Liner-Lock WIP: CAD, Fixtures, Milling... and tiny little screws.

[Erin Burke]

First liner-locks… this should be interesting.

With the exception of some balisongs that I built a few years back, I am not a maker known for his folding knives. The preponderance of my (limited) work has been weighted toward fixed-blade, wood-handled Bowie’s, fighters, kwaiken, hunters, etc. That being said, there were a couple of factors that triggered me into finally taking the plunge into locking-folder construction.

To begin with, I had drafted up this very project several years ago. Since then, it has been patiently waiting on a thumb drive for somebody to pay attention. The design originates from one of my early fixed-blades; I think the similarities can be clearly seen in these photos. (Admittedly, I have a fondness for forward-leaning recurves. Note that the proposed folder has been scaled down significantly from the original… down 25%, or from just about 8” even to 6” even.)

Also of note is that this is not my first folding iteration of this design. Back in 2010, I made a dead-sexy balisong (my first actually) in a similar profile. It is still in my possession, and can frequently be found in my right pants pocket.

Another reason that I chose now as a good time to try a locking folder stems from a general mental fatigue that followed the completion of my last project. The extended run of fixed-blade knives that culminated in the Narwhal Spike left me ready shift gears and try something new (for a while).



So, the first step in this project was to gear up. :thumbup:
Visiting all of my favorite on-line suppliers (USAKnifemaker, AKS, Knifekits, TexasKnifeSupply) I proceeded to order a variety pivots, bearings, stops, screws and other hardware. Purchasing parts for constructing a folder can be daunting, as everything needs to fit together... and tolerances can be critical.

I had really wanted to mess with caged bearings on this knife; my original drawings were intended to be used in a frame-lock configuration in order to provide enough real estate to house the larger bearings I had originally sourced. After revisiting the plans and tweaking the CAD-work, I determined it possible to cram a pair of AKS’s smaller (0.0625”) ceramic bearings under the hood of this knife in a liner-lock configuration while still leaving enough “meat” in the blade and liners to maintain a strong foundation.

Every project is an opportunity to invest in some new tools.! :thumbup:

Searching through Youtube, you can find a plethora of unique approaches to constructing a liner lock. For me – given my goals and my tools – I decided to focus on a method that would lend itself toward repeatability. With that in mind, I set to building a fixture for holding materials that would be compatible with both my milling vise and the new rotary table.

The fixture began as a 6”x6”x1.5” chunk of aluminum. My first attempts to cut this block to shape took place at the DeWalt portaband, but that -- due to the thickness -- was no fun at all. :grumpy: Following a quick internet search, I decided to take a stab at it with the wood band saw. The aluminum was soft enough that the larger teeth and faster speed actually worked out OK.


After rough cutting the block on the band saw, I squared it up using a face mill on the milling machine.

As part of the fixture construction, I decide to build some tiny clamps out of a scrap piece of W2. Large clamps always seem to end up in conflict with my quill when I’m running small end mills; by building custom clamps, I hope to avoid this. This next series of photos might be fairly boring unless you dig fixtures.

Here’s a photo showing the bar of W2 machined to dimensions.

And this is my shop helper giving me a hand with the work.

This photo shows the clamps cut from the bar, prior to heat treat.

After quench.

Following temper and a quick cold-blue, I use a torch and some old motor oil to give the clamps a nice oil-blued finish. This is a working finish that I found to be simultaneously resilient and attractive… definitely more resilient than cold blue alone.

Finally, this photo shows the fixture complete, with a couple 6AL-4V liner blanks clamped in place. Notice the steps milled into the side of the block for clamping onto the rotary table.

More to follow.

 

[plas62]

Nice WIP, looking forward to seeing the rest of the build and the fixture in use.

 

[Erin Burke]

The liners and scales for this knife start out life as 4”x1” rectangles of material. All of the holes are indexed (using the DRO’s) off the rear-right corner of the fixture (set to 0,0). The photo below shows some of my working sheets. I try to call out X&Y coordinates and tool info. In the upper left, you can even see the sweep angle of the stop pin (for the rotary table work).

In this photo, I have pre-drilled all of the holes through the titanium liners, and I am in the process of tapping one of them for the pocket clip. For making 2-56 threaded holes in Ti, I will pre-drill with a 5/64” bit, then follow with a thread-forming tap and some Moly-Dee. The tap is run at about 500rpm through a Tapmatic.

[YOUTUBE]aiot_Xbb0ys[/YOUTUBE]



Here I have started putting the corresponding holes through the scales. I’m using textured G10 from AKS. To protect the textured surface, I’ve covered those faces with painters tape.

In this photo, I’m putting holes through the blade blanks. Both the pivot and stop holes need to be 3/16”; however the pivot hole gets reamed to size and lapped for a nice fit on the pivot pin. I also have drilled a small hole for the thumb stud.

I probably should note that all holes get spotted with a dedicated spotting-bit prior to drilling. Tiny bits -- even screw-machine length -- can wander when starting a hole. The spotting bit helps ensure that all holes end up where they belong.




Here is where I get to delve into new processes. It seemed like a real pain (and expensive) to get a counterbore in the size that I wanted, so I decided to mill the bearing pockets on the rotary table. While I ended up happy with the results, it was decidedly not the most efficient use of my time… especially considering that I had to mill a total of four pockets in each of two knives (two in each blade and one in each liner).

Here I am milling the bearing pocket into one of the blades. For some reason, 5/32” four-flute carbide end mills have a special place in my heart. Something about them just “works” on my little mill. They are large enough that I don’t have to worry too much about them breaking, yet small enough that they won’t overwhelm my under-powered, light-weight machine.

Since I had to repeat this step several times, I decided to make a little photo collage of the process of zeroing the pivot hole on the rotary table. The first step – and the one that I, unfortunately, neglected to photograph – is to center the rotary table itself under the quill. There are a ton of Youtube videos that show how this can be done… but for me, it involved a DTI fixed in a collet. I bought an Indicol years ago to simplify this process, but it turns out that your standard Indicol won’t fit the quill of a Sieg X3 clone. I may have to fabricate my own scaled-up version someday.

Anyway, this is the much-repeated process for zeroing the pivot hole.

And finally, here I have milled a travel-path in the blade for the 3/16” stop pin. I will trim off the excess material at the rear (under the clamp at left)… and this should allow for very “rough” assembly of the parts.

Right about this time, I received a couple boxes in the mail, and had to take a break from construction to focus on “organization”. Space is tight in my shop… so it’s important to be as efficient and organized a possible in order to get anything accomplished. I have been having a bear of a time keeping track of all of the “tiny” stuff, so I ordered a couple of these Akro Mils storage compartments and mounted them to the wall just to the right of my mill bench.

The box on the right houses miscellaneous parts (screws, pivots, clips, detents, etc.), while the one on the left contains drills, reamers and end mills. They are clearly labeled, and even have a color code to quickly identify carbide variants. I kind of geeked-out on this.



Back at the portaband, I began trimming things to shape. Using spray adhesive, I attached some scaled templates to the liner and blade blanks.

After some cutting and grinding.

And here, I have started putting handles together… sans blades. Really starting to look like something, eh? Grinding/lapping all of the T6 2-56 screws to length was a real pain. I don’t have a ton of fine dexterity in these old stubby fingers.

Finally, here are the rough-ground blades mounted. I have thumb-studs installed to make sure that all of the clearances are dialed in. The studs will be shortened significantly later.

 

[john april]

wow, looking forward to more photos. the new rotary table looks very nice.

 

[JoshRG]

Awesome thread. Can't wait to see more! :thumbup:

 

[Justin Presson]

Nice Erin, that is really looking good!

 

[darsk20]

Nice work and I like the look. Reminds me of an old Benchmade I have somewhere, but the blade style is different.

 

[Erin Burke]

Thanks guys.

Nice work and I like the look. Reminds me of an old Benchmade I have somewhere, but the blade style is different.

I'm a big fan of the classic Benchmade liner locks... pre-wave.:thumbup: I've never really warmed up to their axis-locks, which seem to be Benchmade's bread-and-butter these days.
Erin

 

[darsk20]

Very similar point of view. Besides my Nimravus, it is the only Benchmade I have owned. I really do like the liner locks and frame locks.

 

[knife lover]

Looking very nice! I have absolutely no background in knife making, but I am in a mechanical engineering technician program that is 50% machining, so this was fun to look at! I'd love to get a little mill like that to play around with in the shop! I'm looking forward to the rest of the pics!

 

[Daniel Fairly Knives]

Looking good! I like those clamps you made...

 

[Lo/Rez]

Awesome WIP. Thanks for sharing this.

 

[Erin Burke]

Very similar point of view. Besides my Nimravus, it is the only Benchmade I have owned. I really do like the liner locks and frame locks.

I have a CQC7 from back when Benchmade produced them for Emerson; though this CQC7 was part of a limited run stamped with the H&K logo on the front and a picture of the USP on the back. Very cool knife.
I also have a Nitrous Blitz (newer, but also discontinued). It is also a great liner lock, with the addition of a cool liner-driven assisted-opening mechanism.
Both knives share a minimalist, light-weight design aesthetic with textured G10 over titanium.
I won't deny Benchmade's influence on this project. :thumbup:

Looking very nice! I have absolutely no background in knife making, but I am in a mechanical engineering technician program that is 50% machining, so this was fun to look at! I'd love to get a little mill like that to play around with in the shop! I'm looking forward to the rest of the pics!

Before I bought the bench-top mill, I had almost ZERO experience in machining. I can't say that I know a ton more today, but it's fun to fumble around.

Looking good! I like those clamps you made...

The goal was to come up with something minimal and low-profile, and they turned out great. A few weeks after making them, I noticed John Grimsmo using some similar clamps in one of his Youtube videos, so I'm guessing this type of clamping/fixturing is not uncommon.


Thanks again for the comments. I hope to spend some time in the shop this weekend... so maybe a few more photos will surface soon.
Erin

 

[Erin Burke]

Now the rubber hits the road… I get to play with lock-bars and detents.


As mentioned in the OP, I’ve been planning a liner/frame lock project for a while now. Several years back I got a wild hare to buy a slitting saw, on the off chance that I might need to cut a lock. I know there are tons of makers that make their cuts with abrasive cutoff wheels, but I had my heart set on keeping my cuts thin, and opted for a slitting saw. Here’s a photo of me making my first cut. The trick to the slitting saw is running it S L O W. I’m not sure what the actual spindle spindle speed is, but my controls are set a bit below 100rpm. It’s also important to keep the cut moving to avoid work-hardening the titanium.

After cutting the lock bar, and the corresponding lock face on knife #1 (which I neglected to photograph), I noted a couple of improvements that would benefit knife #2. The following photo shows a couple helpful tweaks.

Tweak #1: The titanium liners on these knives is about 0.06” thick, and the lock bars are fairly short. This makes for a slightly stiff spring action. In order to help relieve the spring tension a bit, I milled a small 0.02” deep pocket near the base of the lock bar on the scale side of the liner. This seems to have been quite helpful, so I went back and made the same change to the spring on knife #1.

Tweak #2: There are several related issues here, some of which I can’t even begin to explain. All of the CAD in the world can’t replace prototyping… and one thing that became apparent with knife #1 was that I could save myself some grief by moving my lock-face cut about 0.025” toward the pivot end of the knife. I thought about trying to draw up a simple CAD sketch to explain the (strictly cosmetic) issue, but it turns out that I’m too lazy. One thing I can point to, however, is the following photo of knife #1. See how about 1/3rd of the detent hole is visible in this position? This was corrected on version 2.

On future iterations of this knife, I think I’ll move the lock face slightly further. The original placement was based on a 0.50” diameter pivot bearing, but I found that I have more flexibility with the 0.40” bearings from AKS. :thumbup:


This photo shows how I assemble the knife and use a thin X-acto knife to scribe the alignment of the lock face onto the tang of the blade. It’s important that the blade be seated firmly against the stop pin when this is done.

And here you can see the line. I {very carefully} grind toward the line on my KMG, with my platen angle set to right around 8.5 degrees from vertical… repeatedly assembling/disassembling the knife until I get the lock to seat where I want it.

 

[Erin Burke]

Here I have drilled through the lockbar with a #55 pilot hole for the detent. I had to shelve the project for a few days while I waited for some new drills from MSC. For a 1/16” detent, Internet wisdom tells me I need a #55 and a #53. I’m a big fan of cobalt Precision Twist drills, but MSC will only sell them a dozen at a time… so now I have enough of these to last me for a long while.

After drilling the #55 hole in the lock bar, I need to create a corresponding #55 hole in the hardened blade using a carbide drill. Fortunately MSC allowed me to buy these individually.

In this photo I am holding the blade tightly against the stop pin using these amazing high-tech Omnidirectional Compression Jigs. No expense spared. Using the #55 carbide I drill through the lockbar hole and into the blade.

Finally, after chasing the lockbar hole with a #53 drill, here I am setting the 1/16” ceramic detent ball. I use the washers to control the press depth of the ball. I started with two 0.014” washers to give me 0.028” of ball protruding. After testing the feel of the detent, I re-pressed with a 0.020” plus a 0.005”. This felt a bit better, but the break was still a bit stiff. Finally, I pressed with a single 0.020” washer to get the detent engagement that I was looking for.

Here’s a quick video that I shot showing the “suck” as the detent ball engages the blade hole.

[Youtube]IZFmNR5R3ec[/Youtube]



Below are a couple more random photos from my wrap-up of the build.

The thumb-studs that I bought (from USAKnifemaker I believe) were a bit longer than I wanted, so I drilled a little jig for keeping everything square while shortening them on the disc grinder. Final lapping is done on a surface plate.

In this photo, I'm drilling screw holes in a stacked pair of titanium pocket clip blanks. When I was kitting up for this adventure, I bought some pre-made titanium pocket clips (the smallest I could find) from one of the on-line vendors. Turns out that they weren't small enough for this design... so I ended up building my own.

Final Photos and comments to follow.

 

[Erin Burke]

Here are some photos of the finished folders. Because this is Shop Talk, I’ll point out some of the issues and flaws… and hopefully this will help others avoid making similar mistakes.

It’s not super-clear in the photo, but the closed blade is not centered in the knife on the right. If I were to venture a guess, this is the result of several issues compounded. Firstly, I lapped my pivot holes prior to heat treating the 1080 blades. I had to “re-lap” after HT, and ended up with a slightly looser fit than I’d prefer. It appears that the spring tension pushes the blade off to the side slightly in the closed position. It does not cause any rubbing against the liners, but it still annoys me. Theoretically, I should be able to correct for this by tightening the pivots, but over-tightening negatively impacts the smoothness of the flip.

The blade on the other knife is centered much better. Either way, however, I will not be doing any lapping prior to HT in the future.

This image shows why any future iterations of this knife will utilize a stainless variant for the blades. The discoloration on the knife at left was the result of one day in my knife drawer. Both knives had been cleaned and wiped-down with Breakfree CLP, but (for some reason) this blade ended up discolored.
I like working with plain carbon steels (W2, 1095, 1080) on my fixed blades… but it is just too difficult to keep corrosion out of the pivots on a folder. I may end up checking into Cerakote or something similar to protect these two blades.

This photo shows the lock-up on both knives. The knife at the right has near perfect lockup with the lock bar engaging near the first third of the lock face. On the other knife, the lock bar comes a bit past halfway across the lock face. What this means is that the spring needs slightly more bend to engage solidly… which puts more pressure against the side of the blade when in the closed or transitional positions. Both blades flick open smoothly and lock securely, but now that I more fully understand the implications of lock engagement, I will need to be more diligent when grinding lock faces in the future.

Just a couple of things to note in this photo. The first is the spot of discoloration on the ricasso of the lower blade. Again, future knives will either be stainless or utilize some sort of protective coating. You can also see in this image, how I experimented with the scale relief for the thumb stud. I’m having trouble deciding which one I like better.

Finally, here’s a photo of the backside in the “closed” position. This is mainly just to show off the home-grown pocket clips. I had originally planned to mill pockets into the G10 scales to recess the attachment points for this clips… but I ended up liking the look of this better. I figure that – on a knife this small – a person might choose to remove the clip entirely… and I’d like to leave the scales unmarred should this be the case.


Thanks for following along. Feel free to make comments, give advice or ask questions.

Erin

 

[Lo/Rez]

Awesome WIP. Thanks for sharing and I appreciate you adding the tips at the end.

 

[Salem Straub]

Erin, great thread! Thanks for sharing.

Every project is an opportunity to invest in some new tools!

That is wisdom.

I like the scale relief better on the bottom/right knife more, FWIW. Minimal fits the overall aesthetic.

I like your analytical/systematic approach. I find that folding knives is a thinking man's game, and therefore you are poised for success in this field of endeavor!

 

[Evan Miner]

good threat thanks for the insight on making a folder

 

[Erin Burke]

I really wanted to come up with a solution to protect these blades from rust/patina, so I did some internetting and found a Cerakote company just down the road from my office. The team at Brand X Custom Coatings (bxccoatings.com) was fantastic to work with. I'm really hoping that this finish will hold up to my expectations, because I'd really like to use these guys again.

What do you think?

Erin