First Folder Design

kuraki

kuraki

Fimbulvetr Knifeworks
Joined
Jun 17, 2016
Messages
4,679
I've never built a folder. I have 2 kits arriving today that I will build out to get a feel for how they go together, though I believe I understand most of the relationships involved with the simpler designs. Once I complete those, I'd like to do a scratch built knife, and for that, I've modeled the following. I'd like to know your thoughts.

It's a very basic liner lock flipper. The blade is 3.5" for scale, the G10 scales are .125 thick, the liners are .050" thick, and other than the pivot all screws are 0-80 (phillips head because thats all I have in my content library, but I've ordered torx heads.) I've not yet modeled the detent and my liner lock doesn't spring in this model, also not seen are any washers but they will be added. It's currently modeled to have a .187" pivot that extends through the liners but is hidden by the scales, but I'm on the fence about whether they should be hidden or come through the scale. The stop pin is .062" and stops both in the folded and open position. The scales are screwed to the liners respectively, the liners are held together by screws passing through one and the spacer, and threading into the other, as well as the pivot. FWIW Inventor tells me (with stainless liners) that it will weigh 3.7 oz.

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John, I don't personally like thumb ramps, and think it would be better without it. I've been bitten by the folder bug. I bought some ti for trying some liner locks and gave thicker ti for framelocks.
 
Move the pivot hole in the handle forward. Move the hole in the blade toward the lock face. Making these changes will allow a longer blade and will result in a better blade to handle ratio.

Chuck
 
Warren, I get it. I do like them so I will keep it for this one at least. I don't like thumb stud but imagine I'll end up using them at some point too.

Chuck, I probably left too much meat behind the pivot because I assumed it would encourage stability and reduce end play but I probably went overboard.

Thank you both.
 
Not having made a folder, these thoughts are from a user standpoint.

Clean lines. I like the handle shape, blade length is great, flipper tab looks comfy, and the backspacer is great too. There's only one thing I don't agree with in this design. The thumb ramp. I don't like to use a folder in the same ways as a fixed blade in terms of putting pressure on the back of the blade. Even as strong as todays beefy locks are they can still slip or fail. Personally, I would probably avoid a design with it because I would subconsciously tend to use it.

Nice work,
Anthony
 
John,

Chuck is right on about the handle pivot placement and blade to handle ratio....have a look at a Terzuola folder
and man that thumb ramp :-) it hurts my thumb already....

also I don't know about a dia 1/16" stop pin... I'd like to see at least 3/32" and even 1/8"
 
Thank you H I wasn't sure about that pin size either. I have room for an eighth.

Ok, ok. Usually, some new guy comes in all "if I burn tires in my fire for extra heat can I quench this piece of steel I found in the woods" and everyone gives them really good advice about 1084 and then they come back "ok thank I'm going to get some Z-finit and use my oven" and I can collectively hear heads banging keyboards across the nation.

So I'm going to take the excellent advice I have been given so far. Narrowed up behind the pivot, some by necessity to increase the stop pin diameter, no thumbramp.

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Looking good John. I definitely like the second design better, and do like thumb ramps occasionally, but def like the second one better.
 
Looks good John. You have got some computer skills man! You won't need that little nub on the blade behind the lock face.
You'll be able to feel a lot more when you make a template. That's when you'll get a good feel for whether it flips well or not. Check out internal stop pins tracks too, sometimes you'll get to a point in a design where an internal may be the only way to get the detent, flipper, and lock face just right.
 
Placement of your flipper tab *may* be problematic depending on how well you can set up your detent pressure and pivot friction. Placing it that far back of the pivot means it is harder to build up finger pressure on the tab which will affect the flipping action.

Contact point for your lock bar is relatively close inboard towards the pivot. It would be better to configure it so that it is as far away from the pivot as possible. The liner lock cut is such that the locking bar is very wide. Unless you need to do this for some reason, it really doesn't add anything to the strength of the lockup. The liner should contact the lock face at a single point, and this should be as far as practicable from the pivot. I can see why you have it set up that way in order to clear the stop pin, but by using a narrower lock bar and having it contact closer to the flipper, you will have a better lockup.
 
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DrFish, I understand exactly what you're saying. The knife I based this initial drawing on is in my pocket, and pulling it out to see whether I'd deviated from what's essentially the lever of mechanical advantage the lock places on the blade in my changes, and you're right. In that knife, there is no stop pin because it's utilizing the thumb stud against the frame and liners as a stop pin in both positions, and the liner lock engages the blade along the arc of the finger choil rather than under it like mine. The difference is the diameter of the pin plus some minimum wall thickness to prevent the pin hole from breaking out.

I'm not really sure how to get beyond that, unless I were to remove the finger choil all together. That would allow me to move the pin and the lock point of contact together.
 
Josh Rider said:
Looks good John. You have got some computer skills man! You won't need that little nub on the blade behind the lock face.
You'll be able to feel a lot more when you make a template. That's when you'll get a good feel for whether it flips well or not. Check out internal stop pins tracks too, sometimes you'll get to a point in a design where an internal may be the only way to get the detent, flipper, and lock face just right.
Click to expand...

Thank you.

That little nub is like your appendix and likely will get removed :D
 
I'd like to see a screw holding the frame together up closer to the pivot.


The knife in my pocket right now is a Benchmade AFCK
It has a screw through the stop pin.


It also has only 3 frame screws and it's holding together well.



In making a folder, 0-80 are SO small

Try to bump up all your screw sizes one or two sizes if you can.

If you now have drawn 0-80, consider 1-72 or 2-56
 
Th 0-80 selection again is carry over from the knife I used to start the model. When I brought some 2-56 flat heads into Inventor, the heads seemed too large to use appropriately. I did order some 2-56 screws however to see if their heads are smaller than the ANSI screws in my content library.

I think you're right on with a screw closer to the pivot in this case with the hidden pivot. Again the model I started with has an exposed pivot which retains the scales up front. Since the liners are retained by the pivot, I will remove 2 scale to liner screws from the heel and put one up front behind the pivot. Thank you for that suggestion.
 
Do you have a copy of Bob Terzuola's book on tactical knife design? No flippers, since it's an older book, but it's a standard reference on good design practices for tactical liner locks.

Also: recently came across this on Reddit. https://www.reddit.com/r/knifeclub/...science_vol_4_flipper_physics_its_a_long_one/

Constraints on stop pin placement and lock geometry in order to clear the flipper tab are a big reason why you see so many flippers with either A: an internal stop pin, or B: Thumb studs as stop pins. Both are workarounds to the problem of clearing the flipper tab.
 
I don't have any books. I assume this will be like the first AK I built from a kit with a dremel and a case of beer. The second one vastly improved.

I'm not sure I understand what an "internal stop pin" is. I thought mine was internal? Internal to what?
 
On hidden pivot I like to use a bolster that can be removed to adjust the pivot tension. Your rendering requires the removal of the entire scale. With that in mind the ability to realign both sides can become an issue and affect the flipping action. And if the tension is still not right you have to go through the dance again. The exposed pivot sure makes it easier on the end user to make simple adjustments.

My first hidden pivot was done by drilling a series of holes around the arc and hand filing(won't do that again) simple fixture on rotary table takes 2 minutes!
 
Nice work!

I'd go for even more blade to handle ratio, move the pivot as far forward as you can while leaving some room for detent path, etc.

Drop the pivot a bit so your frame and blade line up at the front lower part when closed.

.125" stop pin at least, you may be better served with 2-56 screws also

Get your hardware from AKS or Ticonnector... especially the screws and pivots. I'm surprised how much difference there is on screw quality and will not use anything else if I can. You will end up with higher, more consistent tolerances.

Flipper tab at 12 o'clock or before if you can for more leverage. (pivot is clock center)

Lockup as low as possible and as underneath pivot as possible... just a goal to go for. The further back and high the lockup area is weaker it will be, also more chance of lock rock. Your design is good, this is just something I always shoot for when designing a framelock.

Multiple screws, big backspacers, lots of standoffs, alignment pins... all good things but can depend on a lot of variables. I find one small standoff can be great with bearings but with washers I like to do a rear dowel pin for frame alignment.

I hope this helps, I'm just trying to throw anything out there that can help. Good looking design!
 
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