SpudFiles

r00kie wrote:While on the subject of pressures, I know you've done a lot of work with epoxy JSR, do you think it's worth using that as a lazy alternative to brazing copper? What kind of pressure would I be able to safely kick it up to with epoxy and brazing?

I've used epoxy in pneumatics up to 850 psi. I've had a few failures, this one being the most spectacular, from which I'm still to this day finding fragments - but every failure can be attributed to bad design. The material can take the strain, but you have to use it properly.

I'm planning on using some steel ball bearings, but as I don't have them yet, I can't weigh them. I'm planning on ordering them from here, they're a bit pricey, but have a good range.

I got my 3mm bearings from them, and yes they are a bit pricey. Have a look on eBay, you can probably find cheaper ones. I remember getting 3/8" bearings that weren't too expensive.

jackssmirkingrevenge wrote:I've used epoxy in pneumatics up to 850 psi. I've had a few failures, this one being the most spectacular, from which I'm still to this day finding fragments - but every failure can be attributed to bad design. The material can take the strain, but you have to use it properly.

At 850 PSI, it's a good thing you didn't take shrapnel. I would have needed a fresh pair of underwear, at any rate.

Using it properly is my worry. I'm not sure how effective it would be on the smooth surface of copper, as well as it being quite sparse once it was sleeved together. To be honest I wouldn't trust my brazing much more, as I've only done it once before.

If you have found it to be safe up to those pressures, I'm sure I won't have a problem taking it up to 400 PSI, provided the QEV can handle it. :p

jackssmirkingrevenge wrote:I got my 3mm bearings from them, and yes they are a bit pricey. Have a look on eBay, you can probably find cheaper ones. I remember getting 3/8" bearings that weren't too expensive.

I did have a quick look on eBay, but didn't find anything much cheaper unfortunately, nor could I find as many sizes available.

Getting the size information proved to be quite a hassle, as the ID of 1/2" copper isn't 1/2" (nor is the OD from what I've heard). I found some good information on the OD/ID for different sizes here, but it's all still a bit confusing.

r00kie wrote:Using it properly is my worry. I'm not sure how effective it would be on the smooth surface of copper, as well as it being quite sparse once it was sleeved together.

Smooth copper can be roughened, that's not a problem. The issue is having sufficient wall thickness vis-a-vis your inner diameter that will prevent the tube from expanding enough to allow the plug to pop out.

Take this minias an example, I used ordinary 15 minute Araldite and it held 850 psi without failure or leaks, in 9mm brass with 0.5mm wall thickness. In this case however, I used a much larger diameter tube with a similar wall thickness, and *pop*

If you post a diagram of what you intend to build it would be easier to give you specific advice.

Do you mean roughening it with sandpaper, similar to the way you clean a joint before soldering it?

I meant epoxy as an alternative to using flux/solder to [url=http://curbly_uploads_production.s3.amazonaws.com/photos/0000/0001/1920/clean_joint_large.jpg]join[/url] two pieces of copper, not actually plug an end.

I plan to cap the end of my chamber as opposed to plugging it with epoxy, just because it looks a bit more aesthetic. That may change, depending on what I can scrape up at the hardware store (I haven't noticed copper caps in their plumbing section before).

You brought up a really good point about the wall thickness and expansion of the tube, I hadn't considered that before.

r00kie wrote:Do you mean roughening it with sandpaper, similar to the way you clean a joint before soldering it?

I usually go a bit more hardcore than sandpaper, cutting small notches with a file or abusing the relevant area with a broken drill bit

I meant epoxy as an alternative to using flux/solder to [url=http://curbly_uploads_production.s3.amazonaws.com/photos/0000/0001/1920/clean_joint_large.jpg]join[/url] two pieces of copper, not actually plug an end.

Have a look at my latest, the 1/8" QD fitting is attached to copper pipe using Araldite and it held 850 psi no problem.

jackssmirkingrevenge wrote:If you post a diagram of what you intend to build it would be easier to give you specific advice.

This is a bit late, but I hadn't actually put anything on paper until you said that. I threw up a rough sketch of what I plan to do here. I won't embed the image, as it's quite large. Perhaps you could critique me on it (the launcher I mean, not how to resize my photos ).

A potential concern I see is that the schrader will severely reduce performance as opposed to a blowgun (if it's effective enough to actuate the QEV at all).

jackssmirkingrevenge wrote:I usually go a bit more hardcore than sandpaper, cutting small notches with a file or abusing the relevant area with a broken drill bit

Ah I see, as long as it gets a better grip. I'll just have to make sure that I don't go so far as to reduce the pressure rating of the pipe.

Ah, so you did end up going ahead and making those mini cartridges, I was rather intrigued when I saw some plans you'd put up, but I never ended up stumbling across that topic.

You said they "didn't perform well in that [as a cartridge] context", mind if I ask why?

r00kie wrote:I won't embed the image, as it's quite large. Perhaps you could critique me on it (the launcher I mean, not how to resize my photos ).

Resized and posted

A potential concern I see is that the schrader will severely reduce performance as opposed to a blowgun (if it's effective enough to actuate the QEV at all).

I don't know about QEVs but for a 1" piston valve a schrader pilot was good enough for my purposes. You could also consider a 1/8" or 1/4" ball valve as a pilot.

You said they "didn't perform well in that [as a cartridge] context", mind if I ask why?

It would have worked well in a bolt operated or straight pull action, but I wanted a cartridge that would generate enough pressure in the breech to not only fire the projectile but also eject itself and push a blowback bolt far enough to enable a following cartridge to be loaded, in this context it was disappointing, especially when you consider that there would already be a forward force on the cartridge from the firing pin.

jackssmirkingrevenge wrote:I don't know about QEVs but for a 1" piston valve a schrader pilot was good enough for my purposes. You could also consider a 1/8" or 1/4" ball valve as a pilot.

You have a very small pilot area in that example, I think that would greatly contribute to it's effectiveness. When the QEV finally gets here, I'll test it out and let you know how effective they are with schraders.

I have tried to steer clear of ball valves, they are quite effective, but in this case I want aesthetics. If the schrader reduces performance noticeably over a blowgun valve, I might switch to one, but I'm really trying to keep it looking as good as I can. :p

jackssmirkingrevenge wrote:It would have worked well in a bolt operated or straight pull action, but I wanted a cartridge that would generate enough pressure in the breech to not only fire the projectile but also eject itself and push a blowback bolt far enough to enable a following cartridge to be loaded, in this context it was disappointing, especially when you consider that there would already be a forward force on the cartridge from the firing pin.

That's a shame, it was a brilliant idea. I imagine they'd still function quite nicely in a bolt action, but semi-auto (or even a full auto) would have been the bees knees.

r00kie wrote:You have a very small pilot area in that example, I think that would greatly contribute to it's effectiveness. When the QEV finally gets here, I'll test it out and let you know how effective they are with schraders.

Technically the cup seal on a QEV should act as a one way valve ensuring it should actuate, but I can't tell you how much it will affect performance. What i can tell you is that on my schrader actuated pistons, pressing the schrader stem sharply gives noticeably better performance.

I have tried to steer clear of ball valves, they are quite effective, but in this case I want aesthetics. If the schrader reduces performance noticeably over a blowgun valve, I might switch to one, but I'm really trying to keep it looking as good as I can. :p

They don't have to be ugly, have a look at what Brian did here

That's a shame, it was a brilliant idea. I imagine they'd still function quite nicely in a bolt action, but semi-auto (or even a full auto) would have been the bees knees.

The Brocock Range uses preloaded cartridges in revolvers, straight pull and bolt actions, admittedly a double action revolver will give you one shot per trigger pull, but there isn't that element of flying brass which personally is one of the biggest incentives

jackssmirkingrevenge wrote:Technically the cup seal on a QEV should act as a one way valve ensuring it should actuate, but I can't tell you how much it will affect performance. What i can tell you is that on my schrader actuated pistons, pressing the schrader stem sharply gives noticeably better performance.

I suppose I could make some kind of hammer that depresses the schrader when the trigger is pulled, but that seems to make it unnecessarily complicated as opposed to a blowgun. It would also mean it would have to be cocked after each shot.

Using the solenoid out of a sprinkler valve to depress it is another idea that comes to mind, it would require power, but nevertheless it sparks some interest.

jackssmirkingrevenge wrote:They don't have to be ugly, have a look at what Brian did here

That's very innovative! Shame he couldn't get it in the competition.

jackssmirkingrevenge wrote: there isn't that element of flying brass which personally is one of the biggest incentives

I know what you mean, I've toyed with the idea of making some cartridges myself just so I could hear the satisfying "ping" of spent rounds hitting the floor.