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Ianbuckwell wrote:Another thing! What Schrader valves/assemblies do people use? Is it just the regular rubber ones pulled through an end cap with the same size hole in as a wheel would have? Or do they go for the metal bolt on ones? It maybe my bad luck but car wise I always seem to have more luck with the regular rubber assemblies as the metal ones seem prone to snapping, say for example the gun/cannon was dropped. It !may just be that I have had cheap alloy ones in the past??

For high pressures, you can't get away with a vehicle type rubber connection. I usually take the rubber ones, strip off the rubber then epoxy the thing in place.

Also can someone just clear something up for me, if I build a simple 'common' gun which is filled from just before the trigger I don't need to pierce a hole in the diagphram, correct or not so?

Correct

I haven't real got any plans set in stone for my gun, just measured tank hole diameter and it is about 8.9mm, so once I get a fitting in there the hole will be so much small

Any restriction smaller than the barrel diameter will hurt performance significantly.

And then have air for.additional shots, or to enlarge the outlet so air can be used without restriction from the tank so any other pipework can be kept short as possible, what do you guys thinks. The best option? My only concern with the 2nd option is having to drill/weld the tanks exit so it needs to be spot on if I inteemd to use 300psi in future.

Not sure what you're trying to say here, a diagram would really help!

Ps I would just like to say thankyou and give a big thumbs up to Jackssmirkingrevenge for the unseen help he has given me via PM, I realize for the knowlegable people on this forum that newbie questions from memebers such as myself the answers must seem obvious, but I thank them for their patience and help.

No worries, that's what spudfiles is for

Sorry it is so hard to explain in words and my art would probably further confuse things.

I waass thinking of making a gun with enough internal volume to power one single shot, then once this is fired and the presurre released it would then refill from attached cylinder, I would then get several shots between. Having to pump it back up.

The other option is to basically boreout the tanks connection point sos that it would be large enough to not cause a restriction to the gun. Hope I have explained better, personally I am leaning, well almost certainly decided on boring the cylinder connection to non restrictive size, partially as it isn't going to rely on complex calculations and iffy maths. at least option 2 maybe less efficient but at least I know it is getting all the air it could want.


Ps - removed paint from my mild steel cylinder and it looks gtreat with a nice brushed look, so I was going to epoxy primer it but now just going to clear coat straight to the brushed steel and see how it holds up.

Ianbuckwell wrote:Sorry it is so hard to explain in words and my art would probably further confuse things.

I would give it a go anyway

I waass thinking of making a gun with enough internal volume to power one single shot, then once this is fired and the presurre released it would then refill from attached cylinder, I would then get several shots between. Having to pump it back up.

The best way to do this for multiple shots is to use a slide valve or other three way valve and two tanks, one small one for firing attached to the A port of the QEV, and one larger reservoir attached to a slide valve which is then attached to port P of the QEV, as detailed in my "Semi auto for under $20" thread.

Thanks, i will have a read up on this when I get home and ha e a se si le size screen to read/see it on. So you are basically saying connect my larger tank to where you have the airline connected to in your setup and then source a smaller tank/cylinder, which I guess I could use large bore copper tubing to make.. How is the size of this smaller cylinder calculated so as to be effeiciemt as possible and to not waste air?


My gun design is open to change as currently I have a 600ml tank, some fottings and and a qev.

is there any advanatage/disadvantage over aesthetics between the black box qevs and the rounder shaped ones?

Ianbuckwell wrote:Thanks, i will have a read up on this when I get home and ha e a se si le size screen to read/see it on. So you are basically saying connect my larger tank to where you have the airline connected to in your setup and then source a smaller tank/cylinder, which I guess I could use large bore copper tubing to make.. How is the size of this smaller cylinder calculated so as to be effeiciemt as possible and to not waste air?

The best way to do so is to use GGDT to model your launcher and change the parameters until you get the performance you desire. As a rule of thumb for pressures in the region of 150 psi and with a fast valve, I would take your barrel volume and make the firing chamber approximately the same size, not more than twice the barrel volume or it's just wasteful.

Ianbuckwell wrote:is there any advanatage/disadvantage over aesthetics between the black box qevs and the rounder shaped ones?

There should be no noticable difference in performance between the two types.

Ok, thanks, I currentyly only have my tablet and phone with internet access,my laptop womnt connect for some reason, so i will try to borrow a computer to download it on to.

Just did a rough calculation of what the tank capacity I have is and it is 962ml, this was using external measesruments and did not include the domed end caps. Also ordered a slide valve and an inline blow gun to keep my options open! . Got a freebie Schrader valve from my local tire shop.

Cant seem to find it, but can someone one post me a link on how to post pictures, thanks

Jackssmirkingrevenge - you say to.me that just as a rule.of thumb at 150psi the barrell.volume should be 1:1 with the chamber volume, does this rule still apply at higher pressures such as 300psi from.a.shock pump? Thanks.

Ianbuckwell wrote:Cant seem to find it, but can someone one post me a link on how to post pictures, thanks

http://www.spudfiles.com/website-discus ... 25659.html

Jackssmirkingrevenge - you say to.me that just as a rule.of thumb at 150psi the barrell.volume should be 1:1 with the chamber volume, does this rule still apply at higher pressures such as 300psi from.a.shock pump? Thanks.

For higher pressures, you can reduce chamber volume accordingly. This is especially important for a shock pump because it is a pain in the biceps to use for anything over 50mL...

Sounds like I may stick with compressor pressure, don't lime hard work!, thanks for the link,

inb4 POLAND suggesting you modify a fridge compressor

http://www.spudfiles.com/how-to-databas ... 24314.html

Hope this picture upload works...

Looks as though I cant upload pictures with my Nokia Lumia 920 windows phone
. I can email diagram if anyone wants to look it over if anyone is willing to PM their email address

Basicaly i have the qev, a barrel on the R port, a small (to be calculated size) tank connected to port A of the qev, port P of the qev has the slide valve which then attaches to the ~900ml tank.

Does that sound about right?

I will look into fridge compressor. Managed to obtain some 32mm and 40-42mm iirc copper tube which will come in useful to make the small cylinder.

Had to email file to nexus, then download, bit long winded but it should work

I Forgot to add a pressure guage, it wont nwcessarily be placed like the drawing, but do the layout of connections seem right? I ordered 15mm od diameter thick wall steel tubing for the barrel, the internal diameter is 9mm so it has 3mm wall thickness, maybe a bit ott for what I am making but it brings the barrel down to a nice size to use with steel slingshot bearings
I also hope there is less chance it will be damaged or bent during delivery.

Your design looks good.

One think about slingshot bearings, they are usually 3/8" diameter which is 9.52mm, they might be a tiny bit too large for your chosen barrel depending on the tolerance.

A gauge on both your main chamber and firing chamber will help you determine how much air you lose after each shot, and therefore the consistency of each shot.

Thanks for looking over the design, didn't want to start to male something that wont even work! I am making the small chamber from 42mm copper tube, couldn't believe the price of the solder on end cap it was £5, about $8 in your money! Think its due to the unusual size,bit guess tube was free which makes me still on top! The steel large chamber and copper tube look great cleaned up to a brushed finish, so once all do e tempted to clearcoat it allowing the metals natural color to shine through.

As for ball bearing ammo I wondered if they had converted from inches to mm and approximated, I will definieatly check before buying a big bag.

Living in the UK it should be relatively easy to get yourself some 3/8" inner diameter tubing for a barrel.

And yep, fittings are expensive. As a poor student, epoxy endcaps certainly saved me a lot of money