I'd never made a friction folder before and wanted to give it a shot. There were 2 things that I didn't like about most of the friction folders I'd seen...one is the long tail that extended from the blade that stuck out when the knife was closed. The other was the lack of anything built into the knife to keep the blade from coming open in your pocket. So I thought I'd try making one with dual detent springs -one built into each side of the frame that would engage the blade when it hit the stop pin in both the open and closed position. This would allow me to do away with the "tail" and would also provide added insurance that the knife would stay closed in your pocket. I thought at first that I had an original idea, but after building the first one discovered that it had been thunk up by others before me...oh well. I took pictures as I was building the first one, but then accidentally deleted them from my camera before I got them downloaded. So, this is a little documentary on how I built the second one. I hope you find it interesting and helpful if you decide to make one.
I start with a rough drawing of what I wanted the knife to look like. I placed the pivot and stop pin locations such that there would be ample space between my washers and the stop pin for my detent spring ball bearings to ride on the tang of the blade without falling off. Heck, just check out the photo and I think you'll get the gist of it.
I made some copies of the drawing and used them as patterns to cut out the blade and a pair of liners. I drilled a small hole in the liners to locate the pivot point and stop pin (use one liner as the template for the other when drilling your holes). I also drilled a hole in the blade to locate the pivot. Then, using a drill bit the same size as the holes I drilled, I "pin" one liner and blade together. This allows me to rotate the blade against the liner and find the open and closed positions that I like. I then use the stop hole in the liner to drill two additional holes in the blade...one for the stop in the open position and one for the stop in the closed position. Be sure to leave plenty of meat around the blade tang until after you are done drilling your holes. I'm using 0.05" thick titanium for the liners and my blade is 3/32" thick ATS-34 stainless.
Next I drill all the holes out to 1/8" since I will use this size for my pivot pin and stop. I drill slightly undersize first and then ream the holes to 1/8". Then the blade and liner are "pinned" together again and an arc is drawn on the blade to show where I need to remove material from the tang to allow the blade to rotate without hitting the stop pin.
Here's the blade with most of that material removed...still have some more checking to do to make sure the blade doesn't drag against the stop pin when the blade rotates. I've also outlined the tang of the blade (closed position) on the liner to see how much room I have to work with on the front end.
Next I drill the holes needed in the blade for the thumb stud, or cut in my nail nick if that's the look I'm going after. Here are 4 blades that I worked up while I was at it. I've also stamped in my maker's mark and these are now ready for heat treatment. While these are in the kiln, I can work on the liners.
This is one of the liners that I've drawn a few lines on. The arc around the pivot represents the 3/8" washer that I'll be using. The horizontal lines are where I need to slot the liner to make the detent spring. I've put this in the middle of the liner so that the completed knife does not have any breaks around the perimeter of the liner. You have to do more cutting this way, but I like the looks of it as opposed to the way a linerlock is made. I drill small holes at the start and end of each horizontal line and then cut from one hole to the other using a cutoff wheel and dremel tool. It's tough cutting and I go through about a dozen cutoff wheels to get one set of liners done. Remember, we're doing this to both liners.
Here's a couple liners that have been slotted for the detent springs. Before cutting the springs loose at the pivot end, I drill and tap any holes needed for handle scales, bolsters, pocket clip, etc, and the screws that go from one liner to the other through the backspacer or standoffs that are needed to hold the 2 halfs of the knife apart. Much easier to do this while the detent springs are still attached and the liners will still lay flat. This knife will have g10 scales, no bolsters, a pocket clip, and micarta backspacer. Here's my method for locating and drilling the holes...I first locate all the holes in one liner using an undersize drill. This liner is then used as a template to locate the holes in the other liner. Once all the holes are located and drilled undersize, I use each liner as a template to locate and drill the holes needed in my handle material. One liner is used as a template to drill the holes for the backspacer.
While I was fiddling with the liners, my blades have been heat treated and tempered. Now they need a little cleanup.
Here's my roughed out backspacer. It's a piece of micarta that is the right thickness. I'll be using 0.02" thick teflon washers in the knife, so I want the backspacer to be the thickness of the blade + 2 washers - 0.005 or so to accomodate compression of the washers. I measured my blade thickness after I cleaned it up from the heat treatment and tempering. In this case, it was 0.090" thick, so my backspacer needs to be 0.090" +0.040" -0.005" or 0.125"...1/8" micarta works great! One caution on the backspacer...make sure there is clearance between the blade and backspacer when the knife is in closed position before you drill the blade for the detent holes. It's a bummer when you forget to do this. More on this later.
Here's my handles roughed out and drilled. I've marked the area where the detent springs will be so I can relieve this about 0.020 or so to give plenty of room for the spring to extent into the handle a little after the detent balls have been installed. This may or may not be necessary depending on the thickness of washers you use and how high you leave the detent ball protruding out of the spring.
Here's the handles with the relief cuts made. I did this on my drill press using a 1/4" endmill.
OK, now it's time to cut the spring bars loose on the pivot end. To do this, I drill several holes along the line representing the 3/8" washer where it intersects the spring bar. Then I use a dental burr to cut the webbing between the holes. The photo is a bit blurry, but I think you can see what I'm talking about. BTW, ask your dentist for some old burrs the next time you go to see him. Mine gave me a few and they had never been used. Now I need to bend the springs, tap some holes and do some shaping so I can put the frame together. I didn't get a picture of it, but once I have the frame holes tapped, I screw the backspacer down to one of the liners. I then place a temporary pin in the pivot hole and mount the blade. Then trace the blade edge in closed position onto the backspacer. I then grind off any excess material off the inside of the backspacer to ensure that the blade stops when hitting the stop pin and not the backspacer. Once this is done, the blade and frame is assembled and the holes drilled for the detent balls in the springs and corresponding holes in the blade. I do this with a #59 carbide drill. Be sure to drill the blade in both open and closed position. The holes in the frame are opened up to #53 before installing the ball bearings.
OK, you're right...that was a little long winded and confusing. Here's a photo of all the parts that might clear things up a bit. After getting the frame and blade working together, I ground the blade on an 8" wheel. Not gonna go through all that with this tutorial cuz the main goal here is the construction of the dual detent mechanism. I'm also leaving out the parts where I shape the handles, jewel/anodize the liners, etc.
And here's the best part...the end! Thanks for taking a look at this tutorial. I'm not real good at doing these, but maybe with practice I'll get better. -Phil