1911 Thread-in Barrel Bushings, Take 2

rdtcu

Finally got some pictures up of the finished product. The bushing i machined from 1-1/4" 304 stainless roundstock, with 25/32"x32 threads. I centered the barrel bore in the slide, as there are no sights to adjust to correct any misalignment. Finish is Duracoat, with their AM Stripe package with OD and Matte Black. Sprayed with airbrush at home shop. This thing has parts from Alaska, Florida, Washington, New York and several other places, I was new to building 1911's after all...
Got about 400 rounds through it now without so much as a hiccup, after some ejector tuning prevented the cases from hitting me in the glasses every round. All the stainless parts were matted with a soda blaster.

http://s241.photobucket.com/albums/ff206/devtucker/

iceracerx

Joe, not much (if anything) is gained by engaging more threads then the "Minimal" thread engagement. This information was been figured out years ago and can be found in any Machinists Handbook.

Standard "Minimum" thread engagements are:

1.0 - 1.5 x the diameter for steel

1.6 - 2.0 x the dia. for alloy (aluminum)

EDIT: PS, internal threads (the slide) have to be deeper (longer) then the corresponding external threads (bushing) to assure clean threads to the proper minimum depth if using a TAP.

rdtcu

Givette, yes the extractor and mag release are "stainless." I know a stainless extractor is not always the best option, but if it's properly profiled (by hand usually) then it should last a long while. And as iceracerx said, the threads in the slide are tapered near the bottom as any tapped threads. Also the treads on the bushing can't be cut all the way to face of the bushing, since it was done with a lathe, and must be fed TOWARDS the face if i want righthand threads, and the brake will not stop it instantly. For this and other reasons, i needed a thread relief at the base. If you can find a safari arms bushing, it has even less threads on the bushing, and the bushing is shorter.
If you have any more questions i will be happy to answer. I also made a custom delrin bushing wrench as well, since it has to be threaded completely out before the spring can be removed

givette

Rdtcu: givette here, again. Thanks. Always willing to learn.

...didn't know about the tapered thread. That's straight taper, like the threads on an oil pressure fitting on an engine, right?

...and no, I didn't understand that the number of threads on the bushing was a direct result of limitations in the manufacturing equipment. Now I get it.

EDIT: rdtcu..thanks for setting me straight on the taper. Joe

rdtcu

When i say tapered threads, the threads are straight to a depth, and then taper in near the bottom, since this is how a tap works. It is tapered on the end to allow the cutting surfaces to remove metal a little at a time instead of in a single pass or turn, which would be very difficult. Also, the threads i cut were cut in 6 passes with a self-ground carbide cutter. Stainless will gaul or deform badly if you try to take too much at once.

PS, it took longer to grind the carbide insert than to cut the threads...