Design Help (barrel mounting)
Hi All.
For the past few months I’ve been working on a lower pressure (co2) air rifle repeater and had a few questions regarding final design (its the first project on my new CNC mill!) 😎 . I have the whole thing modeled in Solid Works 2010 and the design is very sound. I have started to machine the reciever and before I can go any further I need to know how I am going to attach the barrel to it.
The reciever is 6061 AL and the barrel is some kind of chineese steel lol(.560″ OD). In SW I just use a very fine thread that extends 1.25″ in length. I figured I would use the red locktite and call it a day. Is this method OK? How are most airguns steel barrels anchored to AL recievers?
All Replies
Viewing 7 replies - 1 through 7 (of 7 total)
1.25″ is indeed excessive. If you want the best alignment when threading make sure you use a very close fitting shoulder instead of threads for the final 3/8″ or so. Think of it as a shoulder bolt. I wouldn’t trust the threads screwing into the receiver to align it unless you have a big flat diameter like on a powderburner (with a recoil lug).
Finer threads have more tensile strength than coarser threads but you really don’t need that kind of strength here. You need it to be aligned and not unscrew. Hence the need for an alignment shoulder of some kind.
Honestly, I think threading is unnecessary, but it’s up to you. Get the Green Loctite shaft retaining compound, a good fit, and you are good to go.
Jim[/u]
As a rough guide, the thread length of a steel barrel/rod/bar should be equal to the full diameter of the thread if going into steel, if going into aluminium it should be one and a half times the full thread diameter. Any more adds piece of mind but shouldn’t be necessary.
TB, most of the chinese guns just use an interference press fit, followed up with a set screw to prevent walking but those are in steel receivers. In Al I’d probably thread it. No o ring should be necessary in a tight class 2 fitting, of course you probably know barrel fit usually calls for class 3 fit. Don’t use too fine a thread as the Al isn’t very strong. I’d be looking at using at least 24tpi or coarser. You didn’t mention the id of the barrel so no idea how much meat you have to the bore, which might dictate going finer on the thread pitch. Over an inch inward sounds excessive. I would have said 5/8″ or so would be just fine. (headspacing a barrel into a powderburner receiver does not give you much options sometimes; the airguns I’ve done are usually around that length).
walt
Thanks for the help guys. I am just looking for a sound way of mechanically mounting the barrel to the reciever. The barrel extends into the reciever a bit and the bolt has the seals so I am not worried about sealing just a rigid mount that the steel and AL will like playing together with.
if you have 3/8 or 1/2” of thread it would be good (not needed ) , an then a snug fit the rest of the barrel in the breech with out thread , then a set skrew above the air port from the valve. presses the barrel a bit tighter an seals the air .
could put a oring on either side of the air hole in the barrel an just use the threads to hold the barrels in .
I’ve only made a handful of Crosman type breeches, but in my (admittedly limited) experience, a close tolerance fit and a couple allen head set screws is an entirely adequate setup.
Viewing 7 replies - 1 through 7 (of 7 total)
- You must be logged in to reply to this topic.
As Marmot_Militia says above, the shoulder is the important locating part and should be machined exactly square with the rifled bore, just as in the case for threading a barrel to accept a mod.