GTA
Support Equipment For PCP/HPA/CO2 and springers ,rams => 3D printing and files => Topic started by: subscriber on August 14, 2023, 07:38:55 PM
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The Standard Airacuda did not come with a 1/2 20 thread adaptor to its shroud. GTA user Robert 5 mm asked if it would be possible to design him an LDC with a M22 x 1 mm male thread, that would screw into his Airacuda shroud directly. Along the way, four variants were designed, in three different outside diameters: 1", 1.25" and 1.5". All are 6" long.
The better performing three of the four designs are shown below. Their STL files are attached in one zip file, below.
You can see photos of the 3D prints that GTA member TorqueMaster produced for Robert 5 mm, here: https://www.gatewaytoairguns.org/GTA/index.php?topic=209670.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=209670.0)
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SLICK!!!!! Very nice work
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can you do a short fat one? Maybe 3 baffles and 1.75 OD?
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Sure thing, Travis
How long would you like it? 3 or 4" ?
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Fat LDCs create an opportunity to wrap a large primary blast chamber around what amounts to a 1" OD LDC. In this case the design also happens to have a fat last baffle chamber. I may do a more conventional design after this one, but this is what I was inspired to come up with. STL attached inside zip file below.
The rear mounting shoulder to front face length is exactly 3.5".
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The attached STL (zipped) is for a more conventional baffle version of the above short, fat Airacuda .22 LDC.
All other details are the same as the version in the above post, so there is no need to repeat all the images views:
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A third variant of the above short and fat LDCs, with the same external dimensions. Version 2 of the Conventional baffle LDC has the same baffle shape design as the "conventional" design above, but the first and second baffles are shifted, to increase the open volume in the second and third chambers (relative to the now smaller first chamber). Both baffle shifts were 4 mm, closer to the threaded end.
STL attached as a zip file, below.
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Very nice! Great job on them.
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Thanks, Jerry
How they work matters much more than their look. I hope someone is motivated to try all three and can report back if there is any perceivable difference in loudness, "snap", tone and grouping ability.
If I was going to recommend just one, it would be a 6" long version. Else, the first or third short fat one. I might change my mind after seeing results :)
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Excellent work as always!
If I could make a small suggestion, I think the design would benefit from a fillet as indicated in red in the drawing below. It takes up slightly more volume but should result in a more durable construction and more importantly should make it easier for the air to reverse direction and interfere more with the flow coming from the muzzle.
(https://i.imgur.com/PP2bRfW.jpg)
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Ill print one out tomorrow when I get home. Thank You!!! Looks prefect....
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Fat LDCs create an opportunity to wrap a large primary blast chamber around what amounts to a 1" OD LDC. In this case the design also happens to have a fat last baffle chamber. I may do a more conventional design after this one, but this is what I was inspired to come up with. STL attached inside zip file below.
The rear mounting shoulder to front face length is exactly 3.5".
This one has my attention!!!
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Jack,
What you suggested with larger corner radii has been added as alternative short fat "conventional" Airacuda LDC designs below. STL files attached in zip file. Go to bottom of this post to see images of new parts and download STLs.
There are at least two schools of though about air management: Run the air into a wall and let it rebound, or direct the air to flow in an organized manner via larger corner radii. An intermedia fillet causes the air to return flow with more friction and turbulence. So, not as bouncy at a flat wall or square corner, and not a smooth return flow as with a large radius.
I have some designs that take the large corner radius idea to the extreme. They work better the harder you drive them. However the extra wall thickness makes for heavy parts, and steals considerable internal volume. For instance; here are two Avenger inserts that have very organized air flow. They require permanent printing supports that take up additional expansion volume:
https://www.gatewaytoairguns.org/GTA/index.php/topic,196584.msg156312899.html#msg156312899 (https://www.gatewaytoairguns.org/GTA/index.php/topic,196584.msg156312899.html#msg156312899)
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=196584.0;attach=398246;image)
https://www.gatewaytoairguns.org/GTA/index.php/topic,196584.msg156312899.html#msg156312899 (https://www.gatewaytoairguns.org/GTA/index.php/topic,196584.msg156312899.html#msg156312899)
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=196584.0;attach=397296;image)
It turns out that my "plume" Avenger insert work almost as well as the 2" external OD fatso Avenger insert. So being much slimmer and lighter, my simple almost convention "plume" baffle style is what I go to now, most of the time. Here is a version of my Avenger plume design that has a two stage reflex air stripper in the shroud. According to those who have compared them to other options, these small Plume insert work rather well:
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=196584.0;attach=422825;image)
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=196584.0;attach=422823;image)
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There are at least two schools of though about air management: Run the air into a wall and let it rebound, or direct the air to flow in an organized manner via larger corner radii
In the latter case (that is very much in the spirit of Maxim's original design) it seems that the effect comes more from giving the air space to tire itself out spinning in toroidal circles as opposed to using it to actively block the flow from the muzzle so I imagine the extra volume is important and the limitations of 3D printing with PLA means it will always be a compromise.
On a tangential note there is one idea I would love to play with one day, that is to use the airflow to physically block off the muzzle, something like this:
(https://i.imgur.com/0VVikt2.gif)
Of course it would need to be tunable because a premature actuation that would make contact with the projectile would be potentially catastrophic, but if it does work then it could potentially be an effective and very compact way to attenuate muzzle blast.
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Jack, that shot activated air sluice gate is a brilliant concept.
To ensure the gate does not start closing before the projectile has passed, place the gas taps directly after the gate, rather than before.
To ensure the air ahead of the projectile does not activate the gate, add a slight detent. Besides, there is a large hole for the air ahead of the projectile to escape, so I don't think much pressure will build; but it will be above ambient.
Or you could make the gas taps slant such that the air rushing by in front of the projectile creates a suction at the port, like a spray painting gun not worthy paint from a bottle, despite the use of compressed air. Basically, a venturi effect. Once the projectile passes the slanting port, the much higher air pressure will overcome the dynamic partial vacuum, activating the sluice gates.
How and when they open again is the next question. They need to open fully for the next shot, but need to stay together until the pressure trapped behind them has had time to bleed off.
The two sluices will bang together hard, if the action is fast. Needs to close in perhaps 0.01 second. So, the materials must stand up to the task, and not make too much noise as the valve slams shut.
I have thought of a similar concept, but one that uses three rubber heart valve like sections that are blown closed; and held closed until a controlled leak vents the air pressure. Somehow that seems like it would need help with timing, unless an air port system could be configured as for your system.
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Another idea I had some time ago is a simple rubber flap valve. I have attached a very crude mouse driven sketch below to help visualize it.
The valve is opened by the high pressure air blast behind the pellet. When the pressure in the casing is higher than at thee barrel muzzle, the flap slams shut and seals (well enough) against the tube ID.
The rubber could start as a flat disc, or is could have some shape; such as being conical or hemispherical. The disc would be attached at its ID and free to move at its OD.
One might need to support the valve and limit how far it can open (and close) by means of a perforated backing disc of suitable shape. The backing disc would have a smaller OD than the rubber disc to keep an annular channel of sufficient area open around the perimeter of the main tube ID.
Notation:
Black lines = barrel and pellet
Blue = LDC
Red = rubber valve
Green = air flow
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Another idea I had some time ago is a simple rubber flap valve.
It's a concept that has been around for some time, here are some proposed ideas using flaps and balls:
(https://www.spudfiles.com/download/file.php?id=22781)
(https://www.spudfiles.com/download/file.php?id=22783)
With the latter you want to be careful about not pointing your muzzle downwards ::)
One implementation that was apparently made to work is the Kitzmann "gas tong" type:
(https://i.imgur.com/B6Zb6N2.jpg)
There is one moving part, and as it moves forward against the endcap, the two "tongs" are guided towards each other effectively blocking the muzzle.
Combining it with your idea using a flexible component (because we don't have concerns with hot gasses in airguns) it could look something roughly like this:
(https://i.imgur.com/vpFuqCE.png)
A soft rubber piston could be forced against a cone and constrict to effectively block the muzzle.
The crucial element for all of these is timing. The Kitzmann for example would only work with a certain type of ammunition because the system would easily be thrown off balance with different gas pressures.
In a modern world of electronic sensors perhaps a system that doesn't rely on gasses and uses for example a capacitor discharging into a solenoid to block the flow once the projectile is detected as having cleared the device would be an interesting option.
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Maybe it's just me but that's some scary looking stuff right there.
I reckon I'm just more of a K.I.S.S kinda guy.
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Maybe it's just me but that's some scary looking stuff right there.
I agree that it's a very good idea in principle but if done wrong then the consequences could be catastrophic.
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Clever ideas, Jack but blocking the actual muzzle of a centerfire would slam that valve closed so hard, something would deform or crack in no time. Probably should distill that into PCP applications, or someone may take offense.
Back to airguns, I decided to model my crude sketch, as I seem better at that than driving a mouse in place of a pencil. See this as a concept design, minus improvements required for a production version. For instance, the long central tube needs supports near its free end. If this were a 3D printed part, print direction has to be taken into account and "floating features" provided with support.
The concept seems simple enough. Certainly, a 1 mm thick rubber sheet can stand repeated pounding, without cracking the parts it bangs into.
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Probably should distill that into PCP applications, or someone may take offense.
Naturally we're talking about airguns here, just wanted to show some historical examples of the principle at hand.
The design seems simple enough; and a rubber sheet can stand repeated pounding, without cracking the parts it bangs into.
I understand it better now, basically the air accumulates in the chamber via a check valve. It's not quite blocking the muzzle but I can see there being a benefit, I guess it would be relatively easy to do a comparison with and without the rubber to see what difference it makes.
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Think of it as a contactless wipe, Jack. No projectile dodging required.
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Here is a hybrid design: A flapper valved primary blast chamber; with conventional baffles to strip the remaining air going down the central passage.
Again; not a production design. Missing many fillets and other improvements, including supports to prevent the free end of the central tube from vibrating.
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Ok, I may be just an uneducated redneck yankee who migrated to the south with the misconception that I might have less competition in the area above the neck and between the ears but, what affect does stripping and reversing the direction of a nearly 3k blast of air have on the motion/harmonics of the barrel and ultimately the entire gun? Particularly the grub screws securing the breech, the LDC to the barrel/shroud or the shroud to the receiver/barrel?
Would repeated shooting be like tap tap tap of a hammer trying to force things forward?
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Think of it as a contactless wipe
That's essentially what I call the "shut-off valve suppressor" designs are looking to achieve, allowing the projectile exit while trapping most of the gasses much like wipes, but without physical contact that affects power and accuracy.
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=209681.0;attach=440092;image)
With this design you will trap a significant amount of air at high pressure while the projectile is "plugging" the central tube but of course there's still the gas inside the tube behind the projectile some a hybrid with baffles is a good idea, but I would say maintaining volume in the accumulator side is more important for effectiveness so I would see a hybrid looking more like this:
(https://i.imgur.com/kHEEitY.png)
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Depending on the design, Bill there would be some thrust on the LDC trying to pull it off. Depending on the power that force may not be as large as you imagine. Consider how common slip on LDCs are. Even when the thrust is significant, it is delivered as if from a rubber mallet, rather than a steel hammer.
I think that the recoil reduction seen with a powerful PCP gives a sense of the force now taken up inside the LDC (and its barrel mount, and barrel to receiver mount) , compared to a bare muzzle. I don't think this is an exact equation, but it would be fair to state for a conventional open muzzle brake. I would also offer my opinion that for a 30 FPE .22 PCP, the recoil is barely felt and that if all of that force was applied to the barrel mounts, it would be of no consequence. If we are talking about a 1000 FPE PCP then the forces become more interesting.
LDCs can mess with barrel harmonics, or improve them. The air stripping function will often reduce groups noticeably.
Also, just because the air tank is pressurized to 3k PSI does not mean that is what the LDS sees. Not unless the PCP is unregulated and the valve has stuck open, would it see that much pressure. For your typical 30 FPE .22 PCP with a 20 inch barrel the muzzle pressure is more like 400 PSI.
The force that is applied as a thrust on the barrel is not the LDC endcap diameter x the air pressure. Neither is it the baffle OD, because the same air pressure is acting on the opposite baffle wall, cancelling that force. It is the baffle bore area x the pressure differential across that baffle chamber that generates the trust you are concerned about. Yes, successive chambers' forces overlap to some degree, but the first one or two near the muzzle are probably the most significant.
Counter intuitively, the lower the reg pressure is set for a given FPE, the higher the muzzle pressure will be. You can get a sense of this with an unregulated PCP that you shoot from 3kPSI down to 1kPSI. You will often notice that the same PCP, shooting the same pellets, at the same tune, is quieter at 3000 PSI, and a lot louder at 1000 PSI. The reason for this is, to make the same power at lower air reservoir pressure, the valve has to stay open a lot longer. At high tank pressure, the valve duration is much shorter - or it would make much more power.
When I do custom LDC designs for 100+ FPE PCPs, I calculate the average pressure required to generate the power from that barrel length. Then I assume the air tank pressure is near that average pressure, such that the average air pressure down the barrel is the same as the muzzle pressure. Then I do strength calculations based on that. In practice, the muzzle pressure is half to a quarter of the average pressure to achieve a given FPE. It depends on how close the PCP is to producing it maximum power. I add an assumed friction value to the equation, because that increases the assumed average air pressure.
Now, this may seem to be too many assumptions. If I were actually selling these things commercially, I would make them thinner until they blow; then reinforce the failure points. Certainly one cannot go overboard with strength, just in case. It is like reinforcing an aircraft so that the fuselage would survive a crash at 45 degrees to the ground at 600 MPH. Make the plane strong enough and it would be too heavy to fly. Rather avoid conditions that lead to crashes.
I do not design an LDC to stand 3000 PSI, or whatever full fill pressure is. One might say I should, but it would mean the reg has failed (if there is a reg), and the poppet valve has stuck wide open on firing. This is like worrying about brake failure after the wheels have fallen off your vehicle. I do think about what would let go first, and in which direction that part is going to move. I want a "safety valve" of sorts, to achieve a "fail safe" system. Blowing off the LDC or the barrel should not do much harm, as nobody should be in front of you when you shoot. Throwing fragments backward would be very bad.
I recently did a design for a GTA member for a 9 mm Condor PCP. He did not want to place printed parts inside an aluminum tube. So, I made a declaration about how he needed to test the LDC before he could trust it. I did several version of the design, with a range of wall thicknesses, In all cases the area near the barrel muzzle was thicker than the rest. This guy is not in the US, so while I trust he won't injure himself, people in that country are not as ready to file a law suit as they are in the US.
IF we get back to the Airacuda, the end thrust generated by the stock shroud endcap is not zero. I think we can stand to double or quadruple that, without launching the barrel. Especially since we are attaching to the shroud, rather than the barrel.
If you look at all the designs above intended to be screwed into the Airacuda shroud, the male thread that is part of the LDC is the weakest link in the system (I much prefer the male threaded part to be metal). So, if that plastic threaded section holds, I think the barrel retention screws etc are safe.
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Jack,
Your image editing ability is impressive. Piece of cake compared to your animated mechanism gifs.
I agree that the initial uncorking of the projectile from the barrel muzzle is the most significant event from an air management perspective. My goal is to generate concepts that would be fine tuned by actual testing. This includes the relative lengths and volumes each functional zone should occupy.
I wonder if 3D printers with dual extruders could print the whole thing in one go, as a closed system. An elastomer material would be used for the rubber seal. I say that, while having seen 3D printed elastomers, and being less than impressed with their tear strength. So, having the casing made in at least two parts would probably be the best strategy, to enable installation of the rubber flap valve.
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Your image editing ability is impressive. Piece of cake compared to your animated mechanism gifs.
The magic of copying and pasting in MS Paint ;D
In the interest of generating more concepts, here's a half-baked variation that would use synthetic spheres somehow lightly sprung that would act as a check valve in order to avoid relying on elastomers:
(https://i.imgur.com/170zAV9.png)
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Individual spheres will return to their seats more reliably than a single O-ring. The little balls may tend to bounce on opening and closing, unless they impact a slightly soft surface.
Plenty of precision plastic ball options to choose from: https://www.mcmaster.com/products/bearing-balls/material~plastic/ (https://www.mcmaster.com/products/bearing-balls/material~plastic/)
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Seemingly always late to the party.
I WAS going to suggest that "wipes' have been used in 'devices' for decades. They are very effective at increasing the manner in which gasses are trapped and reducing the sound signature of the host weapon. However it also comes at the cost of accuracy, it is not a precission device, but it was effective for what it was initialy designed for.
Also mechanical valves were tried on 'devices' decades ago, but found to get dirty quickly, only be moderately effective as well as contributing to the noise. Of course these two concepts I speak of are a historically referenced from a published book, that I'm not sure I can mention on this forum.
The 'conical flapper valve' is an interesting concept, if it could be made to seal well and hold up to getting slammed shut repeatedly, yet reliably release the air slowly, you might have something there. Biggest issue may be getting a good sealing surface with a 3D printerd part. A secondary machining opp may be needed to smooth up that surface, or the sealing material would need to be very soft, almost gummy.
Along for the ride, love to see where this ends up.......
M
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5 hours later print is done but unfortunately the threads are undersized in the model and it wont screw on the shroud. The thread od on the silencer is the exact size as the thread Id of the shroud so there's no interface between them. ill see if I can change the stl to fix this. It did however print very well with no blobs or stringing so thats a huge plus.
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Sorry about that Travis. The thread size in the CAD model were developed with TorqueMaster Bob and his printing setup. The nominal sizes are larger than what you printed, as Bob used a die to clean off fluff and the layer start-stops for a slop-free thread. See images of thread CAD model, below.
I have taken material out from the full form theoretical thread form, because 3D printed thread are usually to tight to screw in without chasing them with a die. So I "shave" the thread form in CAD with the goal of having a usable thread as printed.
If we look at the nominal dimensions from the link below, you should be able to correct the problem by scaling the X and Y axis by 22/20.917 = 1.0517. This assumes the root diameter of the shroud thread is at 20.917 mm. If it is larger, use the measured diameter instead.
Don't scale the Z axis, as that will change the pitch; unless you have measured it as off. In which case you can apply an appropriate correction factor.
Speaking of measurements, I would appreciate an an ID measurement for the shroud beyond the threads. Also, a measurement of shroud face to barrel muzzle face with stock baffle removed. I am designing a hybrid flapper valve blast chamber to fit into the shroud, with an 80 mm long extension, that matches the assumed shroud OD of 25 mm.
I was not planning to show this shroud insert yet, as it not finished. The flapper valve shape and how it is retained are likely to change. I may extend the blast chamber into the "nose". Also, I intend to add support ribs to help stiffen the long internal cones against vibration. But, as you popped up, I thought I would try to whet your appetite, and increase the odds of you providing the dimensions I need to make the part fit. I have the in-shroud depth at about 4", but can make that match reality to maximize function.
I believe the flapper valved blast chamber will work most efficiently when it is right close to the barrel muzzle; as opposed to tacked onto the front of the shroud. That said, if the internal depth is short, extending the blast chamber beyond the shroud face, and perhaps increasing its diameter may be required to prove the concept.
It would be useful if you could measure your print OD in a few places to see if it is also small by 5%. If it is close to nominal 1.75", then I can create a larger thread form for STL for you; Else scaling should X and Y work.
M22 x 1 mm thread specs:
https://www.machiningdoctor.com/threadinfo/?tid=2041 (https://www.machiningdoctor.com/threadinfo/?tid=2041)
Nominal Diameter 22
Pitch (Distance) 1
Pitch Diameter 21.35
Minor Diameter 20.917
Thread Height 0.541
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As an afterthought, Travis, is it possible that later Airacuda versions that came with a 1/2 20 thread adaptor have shroud cap threads larger than M22 x 1?
If the threads are not M22, then I can make a version with whatever thread size they have. What is the thread OD of your stock shroud endcap? If that is over 22 mm then there is a split in endcap thread specs; and possibly shroud diameters for different Airacuda models.
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Improved design of flapper valve Airacuda insert: Larger volume primary blast chamber, therefore fewer conventional baffles.
Of course, the nose part could be made larger in diameter than the 25 mm shown. It could also be made longer than the 80 mm ahead of the shroud front face.
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Thread OD is 21.2mm same as the tread ID in the shroud. Identical
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Thread of is 21.2mm same as the tread ID in the shroud. Identical
Thanks Travis, but you need to be more specific about which thread you are talking about. The printed thread OD measures 21.2 mm? What does the stock endcap male thread OD measure?
What does the 1.75" OD measure? This will tell us if there is a percentage error that can be corrected with a percentage correction factor.
GTA forum member Robert 5 mm has several inserts with these threads, and they screw into his Standard Airacuda shroud. They were printed by GTA member TorqueMaster. He chased the threads with a M22 x 1 die, but that was not really necessary, as next to no material was removed.
My suggestion is that you print only the threaded end, until you have confidence it will fit. I have attached an STL for just the thread test piece shown below. Printing the whole part before the thread has been figured out will be an exercise in frustration.
My CAD thread OD and root diameters are shown in the image below. I have not changed that for the latest parts.
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=209681.0;attach=440204;image)
Meanwhile, I would appreciate your help, so I can better help you:
https://www.youtube.com/watch?v=S0VO_Q80OXk (https://www.youtube.com/watch?v=S0VO_Q80OXk)
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OD of new silencer thread and ID of shroud is the same at 21.2mm and Stock end cap thread ID is 21.70 mm. I see this happening when people model threads instead of using the thread size under the threading tool in the application. Not a big deal for me I just adjusted the model but could be problematic for others. JFYI
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Travis,
Looking at subscriber's CAD dimensions, his designed thread OD is 21.72mm (22 - 0.14 -0.14)
When I printed it in PETG, it was expected to be slightly smaller due to PETG shrinkage (est 0.5%) ->> (21.72 x .995 = 21.61mm.)
The resulting print was chased, but almost nothing removed. It was reported to fit well on an Airacuda with an endcap measured to have 21.6mm OD threads.
I'd suggest something in your setup is causing undersized prints if you are getting 21.2mm OD on those threads. Did you use PETG? Other materials shrink differently.
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My basic version of Solidworks does not have a thread generation tool. The only way I can generate 3D threads is with a spiral path of nominal diameter as a guide curve for the thread form I specify. As I go to that much trouble, I can fine tune the diameter and thread form for 3D printing.
A 5% diameter error in the printing system pipeline is outrageous. It looks like I need to create a part version with an M23 thread and let you try that...
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Travis,
The attached STLs are for the LDC you wanted to print, and a thread test print. The latter was "cut off" from that LDC. The thread diameter of this LDC is 4.5 percent larger than the one that printed too small.
M23 is 4.5 % larger than M22, so that is what thread the LDC and test print have; both at 1 mm pitch.
Now, if all diameters in your printed part are 4.5 to 5% under CAD dimensions, then the pellet path is also going to be too tight. In which case you may be better off scaling up the X and Y axis in your slicer, until the thread is large enough for a good fit. I have effectively scaled up the thread on the attached part print files, while leaving all other dimensions unchanged.
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Considering Jack's request for more generous internal corner radii, I have created such a version of the LDC that has the wrap around blast chamber, and larger front expansion chamber. The point of the large radii is to create a smooth reverse airflow, driving some Tesla Valve effect.
See image of cross-section below.
STL attached. This has an M22 x 1 mm thread.
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OK; so M23 x 1 is not a standard size. Apparently none of my threads are a standard size ;D
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Biggest issue may be getting a good sealing surface with a 3D printerd part.
I don't think that would be a problem, in fact it could be an advantage - a slightly leaky seal would provide sufficient obturation to reduce the sound while also allowing the excess pressure to leak out slowly once the projectile is clear.
This is how I picture an idea setup, with barrel being ported to ensure gas can fill that first chamber before it has a chance to escape to the atmosphere:
(https://i.imgur.com/v2blkV0.png)
By the way apologies to subscriber for having derailed this thread with a discussion of this principle, perhaps a new one ought to be started.
Considering Jack's request for more generous internal corner radii, I have created such a version of the LDC that has the wrap around blast chamber, and larger front expansion chamber
That looks really good and personally I think this philosophy is optimal in theory; the first chamber accessible by the gas is of maximum volume, while all the subsequent chambers are small and serve only as "plugs" to ensure that the bulk of the gas has time to expand and lose pressure in that first chamber before it can exit.
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My apologies there's NOTHING wrong with the threading. I tried some new filament and it has major shrinking. Back to my old Overture PETG.
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Travis.. would you kindly post a picture of the LDC on the gun for a visual reference?
Thanks.
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Thank you, Travis
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Jack,
I appreciate that you are a clever ideas guy that has made a bunch of working models. That said, there may be two aspects getting in the way of your ball valve in the barrel concept as shown above:
1. Air flowing over a ball from a conical or spherical seat, is notorious for drawing the ball back onto the seat, rather than pushing the ball out of the way, due to the Bernoulli Principle:
https://youtu.be/2G4-pYkqOjI?feature=shared&t=74 (https://youtu.be/2G4-pYkqOjI?feature=shared&t=74)
https://youtu.be/1TQL1ju3RoQ?feature=shared&t=75 (https://youtu.be/1TQL1ju3RoQ?feature=shared&t=75)
2. Making ports in the barrel is not going to be popular, as removing burrs on the inside would be difficult; and the reduction in bend strength undesirable. I would set a goal that no stock parts be modified for any new invention, unless you manufacture the whole system.
If I could make burr-less holes in a barrel (via EDM perhaps) I would populate the last 6" of a PCP barrel with 2 mm diameter holes at a 6 mm center to center spacing. Then enclose that area in a casing with walls partitioning off the discrete air volumes, perhaps 1.5" long. This way, you have a place for the air to get out of the barrel and expand more gently and progressively, than the simple uncorking of the pellet from the muzzle. Notice that there is no mention of valves or balls, because they would add very little functional value.
So, an integral muffler that is perfectly aligned with the barrel bore, and adds no forward length. But it will steal some velocity from the pellet, so start with a barrel that is long enough for purpose. Dandy, but expensive.
For the hobbyist lacking access to an EDM machine, filling that section of the barrel with chamber casting Bismuth alloy, then drilling the holes with a new short 2 mm diameter endmill in a milling machine should minimize burring by supporting the steel as the cutter breaks through into the bore. Then afterwards simply melting the Bismuth alloy out as these melt at very low temperature.
Ultimately, simple is best. But, there is no penalty for considering new ideas, and then analyzing them later for viability.
Below is an airgun muffler that seems very unusual and clever (not mine). I would be very interested to know if it actually performs batter than simple series of baffles, as found on a Marauder, for example. I am not sure the air can get into that organic foam lattice fast enough to be effective.
The pores seem just over 1 mm across (scaled from layer height). I assume the pores could be made larger if they are too tight. I suspect this device might have the pores near the central channel clog with dust pretty fast, and that cleaning it might be a challenge:
(https://www.airgunnation.com/attachments/img_9595-jpeg.385341/)
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1. Air flowing over a ball from a conical or spherical seat, is notorious for drawing the ball back onto the seat, rather than pushing the ball out of the way, due to the Bernoulli Principle
2. Making ports in the barrel is not going to be popular, as removing burrs on the inside would be difficult; and the reduction in bend strength undesirable. I would set a goal that no stock parts be modified for any new invention, unless you manufacture the whole system.
Both very good points, a device that will screw on is a more pragmatic choice.
Below is an airgun muffler that seems very unusual and clever (not mine). I would be very interested to know if it actually performs batter than simple series of baffles, as found on a Marauder, for example. I am not sure the air can get into that organic foam lattice fast enough to be effective.
The pores seem just over 1 mm across (scaled from layer height). I assume the pores could be made larger if they are too tight. I suspect this device might have the pores near the central channel clog with dust pretty fast, and that cleaning it might be a challenge
Interesting, to me this has always been counterintuitive to a degree, in the sense that the air should take the path of least resistance and here you're slowing it down as it attempts to fill the volume, so presumably it would do so at a lower rate.
I can understand this style of device used in commercial pneumatics where there is no muzzle hole for the gas to escape or outer casing:
(https://i.imgur.com/e6RfAR6.png)
I don't see it making too much of a difference in a design that also allows a projectile to go through.
That said given, the wonders of 3D design and printing, what if that lattice on a micro level had a wedge-shaped cross section where air can flow easily past it in one direction but not the other...
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Jack,
A few days ago I experimented with different ways of modeling "foam", as shown above. To generate a 1.5" diameter by 6" long "slug" of foam, using different ways to model it in Solidworks, used up of 50 and 80 Mbytes as a Solidworks files, and much more as an STL. That bogged my PC down to the point that the lack of processing speed frustrated me, and I gave up.
The guy printing those foam filled LDCs is using one of the infill options of a particular 3D print slicer, so that very bit efficient. I include images of my more "open cell" foam, where the filaments are 1 mm in diameter for the basket weave. On the spherical pocket version, the pocket diameter is 3 mm, with the each hole at the connection is 1.5 mm.
Anyway, I am dubious about the ability of such small air paths to accept air as fast as it needs to happen for LDC application. If the foam was just a 4 mm thick layer on the inside of the outer tube to reduce pressure wave reflection, then I would be OK with it. My basket weave idea is such a sleeve, that is both low reflection, with the ability to pass some air to a secondary space, if desired.
Anyway, have defaulted back to using a matrix of round holes in the 2 to 3 mm diameter range, that have a 0.5 mm fillet on the high pressure side, with the opposite side edges left "sharp" for more resistance to return flow. As used here, for example:
https://www.gatewaytoairguns.org/GTA/index.php/topic,210109.0.html (https://www.gatewaytoairguns.org/GTA/index.php/topic,210109.0.html)
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=210109.0;attach=440569;image)
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The guy printing those foam filled LDCs is using one of the infill options of a particular 3D print slicer, so that very bit efficient.
That's quite clever, but of course it wouldn't be optimized for ideal airflow interference.
My basket weave idea is such a sleeve, that is both low reflection, with the ability to pass some air to a secondary space, if desired.
What I was suggesting was something like the basket weave but instead of having a round cross-section, something more like an arrowhead pointing towards the centerline.
(https://i.imgur.com/8EepV7a.png)
I'm not sure how much of a difference it would make in practice, but it would in theory encourage flow in one direction more than the other.
Those offset designs for the Huben look great by the way! A good way of maximizing volume without too much bulk.
That leads me to mention another harebrained notion, what if you connected a hollow plastic stock to the moderator with a length of tubing to give a lot of volume with little extra bulk ::)
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Jack,
O like your arrowhead filament section idea as a concept. With two points to ponder:
There is a limit to how small sharp features can be generated.
Printer mechanisms hate repetitive sharp features because of the jerky motion. So, I generally try to round all transitions to at least 0.5 mm radius. Sometimes Solidworks can't fit in a fillet into a complex shape, unless I reduce it to .25 mm.
That said, your triangular shape could be implemented at a scale where it makes sense, as a differential flow resistance shape. I think if the triangle section was 2 mm long at the longest segment the idea could work. I would model it now; except I have a request for Taipan inserts - part design in process.
If you connected an LDC to a hollow stock, through a short fat pipe, I can see it adding volume equivalent to the rear volume of a shroud. A connecting pipe that is long and skinny wont flow enough air in the amount of time that matters. Somewhere between 1/100 and 1/10 second.
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That printed "foam" in the pictures above is made by using the "gyroid" infill pattern:
At the scale of the infill pattern in the video below, that might even be useful for mufflers. I don't know how one demarcates which areas get infill, and which do not. But, may have found some videos about that, below:
https://www.youtube.com/watch?v=_SaAayWYJPU (https://www.youtube.com/watch?v=_SaAayWYJPU)
https://www.youtube.com/watch?v=jG9SAC-uuwM (https://www.youtube.com/watch?v=jG9SAC-uuwM)
https://www.youtube.com/watch?v=tk7XhV1tSpE (https://www.youtube.com/watch?v=tk7XhV1tSpE)
https://www.youtube.com/watch?v=su_m5zV9rvA (https://www.youtube.com/watch?v=su_m5zV9rvA)
Infill strength test showing different options:
https://youtu.be/upELI0HmzHc?feature=shared&t=443 (https://youtu.be/upELI0HmzHc?feature=shared&t=443)
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That said, your triangular shape could be implemented at a scale where it makes sense, as a differential flow resistance shape. I think if the triangle section was 2 mm long at the longest segment the idea could work
Yes it would have to be a bigger scale and good point about FDM printers not liking that sort of pattern. I have access to SLS printers that wouldn't mind that as much, but alas contrivances designed to dampened sound are a no-no in my part of the world so my interest in the subject is purely academic.
If you connected an LDC to a hollow stock, through a short fat pipe, I can see it adding volume equivalent to the rear volume of a shroud. A connecting pipe that is long and skinny wont flow enough air in the amount of time that matters. Somewhere between 1/100 and 1/10 second.
I'm picturing something like that feeding directly into the forend of a conventional stock:
(https://i.imgur.com/puXNv6b.png)
It would look a little odd and need a specifically designed stock, as drawn it would also interfere with filling etc. but it's an interesting line of thought to have a massive volume without adding too much length and bulk.
That printed "foam" in the pictures above is made by using the "gyroid" infill pattern
That's a great find, it looks like it would absolutely confuse the trousers off the airflow!
(https://i.imgur.com/H85oaum.png)
It would be really interesting to see how a tube filled with this pattern would perform compared to conventional baffles.
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Here, the lower "barrel" is an expended air receptacle:
https://www.pyramydair.com/product/stoeger-xm1-s4-suppressor-pcp-air-rifle-black?m=5321 (https://www.pyramydair.com/product/stoeger-xm1-s4-suppressor-pcp-air-rifle-black?m=5321)
(https://www.pyramydair.com/images/zoomed/PY-5321_Stoeger-XM1-Suppressed-PCP_1620753863.jpg)
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Here, the lower "barrel" is an expended air receptacle
Something like that, and it doesn't have to look too awkward either, simply to show the aesthetics this offering from Ruger is rather handsome:
(https://i.imgur.com/F5ABlVO.png)
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This was the most interesting thread I read here in months.
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This was the most interesting thread I read here in months.
Though I don't get on much due to my work load I totally agree.
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I was wondering, Travis, if you printed and tested that short fat design you asked for? Your results and impressions would be interesting.