Taming the bark of an Avenger

[WhatUPSbox?]

If you are on a PC, the scroll wheel zooms in, right button rotates, and shift and left button translates.
If you look in the menu on the right there is a line for turning on supports. if you expand that, there are a lot of options to play with. After you slice any particular option you'll see the supports (blue) as you go through the layers.

[subscriber]

Thanks Stan,

I am impatient, but learning as I go. 

Found how to set fill to 100%, which what I assume one should do to make strong thin walled parts.  It increases print time by almost 2X, which is why people avoid it.  However, having your LDC blow its top, and then re-printing it is going to take even longer....


When I turn off the inbuilt support walls from my Maxim design, you can see overhanging parts float in mid-air (images below).  They don't do that with the walls I designed into the part.   Floating aspects are impossible to print into functional parts...

I do not want these designs printed with Cura slicer supports turned on, for the simple reason that they will be impossible to remove after the print is complete.  The typical breakout supports are fragile and will break when the airgun is fired, to dangle in the pellet path.  Even if slicer supports can survive shooting, they occupy expansion volume and interfere with air flow. 

If I was designing a 3D printer I would make a dual nozzle system, where one nozzle deposits only water or alcohol soluble material, so a simple soaking and flush would remove all internal supports from the completed parts...

Generally I avoid using any design features that lean steeper than 45 degrees, and have flat bridges further than about 1 mm.  This was not possibly with the above Maxim design, without adding the little walls with the curved arches.


Yes, I section the parts in Solidworks before saving the STLs, as I can't find where to section-view parts in Cura...

[WhatUPSbox?]

Once you slice the model, if you click on the preview button, you will see a slider on the far right that represents all the print layers. You can use the slider to view any of the layers.

[subscriber]

I have used that slider, Stan.  It helps, but I want to cut the sliced part perpendicular to that to look inside.  The inside view you see two posts up was achieved via Solidworks. 

[WhatUPSbox?]

I don't know if it can do that.

[subscriber]

No worries Stan.  A good plan, even if not perfect.

I have vague memories of a Kodama slicer doing what I want; to see "inside" a closed body.  That was a long time ago, and memory in fungible

Cura's flag for this overhang, below, does not start at the lowest section of the floating ring.  Only the start of the horizontal overhang, that would follow printing the floating section....

As with all things, never rely on software to do your thinking for you.

[WhatUPSbox?]

Yeah, I usually start the slider from the bottom and watch for something starting in mid air.

[stylnchris]

No worries Stan.  A good plan, even if not perfect.

I have vague memories of a Kodama slicer doing what I want; to see "inside" a closed body.  That was a long time ago, and memory in fungible

Cura's flag for this overhang, below, does not start at the lowest section of the floating ring.  Only the start of the horizontal overhang, that would follow printing the floating section....

As with all things, never rely on software to do your thinking for you.

Agree -  Cura flags a lot of things needing supports that more modern 3d printers can print without needing the support.    Sometimes you will get a little stringiness but that can easily be cleaned up afterward.  I'm amazed at somethings that needed supports that I tried without just to see how it would do.   

[TorqueMaster]

Thanks Stan,

I am impatient, but learning as I go. 

Found how to set fill to 100%, which what I assume one should do to make strong thin walled parts.  It increases print time by almost 2X, which is why people avoid it.  However, having your LDC blow its top, and then re-printing it is going to take even longer....


When I turn off the inbuilt support walls from my Maxim design, you can see overhanging parts float in mid-air (images below).  They don't do that with the walls I designed into the part.   Floating aspects are impossible to print into functional parts...

I do not want these designs printed with Cura slicer supports turned on, for the simple reason that they will be impossible to remove after the print is complete.  The typical breakout supports are fragile and will break when the airgun is fired, to dangle in the pellet path.  Even if slicer supports can survive shooting, they occupy expansion volume and interfere with air flow. 

If I was designing a 3D printer I would make a dual nozzle system, where one nozzle deposits only water or alcohol soluble material, so a simple soaking and flush would remove all internal supports from the completed parts...

Generally I avoid using any design features that lean steeper than 45 degrees, and have flat bridges further than about 1 mm.  This was not possibly with the above Maxim design, without adding the little walls with the curved arches.


Yes, I section the parts in Solidworks before saving the STLs, as I can't find where to section-view parts in Cura...

Hey hi, I was browsing looking at LDCs for avengers (I have a .177 and a .22) and have been reading along.  I am very familiar with Cura and the Ender 3, so may be able to chime in from time to time...

For the follks doing the printing, are you using PETG?  Have you tested other materials (PLA, TPU maybe even) to see if they deaden the sound better or worse?  PETG seems ideal, not quite as brittle as PLA, but almost as strong.  TPU (shore hardness 95 is what I'm familiar with) is a "flexible" filament, but printed thickly enough it can be quite rigid.  I'd compare it to the rubber on a tire's tread block, perhaps a bit stiffer than that.

Subscriber,
The floating features showing up when sliced in Cura may be because the connecting walls are too thin for the printer to print.  I'm running an older version of Cura, but expect you should have a setting for "print thin walls" which allows walls thinner than the nozzle size.  Speaking of which...0.40mm nozzle is probably what you should select, but could try smaller to see if missing details show up.  Also try smaller line widths.  Ideally designs should not have elements thinner than 0.5mm...1.0mm even better.

No way to make section views/cuts that I am aware of other than the Z-axis layer views.

Within Cura support settings you can choose the overhang angle which will require supports.  This *might* affect what parts of the object get the red colored overhang warnings.  Yes, keeping your designed overhangs at 45degrees or less is ideal!  Finely tuned, we can print horizontal "bridges" (supported only at the ends) across parts of a model of 2 inches or sometimes more.  Usually some droop on the first pass/layer, so not ideal, but doable.  Inside a relatively small model like these LDCs, bridging should not be a problem at all.

Unless there are some very thick areas in these designs, yes, 100% infill is likely the best way to go.  Completely solid print.  Most of the strength comes from how thick the "walls" are printed, and it looks like most of these designs are lots of thin walls...dealing with significant air pressure...which should not be compromised by hollowed infills.  There won't be many/any areas where infill makes sense.  To a degree, sound deadening is affected by the density of the LDC, right, so solid as solid gets should be quieter...

Cool designs btw!!!  I really don't find the Avengers *that* loud, but if I can stuff one of these in the shroud and reduce sound (and/or increase precision???) that'd be cool!  Thanks to all for the efforts!

[subscriber]

Thanks for the info and advice, Bob. 

The 12 "support walls" in the above Maxim inspired LDC are 0.5 mm thick.  I figured that is thick enough for them to do their job, without taking up too much internal volume.   There is no air pressure differential across these support walls in their "flappy" direction - because there is total symmetry in the part and air flow.  Yet, they should help add stiffness radially to the outer walls.  These outer walls, despite looking robust "zoomed in", are only 3 mm thick.

As for the minimum size of detail that these printers can produce; the 1 mm pitch thread surprises me.  Especially as it has overhang.

I hope the guys printing the LDCs are using PETG.  PLA is brittle and droops at temperatures over 50 degrees C.  So, this may be a problem with black filament in direct sun.  PLA is also biodegradable, suggesting it is not really intended for long term use. 

I am busy with a version of the above "Maxim" design that is 104 mm longer than the shroud tube; and has an OD of 30 mm.  The spiral design might be "clever", but it has a lot of solid material occupying expansion volume, so the larger version LDC should help address that.

[WhatUPSbox?]

Bob, are you able to print TPU without direct drive?

[TorqueMaster]

Thanks for the info and advice, Bob. 

The 12 "support walls" in the above Maxim inspired LDC are 0.5 mm thick.  I figured that is thick enough for them to do their job, without taking up too much internal volume.   There is no air pressure differential across these support walls in their "flappy" direction - because there is total symmetry in the part and air flow.  Yet, they should help add stiffness radially to the outer walls.  These outer walls, despite looking robust "zoomed in", are only 3 mm thick.

As for the minimum size of detail that these printers can produce; the 1 mm pitch thread surprises me.  Especially as it has overhang.

I hope the guys printing the LDCs are using PETG.  PLA is brittle and droops at temperatures over 50 degrees C.  So, this may be a problem with black filament in direct sun.  PLA is also biodegradable, suggesting it is not really intended for long term use. 

I am busy with a version of the above "Maxim" design that is 104 mm longer than the shroud tube; and has an OD of 30 mm.  The spiral design might be "clever", but it has a lot of solid material occupying expansion volume, so the larger version LDC should help address that.

The 0.5mm thin walls should be "ok", and 3mm thick walls quite strong.  Ideally printed with a 0.5mm line width to minimize "filling in the cracks" that would be caused by printing it with 0.4mm lines.

For small details, I mean single line details, such as your thin walls.  The XY resolution is at least 0.10mm and closer to 0.01mm.  A 1 cm cube is usually in the 9.98 to 10.02mm range on all sides.  So tiny threads can be done -- the layer height, Z resolution, may need reduction to get tiny threads done well.  1mm pitch threads are pretty forgiving, I think I have printed them at .28mm layer height even.  Edit-- my bad -- I was looking at 2mm pitch bolts printed at 0.28mm layer height.  Often I chase them afterwards, very easy to clean up plastic threads.  Typical printing is 0.20mm layer height.  Lowest practical is 0.08mm.  I've done 0.40mm, but only to max out extrusion rate on large, visually unimportant prints...

PLA covers a lot of range -- some holds up outdoors, some doesn't.  Not much regulation -- no way to be sure.  "Biodegradable" sort of like plastic diapers -- decades not years or months.  In the sun, I wouldn't worry about drooping, in a hot car, yes, worry.  But yes, overall PETG has a better likelihood of survival.  Nonetheless I'm curious which deadens sound better or if there is little to no difference.   PLA is a bit more forgiving to print, it's a "go to" material when you just want it to work the first time with little to no fuss.

@WhatUPSbox --  "Bob, are you able to print TPU without direct drive?"
 I did briefly.  It worked if I printed slow and steady.  And I only tried it with the firmer shore 95 stuff.  Very soon thereafter I printed a bracket to move the extruder onto the hotend, and have never looked back.  It has a bowden tube about 2 inches long now, maybe a quarter inch is actually visible.  I also switched to the red aluminum extruder, but printed a replacement for the base that has a very pointy tip that wedges between the extruder gear and pulley -- giving the filament pretty much no gap to escape.  A couple of times it's jammed with molten plastic -- user error loading/unloading -- and I've had to disassemble and use a hand drill to clean out the solidified gunk.   I'm surprised how well the plastic parts have held up, but this setup has been working great for a couple years now. 

[Mr.P]

Amazing designs here and I missed this thread somehow. I think I just assumed it was about different brands of moderators not about how to approach designing baffles for a shroud.  What is the size are amazing!

Maybe somebody already said this, but the red zones are areas that are past the angle limit you specify that defines where  support is printed.  As you change the minimum angle for support you will see the red zones shift.

I’m curious - do you think designs like this would be suitable for a larger air volume situation,  for example at 100+fpe with larger bores?  This seems to really engage with the airstream, as opposed to designs with say three open chambers of different sizes.

After a long break I’m back messing with this kind of thing and trying to quiet a very loud .357

I assume  that’s a topic for a different thread. 

In a nutshell when starting something like this, is there a rule of thumb for using lots of small chambers like this vs. a small number of large chambers?  I know these are unique chambers and maybe comparing them to standard cup baffles similarly spaced is not a fair comparison.

Previous airguns I had up to .257 / 160 fpe were pretty easy to quiet to my standards* and even basic 3d prints i cooked up worked well.

The .357 at similar power levels is much louder of course and not easy to quiet to my standards* at all.



* My standards: quiet enough that I can  shoot several dozen shots a day over a chronograph during the rainy season in my suburban barn door style garage without attracting the wrong kind of attention from my nosy neighbors.  The doors let a little more sound pass than a typical garage door.

[subscriber]

Bob,

The guys that are printing my designs asked me to reduce the volume of thread form, so that the threads don't have to be chased.  I prefer a full form that is chased, for strength.

Coextruding TPU to coat the inside of an LDC may have value.  Printing the whole LDC of TPU will have it droop into the projectile path.  Ditto for the whole structure ringing in such a vigorous manner that clipping is a risk.

Some of my designs included internal texturizing (images below) to see if these break up reflected sound.  While more experimentation should be encouraged, the measured reduction in peak sound was in the range of 2 dB.  In the noise, so to speak.   The downside was that the texture increased print time and file size.  This was for a Nova Liberty LDC very similar to the Avenger ones.  The printed texture of these LDCs already acts to reduce some sound reflection.  A softer printed texture added to a stiff structure might be just the ticket...

I have tested machined delrin toroidal spiral baffles in a 30 FPE .22, and they seem "twice as effective" as their expansion volume suggests.  So lets hope someone prints the larger version, above.  Perhaps I need to add dimples and a stem taper for a more appealing appearance...

[Outer_Rondacker]

Peter Chris will be printing the longer one tomorrow. Just wait one more day.

[subscriber]

Marco,

For a given FPE, the larger the caliber, the more noise "leaks out".  While this is an over simplification, think about how much sound gets out of your barn door; and how it increases the wider you open the door.  We know that a smaller baffle bore reduces sound, but the bore has to be larger than the projectile; and larger calibers need much larger holes, with much larger hole areas.

What matter is muzzle pressure and volume of air.  That represents waste energy that needs to be dissipated in a manner that reduces shock, with minimal excitation of the LDC structure.

There is another thread running about measuring sound with a quiet trap.  Else all your LDCs measure as loud as your trap, because that is what the meter is "peaking" on:  https://www.gatewaytoairguns.org/GTA/index.php?topic=197179.0

Also, the larger the caliber, the more loudly the trap gets thumped.

As for baffle spacing, there are many factors involved.  For starters, there is the shape of the "plume" that is ejected from a bare muzzle.  As the projectile clear the muzzle, the plume is almost radial, due to the higher air pressure, and the projectile being in the way.

As the projectile travels further from the muzzle the bulk air pressure behind it drops and the air's forward momentum starts to dominate.  This results in a plume that is generally shaped like the last image in my sketch below.    The higher the muzzle pressure, the wider and more radial the plume at its peak "diameter".

So, the shape of the plume suggest that when the bulk air pressure is still high, that air will naturally tend to expand until it meets a wall, so more baffle walls closer together will be effective.   Compared to, when the bulk air pressure in the plume is already low, its forwards momentum will tend to carry it directly through the bore of a series of LDC baffles, rather than changing direction to flow into the baffle space.  This favors wider spacing, just to allow time and distance for the air to divert sideways, rather than leaking out the bore excessively.

The above function is going to depend on the LDC ID.  If the LDC ID is small, then a short baffle spacing will be more effective, because each baffle space lowers the bulk pressure only a little.  If the LDC ID is large, then standing off the baffle wall may prevent air from zipping through in "a tight beam".

What the bulk pressure in the plume is going to be any distance from the muzzle depends on the pressure and volume of the air the barrel muzzle, the already used expansion volume of the LDC, the total expansion volume, and the effectiveness of the baffles/air  strippers.  Then there is the matter of can structure vibration like a speaker cone...

We are told by "experts" that baffle spacing needs to be non-uniform, or a resonance might be set up.   This is probably true for the "can" itself ringing.  As for the air ringing, the air pressure decays towards the front of the LDC.  So its spring rate drops. So its bulk resonance frequency drops; even with evenly spaced baffles.  That said, I do think there is merit in the last expansion chamber being "long".  Including to lower the tone of what gets out.  If would make that chamber 2" long, if I could afford to make the overall length a bit longer...

[subscriber]

Peter Chris will be printing the longer one tomorrow. Just wait one more day.

Jolly good!

[Mr.P]

Each of your sentences has a little education in it. 

Because I had the materials I have been trying a spring-plunger design for the first large chamber.  Sounds like a pogo stick and softens the crack but is hardly quiet. Kind of comical actually.

[WhatUPSbox?]

It may be interesting to track the internal volume of the different designs. If the CAD software does not do that, the mass estimate from CURA may lead to a ballpark number.

[subscriber]

Stan,

Solidworks can be polled for the solid volume of the part.  Subtracting that from the outside volume yields the internal volume.

It would be interesting to compare single chamber LDCs of the same volume, but different diameters and lengths.  I just thought of more work for myself to do  :'(

To remove other influences, there should be no fancy reflex air strippers in that volume.   Just a threaded tube with a single cone or flat wall at the far end.  One could short out the Avenger shroud reflex air stripping, so only the deliberate front LDC volume would be in effect.  One could then test versions with a conical air stripper at the far end, VS a flat wall with a square edge hole.

I know my "mouse-driven" sketch below is "not to scale", but it provides an idea of what I am talking about to make a direct comparison.  I think the long skinny tube will be the quietest because it has the longest pellet "dwell".  Although, if too skinny, air will pass the pellet, making the LDC louder again, and worse; knock it about with turbulence.  As such, the short and medium single chamber LDCs likely shoot the smallest groups.

Longer tubes would have a lower tone than the short ones, but the short ones may be loud because of a lack of pellet dwell.

To keep things meaningful, internal volume should be increments of barrel bore volume.  This is based on the principle that if the bore volume is 15 CC (for example), and the LDC's internal volume is 15 CC, then the LDC exit pressure will be half the barrel muzzle pressure (because the total expansion volume has doubled).  And so on.