My Frame-Lock Tutorial

This was originally posted online in 2002, but it was lost - so I resurrected the photos and added new text....

Starting with the drawing:



I use CAD to design knives, but you don't have to. Regardless, it's a lot easier to make your first frame-lock folder after you have a drawing that shows all the major components with the blade in both the open and closed positions. I do this with every model folder I make - even when I'm simply changing the size of the knife.

With the drawing developed, you can use scissors to cut out the blade and the frame outlines, glue them to some 1/8" thick Micarta, and then cut out Micarta templates.



Here are the Micarta templates, sanded to shape with the holes for the pivot and stop pin drilled, along with mounting holes for the round spacers I'm going to use.

To make sure the templates fit together properly, I install some pins and swing the two parts open and closed to make sure the blade stops where it's supposed to stop.



You can see I've even added the thumb stud and round spacers at the back to make sure the blade doesn't hit them when the knife is closed. (I'm going to use the same size spacers and thumb stud in the finished knife.)



With the templates made and proven, you can now use them to lay out the material. Here, I'm using an Ultra Fine Sharpie marker to layout a sheet of titanium for sawing.

Staying just outside the lines will ensure you have enough stock when match grinding the frame scales. I use a 10-14 tooth variable pitch bi-metal bandsaw blade running at about 110 fpm.

Next, I prepare the frame scales for flattening. To make sure they don't go flying when I touch them to the disc sander, I roll up some 2" wide masking tape - sticky side out.



And onto the slow speed sander. This runs at about 90 RPM.



I'm only going to flatten the "inside" surface of the frame scales at this time. Here's what one looks like fresh of the disc sander.



Notice the lay pattern is visible on 100% of the surface.

Next stop - drill press.

I'll describe my drilling sequence before posting more photos so you understand why certain things are done in a certain order.

First, I drill (and deburr) all the holes in the lock side of the frame. Then, I clamp the two sides of the frame together and match drill the pivot hole through the opposite scale, separate the two pieces, and finish the reaming, counterboring, and deburring of the pivot holes in both parts. This allows me to actually use the pivot pin to tie both frame scales together.

The pivot pin is installed into the lock side, the opposite scale is slid over the pivot pin, and the two scales are clamped together. Then, I begin match drilling the locations of the frame screw holes and the stop pin hole.

If you try drilling both scales independently it is almost impossible to get everything to line up (unless you're using a CNC milling machine). And trying to drill both parts at once creates machining chips between the parts that push things out of alignment. (Not only that, it's torture on the drill bits and reamers.)

It's much better to take things slowly by centerpunching the hole locations, starting the holes with a combination drill, drilling though each hole, deburring each hole, and moving on to the next step (reaming, counterboring, threading, etc. - as applicable.)

Whenever you have all the holes machined in a frame scale, it's recommended practice to take the part back to the sander and make sure everything is still flat.

Flatness, parallelism, and perpendicularity are terms that apply to just about every machining operation on a folder of this type. But, don't let these terms intimidate you - a bit of common sense goes a long way!

Now that I've introduced some fancy terms, let's see how the layman applies them to folder making.

We'll start with perpendicularity - also known as squareness. If you ever watched anyone building a house, you probably notice that some of tools they constantly use are a level, a plumb line, and a square. Keeping things are perfect right angles (90° from each other) not only looks neat, it keeps the doors from sticking.

The same principles apply to machining on a folder. If you don't get the pivot hole exactly square to the blade, the blade will always run crooked. If it's off enough, the blade will actually hit the side of the frame.

I really don't do a lot of measuring when I'm building a folder. (You'll only see a few measuring tools in this tutorial's photos.) The fact remains that you need to be sure of your setup on any "precision" machine before you begin cutting material. A lot of answers to "Why doesn't my folder work the way it should" can be traced back to poor setup of the machine.

Let's pick up with the drilling of the locking side frame.....

Here, I'm using a precision machinist's square to make sure my working surface (the top of the vise) is perpendicular to the spindle. I just place a precision ground rod (the end of a reamer works fine) in the drill chuck and check it with the square to make sure there aren't any gaps. You need to check at least at two 90° intervals around the rod to ensure the work surface is where it needs to be. How often do I do this? Every time I set up to drill folder parts. (It's amazing how things can get bumped around in my shop.) Usually, it only takes a minute or two to make any necessary adjustments.



Starting with the lock side frame scale, I centerpunch all of the hole locations and begin drilling using a combination drill/countersink. Why? They're less likely to bend or go off center than a regular twist drill bit.



I use a larger combination drill to start the (larger) stop pin and pivot holes.



Then, I use regular twist drills (well, maybe 135° split point cobalt drill bits shouldn't be called "regular") and drill the through holes. The frame screw holes get the respective tap drill size. The stop pin and pivot holes are slightly undersize because I ream them later on.

In between changing drill bits, I always use one of the combination drills or a countersink to deburr everything.



After all of the holes are drilled in the lock side frame scale, I pass it over the disc sander to make sure all the burrs are really gone and everything stayed flat.

Next, I'm going to start match drilling the opposite side of the frame. I clamp the two scales together, match drill the pivot hole, and match ream the pivot hole. I use a .003" undersize reamer because my pivot pins are press fit into the frame.



After the pivot hole is match drilled and match reamed, I take the two scales apart and open the non-locking side scale with a clearance reamer. This allows this scale to be fit to the lock side scale without any unnecessary hammering.



Then, I counterbore both scales to clear the pivot head and pivot screw.



The pivot is then tapped into the lock side scale.



I use a steel block with a clearance hole so the scale doesn't go out of flat when tapping the pivot in place.

The two scales are clamped together and I start match drilling the frame screw holes, using the tap drill diameter drill bit.



Drilling just deep enough to make some decent marks in the non-locking side scale.



Then, I use the proper clearance drill and countersink for the screw heads.



... and thread the lock side frame scale.



Now that I can actually screw the two frame scales together, I finish drilling and reaming for the stop pin. Like the pivot, this is press fit into the lock side scale and the opposite scale is reamed slightly oversize. Press the stop pin into place, and it should look something like this.

While we have both sides of the frame screwed together, might as well clean up the profile a bit.



That was easy!

Now we need to do something about that stop pin sticking out too far. I've made an aluminum spacer that is the same thickness of the blade plus both washers. Here it is installed over the pivot. (I've also installed the back spacers.)



And, here's everything fastened together again.



A few passes by the belt grinder to get the stop pin and frame screws close to the frame, plus a little time on the disc sander and everything is nice and flush.



Did the same thing on the lock side, too.

The blade is laid out onto bar of steel (Damasteel, in this instance) using the Micarta template and an Ultra Fine Sharpie.



And the profile is cut out on the bandsaw.



I stay just outside the lines, except for the tang area - where I leave a little extra material.



Next step is surface grinding. Here, just a few thousandths are taken off both sides until the blank is to the desired thickness. The blade is flipped often to avoid overheating and warping.



The thickness is checked with a micrometer throughout the process.

Next, I clean up the profile on my belt grinder.



And use the Micarta template to layout the thumb stud and pivot hole locations. Note the centerpunch marks.



After the holes are drilled and reamed, I start working the blade profile to match the frame.



Checking it in the open position...



... and the closed position.

I make my own washers out of .032" thick Nylatron, using a set of arch punches and a urethane backing pad. You can see the steel guide that keeps the large punch on center with the small holes.



Now, I can assemble it all together to make sure everything fits and the blade travels open and closed without binding.



Here, you can see that the thumb stud hits the frame.



So, it's back to the belt grinder for a little trim.

Next, I pop the blade out and texture the thumb ramp using a checkering file.



I remove the pivot, put the aluminum spacer back in, and clean up the lock side of the frame on the disc sander.



With the side of the frame all cleaned up, I'm ready to layout the lock.



Here the relief hole has been drilled at the intersection of the long lock slot line and the relief notch line.



The face of the lock is cut on the bandsaw.

Next step is cutting the long lock slot. I use a carbide saw in my bench mill. It takes a while to do this, but you get a really clean cut. (I run the saw at about 120 RPM.)



While I'm at the milling machine, I cut the relief notch using a carbide ball end mill.



This is a simple little fixture I use to clean up the lock face. There's a screw that pushes the lock away from the scale so you can get at it without messing up the scale.



Then, carefully clean the face of the lock using the belt grinder at slow speed.



( We're half way there! )

With some masking tape on the jaws, I take a pair of heavy pliers and twist the lock toward the inside of the frame.



Using a chainsaw file, I cut some thumb notches along the front lock edge.



Next, the socket for the detent ball is drilled with #53 drill ( I use .062" diameter 440C detent balls.)



The detent ball is staked in place using a 1/8" flat pin punch.

The area of the blade tang that will engage with the lock is blackend using a Sharpie marker.



Then, it's put into the frame and the lock line is transferred using an X-Acto knife.



I use a digital level to set the lock angle at about 5°.



And SLOWLY start grinding the blade tang to fit the lock.



After a few trial fits, this is what it should look like.

Swinging the blade open and closed scribes the arc made by the detent ball. I centerpunch a mark just beyond the end of the line.



And carefully drill the socket for the detent.





Properly installed, the detent should actually pull the blade into the handle when it's near fully closed.

Placing the pocket clip on the back of the knife, you can see there's going to be a bit of interference with the head of the pivot. (We'll take care of that shortly.) First, we'll take our Ultra Fine Sharpie and mark the forward hole location.



Then, after mounting a 1/2" contact wheel on the belt grinder, we'll cut a clearance notch in the pocket clip.



Might as well shorten the mounting screws while we're at it. Using a scrap piece of titanium that's the same thickness as the frame, mount the pocket clip with the screws, and grind them to length.



It all fits!



Now, we can use the remaining hole in the pocket clip to match drill for the second screw. Here's a shot with the pocket clip mounted with both screws.



While I was at it, I added a second set of pocket clip mounting holes at the opposite side of the scale.

(BTW: I always use the tap drill diameter when putting the mounting holes in my pocket clips. That way I can match drill everything at the tap drill diameter and open the holes in the clip later.)

Here, I'm starting to shape the edges of the frame with a slack belt.



Front side done.



Back side done.



The pivot is also put back in place.



I'm going to put some holes in the frame to dress things up a bit. Here, I'm using the familiar measure, mark with an Ultra Fine Sharpie, and centerpuch routine.

Disassemble the frame, and start drilling - combo drill, 1/8", 1/4", 3/8", countersink, deburr, and check the flatness.



I've bead blasted the scale and polished the chamfers in preparation for anodizing.



The pocket clip is also sanded in preparation for anodizing.



Since the lock side scale has some carbon steel parts (the stop pin and the detent ball), I need to mask them off before sticking the assembly in the anodizing tank. A little nail polish will do the trick.



And, into the electrolyte bath it goes!

28 volts DC should give us blue. Looks like it worked!



Now it's time to turn our attention back to the blade. Every maker has his or her own preferred method of grinding. This is just how I do it. You can use your own method.

First I use the Ultra Fine Sharpie and lay out the main grind on both sides of the blade.



I clamp the blade to a piece of steel angle and start hollow grinding.



After working thru progressive grits to finish the main grind on both sides, I clamp the bade to the steel angle and (using a platen) grind the top edges.



I like to cut a notch at the ricasso using a chain saw file.

This photos shows the level of finish achieved on the grinder.



Now, I hand finish the perimeter of the blade using dowels where necessary and progressively finer grits of paper.



With that done, it's time to start the hand finishing of the flats. Since I use magnets to hold the blade during the process, I first place 2 layers of masking tape on the back side of the blade to avoid unnecessary scratches.



Then, flip over to the other side and repeat the process.



You can see by the reflection of my thumb how far down I take the finish.