Author Topic: pipe/tube  (Read 4083 times)

Offline polecat

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pipe/tube
« on: September 06, 2012, 08:47:49 AM »
how to extend a barrel. the barrel is 10mm and i need to add 9" i could make a sleeve and fit both bits inside the sleeve but very visible any other ways of doing this bearing in mind the 10mm barrel has a 4.5mm hole in and the extended bit a 6mm hole through i,m extending the air receiver for more shots that's why i need to make the barrel longer
thanks polecat

Offline polecat

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Re: pipe/tube
« Reply #1 on: September 07, 2012, 07:52:41 AM »
i'm going to hide the join inside a wider barrel band
polecat

Offline Lew_Merrick_PE

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Re: pipe/tube
« Reply #2 on: September 07, 2012, 10:31:00 AM »
Polecat,

You have a nominal wall thickness of 2.75 mm to work with.  What is the pressure load and/or bending/twisting load you need to carry through the join?  Is there a tensile load for which you need to account in this rework?  These are the conditions that would cause your rework to fail.

Is there any reason you could not make a (say) M8 X 0.5 mm custom thread for the interface?  Were that shouldered to the (male) tenon of the interface, 5 mm of threading should give you good pull-out strength.  An appropriate (light) interference fit on a (say) 6.95 mm bore & tenon should allow for accurate alignment of the 4.5 mm bore.  You would, no doubt, have to heat up the bore-side of the interface (and, most likely, freeze the tenon-side of the interface) to complete the assembly, but that is a PITA rather than a problem.

???

Offline polecat

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Re: pipe/tube
« Reply #3 on: September 08, 2012, 08:01:51 AM »
the barrel iam extending is on a falcon pcp air rifle, iam changing the air reservoir from12" to 19"so as to get more shots. in doing so my barrel is 7" too short so i thought that i could just use a bit of steel tube to make up the 7" then on the end fit my silencer/moderator the barrel extension will have a larger bore than the 4.5mm / .177 barrel size. actually 6mm so hopefully the pellet will not clip/touch the barrel extension as long as i do the job right
i hope this clears up what iam trying to do
polecat

Offline Lew_Merrick_PE

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Re: pipe/tube
« Reply #4 on: September 08, 2012, 12:51:31 PM »
Polecat,

If I assume garden variety merchant (low carbon) steel, then the yield strength of the material is going to be a minimum of 32,000 psi (221 MPa).  You would want to keep your design stress no more than about half that value (16,000 psi/110,500,000 Pa) -- assuming that your "baby" this beastie.

The value you need to figure out is what is the maximum pressure being generated.  For real, propellant-powered rifles, that value lies somewhere in the 28,000 psi (194 MPa) range.  This is an area where I do a fair amount of work, but I know virtually nothing about air rifles.

If I have a tube of ID/2 of r, and a wall thickness of t being pressurized to P, then, assuming the units are all proper, the stress in the tube from pressurization will be: S = Pr/t.  Remember that if you are working in Pascals, then your dimensions are in metres!  Your Pr/t value should be less than your design stress -- and you would reduce it from the 16,000 psi/110,500,000 Pa value if you do anything other than put pressurized gas (behind the projectile) through your barrel!

Offline polecat

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Re: pipe/tube
« Reply #5 on: September 09, 2012, 08:26:42 AM »
the only pressure involved is a very small puff of air to push the pellet up the barrel the barrel extension is for the look of the rifle and to be able to fit a silencer/moderator with a bit of luck the pellet will not clip the extension tube or the silencer thanks for your input
polecat

Offline Jonny

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Re: pipe/tube
« Reply #6 on: September 10, 2012, 09:07:28 AM »
Dead easy done it on my Titan MS020, same rifle to get rid of it in 93.
Turn end of barrel down and bore out a tube to fit over. Can locktite or solder then turn down after concentric and to go through A frame.

Barrel had double choke and cut one end off and therefore became short. Did used to use a Hammerli barrel on it which went on no. 1 rifle i made in 92.


Offline polecat

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Re: pipe/tube
« Reply #7 on: September 11, 2012, 02:58:42 AM »
thank you jonny i thought i was trying the impossible
polecat

Offline Jonny

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Re: pipe/tube
« Reply #8 on: September 11, 2012, 10:39:02 AM »
I have seen a few finished rifled barrels that have actually been joined together, i have one here now made around 1983 ish.
I did ask the person who made the rifles around 20 yrs ago how he did it, he died two years ago.
Have to make a mould of the bore usually lead, problem is getting it out.
Apart from turning and machining both parts of barrels, they are aligned off the mould and silver soldered.