Critical Tolerances for Lockback Knives

[NeoClassic]

Regarding “…“true flat” (Precision Ground)…”
There is more engineering than art in making folders, and in engineering there is something known as GD&T for Geometric Dimensioning & Tolerancing. Within which there is Flatness, Parallelism, and Perpendicularity which are all key to having a folder work. Separately there is Surface Finish.
Flat is the first side of your blade or spacer. You can do a reasonable job with a disc sander, followed by abrasive paper glued to a granite slab, or thick float glass.
Parallel is what you need the opposite side to be.
When you make your hole, you want it to be perpendicular (square) to the surface.

I screwed up the frame lock replacement blade, after having the RWL34 blank all profiled, heat treated and surface ground like it was 600 grit, by not triple checking that the mill spindle at work was dead square to the surface against which the blade sat for drilling and reaming.

One can buy “precision ground” flat stock that looks like it was sanded at 60 grit. It might be flat, but it isn’t smooth enough for a surface that will see friction, like from washers around a blade pivot. Also, things move when heat treated, so flattening needs to be checked, tuned or redone post HT. good news is, you don’t need a big area flat. Bad news is that small areas are harder to keep stable for hand flattening.

Understood. I appreciate the explanation.

 

[ea42]

I think it does and thanks very much for this. Under this premise, is it safe to assume also that the "hook" -- for lack of a more technical term -- on the blade tang that the lock bar "grabs" also should have some clearance between it and the lock bar?

Yes you don't want that to act as a stop before the lockbar is seated completely.

Eric