F-16 (and other modern jets) Two-stage Trigger

After weeks of struggling with the two stage trigger mechanism, I finally got it working!

This is a difficult one. The difficulty lies in making it work consistently with durability. The former is made even more difficult by my desire of using all 3D printed parts, and eventually, I had to use some metal parts made with a mini-lathe. I imagine that you could use drill press with a good file to make this stuff, but it would require a lot of skills and patience. If you had that skill, you most likely has a lathe anyway.

The one stage is easy. It's just the tolerance and nozzle diameter need to be considered and tested. And if you are willing to pay through the nose, you can buy springs at highly marked up prices for small quantity at Lee Springs online. It's not that I have a problem with high markup prices Lee's charges. It's a common practice to charge more for small quantity, as selling a small quantity order costs pretty much the same as a large quantity order, yet it costs way more for stocking costs. I mean, as a retailer, you must order minimum quantity from the manufacturer, say 5,000 of an item. But, for people who buy 1 or 2, how many of such orders do you have to sell to use up all the 5,000? The longer it takes to sell all that, the more capital costs it is for you to be locked up in that 5,000. Plus... you might not sell all 5,000, Then, you have write off costs. So, I have no problem with that practice, but I have a bit of a problem for about USD $10 a pop for the springs... and I need two right in there. That's USD $20. Sure, compared with the OTTO costing $150+ a pop... it's nothing. But can I make the springs myself and save some money? I mean, costing pennies, as it "should" be?

The answer is yes. I have a mini-lathe. I can use it to easily make springs from piano wires. But I wanted to see if it's possible to design some 3D printed parts to make a hand-cranked spring makers. That was a flop.... I failed. So, I quickly went to the mini-lathe and make some springs.

Note: First stage registers about 30 Nf. And 2nd Stage about 49 Nf.

In the first picture, that's my setup for making the spring. It's just simply an OD=2mm steel rod used as a mandrel, the lathe is set up for 1mm pitch. The holder and free center on the two ends are made of OD=1/4" aluminum rods (simple, just drill a 2mm hole, and scroll saw a slit, and drill/tap a 3mm screw hole). The wire "feeding" mechanism is simply a 22/24 gauge wire wrapping tool I have on hand.

Now... I need another spring (not shown) for the two-stage locking pin, for the lack of better terms. This is the pin inside that locks the main piston (the brass one you see in the video above) in, preventing it from getting out of the slot, and it creates the 2nd stage increases of force to be overcome. That's the mechanism that you feel the extra opposing force to get over the 2nd stage. The original OTTO used a smaller spring than the one used for the piston (shown above, the one on the bottom). That will require me to use an OD=1mm mandrel... That.... is tough. So, I decided that this "locking pin" should use the same diameter spring exactly as the main piston spring. Thus I had to modify the design to accommodate this change. That costs some more days.

Now, the 3D printed piston and locking pins... worked.... for about two clicks. Then the ABS-GF got smushed and deformed. Ok... I need harder plastic. POM, or Acetel... is probably what the OTTO used. Bought some POM 3D filament... wait for the shipment. And... then I found out why POM is so rarely used in 3D printing ---- it's freakishly difficult to print! ABS and Nylon are child's play compared to POM.

Fine... go aluminum then. Order some aluminum rods and wait.... hold on... supposedly I only need aluminum for making the locking pin, because that's the part that got smushed. Ok... I made a tiny locking pin out of aluminum. It doesn't get smushed now. Now the damned piston gets smushed! Figures.

Fine.... go aluminum for the piston too! Order... wait... why not brass? Order both aluminum and brass rods. Wait for the shipment.

Now, make a brass piston first, as I already have a aluminum locking pin made. Guess what? The aluminum locking pin got "cut" by the brass piston, after about 5 clicks!

Fine... make a brass locking pin then? It works!

Now I have to test the durability, and figure out the mechanism for light gates for the optical sensor, and integrate it in the whole thing, and the wiring.