Air Cylinders
I’ve been contemplating having a go at making my own air rifle, the one thing that gives me pause is the air cylinder, we are dealing with a great deal of energy there.
I was thinking originally of using a talon bottle I have, but it does limit the designs somewhat.
but then I found that air-guns of Arizona is selling FX air cylinders 😀
you can get 148cc and 180cc air cylinders for what I think is a reasonable price, definitely worth the piece of mind.
they actually also sell the smaller extension so you really could get a pre-fabed air cylinder of the size you want 😯
All Replies
Pinning an endcap does seem like the easiest solution. Then all you have to do is calculate the shear load on the pins, and make sure there is enough wall area left after pinning so that the end of the tube doesn’t blow completely off with the pinned end cap. 🙂
Something that hasn’t been talked about. What type of Orings do you use for a config like that and how do you figure what depth groove they need? How much should they be compressed by the outer tube. Is there some rule of thumb with Orings?
Thats what I was talking about before. The threads after the Orings removes it from the pressure part of the tube. Only side shear on the threads would be an issue.
Also, someone asked why the guy in that link was suggesting bigger tubing than what he lists in his article. He states later that those pressures listed are burst pressures, not working pressures. The bigger tubing is after figuring in a 20% safety margin over the burst pressure.
Use normalised ST52 aka 4130 as Walther suggests. You can use ST37 but you need a bit more wallthickness. Under any circumstance use steel with big difference in tensile and yield strength, that means it’ll tear rather than fragment. Most high class construction steels as St52 and St37 have that tendency.
By axial load I mean the threads are only stressed in the direction of The tubes axis. So not pressureized.
DOM means drawn over mandrell. It can be welded and then drawn over a mandrell to smooth it out. But I’m not shure. Seamless is a different production method as far as I know.
Airarms tubes are way thinner than the BAM’s. Ive seen both.
HPA at 850 to 1000psi requires less tube than a PCP conversion.
which do you want to build?
for PCP use go with 4130 DOM seamless 0.875×0.065″ good to 3,000psi
so which product number from mcmaster would you choose to get a corsman replacement tube for HPA…so 7/8th OD ?
Here is that link to the tubing with pressure ratings on it.
http://www.tube-mac.com/pdf/tubemac_section_a.pdf
Also, http://www.mcmaster.com seems to have the same tubing dimension wise but, I don’t know if it is the same exact pipe as in the above link.
If you go to mcmaster look under the “Fittings, Pipe, Tubing and Hose” section in the “Pipe fitting and pipe” subsection. The black seamless looks like the same stuff.
I haven’t been on in a few days and see now that the site was moved to a different server, probably a backup copy of the site being put up is to blame for the missing post. 🙂
marc why is DAQ then advising against hydraulic tubing ?
my Bam has .068″ tubing, think the airarms was the same
i once saw pictures of a career707 mk2 that had been overfilled…it did not blow up but a long tear in the tube vented the pressure…bet it scared the user shitless
So marc….what material should we choose ?
is seamless the same as DOM tubing ?
uhh and can you tell some more about the axial loads in leymans terms….
i see the bam uses an endcap…with 2 orings that is in the tube about 5mm from the threads that comes after….its aluminium btw
A thread cut into the tube does weaken the tube. But it doesn’t really matter if the pipe has said x working pressure and it’s being pressurized in front of the threads. In other words the o-ring closes the tube befor the pressure is near the threads. That way the threads only see axial loads. And offcourse reactive radial loads. But for instance a 28×2,5 pipe threaded M24x1 can easily hold that load. And has a working pressure of 250 bars.
I don’t know what exotic material AirArms uses but it uses a scary thin pipe with pressure loaded threads. Still everybody uses these gun with confidence.Some with the korean rifles. Key is using high quality seemless hydraulic tubing!
regards,
Marc
yeah there was some good stuff here
heres the DAQ link again http://www.quackenbushairguns.com/steel_for_airguns.htm
ill see if i can recap what i have been wondering about….
several times i have seen posts that .065″ wallthickness is fine….
however reading DAQ’s guide…he suggests .093″ for 3200 psi
but whether DAQ is taking into account crappy DOM tubing or high grade Steel is unknown
MAC1 sells tubing too….. .125″ wallthickness….yet he only rates it 2500 psi ….is that because its been threaded ?…the alloy 4130 seems to be the same that DAQ uses …so that adds to the confusion
look at the link ..scroll to the bottom http://www.mac1airgun.com/pcpcomponents.html
i know there engineers among us…someone must have one of those handy school books with references and can set us all straight on this subject…theres gotta be some generic calculators out there
dont have to take all sizes into account…
the most used sizes are 7/8th (dam i still hate american way of measuring …fucking fractions)
1.25″ seems to be the usual for BAM, AA, daystate, FX
and then an oversized tube for those nuts like me who need a little bit more air a 2″
those are all OD dimensions
What happened to the other post in this thread? 😯 Glitch with the DB?
I’m always amazed when I see people making a air gun or even a custom stock. My backround is in steel fabrication but I read a blueprint and built what ever was on it, with stocks and guns you are starting with a thought and making it real that is impressive. Good Luck and make sure to post pics.
- You must be logged in to reply to this topic.
Cygnus X – I don’t see any 7/8″ OD black seamless pipe on mcmaster. I was just using that tubemac link above to show some pressure ratings on different pipe and also show that mcmaster looks to carry the same pipe.
What is the ID of the crossman tube?