Pivot placement on folders?

Chiro75

Chiro75

Joined
Feb 4, 1999
Messages
5,786
Is there a "rule of thumb" for placing holes for pivots in the handle and blade of a folder? I've been trying to come up with a folder design and it's really frustrating. It seems like if I get the pivot in the right place on the blade that when the knife closes half of the blade is hanging out from the handle and isn't fully enclosed (spine of the blade, not edge/point). It seems like from the handle's perspective most people generally place the pivot smack in the middle, but I seem to be having some trouble placing the pivot and stop pin in such a way that the majority of the blade is tucked away in the handle when closed and I don't have to remove most of the tang to clear the pivot pin. I also want a compact knife, not something with 4 inches of hidden tang to get everything to work properly. Any easy formulas or setup ideas, or, like everything in knifemaking, is it the dreaded trial and error approach again?
 
If you were closer to me I could walk ya through a way to desgn a folder thats basically foolproof... I was the Fool and I could do it!

I usuallt put the pivot slightly offcentered tword the lock (away from the stop) about 55% of the blade is above the pivot and 45 below, twords the lock angle.. If that makes any sense...

Maybe if I can get netmeating runnign on my computer we could et a design class going, i have taught a few guys in the NC guild to do it the foolproof way and it really works easily.. I can get start to finish on a linerlock thats guaranteed to work in like 10 minutes tops...

Can any of you computer Gurus help?? I can comunicate much better with drawings and pictures than I can with words in this particular case...

Alan Folts
 
Welcome to foldermaking :D
This is one of the best challenges, and is the main problem in making some of the cool handle shapes you've seen some guys here churn out. Placement has to be perfect or the handle has to be friggin huge for the blade to fit.

There are a few things you can play with. Picture the handle as a rectangle in front of you, so that the long sides run left and right and the pivot is going to be on the left end.

Basically you cannot put the pivot any higher than the center line of the handle/rectangle. Because you will not have the clearances you need for the blade to swing.

The closer you move the pivot to the left, the lower it has to be in order for the bottom corner of the tang to clear the stop pin when you close the knife.

The lower the pivot is placed, the more blade there is above it which means the handle has to be wider, or the top corner of the blade has to angled off in a thumbramp or something so it isn't sticking out when the knife is closed.

The higher you place the pivot, the farther to the right it has to be.

I hope this makes sense, its very hard to explain with just a keyboard.

One mistake that can throw you off is trying to make the knife too compact, or having to high of a blade to handle ratio. Plan on having about an inch of tang on the blade for your average liner lock, and the handle at least an 1/8" longer than the overall length of the blade.
By trying to shorten the tang, you can't put the pivot far enough to the right in the rectangle I was talking about. The bottom corner (locking face on the tang) will never clear the stop.


It might help you to draw some pictures. Use a compass (from the pivot) to mark out the radius/path travelled by the corners of the tang and the tip of the blade as you rotate it.
 
It will be a friction folder, so no locks necessary. Does that change things? For some reason I keep getting this funky-ass shape to everything, but it might be because I'm setting my stop pin too close to the pivot.
 
I have Adobe Illustrator and you can set it up to rotate around a certain pivot point, so I'm going to see if I can't make a "prototype" this way for the blade and handle. I could print it out with the "holes" marked and everything, arc drawn, etc, and then cut out the blade and handle shape once I have parts that actually move properly together. Keep your fingers crossed! :D
 
A friction folder should be fairly easy I think :confused: You only have 2 points to worry about, open and closed. No lock to worry about so you can round the bottom of the tang any way you want. Or have as little or as much steel there as you want.
For the placement of the stop, moving it back can give the knife a "broken back" look, or forward can give you a hung blade. Vertically, it should be placed pretty dang close to the top edge of the handle/blade. Leave just enough meat about it in the handle to make it sturdy, and just enough blade to ensure full and solid contact.

Try this with a couple peices of thin wood. Make your basic blade shape you want, allowing the for the tang. Drill the pivot in the tang, about 5% below the center line of the tang, and the exact same distance from the back edge.

Now drill another hole the same size as the pivot in an oversized peice. Lay the blade blank on it and put a pin through the 2 holes. Spot where you want the stop to be against the tang and drill that for a pin. Put a pin in that hole, and open the blade against it. Trace the back of the blade blank and continue laying a out what you want the back line of the knife to be. Now swing the blade from the open to closed position (you may need to round off the corner of the tang). This will let you mark the choil on your blade blank, you will almost certainly need one in order to have the knife close as far as you want, I generally just cut a half moon shape with a dremel or file. Cut and check until the blade will close against the stop pin as far as you want it to judging by the line you drew for the back line of the knife.
Now with the blade in the closed position, trace it. Now take it off and take a look at your peice that has the pivot and stop holes marked. It has the back line drawn and the position of the closed blade so that you know where to leave clearance in shaping your handle scale. Use that peice of wood to make a template for your handle :D

This method will work for linerlocks and other friction folders as well, you just have a few more things to figure out on the liner lock. I suppose it doesn't leave you too much room to be creative but it should let you make one that works, and give you an understanding of how to lay one out.
 
After I have drawn up a new design on paper I make a dozen copies. I then cut out the handle and blade from two differant copies. I then over lay them on each other and use a straight pin and punch it through both and open and close the paper copies. I adjust the pin as needed until I get things where they need to be. Ron Lake shows a similar method in How To Make Folding Knives.

Arthur D. Washburn
www.adwcustomknives.com
In knifemaking everyone gets cut and everyone gets burned.
 
The tough thing about the FF I want to make is that I don't want it to look like normal FF's! I don't want a 6 inch tail hanging off the tang. I want just a little tiny tail, so that means having the stop pin closer to the pivot than on a conventional friction folder. Also, I want the stop pin to work to stop the blade opening and closing, which I think it where it's getting complicated, too. I have a Sean Perkins FF that is about what I'm talking about, so I could just copy it more or less, but it's significantly bigger than I am looking for and not really the shape I want. The Adobe Illustrator idea actually sort of worked, kinda, so I'm going to give that a try again...
 
Don't put a tail on it that folds back over the top of the stop pin. No need, use the same configuration as a linerlock.
 
Well, I got Illustrator to work out a pretty good prototype. I got the mechanics worked out using the basic drawing tools, then shaped the handles and blade, then printed a few copies and cut the parts out. Over lunch I spent a VERY frustrating couple of hours working everything out, but as of right now I have my liners shaped and the general mechanics of the knife work. I just need to shape the blade, make a standoff for the spine, cut and drill scales, blah blah blah. A lot of work when you're using a hacksaw! Also, I burned out two bits on my 1084. I have a bar that has frustrated me for years. It's really soft on the outside but the center is hard as hell. I have to just burn through it but it obviously kills my bits. Of the 6 #15's I bought last week from MSC only one is left. :(

But, other than a crappy piece of steel that has plagued me since I started this hobby, the only real issue is that my 1/8" pin got drilled a little higher than it should have, so rather than going with a Wharncliffe like I planned on I'm going to have to use a different blade shape.
 
not much to it Steve :)
if this don't mess you up.. :eek:
this is the figures for my Folder I mapped out in DRO terms..
for every hole in it.
you'll see the pivot point is at x and y 0.O
pictures of it is below

I can sort the figures on the puter to do differant operations.

LS1-03111-B01-B1/?? LS Little sweetheart
.060 6AL4V titanium. 1- first design
03 year made
spec's 11 week made
Folder LS1-2003-B01-B1/?? 1 it's number made that week
B01- liner type and blade materiel
B1 bolsters 1 or 2
Use for drilling ??/ handle materiel

Tap / Drill size
right linner left linner right linner left linner
X L+ R- Y in+ /out- Tap Drill Drill Ream Ream
15 Scale screw front X + 0.9400 Y - 0.1400 1-72 #53 #53
16 Scale screw rear X + 2.4150 Y - 0.2200 1-72 #53 #53
14 Detent ball 1 /16" .062 X + 0.2100 Y + 0.1500 #53 = .0595
12 lock corner X + 0.1100 Y + 0.0650 1/16"
13 lock start X + 2.5500 Y - 0.1500 1/16"
1 Pattern Hold down X + 1.7000 Y - 0.2200 ******> 1/4" 1/4"
6 Bolster screw Front (F) X - 0.2000 Y + 0.0370 0-80 3/64"=.0468 3/64"=.0468
7 Bolster screw Front (R) X + 0.3400 Y - 0.0450 0-80 3/64"=.0468 3/64"=.0468
8 Bolster screw Rear top X + 2.9300 Y - 0.3800 0-80 3/64"=.0468 3/64"=.0468
9 Bolster screw Rear lower X + 3.0750 Y + 0.1200 0-80 3/64"=.0468 3/64"=.0468
11 Back bar screw hole front X + 1.2100 Y - 0.4900 82deg #50 82deg #50
10 Back bar screw hole rear X + 2.4500 Y - 0.4500 82deg #50 82deg #50
5 Pivot Pin X 0.0000 Y + 0.0000 0.123 0.123 0.125 0.125
4 Stop pin X + 0.2100 Y - 0.2900 0.123 0.123 0.125 0.125
3 Alignment hole front X + 0.6455 Y - 0.0830 ******> 0.123 0.123 0.125 0.125
2 Alignment hole rear X + 2.8000 Y - 0.1600 ******> 0.123 0.123 0.125 0.125
Blade Map
Blade pivot hole set ceter at X - 1.5000 Y - 1.0000 D 0.251
17 Stop seat open X + 0.2100 Y - 0.2900 mill 1/8"
18 Stop seat closed and profile X - 0.1340 Y + 0.3280 ( mill 1/8" to X + 0.2250 then to Y + 0.0950
then to X+0.2750 to Y-0.565
19 detent blade seat X -0.2500 Y-0.1000 ?Y - 0.0860 0.046 or 3/64?
20 Blade thumb bob X - 0.6060 Y - 0.1250 #44

Back bar
21 Back bar screw hole rear X + 2.4500 Y - 0.4500 2-56 #50 tap drill
22 Back bar screw hole front X + 1.2100 Y - 0.4900 2-56 #50 tap drill


washers 0.0120 x 2 = 0.024 + 0.002 = order list
blade + .026 for the back bar tap drills
3/64" x 4
detent balls. smaller folders 1/16th (.062) #53 x 4
3/64th (.0469) for the hole in the blade #50 x 4

#53 drill bit (.0595) for the hole in the lock body drills
for the 0-80 .062+ c/s .092
large sizes a 2mm (.076). for the 1-72 .074 #49 c/s .115+
#55 (.052) for the hole in the blade for the 2-56 .085+ c/s .137+
#49 drill bit (.074) for the hole in the lock bar

LS1-2.JPG

LS1-3.JPG
 
I don't know, Dan. I'm afraid if I follow all these coordinates I'll end up out in the woods... Haintree? This river don't go to Haintree! :D
 
:) Steve, you kinda hafta be here to understand it. :confused: :)
of course if I don't keep at it I don't understand it for a while.. :( :D
 
The old rules still apply such as trying to have the blade cover when the knife is closed at the bolster end.

This is just GOOD design.

As for the ratio and dims from old days they work OK if you like the buck 110 look.

Drawing and cutting the folders out on paper is a good idea. Cut the blade seperate and fold it in the handle.

Look at the blade to handle ratio.

This is the biggest improvement in many year over the old time look of knives.





Standard precision hardware is another.



 
I guess if I really wanted to I could just breakdown a few of my production knives and copy them. But, Illustrator worked out well for my "CAD" prototype! Unfortunately I drilled the stop pin hole a little too far south and it screwed up the blade shape . I guess I could drill it again, but that will cause some other problems, so I'll stick with what I have for now and just see what blade shape wants to come out of this.
 
For this folder that is starting to take shape I need a standoff for the spine. I am planning on making my own, but here are my options: what I will do is drill a piece of steel and tap for 1-72 threads. Should I attempt this on 1/8" diameter stainless steel pin stock, using a cheap drill press and a POS drill press vice, or should I just drill and tap a piece of scrap steel, cut it to square and work out a round-ish shape with my good 'ol files? Now I get why most serious folder makers have a lathe and mill and make all their own stuff!
 
For stand offs I use brass or copper tubing ( 1/8" or 3/16" diam.) I cut it close to the desired length with a tube cutter, or sometimes just a hacksaw. Then put a peice of drill rod in your vice so that it sticks up the desired thickness of the standoff. Slip your peice of tubing over and file it down flush. You'll have to file a little on both sides to get it good and flat. If you have a micrometer to check it with and some patience you can do a surprisingly accurate job, and they work just fine for me. On a really heavy use knife I prefer a solid backspacer to standoffs so it doesn't matter that they're a little thin.
 
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