Flipper design input

[Kevin Powers]

I have read just about every liner lock thread, and read the terzoula book. Ive been working on designing my first folder for a very long time, I have revised my design multiple times and during the process I have begun to teach myself how to use a cad program that is free online. Anyways I have a really nice piece of Stainless san mai that I want to use as a pocket knife for myself.I am tired of being the knifemaker that never has a knife. I would really like some input on my design. I am not sure of the lockup so any help with that is appreciated. FWIW I have a milling machine and a rotary table.

 

[Kevin Powers]

I guess the pics are hard to read

 

[Lo/Rez]

Nice looking knife. I'm not sure of the lock up either. Maybe placing your stop pin a little lower towards the pivot would help? I just started on my first liner lock yesterday and am pretty excited about it.

 

[Frank Niro]

Why struggle with wondering if it will work? Make up the knife with the stop pin, pivot position, lock bar out out of some thin sturdy material and see how it works or not.I use formica or arborite for this, Many use plexiglass.
Frank

 

[Bob Ohlemann]

It's all about trade-offs. I think it looks like a fairly well thought out design. There are a few things that stand out to me. First is the lockbar gets pretty thin. In my designs, I try to keep the lockbar cut close to the centerline of the pivot to ensure I have enough strength. Next thing is the closed position stop is on line with the detent. When opening, the detent ball will drop off in that void and friction of the bar against the blade will slow the blade down. Third thing is the pivot seems big for the size of knife. I like to work with the smallest hardware that will be appropriate for the knife. This gives me more flexibility in the design. I agree with Frank and might even go a step further and say build the knife. I have learned a lot by making knives and seeing what does and doesn't work well.

Bob

Edited to add- Also, you will want to move your detent away from the edge of the lockbar. You want about half the diameter of the ball between it and the edge of the lockbar.

 

[Varga Knives]

So far so good. The only thing that looks a little off to me is the short height of the lockbar at the narrowest point. You did say this was for a liner lock and not a framelock so I'm not sure if there is enough meat to hold up for that .001% of usage. Also depends on the thickness of the material. Since this is for your use I'd say give it a try.

The only other thing I'd be concerned about is the path of the detent ball. It looks like it will run out from under the scales and be exposed. Not a make or break type of thing but something I don't like seeing

ETA: Bob always seem to post before I send mine. 😀

 

[Daniel Fairly Knives]

I'd focus on adding some area to the lockbar... after that your detent will be closer to position and I'd tweak it to hide that next.

Great looking design!

 

[stezann]

also the spacer bar looks a bit thin to bear the screw holes.
The lock bar is indeed thin, one of the reason why often the flippers are slotted pin track constructed

 

[Kevin Powers]

Thank you for the input, I was also curious about the lock bar and I have changed the height multiple times. So it brings up a question for me. Is it best to keep the lock bar slot in true horizontal plane perpendicular to the blade? Or could it be as easy as dragging the right side of the line up to gain height in the thin spot? I did draw a circle through the center of the detent ball and it was showing on the blade, I extended the scale out just enough to cover it by about a 32nd. That was all before I posted these pics. I am not opposed to doing a pin track design, it will allow me to bring it in closer to the pivot point, I am just not sure how close I can actually get and still have strength. The way it's currently drawn, I have 1/2" of "meat" around the pivot. This will be an every day carry for me and a way for me to show my work to interested folks. i am planning to use a 1/4" pivot, bearings, and probably .050-.080 Ti.
Edit*
The face of the leaf is about .186" and I think the thin section was about 1/8". I notched the radius of the tang to have a higher lockup but I wasn't sure if I was getting too close to the pivot.
Edit** just studying my pics at the top, in the view of the liner it looks like the slot line is running downhill towards the blade, I'll try bringing up that line and see what kind of snowball effect that has.

 

[Bob Ohlemann]

You want the lockbar face and the long slot to be perpendicular. I would run a 3/16" pivot which would in turn allow a smaller diameter bearing (This is just personal preference). Any extra "meat" you have beyond the O.D. of the bearing is not necessary unless it serves a specific purpose (i.e. lock face or stop). Lockup contact point should be as far from the pivot as possible. If you go back and look at Bob T.'s book, you will see he back cuts part of the lockbar face to keep it out of the way when achieving distal lockup.

Bob

 

[Kevin Powers]

Thanks Bob, I am doing all this design on the PC at work because I have dual monitors and literally have his pdf open on one screen and draftsight on the other. I was specifically looking at the diagrams of the lock bar yesterday.

 

[Kevin Powers]

so I made some edits, now the thinnest part of the locking bar is .25".
The pin was changed to a 3/16" pin and it has enough meat for Alpha Ball bearing pivots.
I have .33" to play with on the lock face.
I left the detent ball low on the leaf so that i can bevel the face for clearance up at the top and so the centerline of the ball will engage the blade immediately when unlocking.
What do you pros say?

 

[Pittknife]

Hi,

Couple of things,

- your detent hole is going to show, add it to the blade geometry or a construction circle to show the path
- the lockbar height increase is better but you will still be losing some of it when you go to cut, you'll need a cutoff disc or a slitting saw so account for that gap
- If you are using bearings, place the construction circle in there to show if they will fit right
- you have to becareful with the detent hole being that close to the lockbar face, you can get a bump.
- right now everything is line to line, you will want to add the stock you need in the templates.

Here is an example of the construction circles on a new design I am working on, it helps to do the mechanisms first.

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[Varga Knives]

Looks good to me. Stezann brought up the backspacer issue and I agree. The backspacer and screws in the thin part are't really even necessary.

 

[Kevin Powers]

Before I left work I double checked all the dimensions and verified that the detent isn't going to mar the blade where it will show, and also the bearing will all fit etc... Then I printed out a couple copies of the design and when I got home I glued them to some kydex to make a working pattern. I really like how it's shaping up. A few things I'm going to change before I make it out of steel. The flipper part of the tang is pointed more than I'll like so I'm going to increase the radius on it, I will also add more steel to it to account for material removed when cutting the lock bar to ensure the blade locks up at a good angle. I think I'm going to raise the clip up a bit higher. All in all I have a working template that actually locks up.

 

[Bob Ohlemann]

I think you are on the right track. I would encourage you to add a little curve to the flipper tab so that it is a bit more forward in the closed position. The extra leverage generated by as little as .050" can make a big difference in the action.

Bob

 

[stezann]

the crazy thing with folders is that minimal tweaking goes a long run....looks like it's going to work now :thumbup:

 

[Kevin Powers]

A couple weeks ago I ordered the supplies to finally make a folder. I waited until Friday to try it. Man what a learning experience. First of all everything is in really rough shape and I didn't focus on doing final finishing. There's still bevel grinding to do, fitting the detent, thinning the scales, a little shimming here and there, but alas it's a working model. Truly the one thing that I have gained the most from this project is that I'm no longer afraid of folding knives. I definitely know of a bunch of changes I'll do in the future, like locate screw holes so they're in the center, and won't conflict with the lockbar.

 

[Bob Ohlemann]

Ain't nothing to it but to do it! Good job, I know you're learning a lot.

Bob

 

[Kevin Powers]

I started bringing the grind line up. I was using my Bruce bump guide to keep the plunges good, but when I flipped the blade over to grind the other side the guide interfered with the platen. So I had to free hand it. This is my first folder blade and also the first time doing a angled plunge. After that I milled the scales down some on my mill. They're now .172" thick and I might take another pass to thin them down some more.