Shrink fit frame-valve collar
Well, my collar in the back of the frame has always been a tad loose and the grubscrew holding dimple has become elongated
So….
Im planning on making a stainless steel threaded bushing with much better tolerances and will be fully threaded so that the bottle is held by much more threads than the normal 1.5 turns of the original.
One thing though, Ideally, I would want to shrink fit the bushing in place, but I don’t want to start waving the blowtorch around the frame so I was wondering if sticking the bushing in the freezer would shrink it enough to be a slight press fit in the frame, but at normal temperatures it would return to size and be a tight fit, and then still use the grubscrew for added security.
If this is not possible, what are the tolerances for a goor press fit, I don’t fancy using a large press on the frame and would go for the “Lump of wood and a good hammer” method?
Thanks
Dave
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I did drill a over sized hole from the scope rail down for half, then an extra thread for a screw from the top.
2 screws keeps it , okay 3 is better at an angle of 120 degree. 😉
A good press fit would be .0004 – .0007 larger for the bushing. Let the frame warm in the sun and freeze the bushing right after machining. As long as the frame has no scratches or nicks on the receiving surface it should tap in easily. You need to tap carefully in 12:00, 3:00, 6:00, 9:00 manner either clockwise or counter to keep the bushing straight, otherwise it’ll cant and dig in one side.
Dave I should have looked before my post, anyway I see now where threads can be added to this collar internally and that can only be better! Also your question on freezing this collar, being it is on the thin side I am going to guess you can get two thousands shrink fit on this and if you can do a test piece on adding a bit of heat might work out well. If you can get this threaded insert to shrink a couple thousands that would be all you would need. I just took a look at mine and it is a good idea, just don’t know about getting it out heat gun maybe and make a small threaded peice you can thread into the new insert with like a small version of a bearing puller slide hammer? to remove it if neccesary? Lots of ways to get where you are going and a great idea to me it is a weak point.
Great Thread and reply. Very interestng as its a very week part of the Rifle design, It would be nice to see where this goes. Good look Davee. Keep us up-dated on your progress and results. This will benefit everyone.
Be Lucky.
D
🙂 🙂 😉
Dave when I worked as a mahcinist for 35 years we used to do that when we repaired many clylinder ends these were out of printing presses bored the ends to a size made a sleave and did what you are talking about, but this included heating process. I don’t think it would hurt to try what you are trying to do, freezing your threaded insert, If I recall the most I ever got out of freezing a part is a thousands and a half, If you were size on size for your fits that might work good, but you might experiment with a couple pieces 😆 the Aluminum frame of an Airforce rifle might not take much heat to expand it a bit either, so what you want to accomplish might work with some heat. if you have a piece of aluminum that you could bore out and mike then mike it quickly after heating it to see how much it will expand might give you an idea of how much heat you need. Not sure but a heat gun of high temp might work for you or a torch and just stay your distance! A trial of a scrape piece would be what I would try see where you are at with what you are trying to do. Keep us informed of what you come up with it is a great idea it is a weak point in the gun with the tank not much support in that area!
Loctite is another option but what to use? and could end up very permanet! and then again heat could be used there to get it out if needed but pulling it out of the frame 🙄 Also you said you would be making it with more threads would you be putting those threads inside the frame more or outside going outside would affect where the top hat ends up?
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Thanks guys, After I have used my gun for a bit (Only just got it upand running) I will try this
I plan on using a hair dryer on the frame and stick the bushing in the freezer covered in ice.
Thanks for all the info and will tell you how it goes.
Dave