GTA
General Discussion To Gateway To Airguns => The Shop => : daved January 09, 2007, 05:11:16 PM
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I've come to the conclusion that the Gamo CFX has a major flaw in the design of the rotary breech. For those not familiar with it, it's a steel cylinder that sits ahead of the piston, and forms the front of the compression chamber. The transfer port is drilled through it, and there's a cut out for loading. The breech to barrel seal is in the front of it, and there's a rather small o-ring that goes around the back of it to seal the compression chamber. That o-ring needs to be soft enough to a) allow the rotary to be installed and b) to allow it to rotate for loading. I think that means it's soft enough to allow some blowby, thus reducing velocity and power.
So here's the challenge. Come up with a way to improve the seal, while still being able to rotate it for loading. The goal is to come up with either a DIY kit, or a mod that could be incorporated into a professional tune. So who's up for it? I already have a couple of ideas, but no machineing experience or equipment (YET!). If you want to hear my ideas, let me know. I DO want to hear YOURS! Later.
Dave
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Sorry, guys, I couldn't resist :-)! I thought there were enough CFX shooters that this would have generated at least a couple of ideas. So lets try this one on for size.
This has been on my mind the last couple of days, but I could use some more educated info. Why couldn't the back of the rotary (or a replacement) be milled for a second piston seal mounted face to face with the regular one? By it's design, a piston or parachute type seal expands under pressure. We alread know they rotate in normal use, so this should allow the rotary motion needed. They're also much tougher than any dinky little o-ring, and should give quite a bit more sealing area. Actually, a new rotary would need to be made, the transfer port would need to be angled for the piston seal mod to work. So what do you think, guys? Is this a viable idea, or am I totally out to lunch? Looking forward to some input here, as long as it's NOT hysterical laughter :-)!
Dave
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...I wish I owned a CFX so I could help out, certainly would love to give this one a shot. All I can think of is to put a nice piece of duct tape over the breach, maybe some bubble gum, silly putty? Sounds like a nice gun with one serious flaw, wish I could help more:(
Is it under Gamo warranty still? Maybe get them to swap ya for another S1K or two?
Dan
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Was once thinking along those lines myself for awhile but because of the initial close tolerances, there would not be enough room for a parachute seal to perform as it is designed without some serious cutting or modifying of the rotary. Most parachute seals are used with an open exposed face. A lip seal might be a better approach as it would not need the depth or width of a parachute seal with perhaps the o-ring behind it as a backup maybe. The only CFX that I have is a Royal and I sure don't want to tear that up for experimentation...lol...
Another thought that I had was a disk, perhaps brass, milled for a larger heavier o-ring made of urethane seated in the bottom behind and against the rotary. There is plenty of room for it but would reduce the volume a wee bit and though it may have a tendency to want to rotate a bit it shouldn't hurt it. The only question was the imapct against the rotary.
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I disagree wiff all of ya..... hehe I like my CFX's da way they are, so until ya all find something better I am stayin with whats I gots... :)
Gene
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Dano, if you read this, I'm ignoring you with dignity. S1K's indeed! :-)
Hi, Bob, glad you jumped in here. As I thought more about it, I realized that a new rotary would have to be made. Not only longer, but the transfer port needs to be re-routed. I thought of a lip seal also, but how do you spec such a thing? Are there standard sizes that could be used, or would it end up being a custom order? One of my first thoughts was a disk with a larger o-ring, although I was thinking plastic rather than brass. But a disk would actually need to be more like a washer, gotta clear that transfer port. Plus, what happens if it gets cocked in the bore, could get ugly fast.
So here's what happens when you send a wood worker to do a machinists job :-)! At least for testing, I'm going to turn a new rotary out of wood. The wood I'm going to use is called Ipe, it's incredibly dense and hard, very stable, and has a very straight, fine grain. Back in the days of steam ships, this stuff was used as bearing blocks for propeller shafts, among other things. And no, it doesn't float. I intend to make it enough longer that it can utilize a standard piston seal, but for the first iteration, no o-ring. Actually, making 6 or 8 will be about the same amount of work as 1, so I may play around with several things while I'm at it. The front breech seal is going to be the biggest problem, too bad it's not on the barrel. So when I come up with the perfect design, then I'll get one of you machinist types to make me one out of metal. That's if I decide I need it, that Ipe is really tough stuff! Later.
Dave