Evanix Rex reflex inserts for shroud

[subscriber]

I guess there's enough complications already! The most important thing I should focus on is keeping the tube from flying off the front

Simple; use a front and rear washer, connected by a few thin threaded rods (bicycle spokes?).  The rear washer is also used to prevent a Heli coil from pulling out of the printed thread at the rear. 

https://www.mcmaster.com/91732A533/

https://www.mcmaster.com/99055A110/

https://www.mcmaster.com/92856A107/

[Mr.P]

There had been some talk about this earlier in this thread. Was that put aside because of the ribs not being strong enough?

I think that Marco simply wanted to make and test his own designs. 

As far as I am concerned I ended up with a working solution after just a couple of iterations. Subsequent changes weren’t making any noticeable difference that I could hear so I decided I had achieved what I needed to.  For example I tried two radically different approaches to filling the shroud space and really experienced no noticeable difference when shooting the gun. 

[Clicky]

I guess there's enough complications already! The most important thing I should focus on is keeping the tube from flying off the front

Simple; use a front and rear washer, connected by a few thin threaded rods (bicycle spokes?).  The rear washer is also used to prevent a Heli coil from pulling out of the printed thread at the rear. 

https://www.mcmaster.com/91732A533/

https://www.mcmaster.com/99055A110/

https://www.mcmaster.com/92856A107/

I like the idea, and I have used bicycle spokes for things they were never meant for

But the rear washer is actually a 10mm thick aluminum puck which needs to go on 1st before attaching the outer tube to that. There's pretty much no access to the rear face of the puck for adding hardware, so the spokes would need to be in place already with some method to prevent them from rotating. One possibility is to form a T-head on the end of the spoke that fits a slot cut into the puck. But that still leaves a small issue with running the spokes through the front baffle section

What I ought to do is cut threads to attach the tube to the puck, but I've never actually done that before, and it's a bit too late for that now as the material needed to form threads is not there anymore. Of course, I could just cut another puck. In it's rough size, it's pretty close to the same OD as the tube

For now, what I'm thinking is to just continue with what I have for now as this build isn't intended to be a final version. I already have decided against powder coating or painting the tube, instead I'm going to wrap it with a fabric cover held on with velcro. One of the other tools in my shop is a sewing machine

Set screws would have issues with the threads cutting into the sides of the holes they would be restraining, and that would introduce slop. I've considered putting in a snap ring, but the access is very limited. I would need to move the tube forwards about 2mm and cut a clearance step in the puck so the snap ring has a resting place before it's put in place. And accessing the ends of the ring would be a bit too much fun for me! At some point I will want to take this back apart and that probably means welding part of a socket to the end of a tube so I can remove the nut holding the puck. I've already decided against setting that puck in place with retaining compound, because I do want to try having threads at some point

So my plan is to pin the tube. The holes in the tube will be counter sunk, and the pins will be peened a small amount to give a lip I can use later to pry them back out. I'll use some scrap to make a steel jig for the peening operation. Then all the pins will be held in place with shrink tubing. I happen to have some 3" shrink tube. All of that being under a fabric outer wrap, so how it looks isn't an issue

What I'm revising is how many pins I'm thinking of putting in. I had been thinking of only putting in four. But now I'm thinking I should see how many I can put in with something like 20mm spacing between them

[Clicky]

There had been some talk about this earlier in this thread. Was that put aside because of the ribs not being strong enough?

I think that Marco simply wanted to make and test his own designs. 

As far as I am concerned I ended up with a working solution after just a couple of iterations. Subsequent changes weren’t making any noticeable difference that I could hear so I decided I had achieved what I needed to.  For example I tried two radically different approaches to filling the shroud space and really experienced no noticeable difference when shooting the gun.

Nothing wrong with that!

I'm an inherent tinkerer, project snowballing is something I'm always getting into if I'm not careful!

This pistol is a back shelf piece nowdays, so I'm not too concerned if it goes through many changes. I think I spent way too much on it to begin with. Bought it for $500, and now that I've seen how well it's designed & built, I wish I had only paid $300. I honestly wouldn't feel right trying to sell this thing for what I paid without making improvements here & there. It's already many times better than how I got it

Seems like I don't buy airguns to shoot them, I buy them to work on...

[Clicky]

I have a carrying case to fit inside of, so I'm going to draw up the rest of the inserts, starting with the very end, adding in the thicknesses of the washers I have yet to source & then working with whatever room remains

So this is what I'm going to put on the end

There's a complicated area that needs to be rounded-off. I decided it would be easier to just print it with a sharp edge, then round it off in post-processing. Going to be some supports on this thing too - the rearmost portion of the vent passage inlet openings, leaving the forward portion sharp-edged to divide airflow

[subscriber]

Interesting brake design.  Will the overhang in red be able to print without adding supports - below?  Perhaps there is another orientation that will work.  Or supports will be easy to break out.

Threaded dowel pins, so you can pull them out:  https://www.mcmaster.com/pins/pull-out-dowel-pins-6/

Bicycle spokes have an "L" shape that will prevent rotation. Select length:
www.amazon.com/SENQI-36pcs-Bicycle-Spokes-Nipples/dp/B01GZPWE2A

www.amazon.com/SALUTUYA-Spokes-Convenient-Installation-10pcs/dp/B08YP1WSPB/

[Clicky]

Interesting brake design.  Will the overhang in red be able to print without adding supports - below?  Perhaps there is another orientation that will work.  Or supports will be easy to break out.

Threaded dowel pins, so you can pull them out:  https://www.mcmaster.com/pins/pull-out-dowel-pins-6/

Bicycle spokes have an "L" shape that will prevent rotation. Select length:
www.amazon.com/SENQI-36pcs-Bicycle-Spokes-Nipples/dp/B01GZPWE2A

www.amazon.com/SALUTUYA-Spokes-Convenient-Installation-10pcs/dp/B08YP1WSPB/

Weird, the red area should be all solid - Oh, ok I see what you mean. I'd recommend using tree supports

Those dowls are nice, but they don't go small enough, however I'll try to find smaller versions - and then I see they list 3/16 diameter. That might work ok, just not sure I want to spend $33 a piece for each one of those!

I'll need to put holes in the brake so there's something solid to run holes into. Probly print a drill guide so I can get the holes in the tube in the right locations

Bicycle spokes need to be cut to length, so putting new ends on is a basic task when using them for things they weren't designed for

I'm printing that with the front face down, all the supports should only be inside the vent passages

And I'm already re-designing the darn thing! Just thinking about it anyways, while it's printing right behind me right now...

[subscriber]

Bicycle spokes need to be cut to length, so putting new ends on is a basic task when using them for things they weren't designed for

A few of those links for spokes had a pull down menu to select spoke length.  Pick the nearest length you want and design your plastic parts to work with that.  Cutting spokes is difficult, and then you are missing useful features.

[Mr.P]

Even though all was working fine I tried another print just for the heck of it.  This model has a little extension of the first and last baffle - a short tube for the pellet to pass through.  I felt the last chamber was not really doing much with the large bore, small diameter, and simple end wall. 

I think this may actually make the report a little louder.  Need to test a few more times because it basically works as well as the last one but it seemed that with these extensions the report has more of a “pop” and less of a “chunk” sound.

[subscriber]

The longer "tubes" increase dwell time, while the pellet is in near contact with the tube wall.  This should make the system quieter.   

However, the longer air stripper "tube" places the entrance nearer the exit of the previous stage, enabling more air to take a "shortcut", rather than fanning out and being blocked by the downstream "wall".

So, you win and you lose.  Which effect dominates is the question...

[Mr.P]

In this case, MUCH quieter with the simpler baffles.  I just retested a few times.  Makes me wonder if the best approach in this case might just be a single large empty chamber…

[Mr.P]

Do you think a design like this has any merits?  I was imagining a large chamber and then some short section at the end of the ldc to resist flow and create back pressure.  I doubt the spacing and angle of those cones in my design here are optimal or even close and it might be that air will just go straight out the end here… this is just a quick mock up of the idea and I am wondering what suggestions you might have for how to create the most friction / resistance to air flow in a brief section like that? 

[Clicky]

Bicycle spokes need to be cut to length, so putting new ends on is a basic task when using them for things they weren't designed for

A few of those links for spokes had a pull down menu to select spoke length.  Pick the nearest length you want and design your plastic parts to work with that.  Cutting spokes is difficult, and then you are missing useful features.

I'll have to admit, I hadn't looked at those spoke links. However, cutting spokes isn't hard for me. I usually use an abrasive cutoff disk on a dremel, or a thin cutoff disk on my angle grinder - which really makes short work on spokes, probly could do 100 at once in 20 seconds

If I need to do any bending, I use a propane torch to get them just barely a red glow. Full-on glowing red is way too hot & the spoke usually breaks later. After bending, I anneal the spoke, reheat and air cool

True though, it could be easier to use the OEM toggle ends they come with & design parts to allow threading spokes into place. For a project like this, maybe a T-slot that the end can just slip into? I could place the hole far enough in to allow running the bent end outwards. Turn a step to clearance the heads, then cut slots to run inwards to each hole. But this again, has the issue of running spokes through all the inserts. I could run the spokes on the outside, seeing as I'm planning on covering the thing with a fabric wrap. I'll consider that for the next build

On the other hand, I like putting new ends on spokes too, because then I get to decide how the end is designed. Essentially, trading off old features in order to gain new ones. It's really not hard at all to peen a head onto the end of a spoke. I use a ball ended drift I made just for this out of a hardened center punch and a very small ball peen hammer. The drift allows very precise placement of each strike. I can get a mirror smooth finish doing this, even better than the OEM head and the end is hammer forged, which improves it's strength

Now that I'm thinking about it, I'm all out of spokes. I think I used the last ones as welding rod

[Clicky]

Even though all was working fine I tried another print just for the heck of it.  This model has a little extension of the first and last baffle - a short tube for the pellet to pass through.  I felt the last chamber was not really doing much with the large bore, small diameter, and simple end wall. 

I think this may actually make the report a little louder.  Need to test a few more times because it basically works as well as the last one but it seemed that with these extensions the report has more of a “pop” and less of a “chunk” sound.

The last chamber probably has the most effect on the sound quality

Why not make that a cone like the rest? The end wall makes a great spring board to bounce off of. What about a energy pulse capturing shape like this?

[Clicky]

Do you think a design like this has any merits?  I was imagining a large chamber and then some short section at the end of the ldc to resist flow and create back pressure.  I doubt the spacing and angle of those cones in my design here are optimal or even close and it might be that air will just go straight out the end here… this is just a quick mock up of the idea and I am wondering what suggestions you might have for how to create the most friction / resistance to air flow in a brief section like that?

Possibly, it's a lot like more traditional designs

I would want the 2nd chamber to be a lot larger though, and then each one after progressively smaller. One idea is to have the resonance of each chamber at a different frequency, with the intention that they avoid coupling effects such as if the frequency is an even multiple. This is the basic design of all world class three-chamber hair curler moderators. You may have noticed those use chambers of three distinctly different volumes

I have a Weihrauch hair curler style for their HW77. It has very interesting ratios between it's three chambers, no two combinations of which will match each other

[Mr.P]

That makes sense - I will make some changes along these lines before I print.  Thank you

[Clicky]

That makes sense - I will make some changes along these lines before I print.  Thank you

Well, if you try an anti-resonant approach, keep in mind the frequency of the 1st chamber will affect the rest. It might be easier if you only have two forward chambers

When trying to use multiple small chambers, it's very difficult to avoid overlapping edge resonance effects

The weihrauch uses a Small/Large/Medium progression

Something I do when picturing how this stuff works. Each shot cycle is just like striking a tuning fork one single time. What happens next depends on how you adjust the fork leg lengths & weights

[subscriber]

Marco,

Stacking a bunch of short chambers near the front end is probably not going to be very effective for an airgun, because the air pressure is not very high, compared to a similar caliber PB.   The higher the pressure, the more the air wants to flow radially into available space.  The lower the pressure, the more it wants to travel forward, straight down the central hole.  You need to allow the air more forward distance to travel radially, the further forward in the device. 

Right near the barrel muzzle the air pressure is high enough that it wants to take up space radially, and can flow into more closely spaced baffles near the beginning of the shot pulse.   As the event takes some time to finish, the second half of the pulse occurs at lower pressure and could make closely spaced baffles less effective.  While this seems "bad", the bulk of the noise comes from the leading edge of that volume of air, so dulling its effect is more important than after the bulk pressure has trailed of.   

The idea is to remove the crash, while recognizing that smooth flow does not make that much noise; as long as the pressure ripple superimposed on it can be filtered out - or allowed to dissipate.    Long chambers near the front end tend to drive a deeper tone, that seems less unpleasant; but is more likely to be audible.

I am not sure what your absolute dimensions are, but would suggest you try leaving about a third of the part length open as the first chamber.  Then have two baffles with simple conical air strippers spaced about 1.5" apart.  Followed by a third chamber that takes up the rest of the length (hopefully more than another third of the total length).  The front end air stripper can have a tubular air stripper, about twice the length of the LDC bore.

I understand the "make the chambers unequal length, to avoid driving a resonance" argument; yet Marauder baffles are all the same, and that PCP is the standard for quiet.  I think it is because the 3/4" long chambers would resonate air at ultra-sonic frequencies; so no one notices.  Yet, the principle Phil mentioned works on tire tread patterns, where the block lengths are varied around the circumference to avoid driving a single tone resonance that would be heard as an annoying drone with a constant block lengths.

It would be interesting to compare just one long chamber, with only a single tubular air stripper at the front end.  It may have a pleasant sound, but my prediction is that it will be louder than a similar design with at least two more baffles somewhere near the part's mid length.

[Clicky]

Marco,

Stacking a bunch of short chambers near the front end is probably not going to be very effective for an airgun, because the air pressure is not very high, compared to a similar caliber PB.   The higher the pressure, the more the air wants to flow radially into available space.  The lower the pressure, the more it wants to travel forward, straight down the central hole.  You need to allow the air more forward distance to travel radially, the further forward in the device. 

Right near the barrel muzzle the air pressure is high enough that it wants to take up space radially, and can flow into more closely spaced baffles near the beginning of the shot pulse.   As the event takes some time to finish, the second half of the pulse occurs at lower pressure and could make closely spaced baffles less effective.  While this seems "bad", the bulk of the noise comes from the leading edge of that volume of air, so dulling its effect is more important than after the bulk pressure has trailed of.   

The idea is to remove the crash, while recognizing that smooth flow does not make that much noise; as long as the pressure ripple superimposed on it can be filtered out - or allowed to dissipate.    Long chambers near the front end tend to drive a deeper tone, that seems less unpleasant; but is more likely to be audible.

I am not sure what your absolute dimensions are, but would suggest you try leaving about a third of the part length open as the first chamber.  Then have two baffles with simple conical air strippers spaced about 1.5" apart.  Followed by a third chamber that takes up the rest of the length (hopefully more than another third of the total length).  The front end air stripper can have a tubular air stripper, about twice the length of the LDC bore.

I understand the "make the chambers unequal length, to avoid driving a resonance" argument; yet Marauder baffles are all the same, and that PCP is the standard for quiet.  I think it is because the 3/4" long chambers would resonate air at ultra-sonic frequencies; so no one notices.  Yet, the principle Phil mentioned works on tire tread patterns, where the block lengths are varied around the circumference to avoid driving a single tone resonance that would be heard as an annoying drone with a constant block lengths.

It would be interesting to compare just one long chamber, with only a single tubular air stripper at the front end.  It may have a pleasant sound, but my prediction is that it will be louder than a similar design with at least two more baffles somewhere near the part's mid length.

Good point about the pressure regime. I keep trying to treat the flow like it's much denser than it is. Most of what I've done is on gasoline exhaust systems, and the operating conditions are much more challenging. I've made my own design mufflers, some which work really well, in very interesting ways. And some which failed in interesting ways. My best design is quiet until you open up the throttle, then as the engine speed picks up becomes ricer-loud! That's where I get my experience with over-driving baffle systems

The single baffle/single chamber approach is how my .22 Origin works. It's pretty effective like that

I think a key part is having that one baffle far enough forward that it doesn't get over-driven by the initial pressure spike

The Origin barrel is fully free-floating inside the shroud, so I'm very careful about not knocking the shroud against anything. I made that mistake on a .22 Gauntlet. I had to remove the extra brace they added because the shroud was pushing the barrel off to one side. With the Gauntlet, there's a bushing at the front of the barrel to center the shroud. In the Origin the end of the shroud could easily wind up out of alignment with the bore if that tube gets bent. And the tube is the exact same soft aluminum, in the same wall thickness

On the other hand, the Gauntlet has a multi-chamber monocore which never worked well. I bought a 3D printed core that's designed to vent each chamber backwards into the shroud. Seems to work ok. Someone on ebay who doesn't sell them anymore. I think they didn't get enough business to keep putting that one out. I went to their listings to see what other guns they covered, and there weren't any others

I'd forgotten about tire treads. I have a small motorcycle that I've switched over to dual-sport tires. It has that droning effect because the tread pattern is a lot of the same size shapes, so the air pockets are all the same size. I hadn't caught on to that right off, and changed out the front wheel bearings because it sounds like they're shot

[subscriber]

Marco,

If your .357 produced as much energy by area ratio as a 30 FPE .22. then that would be about 80 FPE.  Assuming a similar barrel length and average pressure, thus a similar muzzle pressure at 2.63 times the air volume.  However, if your .357 used a barrel around 11" length, and produces 120 FPE, then the job you are trying to accomplish becomes about 60% more difficult (depending on similar air tank or reg pressures being used), because the muzzle pressure would be that much higher than for a 30 FPE Avenger .22.   

The point is that the airstripper spacing and cone angles that help for an Avenger, may be longer and shallower than would still benefit your Evanix pistol.  Or, that the Evanix could work with closer baffle spacing and shallower cone angles, due to its higher muzzle pressure.

The attached image is a crop from a rather effective design I did, posted on the thread "Taming the bark of an Avenger".  The reason for showing it is not for you to copy it directly for your Evanix, but for you to understand the principles of increasing stand-off distance and shallower cone angles as the bulk air pressure in your LDC drops towards the front end.  It so happens that as the pressure drops towards the front of the LDC, the same air needs to occupy more space, because it is less compressed.