Evanix Rex reflex inserts for shroud

[Clicky]

Took a look at that video with the tapering suppressor:

I think I've seen that before, on various 2-stroke exhaust systems. The taper is intended so that there's no end wall for a energy pulse to bounce back off of. It needs to be narrower than a certain cutoff point where the taper stops acting like a resonant chamber and gently squeezes the energy pulse into a very small area. So the idea is to get it into the smallest area/create the highest pressure peak possible. Having that much energy focused into such a small area has several different things happening

The squeezing process introduces a delaying effect and also increases the contact time & total area being heated from the energy pulse, thus absorbing energy & indirectly reducing the energy level of the sound wave. Thermal transfer is key to this process

Reducing the bounceback effect of a end wall or end chamber, means that the energy return will be much slower. So the peak of the reflected shockwave will be more averaged-out - thus quieter

Some of the more advanced factory exhaust systems that use this trick, will cascade these tapered chambers in such a way that the flow will move from one to the next in a concentric pattern, either beginning at the center & exiting at the outside, or the other way around

At any rate, I'd like to see that tapered suppressor get cut apart and torn down. I'm curious to see if it's just one single chamber or if it's hiding a cascade

[Mr.P]

Little bit of progress today. Practicing the art of pounding square pegs into round holes

Nice!

[Mr.P]

Got a cheap Lee mold for 148 grain “trash cans” - I read somewhere that these are decent projectiles and the mold was only $45 or so. Also got a simple magpul ak grip to replace the odd one contoured one that comes with the Rex.

[Clicky]

Got a cheap Lee mold for 148 grain “trash cans” - I read somewhere that these are decent projectiles and the mold was only $45 or so. Also got a simple magpul ak grip to replace the odd one contoured one that comes with the Rex.

Nice score! I've tried my 175 Pro Slugs in the Rex-P, and the recoil is pretty fun to play with

But I'd have to wonder if that grip will play nicely with the grip screw. Unless they changed that in newer production? On mine, the screw is perpendicular to the action, so it doesn't hold AR grips correctly. The outer edge of the screw only touches in a very small area, so it works loose quickly

Does an AK grip have it's screw vertical?

I've just finished drawing up a retaining nut to take the place of the rear bushing I was playing around with. Now that I'm going with solid aluminum for the rear bushing, all I need is something to brace that so it can't work it's way forwards. So I'm 'cheating' this build. For keeping the tube locked to the rear bushing, set screws could make more sense. I'm still considering that

[Mr.P]

The grip fits but the angle is a poor match as you predicted.   it did take a little finesse to get the grip screw in.  Basically had to start with the grip rotated 90 degrees and then turn it in line once the screw was started in the hole.

 i have that same grip on the Rex and Rex p now and much prefer it to the stock grip.

[Clicky]

The grip fits but the angle is a poor match as you predicted.   it did take a little finesse to get the grip screw in.  Basically had to start with the grip rotated 90 degrees and then turn it in line once the screw was started in the hole.

 i have that same grip on the Rex and Rex p now and much prefer it to the stock grip.

Maybe a small wedge could be printed, to fit it in better?

[Clicky]

Rear nut partially finished when the printer stopped working. Got 6.5mm complete on a 10mm part. Probably still work for test fitting the new bushing, but I haven't printed the front yet!

Looks like it's either the temp sensor or the heating element. Nozzle is running cold

[subscriber]

Marco,

I presume that after blowing off the nose on one of your recent LDCs you set you printer to 100% fill?

Just something to consider.

[Mr.P]

Good advice.  Indeed I have been printing at 100% infill for these. The current model has held up to many shots at this point so i feel reasonably confident. 

[Clicky]

I was a bit inspired to do some work on the grip. Rasp on a dremel, followed up with sandpaper, scraping & more sanding. I flush fit the top of the grip to the upper block

[Mr.P]

All right - that looks great.

[Clicky]

Printer is working again, so I've printed the long version of the 47.2mm baffle, because the tube will be needing that support & the reduction of volume isn't that great. I went with 60% triangle fill. I'm going to be adding a stainless washer, cut to fit, to the front face to help prevent the front of the print from blowing out

I was thinking it would be nice if the rear portion of the ribs were curved to give a spin to the airflow, with every other rib ending short of that transition & the trailing edge ending at a 14° angle

A bit more advanced than what I've been doing so far in Fusion360, but that's the direction I want to work towards. There's a few other items I'd like to draw up, with geometry like that

The STL's are the wrong end up, I'm rotating them inside Cura which isn't a real issue. The bridging just as the ribs collect into a joined circle seems to be working perfectly for me with this gray eSun PLA+

Just for the fun of it, I tried this out without the outer tube, as that still needs to be cut down & assembled. I actually thought I was gonna hold that on there...

Running a 175 on full power, cylinder at 220. Holding as tightly as I could, couldn't even feel the print sliding out of my hand, knocked the insert out of the bottom of the grip, print went flying like that's what we were planning on doing - oh man, if only this thing had fins!

So I have the impression that there's going to be a lot of force pushing the tube forwards off of the rear bushing, and that's basically all that's going to be keeping this together. I might revise my plan on how to attach the outer tube to the rear bushing

[subscriber]

Phil,

He front support washer is a good idea.

The internal fins are thin.  If you angle them the have to do work that was not intended.  I predict they will crack and than rattle...  Or am I mistaking your design for one of mine?

What caliber is that pistol?

[Clicky]

Phil,

He front support washer is a good idea.

The internal fins are thin.  If you angle them the have to do work that was not intended.  I predict they will crack and than rattle...  Or am I mistaking your design for one of mine?

What caliber is that pistol?

The Rex-P I have is a .357

For the moment, I'm only considering drawing my own design from scratch, but I'm also wondering what else you might think of it, if not try it out too

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

Good point about the ribs, need to make them thicker and maybe reduce the height of the passage for the transition to spin. Centripetal force will play into that to some degree. If the rib height is reduced, it's bending moment will also be reduced

[subscriber]

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 for spinning air with vanes, Maxim had a patent that included that in 1909:  https://patents.google.com/patent/US916885A/en?oq=916885

I have had a few designs that use vanes in the "blast chamber", with toroidal spirals that also  delay air via centripetal force, down stream from there.   

The attached images further down are for inserts into a robust tube or a shroud (if scaled down).  Did that design for another GTA member (for free) about two years ago.  Have many more, for the same person; and others.  Just wanted to show you that most good ideas have already been thought of.  Not meant as a snub to you: I have had thousands of "good ideas", but have only 25 US patents.

[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 for spinning air with vanes, Maxim had a patent that included that in 1909:  https://patents.google.com/patent/US916885A/en?oq=916885

I have had a few designs that use vanes in the "blast chamber", with toroidal spirals that also  delay air via centripetal force, down stream from there.   The attached images further down are for inserts into a robust tube or a shroud (if scaled down).

All interesting. Maxims idea is a totally different kind of flow, I'm not sure how I could work with that. If it was changed from a torus shape into a pair of rectangles, then there's an opportunity to vent the center of each spin chamber to avoid over-pressure

There's a circle track muffler that does this: https://spintechmufflers.com/ - they started out by telling everyone how their baffles worked. I got a brochure from the company back in 1996 that explained it in detail. Back then, the company was called 'Spin Trap'. Thermal transfer is a very big part of how that works. Of course, airguns don't provide as much heat energy, so that's not as usable. Hot & cold zones are too close in temp. But the chambers also had holes stamped into them with the stamping intentionally done so each hole would project into the chamber. That would make it harder for exhaust flow to turn & enter the hole until the velocity slowed enough. These holes were placed in a small area where they could vent into a large exit chamber that would then lead out of the muffler. You can see the spot welds where they place the spin chambers, but they're not talking about the other little details like they used to

Yours is a bit closer to what I was thinking of, with the main exceptions being that flow isn't guided into the final trailing edges with quite as much control, and it's not a 'pumping' method with flow separating into high & low energy states. My idea wouldn't work as well in a forward chamber like that anyways. What I want to do is more like a cyclone dust filter, but with a tube in the center

[subscriber]

I found my design that uses both toroids, and vanes in the "blast chamber". The attached STL is a half shell for printing flat on the platen, because else the last expansion chamber has a floating ceiling - along with the toroid "nozzles".  The idea is to glue two shells together and place inside an outer tube.

Zipped STL attached for half shell. 

The mind boggles at the possibilities...

[Clicky]

I found my design that uses both toroids, and vanes in the "blast chamber". The attached STL is a half shell for printing flat on the platen, because else the last expansion chamber has a floating ceiling - along with the toroid "nozzles".  The idea is to glue two shells together and place inside an outer tube.

Zipped STL attached for half shell. 

The mind boggles at the possibilities...

Also interesting. I think the spin chamber is too small, but if it were to be reversed and located back over the barrel, then a lot more room is available

Have you considered printing lost wax cores & casting with zinc/aluminum alloys?

[subscriber]

I have not considered any material for my own use that would be robust enough to use with PBs.  What I would design for myself does not limit what I might design for others.  One could probably use lost wax to define the shape of a cavity that is filled with reinforced resin.  After that cures, the wax could be melted out.

I designed vanes for a shroud not long ago, posted in this very thread:  https://www.gatewaytoairguns.org/GTA/index.php?topic=203675.msg156383702#msg156383702

I prefer the latter vane design that lives near the ID of the shroud, rather than the earlier ones near the OD of the barrel: https://www.gatewaytoairguns.org/GTA/index.php?topic=203675.msg156383950#msg156383950

The vanes for supporting the barrel behind this reflex air stripper could be made into a spiral to get closer to what you might have in mind.  That said, making it harder for air to get into the rear shroud volume (because the vanes will increase back pressure, if they are too steeply angled) could be counter productive.

[Clicky]

I have not considered any material for my own use that would be robust enough to use with PBs.  What I would design for myself does not limit what I might design for others.  One could probably use lost wax to define the shape of a cavity that is filled with reinforced resin.  After that cures, the wax could be melted out.

I designed vanes for a shroud not long ago, posted in this very thread:  https://www.gatewaytoairguns.org/GTA/index.php?topic=203675.msg156383702#msg156383702

I prefer the latter vane design that lives near the ID of the shroud, rather than the earlier ones near the OD of the barrel: https://www.gatewaytoairguns.org/GTA/index.php?topic=203675.msg156383950#msg156383950

The vanes for supporting the barrel behind this reflex air stripper could be made into a spiral to get closer to what you might have in mind.  That said, making it harder for air to get into the rear shroud volume (because the vanes will increase back pressure, if they are too steeply angled) could be counter productive.

Lost wax cores are printed using a filament that melts at a very low temperature. It's called a 'wax filament', but it's really just a thermoplastic with a low melting point, intended to be used with investment

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