Taming the bark of an Avenger

[TorqueMaster]

Thanks, Bob

So, to avoid interference, the LDC radius should match the shroud for another 25 mm from the front of the shroud.  Then it may be increased by 8 mm further forwards.  At 100 mm from the front shroud face the LDC radius can be increased, with a curved path in between. 

Good to know, although a design that just clears the green line may look "funny".

So, what might look OK in that space?  Food for thought on that, attached below (dummy layout models without all of the internal details).  Obviously other diameter / length combinations would be possible:

I think you've got it.  Bear in mind this is the bare minimum for *MY* pump.  And some parts of the curves measured a little bit sloppily.  Anyone with a longer/wider connector on the pump, or fatter air hose, will not be happy if you use the green line without some clearance.  So that 25mm might better be extended to 28mm, or even more, I really don't know what other connectors are out there.  The +8mm radius is going to be *just* clear of the hose by whatever fraction of a mm the reservoir/shroud gap is over 1mm.  I.e. if that gap is really 1.2mm, that leaves the +8mm radius part of the LDC just 0.2mm to miss the hose. 

Yes, following the green line would look odd and possibly not enough clearance.  I like the style of the angled models you posted.

I like the idea of 2-piece design as well.  I did not realize how long these were getting.  Height increases chances of print failure due to height (nozzle leverage if it bumps the model can unstick it from the bed) and the longer duration the print, more likely something can go wrong.  Interchangeable innards is a cool idea, too -- for testing mostly I think-- less to print each time -- but final designs should be printed altogether if possible, for strength.  Or two-pieces, as we're suggesting, to reduce print heights.

It makes some sense the connection point of the two pieces should be at the front of the shroud, using "industry standard" threads for compatibility.  But far from necessary.  Any threaded or even slip fit or, slide on and quarter-turn lugs could work.  We can glue the two pieces together if needed.  What fits the internal geometry best is probably what makes the most sense.

[Outer_Rondacker]

No glue for me. You can glue not me.

Point for me is I can run with internal only and if I want more then add the extremal. Gluing it defeats the propose. If I glue it I can not try different ones on the end. I would have to reprint both parts over and over again. I would prefer not to glue. The reason I suggested two parts was to save on printing the internals over and over. Not trying to be a jerk It just come naturally and I have only had one coffee this morning.

[JimD]

One of the reasons I have the printed moderator I have on my Avenger is it fits within the shroud.  Yet I measured it at lower db than my Tatsu or the longer printed moderator I tested.  I like not having the gun be longer and I also do not have to worry about a potentially fragile plastic moderator hanging out the front.  I saw no difference in accuracy.  The only thing I'd like to be better about this moderator is it would be nice if it improved accuracy. 

My point is just that I think we don't really need to worry about plastic moderators being fragile until they extend past the muzzle and to the extent they extend past the muzzle.  The longer they get, the easier it will be to damage them.

Another potential benefit of a screw together design is illustrated by my P35's shroud.  With the 7 aluminum baffles it came with I measured about 85 db.  With 2 or 3 baffles and hair curlers wrapped in felt taking up the space I measure 77-82 db.  Lowest seems to be two baffles with a full curler plus a half.  I don't see how you could print a design like this but it is easy to put together when you can take an end cap off.  The Avenger does not have the space in the shroud ahead of the barrel that the P35 has so I think a screw together would have to extend at least some but it could be a pretty quiet design.  I'm not sure if the P35 shroud helps it's accuracy but it seems like I put the first baffle in backwards once and accuracy was adversely affected - so maybe it does help.  The first aluminum baffle fits down into a piece screwed to the barrel and O-ringed to the shroud so it may be an effective air stripper.

[TorqueMaster]

My point with the glue option is to keep the length of the device at a minimum.  If he adds a threaded section to the end of the internal part, it may require the overall length of any design to be even longer.  Without the threaded section interfering, all the functional elements can be as compact as possible. It's all just for testing purposes, and ease of printing.

I would prefer an all-internal solution too.  It may be enough for me as well.  And if more is needed, I have to admit there is a "cool factor" to having threads there, and adding on external extension -- short, long, fat, skinny, dimpled, ribbed, spiraled...looks and function both matter.  (that's what she said)

[TorqueMaster]

So, what might look OK in that space?  Food for thought on that, attached below (dummy layout models without all of the internal details).  Obviously other diameter / length combinations would be possible:

I just got to looking at these sample designs again -- I personally prefer the looks of the last two, the ones with 34mm OD. 

[WhatUPSbox?]

Looks like these designs could have an internal thread on the front face of the internal section. That way it is still easy to print and you just put the male thread on the external LDC if you use one. If you use an existing commercial LDC you just add a coupling.

[subscriber]

Thanks for thinking about this Stan; and for the suggestion.

Yours is a good option, compared to a male thread similar to Matt's Thingyverse sample.  The problem being that my air stripper design has to be printed with the muzzle standing on the printer platen.   My as yet undeclared suggestion would be to use a M24 male thread so the print is more stable.    Using female thread at 1/2 20 or M24 x 1 should both solve that printing orientation stability problem.  There may be other advantages to your approach; such as a hidden thread.  For the sake of reducing potential damage, and not needing to be covered, to avoid the question, "what is that for?"

I am also concerned about the bend strength of a 1/2 20 printed male thread, supporting the weight of any LDC screwed onto the front of the in-shroud section.   In theory, simply tightening that thread hard will force the shoulders to square up the parts.  I am not sure printed plastic is up to the task.  Especially for the 1/2 20 male thread, with a 7 or 8 mm hole down the center.  That does not leave much wall thickness to take and stay under high tension.  So, if 1/2 20 threaded studs are imperative, they should be metal; in my opinion.

The problem is "creep"; where plastics flow under loads that are well below their yield strength, when applied over time.  With plastic injection molded parts, creep is avoided by using glass or other fiber filling materials to stiffen them up.   I know that carbon fiber printing filaments exist, but don't like the idea of forcing the use of more expensive materials.  I would rather use larger diameter part to part interfaces that can take "drooping loads" at lower material stress. 

I intend to make up some models with different interface options, as not everyone has the same ability to visualize designs without pictures.

[subscriber]

Bob and Matt,

Rather than argue about glue in principle, argue about the pros and cons of when threads or glue are appropriate to a specific design.   Right now, there is no specific design beyond this:

The in-shroud section needs to be a separate part  that can accept different nose sections, via a threaded connection.  Some of those nose sections may be printed in one piece, or as multiple parts.  Some of these separate parts can be threaded together, or be glued permanently.

For an argument to be useful, it must contain specific information.    Else, from the "outside" it sounds a bit like the movie quote, "we don't need no stinking badges"  (or glue; or threads) 

[Outer_Rondacker]

Peter the thingivers one I showed you a picture of was printed thread side up. I have an idea. Does not mean its a good idea but its an idea.

I am going to butcher one of your designs. So I can take a picture and show you my idea. Time to find out how hard this stuff really is. Off to the band saw.

Wow this stuff is hard. Took a lot more then I thought to cut it. Here is the picture. You could make this one inch or whatever you feel it would need to be long enough to be strong. So Peter before I said make the threads shorter now I think we should make them longer. A simple cap can be put on while not using. Could even put a small none threaded spot in the middle for a stop so it doesn't go in the barrel shroud to far.

This would make for the first chamber if left hollow.

Bob I think you know this but I will say if for Peters sake. I'm not arguing with you. The design beyond this point would be gun specific where as a 1/2-20 could be used on many different air rifles. Pros conn conn pro.

Bob Stan and Peter what are you thoughts? Oh and Chris is with us today so what are your thoughts?

And I forgot the picture one minute. That is better.

[subscriber]

Matt,

The fat end of the Thingyverse part is designed to be printed with it down on the platen.  My air strippers have aspects that "float" if you invert them, so they need to be printed part muzzle down.

I had a number of optional designs in mind.  I left this conglomeration open in Solidworks until I could get back to it - image below.  It has a flange with shoulders to tighten against.  This design is the easiest to implement with regard to speed in getting a 3D model out - but this component is only part of the system equation.

After more thought, using the M24 frontal stud will force the mating part's OD to be larger than the non-interference envelope Bob provided.  The version with the 27 mm extension should help with that.  Image below.

Also; I think making the frontal thread M18 x 1 might be better, because the mating part OD could be the same as the flange OD (the 26 mm I have been using for the smaller diameter LDC frontal sections).    M18 x 1 is a standard size if one looks at DonnyFL adaptors.

Based on Stan's input, a female thread on the front might be a good idea.  In that case, I vote for 18 mm.

I argue for sport, and don't see the practice as hostile.  Providing it is not just people contradicting each other in a mean spirited manner.  Arguments are how one persuades others of the value of a train of thought; and them you.  My comments about you and Bob were meant to add a some levity, while making a point.

[Outer_Rondacker]

Yes the top design is what I was referring to. The thread area could be hollow.

[subscriber]

Here is an interpretation of that design: 
STL download link, valid for 7 days: https://we.tl/t-RShBn6WCqd

For version with wider cone at muzzle - see last image:  https://we.tl/t-fKJYZ1Uty1

[Slimdog]

Hope I'm not derailing the conversation at hand.  I was tasked with printing several of these air strippers by swoab47.  I apologize as I don’t know which designer’s files we printed, but I would like to commend all of the designers on their work.  It’s truly amazing.

The strippers were printed on an Ender 3 Pro with no modifications other than replacement bed springs and wheels.  STLs were sliced in Cura using a profile called CHEPV4.5_0.12(RoundNoSeam) from Chuck Hellebuyck (CHEP, Filament Friday).  This profile starts each layer in a different location so there isn’t a seam.  I chose this profile as I thought it might help eliminate possible issue with the threads.  The layer height is .12mm.  I used a raft to help with bed adhesion.  The filament used was Atomic Filament’s Neon Green UV Reactive PLA as that is what swoab47 selected.  These prints took a while (approx. 6-10 hours each).  I feel this is a fair trade off for the quality.  There is very little post processing.  I do see a few wisps of plastic internally.  A quick shot or two with a heat gun should take care of them.

If they work as swoab47 desires, we may look at printing them in Atomic Filament’s Extreme Impact PLA or PETG for durability.

Looking forward to swoab47’s findings once he receives them and puts some lead down range.

If anyone has any questions, feel free to ask.  I’ll try to answer them as best a 3D printer newb can.

Apologies for my poor photography...

[subscriber]

Hi Corey,

Very nice looking printing job.

I hope you and your friend know that the version with the radial holes near the front is intended for maximum air stripping, rather than sound reduction.

You might be interested in printing some of the more recent designs.

Thank you for sharing

[Slimdog]

Hi Corey,

Very nice looking printing job.

I hope you and your friend know that the version with the radial holes near the front is intended for maximum air stripping, rather than sound reduction.

You might be interested in printing some of the more recent designs.

Thank you for sharing

Thank you, sir!

I can't speak for Swoab47, but I believe his goal is maximum air stripping over sound reduction.  We'll definitely take a look at the newer designs.

Thank you all for sharing!

[subscriber]

I can't speak for Swoab47, but I believe his goal is maximum air stripping over sound reduction.

I went and checked swoab47's profile, and realized I might have created that air stripper version on his request.  Or I may be confusing user names. 

[WhatUPSbox?]

Once you move away from the 1/2-20 thread, You could go with a bayonet or twist lock without a constraint on OD since you would remove the external portion to fill. A thin gasket or o-ring would seal the mating face.

[swoab47]

I can't speak for Swoab47, but I believe his goal is maximum air stripping over sound reduction.

I went and checked swoab47's profile, and realized I might have created that air stripper version on his request.  Or I may be confusing user names.

Yes Peter, we corresponded via email and I asked about maximum air stripping and sound suppression as a byproduct.

I can't wait to try them out.

Thanks to everyone that has contributed to this thread!!

[subscriber]

Once you move away from the 1/2-20 thread, You could go with a bayonet or twist lock without a constraint on OD since you would remove the external portion to fill. A thin gasket or o-ring would seal the mating face.

Stan,

Whatever the means of attachment, it needs to pull the external device against a shoulder and center it, or there will be some dropping and non-concentricity.  Now, a bayonet fitting could and should have ramps to it, effectively turning it into an interrupted, or multi start thread - which may be easier to print (especially if coarser than a 1 mm pitch).  This is not a bad way to go, but is not standard on airguns.  If anyone has dimensions for such fittings I could give it a go; else, I would need to design them from scratch.

To better address drooping moments, I almost want to make the external device wrap back against the barrel as a reflex design.  That will demand a quick release system for the Avenger, to prevent interfering with air filling.

Now, as much fun as it would be to design a mounting system from the ground up, I don't want to put 40 hours into it, then be told that no one wants it because it is non-standard.  Yes, I know; a bit of chicken and egg, as no one can like or dislike a design until it exists...

[TorqueMaster]

I printed off a few models and did a quickie test this evening as it was getting dark.  These results are by no means final, but gave me some idea what reductions to expect.  Phone was the level meter, about 2 feet down and 2 feet to the right, pretty even with the muzzle.  My .22 Avenger is currently set for 1000-1200 psi.  All test were "dry fires" with no pellets.

1 No cap -- loud -- don't do this.  82db.  I am fairly sure my meter tops out at 82, so this is borderline meaningless.
2 Stock cap -- kinda loud, I'm used to it -- 78db
3 Internal part only of "LDC buckrail baffle style with two stage reflex air strippers2" -- so I think this is just air strippers?  -- now we're getting somewhere -- 70db
4 Whole "LDC buckrail baffle style with two stage reflex air strippers2" -- wow, just wow -- 60db.  Really I hear the hammer spring more than anything
5 "Maxim Fatso LDC 5CH"  -- this thing  is huge -- used up 1/5 of a spool, so it weighs .44 pounds!  -- and it rang in at 64db.  Again, I think I am registering the spring noise more than discharge.

Need to run the tests at higher reg pressure, no doubt, to better assess the measurements.

For funsies I put 10 actual shots through Fatso.  POI seems unaffected.  Insanely quiet, I can't imagine not running an LDC in some from from now on.

Prints were done at 0.28 layer height.  Threads are adequate to engage the shroud but far from clean and sharp.  Used PETG.

Photo of 3, 4, 5...