Two-Stage Trigger Remake

After months of keeping the finished two-stage trigger mechanism on my work desk as a fidget toy.... I broke it. It's not as scientific, nor as gimmicky, as how Ikea showed you how they tested their POÄNG chairs in store. But I figured, if I can't even pass this simple durability test, forget scientific methods.

It... still works... it's just that the 2nd stage force is no longer as strong as new. It's still very distinct, but, I can feel that it's breaking slowly.

So, now I have two choices, assuming the main design does not change.

1. Go Hard
2. Go Flexible.

This merits a bit of explanation.

The original Otto two-stage trigger uses plastic, mostly plastics of various kinds... I am NOT sorry to break all your all-metal mythologies... My guess is that they are made of Delrin, aka Acetal. Delrin is a very slick substance, not as slick as Teflon, but very close. But... it's very hard, as far as plastic can. It's almost as hard as aluminum. So, you can easily machine it, provided proper heat dissipation is provided, like flood coolant. Yet... it's still far more flexible than aluminum, where aluminum would deform permanently, very often Delrin would bounce back like nothing happened, within limit. This is what I think what the original Otto Delrin parts rely on. Teflon, on the other hand, is a very annoying material to machine. It flexes... that is.... it moves away when you try to cut it with an end mill or something, and it bounces back when the cutter is gone... leaving you with an inaccurate cut. So, machining Teflon is a specialty, if you want accuracy. My PTFE ring for Warthog, for example, first I had to hand cut it (difficult and dangerous trying to hold down the slickest substance known to man to cut it with a very sharp eXacto knife). Then I tried to buy one side bondable Teflon and epoxy glued it to a piece of aluminum for milling. Then I tried screwing it to a mandrel, and then spin it fast, and use centrifugal force to spin and flatten it for cutting.... then to laser cut... with different thickness of Teflon sheets! All because this thing is very annoying to machine. That's what the "first" guy have to pay for R&D costs!

The original Delrin made parts have two characteristics.

• They are slick, so very little wear.
• The dome of the plug is very thin (probably 0.5mm), so it's flexible. It will deform when pressed by the neck of the piston, increasing the contact area, thus reducing pressure, thus reducing wear.

But.... they are injection molded, I guess.... I guess I could machine Delrin to the exact sizes... but I decided not to for the reason that I don't want to "blindly copy" exactly what Otto did... the joy in designing and prototyping your own stuff is that you understand the problems, and solve the problems. Note that... a design is not just the arrangement of the parts and the drawings... a design also includes the materials, and manufacturing process. That Otto piston and plug arrangement is not novel, it's a well known mechanism. But Otto applied and solved the "design problems" by using injection molded Delrin parts. I am doing my own different solutions in solving the same problem instead of blindly copying Otto's.

Going hard.... well, if they wear... you could increase the material hardness to retard the wear. No, I am not going tungsten carbide hard. That's crazy. And most likely unnecessary. Not to mention expensive. I don't need to escalate it that much yet. So, the next best I can still "easily" drill and cut the material (relatively speaking) is tool steels. I selected O1 tool steel, for no other reason than it's one of the commonly used general purpose tool steel, and the first one popped into my head,. And...... it's a mistake. I should have gone with W1 tool steel, because burnt oil stank up my whole house, when I quenched them! I mean, just look at the size of these two parts... how much burnt oil could there be... no matter, it stank up my whole house for hours. Avoid that if you could, particularly in winter.

So, as you can see in the picture below. The piston head (the bright silver color portion) is made of O1 tool steel, and the stem and tail ring are made of brass. The head and stem are brazed together, and then quenched right after the brazing (convenient, just keep heating it after brazing until red hot, and then dunk it in a can of oil). After cooling, the tail ring is brazed on with a positioning jig. The black plug in the picture is oiled quenched without post processing. I will probably best get rid of the burnt oil film.... 

Assuming I hardened them correctly, I don't think I stand a very good chancing in wearing them down. The plastic part holding them will most likely wear down before these. But, the plastic parts are 3D printed... I can always print more.

I will tell you in a few months! ;-)