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Kit Carsons folder lock

Kit Carson liner lock making – 101

Thanks to Dexter Ewing for editing it and helping me with words that had more than 2 syllables

The following is my technique. If you have a different way of doing any of the steps, feel free to contact me or post on the thread. I'll pick up where I left off when the time is right. I also hope to get some pictures of a few of the steps. Line drawing

Since this will be a mid sized folder I'll use .060 6AL4V titanium. I have hardened patterns for all my folders which also serve as drill guide since all the holes for pivot, backspacer, and handle screws are in it. Trace the outline of 2 liners onto the sheet, using a fine point permanent marker. Band saw the liners out, leaving about 1/16 excess around it. Identify which piece will be the solid side and which one is the split side. Using Dykem, I coat the outside of the solid side piece. Clamp the pattern on this piece and scribe around it, making sure there is excess material all the way around. I use an Exacto knife with a #11 blade, upside down, that lets me get a clean, crisp line. Drill all the holes in this piece. Clamp the pattern on the other piece and drill the holes. No need for Dykem or scribing this one.

Using a tap and a Skil Twist power screwdriver with a chuck attached, tap the backspacer holes and the pivot hole in the split side piece. Drill the same holes in the solid piece but make them a pass thru for the screws. Screw both pieces together and grind to the scribe line. After it's ground down to the line, remove any burrs and clamp with Vise Grips. Remove the screw that is in the pivot hole. My pivot and backstop pin are the same size so I drill and ream both to .1865. (I use a #16 Hi Roc carbide drill and a .1865 carbide reamer). Unclamp them, remove any burrs, and tap the rest of the holes. I chamfer (bevel) the .1865 holes, which makes it easier to insert the pivot/back stop pin. Counterbore the holes on the solid side for the 82 ° flat head screws through the backspacer.

Clamp the hardened blade pattern on the blade stock and drill the holes. I use a #52 bit for all 3 holes (any time I make a hardened pattern, all the holes are the size of the smallest one). One is for the thumb button, one for the pivot and one for the closed blade stop area where the blade rest when closed. Using the same #16 drill and .1865 reamer, enlarge the pivot hole and stop area. The pattern has some extra material around the stop area hole so after it is reamed, it can be sawed and ground to the scribe, leaving half the hole to rest on the back stop pin. Saw and grind to the scribe line.

I have a hardened pattern for the backspacer. I use .015 Teflon for the washers so the thickness is the blade plus .028 (allowing .002 for compression). After scribing, cutting and drilling the backspacer I use double stick tape and attach it to a steel plate and surface grind it.

The key to success when building a folder is keep it flat and parallel, so this thickness is critical for the blade to open and close smoothly.

Screw the finished backspacer to the split liner, tap the stop pin in, and use the pivot to put the blade in. Test the blade for fit in the open and closed position. It is easier at this point since you can see what you are doing.

Now we are ready to cut the lock. I have tried several different ways to cut the split in the liner, but I still prefer to do it this way. When I was drilling the liner holes from the pattern, there are 2 that get drilled on the split side only. These indicate the inside corner and the stop point of the split. For lack of a better term, I call the part that contacts the blade tang the short cut, and the lengthwise cut, the long cut. The short cut is 90° to the long cut and the long cut is parallel to the centerline of the knife and is 2 – 2 ¼ inches long. I use a 24 TPI saw blade to cut the short cut, and a Foredom tool with a 1" cutoff wheel to cut the first ¾ inch of the long cut. I then turn the liner sideways and slip that cut area around the band saw blade then twist it sideways so it lays flat and cut the remainder of the long cut.

I made a piece of U channel that is 1 inch wide, ½ inch high and 3 inches long. I lay the long cut on the top of the channel and clamp the side of the liner to the side of the channel, leaving about 3/16 inch of it sticking out in front of the channel. I hold it with my right hand and push the lock part away from the liner. Since the short and long cut are at 90° I use the tool rest with the platen at 90°. Using an X weight 120 grit belt, I grind the end of the lock, keeping it square and at 90° to the split liner.

To bend the liner, I have a piece of steel bar with a slit in it wide enough to fit over the thickness of the liner. Clamp the part of the split liner below the long cut into a vise. Slip the end of the bending bar over the end of the split and bend the liner to the inside. It should be a good radius from the back to front, not a single bend.

Cut the backstop pin to length (backspacer + both liners). Tap it into the solid side, screw the liners together and tap the other end of the pin into the split liner.

Now, it's ready to fit the lock.

Make sure that the blade is in the correct open and closed position.

Dykem the tang of the blade on the split side. Put the blade into the handle, slip 2 washers onto each side of the blade and put the pivot bolt in. Holding the knife in the open position, use the Exacto knife to scribe the end of the lock onto the blade. One good crisp line works best.

If you have an adjustable tool rest, adjust it to 7 ½ - 8°. If you don't, cut a wedge of hardwood to the same degrees and use it to raise the tip of the blade off the tool rest. Very slowly, grind to the scribe line. As you get close, put the blade into the handle and use a pin or the pivot to check for fit. Your aiming point is for the lock to engage a full thickness of the liner (surface of the blade and liner are flush with each other). Contact should be tight where the liner meets the blade on the outside and less on the inside. This prevents it from rocking up and down if there is ever any wear. Open and close it several times and look at the tang of the blade. You should be able to see where it is hitting and how much contact it is making.

Put the blade into the handle with the washers and pivot bolt. Don't do anything to the end of the liner. Take more off the blade, if necessary, until you the proper fit.

Part 2___

Okay, now that the lock is fitted, all holes have been drilled and tapped, the pivot bolt fits the holes through the blade and liners snugly, and the knife is flat and the gap between the liners is the same, we can continue.

If it is going to have full scales (no bolsters), make sure the handle material is flat and smooth on the inside. Clamp the pattern onto the handle material, scribe the profile and drill all the holes. Band saw the profile, leaving a small amount of material all the way around. Enlarge the #52 holes to #49 (pass through for a 1x72 screw). Enlarge the pivot hole to .1865 and countersink for the pivot bolt head and the screw. I use 6x32 buttonhead screws and they normally measure .255+/-, so I either turn them down to .248 or use a 17/64th countersink. You can force the pivot head into its countersink but you never want to have the screw tight in the countersink. If the blade "grabs" the pivot, and the screw is tight in the hole, it will tend to unscrew the pivot.

Countersink the handle screws. I use 1x72 82° Flathead screws and use a #1 82° piloted countersink for this. It's the same one used on the solid liner for the backspacer holes. Screw the handle onto each liner, cut the excess off and grind them down to the liners.

Take the handle off the solid side, exposing the counterbored holes for the backspacer. Screw the liners together with the backspacer and stop pin in place. Screw the handle scale back on and put the blade and washers in and install the pivot and screw. Saw or grind the excess off the head of the pivot, and screw. The handles should be flat on both sides. Grind off the excess handle material down to the liners. If the knife has bolsters there are a few more steps that are required.

On the hardened pattern I have a scribe mark indicating the end of the bolster, where it and the handle meet. I gave up trying to grind the ends of the bolsters years ago. For a good, tight fit and a true 90° a milling machine works best (this is what I use). At the same time, I mill the end of the handle pieces. I leave both bolster and handle pieces cut in a rectangle for easier clamping in the vise. Now that both are flat, straight, and have 90° ends, I then fit the bolsters. Clamp one bolster piece on the pattern aligning the end of it with the scribe mark. Drill the pattern holes (#52) for the pivot and rear bolster screw. Remove any burrs and clamp the drilled piece to the other one. Drill the two holes with #49 and then enlarge the pivot hole to .1865 and countersink both. Countersink the rear bolster hole with the 82° piloted countersink. Attach these to the liners, grind off excess pivot head and screws. Fit the handle scales to the bolsters, clamp, and drill and countersink the handle screws and grind off the excess. Now is a good time to grind off the excess around the bolsters/liners.

Take off the handle on the solid side, exposing the backspacer screws. Screw the liners together with the backspacer and stop pin in place. Put the blade and washers into the handle and install the pivot bolt and screw. If everything is flat and parallel, the blade should open, lock, and unlock, and close to the correct position. If it doesn't, back track and find out what you did wrongJ I'll wait here on you…

At this time, I like to grind the perimeter of the handle up through 400 grit. As you grind, remember the back stop and backspacer screw countersink. If you grind into them, you might as well start over. Do a quick check of the folder - - blade locks open, lock engages in the right position, and closes into the handle. If it doesn't there are usually 3 things that could be wrong: 1) The blade is hitting the backstop pin early (remove a little more material in that half moon area of the blade; 2) blade is hitting the backspacer – (take more off either the blade or backspacer); or 3) the blade is hitting the screws on the inside of the liners.

Okay, now that the blade is doing right, continue to check that the bolsters and handle scales are laying flat on the liners, that the bolster/handle scale joint is tight with no gaps, and the edges around the handle are smooth and flush.

You should have a working folder with a big thick blade (we grind in a few minutes) and big square handles that are going to be shaped now.

I Dykem the edges of both sides and use a small set of dividers or a blade scribe (I'll add that to my pictures to do) and scribe a line where I want to grind to, usually about .030-.040 from the edge of the liner. I use a 10" contact wheel and grind with the knife horizontal to the wheel. Before I start, I take the handle scales off and replace them with pieces of scrap handle material. These are an inch long and the width of the handle. You can fit these before the Dykem/scribe step or just grind them as you grind the bolsters. I do this with all bolstered knives, fixed or folding. If you have a problem with rolled edges or gouges where the handle scales meet the bolster, try this step.

With the knife horizontal, I grind in the scribe line on the top edges, keeping it parallel to the wheel. As I reach the scribe I roll the handle so it grinds down to the center of the bolsters. I do the same thing to the underside. With titanium bolsters I start with 120 and clean it up with 220 grit belts.

Take the scrap handle pieces off and put the good handle scales back on. Using a 320/400 grit belt, I grind the handle scales to the scribe line, rolling the handle like I did with the bolsters. The point here is that the handle material is softer and grinds faster than titanium.

When I get the grind to the scribe line I turn the knife, point up, and with a 400 grit belt I lightly grind up and down. Be cautious with the pressure you use. Once the handles are smooth, you can clean up the edges, removing the Dykem and scribe mark.

If you do it right, there is very little hand sanding to do. I put the scrap pieces back on and use a BearTex convolute wheel to blend the bolsters then remove them and put the scales back on to do any final hand sanding.

At this point I grind the blade. I prefer to remove the handle scales if they are natural material.

Part 3

At this point:

  • The handles are shaped and finished.
  • The blade is ground, heat treated, and at the desired finish.
  • The lock is fitted and operating correctly.
  • The blade is in the correct position opened and closed.
It's time to do the detent ball.

I use 2 different size detent balls. For smaller folders I prefer a 1/16th (.062) inch one and
on the large sizes a 2mm (.076). The drill bits needed for the .062 ball are a 3/64th
(.0469) carbide for the hole in the blade and a #53 (.0595) for the hole in the lock.
For the 2mm, a #55 (.052) carbide for the hole in the blade and a #49 (.074)
for the hole in the lock bar.

Remove the bolsters and handle pieces. Fit the blade into the 2 liners with the washers and pivot bolt in it. Scribe a small line 1/16th inch back from the edge of the lock and the same distance up from the bottom of the lock. Open and close the knife and insure that the ball stays in contact with the blade throughout the arc. If it drops off the blade, you need to do some more design work.

Use a center punch and spot a mark where the lines intersect. This point is the center of the ball position. Close the knife back up and use a spare washer to raise the lock up to the same level as the rest of the liner. Insure that the blade is centered in the handle. With the carbide 3/64th bit, drill through the liner and into the blade. Remember that the blade is hardened so use light pressure. Drill about 1/16th inch into the blade. The intent is to let just a portion of the ball drop into the hole, not the whole ball. Take the knife apart and enlarge the hole in the liner to .0595 (#53). Remove any burrs on the liner and the blade.

There are several ways to set the ball to the correct depth. I use a shop made punch fabricated from 3/16th rod with a shallow hole in the end. The best way I have found to make one is by cutting the rod to exactly 2 inches and drill the hole so when the ball sets in the hole, the total length of the rod and ball are 2.014 inch (.014 is the compressed Teflon washer thickness). When you punch the ball (.076) into the hole (.074) and let the punch bottom out, the ball will be the correct distance inside the lock. The end of the lock may bulge a little with the ball swelling the hole, but it can be easily filed down. If you use thinner liners, the ball may stick out the other side too much. Either grind the exposed part down or make a shallow hole in the inside of the bolster. The liner has to go back flush with the bolster or the detent ball will be too far inside and bind the blade.

Put a drop of oil on each side of the blade, put the knife back together with washers in place, bolsters and handle pieces on, and the pivot bolt in place and tightened down with the screw.
Open and close the knife a few times and adjust the pivot screw if necessary. It should open smoothly with no binding, into the locked position. Close the knife and watch as the detent ball drops into the detent hole. The lock should have enough tension to snap the blade closed and hold it there.

On a side note, this process can be done before the blade is heat treated but I prefer to do it as the last step. If you decide to do it before heat treat make sure the closed blade position is correct and do not, I repeat, DO NOT put the detent ball in. The hardened ball will create a groove in the blade.

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