Right place? Automatic and inner workings


Well-Known Member
I now have 3 automatics. They are all cheap (cost wise) but I am focusing on just one for this.

First of all, correct me if I get the terminology off since I have yet to find good documentation on the inner workings and most forums I have perused tend more towards the collecting and using rather than the repair and building of them.

The one I have is pretty small 2" blade 3" OAL closed. It is a swing or out the side opener. It operates on a button press, which is also the action for locking so the button must be depressed for the blade to close. There is a rotational safety that prevents the button from being pressed by interfering with it. The mechanism of this knife is controlled by a torsion spring with what appears to be pretty standard bends in it, one vertical to go into a hole in the blade, and one horizontal to be captured underneath the bolster.
There is an actual spring cage made from either paper micarta, or delrin or some other non-metal. This cage reduces a hole in the liners from .433 down to .354, and provides a surface for the blade to ride on, on the side that has the hole for the spring leg.
In looking for springs I find that there are 3 standard sizes that most places carry one or more of. Some even carry a type of hole saw specific to cutting the race that this spring fits inside of. It also appears that unlike mine some of them have the race, now only in the liner/bolster/scale area but also in the tang of the blade. And some of these suppliers also tend to supply thrust bearings, though I am not sure if they are intended to go spring side or opposite side of the blade.

So, I seem to understand how this particular knife works. And, if I wanted to, I think I can duplicate it. Unfortunately, it uses a smaller than normal torsion spring that doesn't match any of the ones the suppliers are carrying. I am going to try 2 things, 1 winding my own spring from music wire, and 2 ordering one from MSC and modifying it to the traditional shape. The existing spring works but is rusty and I don't know how much life it has left, so I want to replace it. I think I will be able to reassemble this knife and get it functional without much question.

The question comes with making one of this design. I understand how the FB style with the picklock, and rotating bolster work, as well as the general OTF styles. But this style using the torsion spring leaves me with a few questions. Most of them are relative positioning of the spring body to the blade vs liner. This particular one with the "cage" could essentially be duplicated with a shouldered flange bushing. I assume the idea is that the leg that engages the blade is all that would protrude from the bushing and the blade wouldn't contact the rest of the body of the spring. However, I assume there are designs where the spring is not caged at all, and at least the top coil is housed inside the tang of the blade, and possibly some other design where the whole of the spring is below the liner, with just the leg that engages the blade sticking up enough to catch the hole in the blade.

I don't really want to answer my own questions with guesses that may be right or wrong for someone to choose :) Though perhaps it will make clear what my current thought process is and how I might be misunderstanding the basics of the design. Is there a good document on this type of design, or perhaps a library of photos that might make it more clear?