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Author Topic: Threaded aluminum end plugs?  (Read 456 times))

Offline rkr

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Threaded aluminum end plugs?
« on: April 15, 2021, 02:43:28 PM »
Is aluminium OK material for threaded endplug in a 3000 psi airtube? M21x1.0 threads in this case.
Huub Viking Mk2 .177/.22 bullpup - grab'n go gun
BSA Scorpion SE .177 - plinker/training gun
BSA Scorpion .25 - 100M BR gun at 60 fpe
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Exanix Sniper X2 .357/.45 - 210/270 fpe silhouette gun
Drozd Blackbird HPA - 1200 rpm full auto fun gun / meat grinder
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+ a couple of springers

Offline rsterne

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Re: Threaded aluminum end plugs?
« Reply #1 on: April 15, 2021, 03:15:40 PM »
Depends on the grade of aluminum and the (axial) thread depth of engagement.... I use 7075-T6 when I can, otherwise 2024-T3.... 6061-T6 is significantly weaker.... Load depends on the ID of the tube, assuming the O-ring is inboard of the threads, so that they are only in shear.... If the O-ring is outboard of the threads (and therefore they are under pressure) the hoop strength of the tube is decreased (thinner wall because of the threading), and that will decrease the effective thread (radial) engagement if the tube expands.... Much better to have the O-ring inboard of the threads....

Bob
  • Coalmont, BC, Canada
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsenal:
1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), XS-60c HPA in .30 cal (90 FPE), .22 cal QB79 HPA, Disco Doubles in .22, .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, 7mm, .308 & .357; Mk.III is .410 shotgun and .458 cal), .257 "Monocoque" Benchrest PCP, .172/6mm Regulated PCP and .224/.257 Unregulated, Three regulated BRods in .25 cal (70 FPE), .30 cal (100 FPE) & .35 cal (145 FPE), .257 Condor (180 FPE).

Offline PikeP

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Re: Threaded aluminum end plugs?
« Reply #2 on: April 15, 2021, 03:22:23 PM »
FWIW most manufacturers have been using 2024-t3 aluminum or similar for their end plugs for longer than I know, mostly because I don't know much 🤷
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Offline BigBird

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Re: Threaded aluminum end plugs?
« Reply #3 on: April 15, 2021, 04:32:29 PM »
If I remember correctly 7075 has strength close to or better than mild steel and less fatigue than 6061.
https://www.makeitfrom.com/compare/7075-T6-Aluminum/SAE-AISI-1018-G10180-Carbon-Steel
The delrin guy has 7075 drops on ebay rather cheap.

« Last Edit: April 15, 2021, 04:35:15 PM by BigBird »
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Offline Rob M

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Re: Threaded aluminum end plugs?
« Reply #4 on: April 15, 2021, 05:49:27 PM »
i use 6061 in 3000 psi applications often.. But , i also plan around it as bob alluded to  above.. Thread depth , wall thickness, oring location , etc are all critical... the smaller diameter the apllication , the less stress its under..
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Offline lennyk

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Re: Threaded aluminum end plugs?
« Reply #5 on: April 15, 2021, 10:18:25 PM »
So a marauder fill end cap is under less than the 3000psi ?

Depends on the grade of aluminum and the (axial) thread depth of engagement.... I use 7075-T6 when I can, otherwise 2024-T3.... 6061-T6 is significantly weaker.... Load depends on the ID of the tube, assuming the O-ring is inboard of the threads, so that they are only in shear.... If the O-ring is outboard of the threads (and therefore they are under pressure) the hoop strength of the tube is decreased (thinner wall because of the threading), and that will decrease the effective thread (radial) engagement if the tube expands.... Much better to have the O-ring inboard of the threads....

Bob
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Offline rsterne

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Re: Threaded aluminum end plugs?
« Reply #6 on: April 15, 2021, 11:09:21 PM »
Quote
So a marauder fill end cap is under less than the 3000psi ?

Where did that come from?.... Nowhere did I say that you can't use aluminum at 3000 psi.... In fact, I have used properly designed aluminum end caps at 4500.... but you better know what you are doing, for the materials you choose.... Look at not only the shear strength of the threads, but the axial load on the remaining tube wall above the threads.... If the O-ring is not inboard of the threads, there are other things to look at as well.... Basically, asking a question without giving all the details of the tube and end plug will (or at least should) get you a non-committal answer.... Always engineer for at least a 3:1 safety margin....

Bob
« Last Edit: April 15, 2021, 11:11:24 PM by rsterne »
  • Coalmont, BC, Canada
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Airsenal:
1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), XS-60c HPA in .30 cal (90 FPE), .22 cal QB79 HPA, Disco Doubles in .22, .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, 7mm, .308 & .357; Mk.III is .410 shotgun and .458 cal), .257 "Monocoque" Benchrest PCP, .172/6mm Regulated PCP and .224/.257 Unregulated, Three regulated BRods in .25 cal (70 FPE), .30 cal (100 FPE) & .35 cal (145 FPE), .257 Condor (180 FPE).

Offline rkr

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Re: Threaded aluminum end plugs?
« Reply #7 on: April 16, 2021, 06:27:29 AM »
This was meant as a generic question but if you guys can provide more specific answer then even better. I'm trying to make an end plug for AR6 pistol to be able to install a drop block. The threads are M21 x 1.0 and 16mm long. As Evanix designed it the threads are pressurized as o-ring is after those threads. However, I could probably install it in front of the threads leaving them unpressurized. Tube thickness at threads is 1.6mm and tube diameter 23mm. So, can aluminum be used in this application and can I use 5000 or 6000 series alloy from scrapyard or do I need to get some 2000 or 7000 series alloy?

Edit, after writing this I decided to give one final go for threading a steel plug and what do you know, it finally worked. So, no need to do that math now unless you really want to.
« Last Edit: April 16, 2021, 06:55:07 AM by rkr »
Huub Viking Mk2 .177/.22 bullpup - grab'n go gun
BSA Scorpion SE .177 - plinker/training gun
BSA Scorpion .25 - 100M BR gun at 60 fpe
BSA Scorpion .224 - 100M BR gun at 100 fpe
Evanix Blizzard .257/.357 - 150/230 fpe
Exanix Sniper X2 .357/.45 - 210/270 fpe silhouette gun
Drozd Blackbird HPA - 1200 rpm full auto fun gun / meat grinder
Evanix AR6 carbine/pistol
+ a couple of springers

Offline rsterne

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Re: Threaded aluminum end plugs?
« Reply #8 on: April 16, 2021, 12:04:15 PM »
Just so I understand, the tube is 23mm OD x 19.8 mm ID (1.6mm wall)?.... If the threads are 21mm OD, then the remaining wall thickness could only be 1mm in the threaded portion.... and that portion is pressurized?.... What is the tube material?.... At 3000 psi, I find the following....

Taking a guess on the tube material as 1010 mild steel, with the above dimensions the plug threads are not the issue.... A 6061-T6 plug, with properly formed 21mm x 1mm threads with an engagement of 16mm has lots of strength in shear (~ 10:1), and the axial strength of the tube wall at the thread root is about 3.5:1, which is fine.... Using the tube dimensions above, the hoop strength of the tube where the wall is 1.6mm thick is marginal, with a yield of 2.6:1 and 3.1:1 to burst.... My concern is that the threads are pressurized, and so the wall thickness there (23mm-21mm)/2 = 1mm is not sufficient for 3000 psi, with safety margins of just 1.6:1 to yield and 1.9:1 to failure, based on that material.... Even upgrading the tube material to 4130 CrMoly, it is only 1.9:1 to yield and 2.9:1 to failure.... The plug is not the problem, IMO the O-ring must be moved to inboard of the threaded area, where the tube is full wall thickness....

This is a perfect example of not responding to a simple question when all the details are required to ascertain the safety of components.... Please note, I am NOT an Engineer, these numbers are provided for reference only, and YOU are responsible for the safety of your build....

Bob
« Last Edit: April 16, 2021, 12:29:09 PM by rsterne »
  • Coalmont, BC, Canada
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsenal:
1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), XS-60c HPA in .30 cal (90 FPE), .22 cal QB79 HPA, Disco Doubles in .22, .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, 7mm, .308 & .357; Mk.III is .410 shotgun and .458 cal), .257 "Monocoque" Benchrest PCP, .172/6mm Regulated PCP and .224/.257 Unregulated, Three regulated BRods in .25 cal (70 FPE), .30 cal (100 FPE) & .35 cal (145 FPE), .257 Condor (180 FPE).

Offline rkr

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Re: Threaded aluminum end plugs?
« Reply #9 on: April 17, 2021, 05:07:56 AM »
Just so I understand, the tube is 23mm OD x 19.8 mm ID (1.6mm wall)?.... If the threads are 21mm OD, then the remaining wall thickness could only be 1mm in the threaded portion.... and that portion is pressurized?.... What is the tube material?.... At 3000 psi, I find the following....

Taking a guess on the tube material as 1010 mild steel, with the above dimensions the plug threads are not the issue.... A 6061-T6 plug, with properly formed 21mm x 1mm threads with an engagement of 16mm has lots of strength in shear (~ 10:1), and the axial strength of the tube wall at the thread root is about 3.5:1, which is fine.... Using the tube dimensions above, the hoop strength of the tube where the wall is 1.6mm thick is marginal, with a yield of 2.6:1 and 3.1:1 to burst.... My concern is that the threads are pressurized, and so the wall thickness there (23mm-21mm)/2 = 1mm is not sufficient for 3000 psi, with safety margins of just 1.6:1 to yield and 1.9:1 to failure, based on that material.... Even upgrading the tube material to 4130 CrMoly, it is only 1.9:1 to yield and 2.9:1 to failure.... The plug is not the problem, IMO the O-ring must be moved to inboard of the threaded area, where the tube is full wall thickness....

This is a perfect example of not responding to a simple question when all the details are required to ascertain the safety of components.... Please note, I am NOT an Engineer, these numbers are provided for reference only, and YOU are responsible for the safety of your build....

Bob

Re-checking, tube OD = 23.25mm, ID at o-ring = 21.7mm, ID at threads = 20.2mm, end plug thread OD 21.0mm. It's Hunting Master P AR6 from Duk Il Arms Co. and sold as 3000 psi filĺ gun, one of these things: https://www.airgundepot.com/evanix-hunting-master-ar6.html Now I'll be using it with 2200 psi regulated air from a paintball bottle so that increases margins a bit. It seems Duck Il / Evanix is not too concerned about safety margins  :o
« Last Edit: April 17, 2021, 05:28:10 AM by rkr »
Huub Viking Mk2 .177/.22 bullpup - grab'n go gun
BSA Scorpion SE .177 - plinker/training gun
BSA Scorpion .25 - 100M BR gun at 60 fpe
BSA Scorpion .224 - 100M BR gun at 100 fpe
Evanix Blizzard .257/.357 - 150/230 fpe
Exanix Sniper X2 .357/.45 - 210/270 fpe silhouette gun
Drozd Blackbird HPA - 1200 rpm full auto fun gun / meat grinder
Evanix AR6 carbine/pistol
+ a couple of springers

Offline rsterne

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Re: Threaded aluminum end plugs?
« Reply #10 on: April 17, 2021, 12:54:37 PM »
I'm not about to get into a fight about safety margins.... but my calculations show that for a 23.25 mm OD and a 21.7 mm ID where the O-ring is.... the MSWP is about 1,200 psi for mild steel tubing, and about 1,800 psi for CrMoly, to meet the 3.5:1 minimum to failure required by the ASME.... The wall thickness at the O-ring groove is only 0.0305"....  :o  ::)

I haven't seen a drawing of the parts, but given your information, that's what I get....

Bob
  • Coalmont, BC, Canada
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsenal:
1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), XS-60c HPA in .30 cal (90 FPE), .22 cal QB79 HPA, Disco Doubles in .22, .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, 7mm, .308 & .357; Mk.III is .410 shotgun and .458 cal), .257 "Monocoque" Benchrest PCP, .172/6mm Regulated PCP and .224/.257 Unregulated, Three regulated BRods in .25 cal (70 FPE), .30 cal (100 FPE) & .35 cal (145 FPE), .257 Condor (180 FPE).

Offline Rob M

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Re: Threaded aluminum end plugs?
« Reply #11 on: April 17, 2021, 03:07:00 PM »
Having worked on an evanix tube , i can say it an odd setup ,not ideal as the thin lip at the end is exposed to max hoop stress .. It is likely a chromoly tube..
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Offline Klug932000

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Re: Threaded aluminum end plugs?
« Reply #12 on: April 22, 2021, 09:22:13 AM »
Bob could I get some help on figuring pressure load calculations (for reference only)? If I am using 6061 tube, Od 1.25, Id .812, with 4041 end caps, o ring inboard, what kind of load difference could be handled between a 1"-8 thread and a 1"-16 thread? is there enough wall thickness where the 8 tpi doesn't weaken it to much?
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Offline rsterne

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Re: Threaded aluminum end plugs?
« Reply #13 on: April 22, 2021, 12:44:29 PM »
I use Lloyd's tube strength spreadsheet, which allows an easy change of TPI.... There is almost no difference in the shear strength of the two threads, with equal engagement (I used 0.50").... I don't know what 4041 material is, and it isn't one of the options in the spreadsheet, but using 6061 for both the tube and plug, I get in excess of a 10:1 safety margin at 3000 psi for either thread count.... This also applies to the axial load on the remaining tube wall at full thread depth.... The 16 TPI choice requires that you bore the ID to 0.938", removing 0.063" per wall, while the 8 TPI requires boring it to only 0.875", removing 0.032" per wall.... With the OD being the same, the remaining wall is about the same as well....  The yield margin on the tube hoop strength is 5.4:1 and to failure is 6.1:1.... I wouldn't have a problem with either thread, depending on what material "4041" is.... When I type that into Google, it changes it to 4140 CrMoly.... ???

Bob
« Last Edit: April 22, 2021, 12:46:35 PM by rsterne »
  • Coalmont, BC, Canada
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsenal:
1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), XS-60c HPA in .30 cal (90 FPE), .22 cal QB79 HPA, Disco Doubles in .22, .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, 7mm, .308 & .357; Mk.III is .410 shotgun and .458 cal), .257 "Monocoque" Benchrest PCP, .172/6mm Regulated PCP and .224/.257 Unregulated, Three regulated BRods in .25 cal (70 FPE), .30 cal (100 FPE) & .35 cal (145 FPE), .257 Condor (180 FPE).

Offline Klug932000

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Re: Threaded aluminum end plugs?
« Reply #14 on: April 22, 2021, 02:49:54 PM »
Sorry that was a miss type, 4140 is what I meant. But again I wasn't even thinking right there, looking at Buckley's book, I'm looking at doing the air tube out of 6160, random stainless I have for the inlet/outlet, and 4140 for the striker body.

Anyway thanks for your input
Pat
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Offline rsterne

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Re: Threaded aluminum end plugs?
« Reply #15 on: April 22, 2021, 05:39:11 PM »
Now you list the air tube as 6160, I have never heard of that, and Google refers me to 6061.... "Random Stainless" is likely to be 304, being that is the most common SS, and it has a yield strength of only about 3/4 that of 6061-T6 aluminum.... It might be 316 SS, which is stronger than aluminum, but if you don't know what it is, I can't (and won't help) you....

Bob
  • Coalmont, BC, Canada
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsenal:
1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), XS-60c HPA in .30 cal (90 FPE), .22 cal QB79 HPA, Disco Doubles in .22, .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, 7mm, .308 & .357; Mk.III is .410 shotgun and .458 cal), .257 "Monocoque" Benchrest PCP, .172/6mm Regulated PCP and .224/.257 Unregulated, Three regulated BRods in .25 cal (70 FPE), .30 cal (100 FPE) & .35 cal (145 FPE), .257 Condor (180 FPE).

Offline DarwinsLaw

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Re: Threaded aluminum end plugs?
« Reply #16 on: April 24, 2021, 01:35:04 PM »
Where can one find Lloyd’s tube strength spreadsheet?
« Last Edit: April 24, 2021, 01:38:49 PM by DarwinsLaw »
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Offline rsterne

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Re: Threaded aluminum end plugs?
« Reply #17 on: April 24, 2021, 01:46:50 PM »
Sorry, it's proprietary.... I'm fortunate enough to have a copy, but cannot share it....

Bob
  • Coalmont, BC, Canada
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsenal:
1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), XS-60c HPA in .30 cal (90 FPE), .22 cal QB79 HPA, Disco Doubles in .22, .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, 7mm, .308 & .357; Mk.III is .410 shotgun and .458 cal), .257 "Monocoque" Benchrest PCP, .172/6mm Regulated PCP and .224/.257 Unregulated, Three regulated BRods in .25 cal (70 FPE), .30 cal (100 FPE) & .35 cal (145 FPE), .257 Condor (180 FPE).

Offline DarwinsLaw

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Re: Threaded aluminum end plugs?
« Reply #18 on: April 24, 2021, 02:28:04 PM »
Ahh, understood, no worries.
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