Timed threads

[82nd airborne]

Im not the most experienced machinist. I was pondering building an FAL somewhat from scrap, mainly for the challenge. I found the challenge is that the barrels have timed threads. I have acces to cnc equipment but I want to do it on manual machines, mainly because, well I'm a retard. I know it can be done because FAL's have been made long before the adnvent of CNC/CAM. For the life of me I cannot figure this one out. Anyone know how its done?
Aaron

[yarro]

1) Drill that hole first and thread it, screw barrel in and remove material until it hand times to 10:30. At that point do all the other work on the receiver.

2) They used a fixture on the lathe to position the receiver so that the cutter anyways enters at the same spot when the carriage is engaged at the same spot on the lead screw.

3) Build an inch FAL and use a breaching washer like all inches do.

4) Build a threaded fixture that goes on the front on the receiver that the tap threads into first before cutting the threads in the receiver so they start at the right place.

-yarro

[82nd airborne]

Thanks Yarro, not near as complex as I had conjured up in my mind. Sounds like youve built a few before...

[yarro]

I helped a friend, now gone, who was much better a machinist than me (since he actually did it for a living) build a project that required 4 threaded holes on a face that had to be timed the same. He went with a tapped fixture that could be positioned over each hole and the tap run into it first so the threads all started in the same place. On another he drilled the critical hole first, tapped it, screwed in the other part to see how much had to come off and just removed material until it timed right, he then used that face and the center of the hole as 0,0 for all the other work on the piece. He of course explained how he used to do it back when you had to walk to the machineshop up hills both ways. Wish I could have spent more time with him. I have built a couple of FALs as well, but from DSA receivers.

-yarro

[82nd airborne]

I'll probably asking you more questions then, as i have never built one, yet. Ive got a few old timer machinists that i hang around, I never stop learning from them.

[randyrat]

Seems to me , you have to figure in 200 ft lbs of torque also when timing your barrel. That's the number that sticks in mind at least.
Don't forget to put the hand guard ring on before you crew the barrel on also.

[JIMinPHX]

I had to time the threads on some parts that I made for a piece of medical equipment about 10 years ago. The Fanuc 6T controller on the CNC lathe I was running was supposed to be capable of doing that, but I never got it to work reliably. So instead I made an indexable taping fixture & threaded the parts by hand.

If you are going to single point the threads on a manual lathe, then you can control your start point by running your compound parallel to your Z-axis & just make up the offset on the compound. If your threads are 16tpi or finer, you probably will not need to do the 29.5 degree trick. That should set you up with everything that you need except a way to measure where you need the thread to start. That might get a bit more complicated.

Good luck with that. It's going to be a touchy proposition.