin part CRACKS then the blade can lean on the side plates of the handle to get support.

I have an arrow pointing at the frame lock. In the picture, I worked on it so it goes way under the blade as shown. A lot of knives are not as good, some engage only like 1/2 way. If the blade starts wobbling after it's broken, it might disengage from the frame lock and collapse onto the hand. This is NOT as forgiving as the car door in your example.

As I said, there are knives that made the critical part thicker, it doesn't take a scientist to do that. I have a few knives that has 0.05" or thicker on that part. It's just pure negligence or stupidity they have that part so thin.



EDIT: If you look at the frame lock part of the knife, it has to be quite precise. Notice the bottom of the blade where it touches the frame lock, it is SLANTED. It only works if everything is quite precise and no slack. If the blade start wobbling, it might create a gap in between the blade and the frame lock, the blade can be freed up to close onto the person's hand. It's NOT very forgiving.

 

[Alan0354]

Let me show another picture of the knife that actually has very thin part, the Sencut Acumen. The thickness is only 0.03". Look at the gap between the side and the blade on both sides are WIDER than the one in the last post.

Look at it, there is NOT SUPPORT of the blade other than the ball bearings on both sides.....until it cracks. Also, notice the frame lock metal is NOT as thick as the other one, it can easily slip if the blade start to wobble.

 

[tkdroamer]

Out of curiosity, would you be able to keep the connection tighter (more force holding it closed) with a bearing than a washer? I'd assume the rolling ball would move much more readily under those conditions than a flat washer. And if that's true, would the difference in force need to be significant?

I'm having trouble picturing all the moving parts of this.

A bearing will move more freely under the load a knife would typically see, assuming as you say the connection or assembly is correct.
The heaviest recording moving (not rolling) loads are on thrust bearings (flat bearings, aka washers).
It is amazing the variation in bearing quality. Two bearings can have the exact same numbers stamped on them and the life cycle and load they can handle be very different.