Is this concept printable?

[Mr.H]

Ok, here are a few more pics with dimensions.
I measured the gap with gap feeler gauges, and just for kicks I threaded on the aluminum extension, and both of the moderators that I have, and it did not seem to change the gap. But who knows what happens when you pull the trigger.

I did use calipers to take most of the measurements. I just posted the pictures, too get confirmation from you that I am measuring the correct part.

I am going to go back to read all of your posts from last night, after my last post. Just to make sure that I’m getting you all the information that you want.

 

[Mr.H]

I forgot to include the barrel diameter, 15 mm, you were correct in your assumption.

I think I could make up a model out of quarter inch thick plywood of what I think you have in mind and overlay it and send a picture. Is there any value in that for you?

 

[subscriber]

Thanks, Mr.H

Below is an image I generated to show my printer guy. I think it achieves what your plywood profile would do; unless I am mistaken. The image does not have your latest dimensions applied. It will need to be about 10 mm shorter overall to print. Internally there is no detail yet.

This image shows a nose OD of 45 mm. You may want something else.

The air tank and shroud are unusually close at just over 0.5 mm. I really do think that a supportive barrel band coupling the shroud and air tank towards the front of the tank (not over the fill port cover) may be required, regardless of what else you do - unless it is to use a smaller ID shroud tube to increase air tube clearance (not advocating for that). A half mm gap can easily bounce shut and then the shroud could do strange things.

Just for general interest, what are the cone IDs? Any sign of clipping there on any of the cones?

The part that looks like a spoked wheel that screws onto the muzzle has what OD?

If I am right, the shroud tube has one end threaded. Can you measure the OD of the threaded part that screws into the shroud, please; with pitch? Probably 28 x 1 mm.

I will come back to this, this evening; but I thought that mapping some basic dimensions and ideas already would be helpful.

 

[Mr.H]

Here are some more dimensions for you with photos.

I would be guessing on the TPI on that shroud cap. I have a question in on the PCP forum to ask if anybody happens to know for sure.

I like your idea about a barrel band, if it can be integrated.

You had also asked about the ballistics. It is shooting the 25 grain pellets at 865 fps.
for comparison, a friend of mine had the standard size. The barrel was 17 inches, and the shroud was approximately 4 inches longer as well. And he probably had five cone baffles, not three like mine. And he was shooting at the same FPS, as mine, so he was using less air than me. His gun much quieter than mine

The exit hole on the shroud cap is 21/64 of an ounce or .328”

Also wanted to mention that there is no sign of clipping on the baffle cones. And the exit hole on that STO unit that I have is also .328.

 

[TorqueMaster]

Sub's "Printer guy" here -- not print related but I noticed a possible issue from your measurements --
I am not familiar with this particular moderator, but I would say the cones have been installed backwards at some point. I expect the entry to be small, and the exit large. It should strip away the air, not funnel it all down the pipe.

It is most likely the shroud cap is metric, 28x1.0 -- based on your OD measurement and eyeballing the thread pitch compared to the known 1/2"-20. A calipers to measure "x" threads, then divide by "x" should get you close. A quick google says it should be 1.0, 1.5, or 2.0 for a 28 mm. ASSuming it is a standard pitch.

 

[Mr.H]

Sub's "Printer guy" here -- not print related but I noticed a possible issue from your measurements --
I am not familiar with this particular moderator, but I would say the cones have been installed backwards at some point. I expect the entry to be small, and the exit large. It should strip away the air, not funnel it all down the pipe.

It is most likely the shroud cap is metric, 28x1.0 -- based on your OD measurement and eyeballing the thread pitch compared to the known 1/2"-20. A calipers to measure "x" threads, then divide by "x" should get you close. A quick google says it should be 1.0, 1.5, or 2.0 for a 28 mm. ASSuming it is a standard pitch.

View attachment 427158

Nice call Mr. TM. You must be correct on cone alignment. I just checked owners manual.

 

[dgeesaman]

JMO ... anything printed is going to LACK the structural strength and ability to hold alignment with handling and temp changes etc ...

The commercially printed glass filled nylon is quite sturdy. But I don’t know if threads are goi g to work

 

[subscriber]

Thanks, TorqueMaster for paying attention to the "entry" and "exit" measurement designations for the baffle cones. Certainly, if the cones were installed backwards, not only would sound suppression suffer, the air flow down the spigot that then necks down to what should be the baffle inlet is likely to upset the pellet. This alone might explain the poor performance with regards to sound suppression and grouping.

If I understood correctly, even the Huggett attached to the muzzle directly did not do well - unless that was about sound, rather than grouping or point of impact shifts. Now, a 15 mm barrel OD with a chamfer at its stud shoulder, mated to a muffler with a chamfer at the edge of the female thread, leaves very little flat shoulder to overlap between barrel and Huggett. So, it is possible that there was some misalignment with the Huggett directly mounted too. Apart from actual clipping, a large slant in the air flow can push pellets around.

If the Hugget did tend to mount in an angular fashion due an ineffective shoulder, who is to say that it would not mount in a different angle every time it was installed? That could account for shifting POI. Or, perhaps the Huggett could waggle shot to shot, and upset groups. Even if the problem was not airflow related, having something attached to the barrel that is able to migrate shot to shot, is bad for system harmonics.

The stock baffle bores seem tight to me, for a system where there is any doubt about shroud droop; but the above observation about baffle reversal is a very significant one.

I agree that the shroud endcap thread is most likely 28 x 1 mm. I count at least 8 threads, with a bit more, removed by the two chamfers at either end of the thread - see image below. If there are any doubts, then using any 1 mm pitch thread form as a thread gauge will settle the question. Assuming a proper thread gauge is not on hand.

All that said, I think this PCP would benefit from a longer and wider expansion volume ahead of the barrel muzzle. Certainly, we can get that to over 8" long at the max print height you can handle. But, rather than being overcome by eagerness as I often am, I think Mr.H should try to see how his airgun shoots with the stock baffles installed with the small ends of the cones pointing at the barrel muzzle. Does it shoot better, and it it quieter? If yes, but not quiet enough, then that seems like a go ahead for this project. I will carry on with a design, regardless. Unless I am told to stop.

 

[subscriber]

The commercially printed glass filled nylon is quite sturdy. But I don’t know if threads are goi g to work

Glass filled nylon is not only very stiff and strong, it has very good creep resistance. The latter is something that FDM printed materials are lacking; especially PLA at temperatures that are easily reached in a closed vehicle, parked in the sun. That is why PETG seems like a better choice.

 

[Mr.H]

Thanks, TorqueMaster for paying attention to the "entry" and "exit" measurement designations for the baffle cones. Certainly, if the cones were installed backwards, not only would sound suppression suffer, the air flow down the spigot that then necks down to what should be the baffle inlet is likely to upset the pellet. This alone might explain the poor performance with regards to sound suppression and grouping.

If I understood correctly, even the Huggett attached to the muzzle directly did not do well - unless that was about sound, rather than grouping or point of impact shifts. Now, a 15 mm barrel OD with a chamfer at its stud shoulder, mated to a muffler with a chamfer at the edge of the female thread, leaves very little flat shoulder to overlap between barrel and Huggett. So, it is possible that there was some misalignment with the Huggett directly mounted too. Apart from actual clipping, a large slant in the air flow can push pellets around.

If the Hugget did tend to mount in an angular fashion due an ineffective shoulder, who is to say that it would not mount in a different angle every time it was installed? That could account for shifting POI. Or, perhaps the Huggett could waggle shot to shot, and upset groups. Even if the problem was not airflow related, having something attached to the barrel that is able to migrate shot to shot, is bad for system harmonics.

The stock baffle bores seem tight to me, for a system where there is any doubt about shroud droop; but the above observation about baffle reversal is a very significant one.

I agree that the shroud endcap thread is most likely 28 x 1 mm. I count at least 8 threads, with a bit more, removed by the two chamfers at either end of the thread - see image below. If there are any doubts, then using any 1 mm pitch thread form as a thread gauge will settle the question. Assuming a proper thread gauge is not on hand.

View attachment 427263


All that said, I think this PCP would benefit from a longer and wider expansion volume ahead of the barrel muzzle. Certainly, we can get that to over 8" long at the max print height you can handle. But, rather than being overcome by eagerness as I often am, I think Mr.H should try to see how his airgun shoots with the stock baffles installed with the small ends of the cones pointing at the barrel muzzle. Does it shoot better, and it it quieter? If yes, but not quiet enough, then that seems like a go ahead for this project. I will carry on with a design, regardless. Unless I am told to stop.

Thank you for the post. This last week the temperatures have barely been above zero Fahrenheit. this next week we’re going to have some weather 30 to 40°F so I will be able to test this with the cone baffles correctly assembled. And on FYI, I am not the original owner of this gun.

Interesting aspect of this gun, un-suppressed, it is a tack driver. Half inch groups at 50 yards. And that is when the baffles were installed backwards

 

[subscriber]

Mr.H,

Could you provide a direct measurement the of from the barrel shoulder to the front end of the air tank, please?

I am expecting a value of 153 or 154 mm. If so, then my insert model is on the right path. If that measure is over 156 mm, then I need to create more clearance for the air tank.

The top image shows the barrel shoulder, but not the end of the air tank. The second image shows the end of the air tank, but infers the barrel shoulder, because the Huggett buts against it:

The insert design is a shell without baffles at this point, but this is what I have right now:
The perforations are rounded on one side and sharp on the other, to provide differential flow resistance. The perforated wall is intended to act as a poor sound wave reflector; like felt, while allowing more air flow to pass into the secondary space; and to delay its exit.

The perforated section will be divided into at least two spaces, via baffles. The baffles will extend into the secondary space, thereby bracing the perforated tube and outside wall.

 

[subscriber]

Dimensions requested above are pending. Design will be updated after receipt / confirmation

Images below show current state.
There is a reflex air stripper to feed the rear of the shroud.
Design sports three sequential Tesla Valve baffles sets.
The support structures for the Tesla Valve airfoils that separate airflow direction still need to be added to the design.
The mounting threads that screw onto the barrel stud and shroud end ID need to be added.

This thing looks a bit like a WW2 stick grenade. Hopefully it won't be as loud

I have been at this all night, and am fading fast. So completion will have to wait...

 

[Mr.H]

A stick grenade, precisely!! Lol!

That is pretty awesome looking subscriber.

The missing number you’re looking for is 6 1/16 of an inch or converted, 154mm

That is a tight measurement

 

[subscriber]

Based on your 154 mm measurement there would be a nominal 2 mm clearance between air tank end face and the large OD section at the beginning of the taper. So, I moved that tapering wall 1 mm, to increase the nominal clearance to 3 mm. See red arrow pointing to the right, below.

I also made the shroud OD "stem" section 1 mm thicker because it has to carry the bending moment generated by the large head section. See two vertical arrows indicating new wall thickness.

Solidworks report a solid volume of 112 CCs as shown below. That will increase slightly after I add the airfoil supports and threads. For a material with a SG of 1.2, the expected mass would be around 140 grams; after adding the missing features.

 

[subscriber]

I have added the Tesla Valve airfoil support structures - images below. I added such a TV airfoil to the fourth expansion chamber, so this muffler is fully Tesla Valve baffled, followed by a dual large "soft" expansion chambers.

 

[BlackICE]

If it works as good as it looks you won't be able to hear a thing. Your CAD work is exquisite.

 

[Mr.H]

If it works as good as it looks you won't be able to hear a thing. Your CAD work is exquisite.

My thought exactly!! Can't wait to try this out.......

 

[subscriber]

I stiffened up the front end with some perforated walls between the inner and outer tube. I may reconfigure those walls to lean the opposite direction.
Added the 1/2-20 thread.

Missing:
M28 x 1 thread

May add some 0.1 mm tall ribs to the 27 mm OD section to ensure a tight fit in the shroud. The nominal 27 mm CAD tube will print smaller than nominal by perhaps 0.2 mm. Using ribs makes it easier to see where the part is tight and to file or sand that area down a few thousands of an inch.

TorqueMaster will print subsections of the part to help fine tune the fit, before printing the whole part.

 

[beerthief]

Mr.H

You have provided a lot of information, but there is a lot of detail missing that might enable us to understand the cause of your POI shift problem.

If you need to adjust your POI up after attaching bits to the front of your airgun, is it possible that the added weight is causing some barrel droop? Or a change in harmonics. If the latter, the POI could shift in any direction, including up.

It would seem that some POI shift is typical when adding a moderator, providing it is not excessive. What is unacceptable would be if good grouping without a moderator opens up wildly after a moderator has been mounted. So, it might be useful to provide more detail about what is happening to your system.

It might be worth asking if the barrel is snug in the receiver, or if it can be made to move angularly when light force is applied. A little spring in the barrel and or shroud is typical for light airgun barrels, but I am talking about slop in the barrel retention that might be the root cause of your observed results. I would like to think that you have looked for such causes and eliminated them, but you know what they say about assuming anything.

A simple way to extend your shroud to be slightly ahead of the air tank is to undo the shroud's rear endcap clamping screw and slide the shroud forwards. It is free and can be restored if you don't like it. That said, the longer shrouds that bigHUN listed seem like attractive options. But, they won't fix a loose barrel socket, and cost a bundle.

I assume that the stock air diverter is screwed snugly to the barrel muzzle, and that its O-ring is snug in the shroud ID? If either of these are neglected, that alone could explain why hanging more bits from the shroud is making the system unhappy.

I am impressed with how many bits of custom hardware you have had made. The fact that this has not helped is perplexing, and might suggest there is something else the matter that is not being helped by the addition of precision hardware. If that is true, then adding a one piece shroud extension moderator combination is unlikely to help either. That is not to say that I am unwilling to design you a custom muffler to your specs.

It would recommend that you do some diagnostics, including the obvious, such as checking barrel mounting and centering at both ends. Angularity of the shroud faces and threads. It may be that if you flip the shroud end over end and use the more perpendicular face and thread, that there is an improvement with the hardware you have.

You can firmly apply a layer of masking tape to the front of your moderators, over the bore opening, then shoot a few shoots to see how well the system is aligned. Pellet holes near the edge of the moderator or shroud front cap bore indicate a problem, but not the cause. So testing with and without moderators should provide comparative data that you can think about, and should help with the diagnosis - even if it takes a few steps to get there.

If the masking tape shows pellet holes that are very far off center you may be seeing light clipping, that will not just shift your POI, it may blow groups. Depending on the type of moderator, offset pellet travel may aerodynamically steer the pellets to shift POI, or blow groups, if barrel harmonics or mounting slop are involved.

So, I would be happy to design something for you, but have a suspicion that a printed moderator is not going to solve your problem. To hedge my bets with what we know know, I would use extra generous projectile to baffle bore clearances. Just in case you are seeing a little clipping or projectile steering effects, regardless of their cause. Else, clipping with a printed moderator will damage it, and may result in a cascade failure with subsequent shots, as larger bits of plastic get in the way if the next pellet; and so on.

I hope this does not seem like a lot of words that say nothing. It is intended to help you confirm or dispute assumptions, and to gain clarity. Some of the assumptions include that your custom machined bits are as well made as the look. It may be insulting to your friend to check that, but it needs to be done. If the problem is present without adding custom bits, then the stock hardware is suspect. Adding even good extensions may make misalignment of the moderator worse, it the stock hardware has an angularity problem.

This is probably about as far as I should go, without more information; and hardware confirmation.

Well done , impressive thought process . a good read over my first cup this AM

 

[OldSpook]

I stiffened up the front end with some perforated walls between the inner and outer tube. I may reconfigure those walls to lean the opposite direction.
Added the 1/2-20 thread.

Missing:
M28 x 1 thread

May add some 0.1 mm tall ribs to the 27 mm OD section to ensure a tight fit in the shroud. The nominal 27 mm CAD tube will print smaller than nominal by perhaps 0.2 mm. Using ribs makes it easier to see where the part is tight and to file or sand that area down a few thousands of an inch.

TorqueMaster will print subsections of the part to help fine tune the fit, before printing the whole part.

Nice looking moderator.

The Tesla valve (in that form) is tunable. Our testing has shown that the ratio of bore area to vent area can be tuned to favor accuracy or suppression.

We have ascertained, by testing, that total vent area over bore area should be approximately 10 or 12 to 1 to achieve maximum accuracy.

A lot of moderators will make a gun quiet at the cost of accuracy.

Those ratios in the first battle and the jump between the barrel and the first baffle have a heavy influence upon accuracy.

There is a "lag" time established by the distance the air/shockwave being redirected has to travel before it meets back up with the out flowing air stream. If that lag time is too short it will destabilize the projectile. Air is compressible. Another way of putting that is we have, by testing, also shown that there is a minimum velocity associated with any Tesla type valve. If the muzzle velocity of the pellet is not high enough it will be hit by that backwards flowing stream/shock wave and be destabilized. You can calculate that number because you know the distance of travel from the time pellet enters the baffle to the time that it traverses out the exit and you also know the time it takes for the shock wave exiting behind the pellet at the muzzle to make the round trip.

HTH