1/2 - 20 Moderator long and short versions

[bduares]

Here is the smaller moderator from that file Subscriber sent, next to the one I posted. I have not had a chance to try it yet. I seem to be getting a collection of these things. Maybe I should start selling them as a side business



 

[subscriber]

Jared,

Those prints look good.  If you want to sell them you might want to consider black or dark grey material.   That makes me wonder if the material will take a stain.  Camo tape or paint may be options, but that seems like extra work.

Anyway, the first order of business is, do they work as well as expected?  If yes, then material color preference might come into play.  If you are using PLA, it is very stiff and strong.  Perhaps to the point of being brittle.  Unless it is special PLA, its creep resistance at elevated temperature may have it droop over time.  I don't know if it will droop when shooting in the sun, but it may if stowed in a hot parked vehicle with something pressing on it for a few hours.   Not a huge problem if you can just print another one .   This is where PETG is probably a better choice for airgun mods:  Less brittle and better UV and thermal creep resistance.  Which reminds me, my designs assume PETG, and the as printed thread size for PLA may be different.

Before "creep resistance" sounds like a monsters under the bed, I design baffle bores with generous coaxial clearance (1 mm radial over caliber), and able to tolerate an additional 0.25 degree angular misalignment by making the bores follow a divergent cone shape towards the front.  A few years ago I had a some customers report clipping near the front baffle on some mods, but after opening up baffle bores to what one might call "+ 1 caliber", no one has complained about losing a dB in sound reduction; or an odd dispersion or shift in shot placement.

[bduares]

So I decided to shoot a few shots off with the Sumatra and try out these 3 moderators.
First the long one from Subscriber. 2 shots, still quite loud, but otherwise uneventful. It was expected. Can't really quiet the supersonic beast, and it is pushing 70+ fpe.
One after the other with the PLA+ and PETG moderators. Both had impressive explosive deconstructions. Very strange. The first one I printed of that design is still just fine and so far the quietest I have found for the Sumatra.

I admit I had been playing with slicer settings before printing the other 2. It is possible my slicer setting modifications made something weaker. I am almost certain I had used 100% infill, but it is a possibility I did not. So I reset my slicer settings for both the printer and the filament and am printing a new batch.

 
To answer your question, I usually print with whatever I have in the machine at the moment. Right now I have a roll of white PETG in it because I was testing a roll out of a 10 pack case I just picked up the other day. The grey one is PLA+, a stronger and more flexible PLA than the old stuff.

If I want something black I usually just spray paint it a couple of coats, like I did the last moderator I put on my Sumatra. They paint very nice.

[subscriber]

Interesting results, Jared

Is your Sumatra shooting at 80 FPE?  The large mod that survived I designed for 30 FPE.   I think its large first chamber volume and thicker walls at the rear helped it stay together.  That said, I usually ask customer what they intend to shoot through it, so it is robust enough, and not heavier than required.

Because I have no control over printer, settings and material, material condition, I do not offer any guarantee for designs posted publicly, for free.   When I do custom designs for over 100 FPE I usually suggest capturing or glueing a printed insert inside a CF or aluminum tube.  If fully printed for higher power I make the rear end of a mod a lot more robust, as that is where it works the hardest.  I also do some rudimentary calculations to ballpark muzzle pressure, applied forces and material stress.  I assume the Z-axis strength for PETG to be 4000 PSI.  Printing with less than dry filament or less than ideal settings can reduce that enough to matter.

From the your photos, the two mods that let go seemed to "fail safe", as bits went forwards from the threaded base and perhaps radially, away from you.  Other than print settings, a roll of filament left in the printer may have absorbed moisture from the air since last used.   That can weaken prints somewhat, depending on how much water was absorbed.

Any printed mod should be treated with suspicion for at least 10 shots.  This includes considering the risk of projectiles  being deflected away from the target trap or backstop.

My most hard working mod designs are for the Huben GK1 pistol in .25.  Some of those are super lightweight, because that is what customers want.  The only one of those that has let go unintentionally was from a valve dump event, where the muzzle pressure and air volume would have been much greater than for normal shooting.  Discussion here:
 
https://www.airgunnation.com/threads/gk1-what-silencer-for-backyard-quiet-or-almost.1310711/post-1831983

Image below:

[Robert 5mm]

WOW is what I say.

My air guns max out at 30 fpe so the only failure I have seen is clipping.

( I saw, but I am not going to try the 10/22 Thingy model - just staying with air guns )

[subscriber]

Jared,

I forgot to mention, an unshrouded PCP such as your Sumatra requires a stronger mod than a shrouded PCP of similar FPE. 

While we are at it; shorter barrels produce higher muzzle pressure than longer ones at similar FPE.  Think of the GK1 as very potent PCP, despite the short barrel.  Hence how loud they are unsuppressed.

Smaller calibers producing high FPE are more stressful on mods, than larger calibers producing similar FPE, from similar barrel lengths.  The key to producing power is expansion volume inside the barrel.  That is affected by both caliber and barrel length.  The larger the expansion volume, the easier it is to make power, while keeping the muzzle pressure down.  Else, more expansion volume needs to be added to the front end, in the form of a large enough mod.  Clever baffles can be used to make the exiting air get in its own way.   STO has a swarm of mods that work on this principle.  OldCrow on this forum has a number of mods that use a simplified, more compact form of Tesla Valves than STO, to good effect.

[bduares]

The Sumatra is shooting at 72 fpe with the slugs I shot through it today. The shorter of the 2 moderator files you posted survived that power level just fine. Right after the destructions I even shot a couple through the very first moderator I had printed of the design that blew up. It is just fine too, and was printed with the same roll of filament as one of the ones that blew up. It was, however, spray painted black.  The moderators that blew up both blew up at approximately the same distance from the barrel, within a 1/2 inch of each other. The parts in the photos are what was screwed to the barrel adapter. The rest of the moderators are shrapnel that shot straight forward and are scattered in my yard.

I use an electric Sunlu filament dryer and I print directly out of that machine at <40% RH using it as the spool holder. But lately I have been trying to tweak the printer/filament settings in Orcaslicer to try to squeeze out a little more speed as well as trying to tweak it so supports are easier to remove. It is highly possible that something in those tweaks weakened the prints that blew up. It is also possible I might have printed them at 50% infill, though I don't think so. I print almost all my air gun pieces at 100%.

So far the differences between the moderators of that model I printed that survived 70+ fpe and those that didn't are some differing slicer settings and the survivors have a couple of coats of spray paint on them.  When the one I have printing now finishes I will give it a couple of coats of the same paint and then give it a go. I may try to do it with a camera recording this time, for possible future amusement.

[subscriber]

Sounds like slicer settings are the most likely culprit.

As always, the devil is in the details.

[bduares]

At least when they went boom I was disappointed rather than shocked.

[bduares]

I took a look around the yard just now. The moderators did not explode in a shrapnel mess like I thought. Both moderators, made from 2 different materials, busted at the same exact place.

Strange

[subscriber]

I wonder if the designs could be reinforced around that area?  There also seems to be a seam that failed along a vertical line.

If you point to the STL file that you used, I will see if it seems to need a thicker wall, and then reinforce it there; if you like?

[bduares]

I wonder if the designs could be reinforced around that area?  There also seems to be a seam that failed along a vertical line.

If you point to the STL file that you used, I will see if it seems to need a thicker wall, and then reinforce it there; if you like?

That would be the very first file in the first post of this thread. Suppressor.stl.zip

[subscriber]

Thanks, Jared

I opened that STL file in Cura.  Unless I am mistaken, I set Cura to a line thickness of 0.4 mm.  When counting the lines in the wall after slicing, around where your printed mods broke, I see four lines; as in 1.6 mm thick.  That seems a bit thin for that section, because the first expansion chamber and baffle take the brunt of the blast, after the pellet leaves the barrel muzzle. 

My version of Solidworks (2015) on my 6 year old PC chokes on the STL:  After waiting 20 minutes for it to finish opening the file, I gave up.   It amuses me, because my version of SW can produce much larger STL files than it can open.  So, I cannot edit this file, unless a STEP file version can be found. 

If I could open the STL, I would double the wall thickness of the first expansion chamber wall; and thicken the first baffle.  The rest of it should be OK at current thickness.

I know that there are some other CAD packages that can open STL files and edit them, or convert them, so perhaps someone else might have a go.   Cura opened the STL file in less than one second on my machine; so why does SW battle with it...  I tried to use Cura to save the file in other formats, but SW could not be coaxed into working with them.  If someone could convert the STL to a STEP file, that would a massive help.

[OldCrow]

Can it open a .3mf file?  They are much smaller.

Usually I see a 75% reduction in size between an STL and a 3MF for the same object.

[bduares]

I thought that backwards converting from an STL was not really any good from a structure point of view because an STL has been converted to triangular meshes while the step is actual solids.

[bduares]

I managed to track down the designer of the moderator, let him know that Thingiverse had taken some of his designs down,  and I sent him photos of where my 2 broke yesterday. I asked if he had a SLDPRT or STEP for it and he had this to say:

Hi bduares.

Thank you for letting me know.
I will try to look into it.

I did not know that thingiverse has blocked some of my designs, i have send them a message about it.

I do not have SLDPRT or STEP file for this model as it was designed in tinkercad.

[TorqueMaster]

Only the owner (or possibly anyone the owner shares with) can edit the Tinkercad file via it's core components.  Any thickening would be via unioning thicker walls to the existing model.  Not impossible by any means... but tricky since it has that octagonal-ish cross-section.  I could give it a go.  The outer walls are about 1.6mm (everywhere, I presume?) how thick should they be?  I *might* be able to taper the outer wall thickness -- if that's possible, what thickness at entry, and what thickness at exit?

 Actually, I think there is an "easy" way to do all of the above -- can only be sure once I'm patching it, though.

[TorqueMaster]

I went with ~3.2mm at the entry and ~1.6 at the exit.  Made the exit cap 4mm.  Can be "easily" re-adjusted now that I have the edited pieces in Tinkercad.  Sliced in half here and a random height cross-section.   The layer view looks good in Cura, it should be printable.  Let me know if anyone sees any issues.

[bduares]

Im doing a reprint of the original file in 100% infill with reset Orcaslicer settings, and am at 94%. When it finishes I will print this fixed version in 100% infill as well and see what they do

[subscriber]

Can it open a .3mf file?  They are much smaller.

Usually I see a 75% reduction in size between an STL and a 3MF for the same object.

Mike,

I tried that and my version of SW does not recognize the format.

Something else I might try for giggles is to use Cura to scale the part down by a factor of 10, because that might make the files 1000 times smaller.  Or it could have the same detail, but much smaller.     What I was thinking was to compress the detail, as in lowe the resolution in Cura, then try SW again. 

SW actually warned me that the file has too many points and lines.  Asked if I was sure I wanted to open it.  Now I know the answer is "no".


Jared,

I know SW will open STL files, if they are small parts, or very simple.  Editing STLs is very messy because SW sees each little triangle as a separate plane.  Often it is easier to start designing a new part from scratch, but that can force me to estimate some of the dimensions.

Once one adds material or cuts it from a part saved from an STL. it behaves just like a STEP file; solid.  The facets are only on the surface.

STEP files are Universal 3D solid models, so those are preferred.   Due to Solidworks business model, I cannot open part files generated or saved by a younger version.  So, even if the mod was generated with SW, if it is a 2020 version, for example, I just get a "cannot open file" message.   My stand-alone SW licence cost me 4000 bucks in 2015.  It would cost me about as much to get a current licence.  For what I do, I am not motivated to spend that, and another 1k per year "maintenance fee".  I am not eager to dump SW either, as I know my way around it.