I have been in the early to mid stages of designing and making my first set of cannons. One feature that I would like to include is a removeable accumulator, so I could avoid needing to remake the ball valve assembly if I need to resize the accumulator, reconfigure the accumulator, or service the ball valve. It seems it would be advantageous to be able to unscrew the accumulator, and thread another back on. What I'm getting at is if the I.D. of 1" PVC were threaded, would the threads be strong enough to keep it from blowing apart??? Anyone have any experience with something like this??
Removable PVC accumulators usually have an insert in them, which is what carries the thread, as well as the sealing surface for an o-ring. Threading the PVC accumulator body itself is not practical, as the sidewall of the tube is too thin.
I would recommend a switch to aluminum then. It can hold threads nicely with a relatively thin wall. I have some big gun style torps that are built that way. I didn't construct them, but I couldn't pass them up when they came available. The valve body can still be some form of plastic. The biggest thing is an o-ring seal. The accumulator tube compresses an o-ring that is at the base of the threads on the valve body. Mike Butts MN2 USN
There can be issues with CO2, water and aluminium, primarily corrosion on machined surfaces, like threads. Not good. Brass, while more expensive, is stronger and less prone to corrosion. If you do use metal accumulators, fit a safety pressure relief in your system. Metal will hold a far higher and more dangerous amount of pressure before failing than PVC will.
True, my torps are probably going to use compressed air (single shot setup). In addition I tend to regularly oil my air systems. Many battlers don't do this to the detriment of... everything that passes co2 through it and is exposed to water. Mike Butts
Doh!!!! I didn't know there was an increased corrosion issue with aluminum when exposed to the co2 and water...... uuuggghhh!!!! I've already made a few cannon parts out of it, and some of the clearances are pretty tight. Particularly between the manifold and the sleeve it rotates on....... Hummmm... I wonder if anodizing would help, and if so, where to get short runs of it done cost effectively...... As far as accumulators go.... maybe copper would be a better option????? I could turn a threaded brass "coupler" to solder on the ball valve end of a piece of 1" copper pipe, and have that thread onto the ball valve housing possibly. I just have to watch that the brass doesn't contact the aluminum parts anywhere, due to that whole galvonic reaction/ corrosion thing....... The copper would have a shorter cross section, it would fit into my crusier better......... Any Thoughts????
Anodizing AL is pretty easy to do at home if you dont mind dealing with strong acids, stong bases, and electricity. Tip - Do it somewhere with lots of ventilation... I doubt the corriosion you'll see in our use will be significant or fast enough to be much of an issue, especially if you take care of your toys and clean then when you're done using them. I'd just go with copper.
Now that you mention it, I remmber reading an article years ago on anodizing at home. And yes, I seem to remember that a by product of the process is hydrogen gas, so outdoors would be the best place to do it I think I'll look into that some more, might be fun to try...... only problem is that I have currently made about 85 pieces from aluminum, with another 20 ish to go (enough for 20 cannons)...... It would probably take me 15 years to get them all anodized at home!!!! I guess I could do just the ones I NEED as i need them.... Back to accumulators...... I remember posting a link on a how to on copper accumulatores for someone a few years back, but when I searched out the post, the link no longer works..... anyone know where one is???? I'll keep searching...... and on a little down note, I hunted down a piece of 1" copper to get some measurements..... uuugghhh..... it weighs about three times as much as the pvc...... but does take up much less space.... so many options!!!!!!!
There's also the handy fact that PVC's failure mode under pressure is _shattering_ Not the best choice, I think.
Anodizing doesn't take that long...you can do it in batches if you have a beefy enough power supply. If you're going to go with plastic accumulators use ABS, like Tugboat says PVC doesnt fail nicely, ABS fails without fragging.
Just as a reference, up in my neck of the woods, so long as all the aluminum parts are the same alloy, it was between 80-100$ per lot of parts. with that said a lot can be dozens and dozens if they are not too troublesome to set up... -Greg
Wow, I'll have to look into the anodizing around here...... that would be awesome if I could get it done for that price!! Seems like my work is paying a few dollars a piece for anodizing, but their parts are a bit bigger. As long as it doesn't add too much thickness to the parts...... I only left .0015" clearance between the manifold and rotation sleeve it rotates on, wasn't planning for anodizing at the time. Thanks to everyone who has provided information, that's one of the things I like most about this hobby, everyone is always willing to help
Just spec the thickness... what I had done was Type 2 Class 3 hard anodize black per the milspec that I forgot the name of. came out to .005 inches of surface growth out. a regular anodize rather than a hard anodize will be much much thinner, and you can get acceptable corrosion resistance at less than a thou of growth. the last lot I had done a few years back was two parts that were ~8 inches x 4 inches X 1 inch, a couple of tiny parts and a 4 inch cube, roughly
Thanks Greg. I've been checking out the standard anodizing, and it seems that the typical thicknesses range from .0002" up to around .0015", with half of the thickness going into the part, and half out. Based on that, if I could keep the thickness closer to the lower end, once I anodize the aluminum rotation bushing and the manifold, I *might * still have enough clearance for it to still rotate. I only left a thou and a half clearance........ it's times like these that I ask myself why I always design things so tight!? Unfortunately, anodizers aren't always known for accurately holding thickness tolerances, unless the parts are mil spec'd and going to the military or another customer that can actually verify that thickness...... we get parts at work back from anodizing fairly regularly that seem to have "overgrown" compared to what we spec.... problem is, we don't really have an easy way to prove it..... and the parts usually work anyhow so it's not worth pursuing........ hummmm to anodize, or not to anodize.......
Definately worth a try. One other thing you can do (although I am hesitant to admit to doing this) is to ream the anodize layer, not thru but in. dulls cutting bits something fierce but it does work. do you have a diagram of your cannons? I'd be interested in seeing them.
Yes, I've drilled and machined a lot of anodized aluminum, and it is really nasty on HSS tools. The hard coated aluminum throws sparks when you mill it fast enough and will eat up carbide cutters!! Good point though, I could ream the hole if it got too small, and still leave just a little anodizing on it I do have what is basically a CAD section view that I can try to post, I'll have to figure out how to get AutoCad to output a bitmap again, and then re-read your post on how to effictively post photos for easier viewing, I can post a couple shots of the parts I have currently made (rotation sleeve, manifold, and magazines). Of course, after making some of these parts, I see numerous reasons I'll probably have to remake them for design flaws that become more obvious after I have a physical part in my hand I'll try to get the pics together, and I'll post in a new thread, since this one isn't really applying to threaded accumulators anymore
Greg and others, I have started another thread called cannon design/ construction in the weapons section. Here is a link: http://www.rcnavalcombat.com/Forum/...fault.aspx
I've been continuing a little research here and there on this subject since I have begun work on a small destroyer. Of course light weight is a necessity, so I'm inclined to look at machinable plastics and composites. I had seen in a thread that someone mentioned that abs would be a better choice than PVC due to better impact resistance and a more favorable mode of failure if it were to fail ( it doesn't tend to shatter like PVC does ). That being said, what is the feasibility of threading an accumulator made from ABS? Outside diameter would be 1-5/16, threaded internally with a 1-1/8 - 32 thread. Lexan (polycarbonate) would be another candidate for material. I suppose I could even fit a thin aluminum ring over the threaded portions with a very light press fit to reinforce it. I would have to check the coefficient of thermal expansion on the materials first to make sure the ring couldn't slip off if the temperatures changed too much - especially with the co2 going through it. I.D. threads would be about .400" long. Anyone have any thoughts or experience with these materials under pressure?
