Help me understand folding knives design

Patrice Lemée

Patrice Lemée

Joined
Aug 13, 2002
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I have a couple of specific questions but I figured I'd use a little broader title since I am sure more questions will pop-up in my mind and I thought it would be nice to have them all in the same place.

First here is what lead me to those questions. I quickly realized that of course, compared to a fixed blade, you are limited as far as the handle to blade ratio is concerned. And, to me at least, a blade shorter than the handle is not the most aesthetically pleasing look.

So how do we remedy this or at least minimize the visual impact?

The first thing that became obvious is the part that bolsters played in this. I guess they are there primarily to reinforce the pivot area which is where a lot of the stress is applied. But visually they are great at tricking the eye into a more pleasing longer blade/shorter handle ratio. Even more so if the bolster material closely resembles the handle material.

Ok, that works in tricking the eye but we've put the carriage before the horses here. First thing that we need to do is get the blade length as close to the handle length as we can get it. Of course there are folding gizmos that lets you have a blade longer than the handle but that is for another post. ;)

Towards that end here are my 2 questions:

1) The smallest you can make the region in green, the closer you can get to a 1:1 blade/handle ratio but in reality, how small can you really go? I imagine it depends a lot on the size of the blade/knife and intended use but are there any generally accepted rules of thumb? (PS: Disregard blade size, it is only to keep the drawing small)



2) How much of that region can peak above the bolster when the knife is closed? It does look a little better when this is all hidden behind the bolster but I've also seen knives where a good portion protruded. Again, any general rule about this?

Like Don pointed out, I am an over-thinker by nature. :o But these days I get very little shop time so thinking is pretty much all I can do. Plus you guys usually have such great advices that may actually help reduce the thinking, something I can't seem to do by myself...without medication that is. ;)

Any input yo have would be greatly appreciated. Thanks.
 
I'm of the opinion that a blade shorter than the handle isn't necessarily bad looking. For me a 5" handlle on a 4" blade works out to be both practical and eye pleasing. RJ Martin once told me that he strives for the blade to be 80% of the handle.

1:1 sounds great on paper but to get there will take too many sacrifices and actually impossible to do. A literal 1:1 would mean the center of the pivot would be half way off the front half of the handle. Reducing the tang aft of the pivot will severely detract from laterally stability, at least in my mind, and to go the other direction and have the tang extend beyond the front of the handle has a few issues as well. If it's liner or RIL then the lock face should stay covered for protection while all blades need to at least have the washer area covered.

Making a folder is hard enough, Patrice, without having to aim towards 1:1. I know you like to challenge yourself so why not give it a whack?
 
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It is a balance of compromise, each part plays a critical role and must be chosen wisely! :D

Your washer diameter, stop pin placement and size, lock geometry, placement all play off of each other...

want a big stop pin? - it has to go further away from the pivot or your lock up area needs to be smaller... that further distance with the pin also leaves more knife hanging out the front when closed.

Want a better distance for lockup - the stop part has to allow it to clear... etc... for the best ratio possible you need to pull all of the parts as close to the pivot end of the knife as possible

I go for the best lockup geometry (lock as far from pivot and as close to "6am" as possible) and work around that... I see some folders with repeated lockup issues mentioned here and can say the blades usually have a tiny amount of steel below the pivot.

I can have a design "ready" and play with the lockup options in CAD for days on end until I am happy...
 
Oh yeah, I wrote a book about making folders, it's pretty short reading. :p Here it is.

1. Terzoula Book
2. Tram Your Drill Press
3. Spend about 1000 hours making about 40 folders, throw them all away, finally make one that is good, sell it, say it was easy money!
 
Notice how the above knife has a larger stop pin and how the blade ratio changes. Check how the stop pin, pivot and stop area are in a direct line too. Between my lock up area, stop pins and end of handle there is little wasted room. I posted the original top deign on a forum and Tom Mayo said to work on my blade to handle ratio so the second knife is a result of another year of design and has a much better ratio. I had to step down a bit on my stop pin to get the lock up where I wanted it but now that it is done I can relax and make the folders!

Fairly RF1 snd RF2 Framelocks



 
I picked up Alan Elishewitz's dvd on folding knife design from Chris Crawford, and in that he explains all the geometry and why things are they way they are. I've watched it about 20 times, and still pick up something new every time. The other DVD in that series (Basic Tactical Folders, IIRC) is also a great resource on framelock knife design. I also watched Chris Crawford's DVD on making a basic slipjoint in which he discusses a lot of the particulars of slipjoint geometry. Also extremely helpful.
 
Thanks guys, good stuff. :thumbup:
Of course I have to read it over a few times to understand it all. :o
I will put those DVD's on my ToBuy list.

Daniel, when you say tram your drillpress, are we talking ballpark or tens? I sure hope I get it right before 40 knives cause you know that at the speed I make them, that may never happen. ;)

First one I am trying is a framelock by the way. But of course you know me, a bit "different" looking. ;)

Thanks again for your help, much appreciated.
 
I'm in the middle of moving, so everything is in boxes. If you still need the dvd's in a couple of weeks, I can send them to you (it'll have to be the first week in Sept at the earliest, though).
 
Great topic!
Haven't made folders in a while, but I started with the assumption that since all the sideways support the blade has comes from the washers, the starting point would be full bearing on the washers, with the washer coming right out to the "nose" of the frame.
In order to get the lock as far forward as possible (and minimize the "green zone" in your drawing), some of the Benchmade folders I've taken apart use a washer on the lock side that has a cutout for part of the lock, and is not free to spin with the blade. That way the blade still gets good support, but the lock can be farther toward the nose of the frame. The one I rebuilt actually had the lock right below the pivot instead of behind it....another interesting approach.
 
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Patrice Lemée;13848132 said:
Thanks guys, good stuff. :thumbup:
Of course I have to read it over a few times to understand it all. :o
I will put those DVD's on my ToBuy list.

Daniel, when you say tram your drillpress, are we talking ballpark or tens? I sure hope I get it right before 40 knives cause you know that at the speed I make them, that may never happen. ;)

First one I am trying is a framelock by the way. But of course you know me, a bit "different" looking. ;)

Thanks again for your help, much appreciated.
Click to expand...

Tram it as well as you can... use your mill if you can with collets vs the press also. Reamers are key too. I like to tram within .001" on the mill.

I have the Elishewitz video on basic tactical folders and it is worth it's weight in platinum.

As far as the tang sticking out I think it can be done well, on my RF2 it sticks out but the lines go with the knife and there are no spots for anything to catch on.
 
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I don't want to hijack the thread but tramming is my current issue and the only thing that has me disappointed with the operation of my first flipper. I need an LMS 3990! My drill press table is not adjustable so I need to work on shimming a piece of G-10 or something. Still the most fun to be had in the shop.
 
There is to me two simple ways to maximize the blade length. You draw out your b lade and then make the handle scales to fit or do the opposite which is draw out the handle and draw in a blade that will fit. Yes, folder blades will always be shorter looking and especially to those who are not to familiar with folders. I'm presently involved in a collaboration with a client. It is a design he has drawn up with very few changes needed by me to make it workable. The very thing of the short blade really showed up when he showed me he wanted a certain small specialty area right in front of the bolsters on the blade itself. What to do? Would he want to remove that special little feature or go as he first drew it in? He was having a custom folder made as to his liking,so why not have done what he wanted? There are many small items that make a folder acceptable or not in it's make up. On liner locking folders, the longer tang that shows beyond the bolsters is a common seen thing on EDC folders but not on collector pieces. AS well often seen are blades that when are closed that are below the bolster at the front end of the bolster . And what about a short back bar using a stop pin for the blade? Sure all these things can be used to get that liner locking folder made and why not if that's what you want to make? These is a very accommodating folder to make for the so many small changes that you can go with. By the way why would you decide that the sideways support of the blade comes just from the washers when they are backed by the liners and being held together with the pivot pin as well as the screws holding the back bar creating a parallel spacing as the blade with the thickness of the washers, and a back bar with screws in place? The idea I was shown that made up a liner locking folder is one where the front and back of the blade fit within the liner and that a full length back bar is part of the construction. This construction does not call for thick liners and certainly with those a different rigidity for strength is created. Frank
 
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