Coaxial help..

[daniel0663]

So i recently made a coaxial from parts i had around home...
only problem is, it does not work.

I was wondering what the problem might be, i'm guessing it's the schrader valve not releasing the air quick enough, or i don't have enough air volume.

Anyway here is the specs;
total length- 280mm
chamber total length- 255mm
operating pressure- 60psi
piston- wooden piston with rubber sealing face.

O.D of camber- 20mm
I.D of chamber- 19mm

O.D of barrel- 12mm
I.D of barrel- 10mm

Polyester resin plugs- 20mm each ends.
Which leaves me with a total volume of 47.41cm3
which should be enough?

here are some pics





advice is most welcome....
i can't use GGDT because i am not the administrator of the computer or something..
thanks in advanced,

[jackssmirkingrevenge]

Does it just dump all the air out of the schrader?

If so, your piston is either stuck, or not tight enough. I'll wager it's the latter.

19mm pipe cross sectional area = 2.835 cm2

18.5mm piston cross sectional area = 2.688 cm2

Gap cross sectional area = 0.147 cm2

Schrader cross sectional area = 0.024 cm2

As you can see even a 0.5mm gap is too much, as when you open the schrader, more air can flow to the pilot from the chamber than can flow out of the schrader.

edit: can't see your video, "an error occured"

[daniel0663]

I will be damned if the piston is to snug(if i shake the gun, you can hear the piston move up and down.)

hm.. i may have to try again.. decrease the gap and make the piston more sensitive...

Looks like i may have to get the acetone out..

also the video works now, (i suspect to much air is released when i disconnect the hose.. it's to late at the moment for test.)

Thanks JSR,

[jackssmirkingrevenge]

My rule of thumb is that it should be tight but you can still push it with one finger.

You can wrap the piston with tape to get a good fit, but in general I would not recommend wooden pistons due to the instability of the material when it absorbs humidity.

You've got polyester resin, why not cast one?

[wyz2285]

Agree, epoxy pistons are good in this case. With the size of you chamber you may want to reduce the bore too, and higher pressure, 4 bar is nothing, a shock pump is good for this size of chamber, you could get 400 psi easy

[daniel0663]

mm.. thanks guys, i might call this one a fail for my collection. It's been a learning experience and was made just for fun/testing.....
i cant really take out the plugs... so i might cut it up and just take the schrader.

Next one will hopefully be improved.

you could get 400 psi easy

possibly but i wouldn't really risk it blowing up on me, i'm sure the aluminium can hold up, but it's the plugs i'm worried up, hence i only use a maximum pressure of 60psi.

[wyz2285]

Normal epoxy holds +- 400 psi easily in small areas like this

[Gun Freak]

Lol, I just made a pengun but I think the piston will be too loose to actuate Can always remake it

[daniel0663]

Well, my pursuit of increasing the pressure has finally took its toll.
The coaxial failed at 70psi,
Guess there is a reason why JSR uses epoxy..

[jackssmirkingrevenge]

Guess there is a reason why JSR uses epoxy..

Well, at least you have access to the piston now

You should have done more to promote adhesion, if roughening the tube is not enough then drill some holes and mask them while you pour the resin, or even better inlet a few screws.