Lockback Folder Tutorial

K R Johnson

Well-Known Member
#1
I'm going to show step by step how I go about making a lockback. I'll start by recommending a book, "The Lockback Folding Knife From Design to Completion", by Peter Fronteddu & Stephen Steigerwald. It's very well done with lots of step by step pictures. It also explains how to make a lockback with basic hand tools.

You can get it from BossDog 's store, http://usaknifemaker.com/books-vide...-folding-knife-from-design-to-completion.html,
I bought it just for the instructions on how to make the lock bar and notch.


Here's the pattern I'll be using.
LockbackpatternCustom_zps95cb2273.jpeg
I surface ground 2 pieces of CPM 154 CM and I'll glue the patterns on.








The book recommends 90 degrees at the front of the notch and an 8 degree slope at the back. The author tilts the head of his milling machine but because I don't have an easy way to dial the head on my mill back to vertical, I devised another method. By the way, exactly 8 degrees isn't critical, I've seen another tutorial that, IIRC, recommends 2 degrees.
I made a bar that's 1/16" thick and 8 degrees to set the angle of the workpiece. This would work nicely for mini-mills where you can't angle the head.



First step is to clamp it in the vise and cut the front of the notch 90 degrees.


Then I reset it with the 8 degree bar and cut the back of the notch.



To be continued...........
 

K R Johnson

Well-Known Member
#5
OK... I left off with the notch cut with the milling machine. This morning I used a 600 grit diamond file to polish all three surfaces to prepare it for matching with the lock bar. After making sure the end of the lock bar was square with the back I compared the bar with the notch to see how much material I had to remove.



The pattern was true so I set the lock bar on the 8 degree bar and clamped it in the vise.


I carefully removed material until the notch would just start to fit over the lock bar. As you can see it fits well enough that it hangs by itself.


I always cut the lock notch and bar first because this is the most critical part of making a lockback. If the angles aren't exact, the lock will be sloppy and unacceptable. Here you can see the bar doesn't fit far enough down in the notch but I'll leave that until after heat treatment. The only surface left to polish is the 8 degree angle on the lockbar.


Next I saw a kerf from the end of the bar to a 1/16" hole to form the spring, drill the pivot hole with a # 14 bit and ream it to 3/16" for a bushing. All the surfaces are sanded remove saw marks prior to heat treating.


The blade's been profiled, the pivot hole also drilled and reamed to 3/16". Notice I left extra material on top of the blade and lock bar if needed for profiling. There's also extra material behind the kick to allow adjustment as the knife comes together later. I've also bent the spring. It's too thick now but I'll be grinding it thinner to adjust the spring tension as I assemble the knife.



All for tonight. Got questions?
 
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K R Johnson

Well-Known Member
#9
The only surface left to finish is the cam end of the tang so I did that this morning. I drilled a hole in the work table on my flat platen and pinned the blade and a temporary bushing to the table. I adjusted the table to grind the tang round and ended up at 800 grit.



I needed to drop the latch further into the notch so with a well worn 400 grit belt I slowly took a little off at a time, checking often to be sure I maintained the correct angles. After heat treating I'll have to polish all the surfaces but shouldn't take off enough material to make any difference. If it does there's still room to take a little off the bottom of the latch and not drop the lock bar too far.



I have to cut a long nail pull into the blade before it's heat treated so I drew some lines to help with setup in the mill.


The blade is clamped in the vise using a lathe cutter to level it.


This is a 5/16" dia. Dremel HSS cutter in a collet.


Using lots of cutting oil I set the stops on the mill table and cut the groove .040" deep in two passes.



Using another bushing in the lock bar I located and center punched for the holes for the lock bar pivot. I painted on some layout marking fluid and marked off the area where I want to relieve the liners to prevent rub marks on the blade. I usually relieve the liners about .007".


I have another smaller milling machine set up with a 4" rotary table to do the mill relieving. Tony Bose has a great tutorial on his website on how he does this.....http://boseknives.com/liner-milling/



The lock bar pivot hole is drilled and in the second picture you can see that there's plenty of material to take off the kick and the end of the tang later to make adjustments.



The lock bar and blade are in foil envelopes awaiting heat treating. Have a good weekend!
 

K R Johnson

Well-Known Member
#13
what RC are you going for on the spring?
I'll heat both the blade and spring to 1925F and plate quench. I'll then draw the blade two hours two times at 385F and the spring two hours two times at 1100. The spring will be @ 43 RC.

From Crucible's specs: Note: As with all martensitic stainless steels, tempering at
800-1100°F (425-600°C) will result in sensitization which
causes a minor reduction in both corrosion resistance and
toughness. We recommend that this tempering range be
avoided.
 

BossDog

KnifeDogs.com & USAknifemaker.com Owner
#16
Great Tutorial. I think my very first attempt at knife making was a lock back. I really liked Ron Lakes designs and wanted to make one. I still do as I never got that first one done. I will have a lot better luck after studying Keith's tutorial here..
 

K R Johnson

Well-Known Member
#18
I missed some shop time but I'm back. The next thing that needs doing is to clean up the holes in the blade and spring with a barrel lap and some 600 grit lapping compound.



I turn and bore my own bushings from bronze bearing rod from McMaster-Carr. and part them off a little longer than needed.


Next I lap the end of the bushing on 1500 grit paper until it's 3/4 of a thousandth longer than the thickness of the blade (or lock bar). BossDog has pivot laps available too: http://usaknifemaker.com/tools-hand-power-c-96/hand-tools-c-96-28/pivot-lap-basic-knifedogs-3-bushing-model.html
Here again, Tony Bose has a very good tutorial on his website. http://boseknives.com/pvtbushing/


Since the hole might not be exactly in the center of the bushing, an indexing mark is scribed on both the bushing and the blade. This helps keep the bushing in the same position during fitting and final assembly.


With the bushings installed, the knife can be assembled. I had previously scribed a line for the top bolsters so here I've drawn a line for the bottom bolsters.


This is a bar of aluminum with a milled slot so I can clamp it on the frame to scribe corresponding lines on each side.


The spring, blade and frame have all been ground flush.


And I carefully ground off the kick and the 'corner' of the tang so the lock bar will be flush when closed.


Next up: Milling the frame.
 
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