GeckoSub Mirage Evo - And Adventures in 3D Printing Speargun Parts

popgun pete said:

Great progress and a magnificent job, this is one of the best considered pneumatic speargun projects ever. The real pay-off will be when you use the pumping barrel and can feel the pressure progressively falling away in the rear of the gun. Transfer and insert the spear into the main barrel with very little effort, then the KABOOM moment when you pull the trigger for the first underwater shot and see the shaft rocket away in a blur of cavitation bubbles.

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DON'T JINX IT!!!
Haha, just kidding but thanks so much for the nice words. In reality, I have more or less just reverse engineered an existing product, tweaked a few things and made some new parts. I haven't really brought anything new to the table - except hopefully show that 3D printing is a potential way for the home tinkerer to make certain gun parts.

And you are absolutely right about the feeling of loading a Mirage - the first pump stroke can be a bit hard depending on your pressure, but then they get easier and that last insertion into the shooting barrel where it almost feels like you cheated. Flick the regulator, hear the swoosh and know you have a high pressure gun in your hands. It's a sweet feeling, indeed.

1st Assembly - Not Good...
Don't really have time for a super in-depth post but I put the gun together for the first time yesterday. I will do a proper show and tell later on.
For now, it's bullet form:

• The newest nose cone leaked badly - it had cracked the thin wall under the pumping barrel. I changed to the first one I did and that one holds air (as does the rest of the gun)
• The bulkhead kinda worked. Well, it worked but then it stopped working. So, I will take the gun apart and see if the o-rings got blown out of their seats. I will probably try putting in some stronger/longer springs as the ones I have in now are the weakest I could find
• Worst though is the fact that the o-ring on the power regulator gets blown off its bushing when you switch it rearwards to open the bulkhead after the pumping procedure (I tried twice and it happened both times). I will likely have to try an o-ring stretched more to help it stay in place but that will reduce the compression and the o-ring may no longer seal. In that case, I will have to machine a new bushing to make up for the o-ring being stretched more

For now, these are not deal breakers except for the fact that I am fast running out of time. I am hoping the reason the bulkhead valves not working is something benign as I surely won't have time to redesign, print and machine a new one.

Back to the "workshop" it is, then - and in parallel I will have to work on the alternative project I alluded to in an earlier post. I'll share more later.

popgun pete said:

A photo would be good as is, I am sure the set backs are only minor. A quick fix may be double "O": rings as Mares tried that themselves, not necessarily the same size, one stacked behind the other.

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Double o-rings on the power regulator front?

Can't really do pics yet - the gun is still assembled from yesterday (that's how I know that at least it held air). Also, the the check valves are kinda hard to shoot. But will go take the gun apart now and share findings later.

popgun pete said:

On the regulator shaft and the pumping barrel nose, that is where "O" rings were doubled up in the past. The photo being of the fully assembled gun, as it is right now. I don't know why the "O" ring on the piston plug is blowing off unless it is being peeled off by being not a tight enough fit in the transfer port.

Maybe on the parts diagram you could indicate which "O" ring you are talking about.

Click to expand...

This is the culprit:


I think it's the sudden airflow when you open up after the pumping procedure. I've done some measurements and think I have two possible solutions. Just need to wait for the o-rings I ordered to arrive.

As for the check valves, I've swapped out the o-rings and springs so can test that again shortly.


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popgun pete said:

You can obtain higher shore hardness "O" rings that are more likely to stay put. When I think about the early "Mirage" which had much the same hardness "O" rings everywhere except one, the reason the "O" ring never was peeled off the brass piston plug was the stifled airflow as the air rushed to fill up the inner barrel and pre-chamber. That saved the "O” ring, but the same effect applied during the shot and that effectively throttled the gun while on “full power”. No wonder then my "Sten" 90 cm pumped up until the hand pump shrieked and then cocked with my double-handed loader could outshoot the "Mirage" 80 cm, but it was too hard to load like that and I let the excess air out before I busted something, either myself or the gun!

Click to expand...

The green o-rings I am increasingly using indeed are a bit harder. I even have a durometer, but it's not easy checking the shore hardness on a 1.5mm section width o-ring;-). But just to the touch, or rather bite, the green ones are harder.

Backing Up
Allow me to back track a bit before I catch up to my post from a few hours ago about the gun having issues - I still have some pics of how I finished the gun to that stage.

After finishing the resin impregnation of the bulkheads and the newest nose cone I needed to finish the shooting barrel. But turning these long barrels and shafts in the lathe is frustrating as the rear end starts flopping around. Until now, I have just supported the barrels with a tripod and a drop of oil but I whacked these together real quick:


(The goo on the print bed is regular PVA glue stick which helps with bed adhesion for most materials).

The Roller Jigs work a treat:


With the shooting barrel properly supported I cut two o-ring grooves at the front:

And one more - in addition to the one one that was there already - at the rear:


(The three grooves are (L-R) retaining ring groove, original o-ring groove and new o-ring groove).

For keeping the bulkhead in place, I went with the simple method of using a Delrin clip. I cut a few in different thicknesses. It was a fast job and heating the blade of a Stanley knife made cutting the rings easy:


But the Delrin retaining ring takes up a bit of space and interfere with the little insert peg I made for coupling the pumping barrel to the bulkhead so I had to make a little cut in the peg. Once again, I used the lathe as a mill. The ER collets make it quite easy to hold small, cylindrical parts:


And after the cut:



With these steps completed I was ready to put the gun together - and as already "admitted" a few posts back, it leaked from the first nose cone but that was solved by using an earlier version. But worse, the bulkhead valves were action up and the o-ring on the power regulator plug got blown out of its seat.

Solution Time (Hopefully....) - Part 1
Honestly, I freaked out a little when I put the gun together for the first time and instantly the nose cone broke, the valves seized and the power regulator of the stock Evo handle turned out to not work in a Mirage style gun...

It's been almost five months since I started this project and I guess I really just wanted it to work and succeed. Also, I am leaving town in five days and though I am not going straight diving, I wont be near my machines and spareparts until I do. So, the pressure was on.
But I sat down, took a deep breath, resisted the temptation to work on another gun and tried to think of simple solutions before I opened the Mirage.

I feared that the o-rings in the check valves had been blown out and skewed but while the pic is hard to read, the o-ring sat where it should:


The one in the other bore did as well and this was semi good news. It means, the captive seat design I changed to has at least worked. But something else was amiss. I figured I would change two things. Find some slightly bigger o-rings and some longer springs. Luckily, I have a ton of o-rings by now and these few bags are some of the ones I felt could work:


Of course, not all o-rings are created equal and some are far from their stated sizes and it turned out that the ones I had in the bulkhead were quite a bit off. I found some better ones which in the end were only 0.4mm larger in OD and 0.2mm larger in section width.

I have also been buying quite a lot of springs and changed out the 10mm long springs I first used for some 12.5mm ones:


(Again, China is amazing for stuff like this. The online shop that sells these piecemeal has a minimum total order amount but since it is about USD 1.5 it's quite reasonable...;-))

After these two small changes - well, small because I had the parts on hand - I assembled the bulkhead once again and tested it by attaching a Mares pump (without its threaded front piece) directly over the peg where the pumping barrel goes:


I then took it to the kitchen sink and gave it some pumps and it looked good - though this method can't test all the "directions" of the check valves I was hopeful it would at least be better than the first time around.

Solution Time (Hopefully....) - Part 2
While I was hoping the changes to the springs and o-rings would cure the bulkhead ailments, I was quite nervous about what I saw when I first pulled the handle out of the bulkhead after the leaking first assembly:


Obviously, the o-ring should not sit in that place at all. And I was quite sure that the sudden rush of air when you open the valve (I guess it's a valve) after having pumped most of the air forward of the bulkhead during the Mirage'ulous Loading Process was what caused the o-ring to leave its home.
I know it must have happened then as after I let the power regulator slip back to open the first time, I could freely move it back to the front with no extra friction from the o-ring being squished in the bore and after that, the Mirage loading didn't work any longer.

To solve this problem, I had to figure out what caused it and I think the calipers offer an explanation:


Now, this looks like a beautifully spot-on bushing for an 8mm bore but the thing is, the air transfer bore of the Evo bulkhead (both the original one and mine) is 9mm... This may not sound like a big deal but it means that the shoulder behind the o-ring is 0.5mm smaller than it could be (on each side) and since the depth of the o-ring groove is only 0.85mm in this bushing an 0.5mm increase would be quite substantial.
I know Mares did not intend to make this as a Mirage and perhaps they slimmed down the bushing to have less drag around it during the shot (which would be flawed as the o-ring is still "sticking out" and will be what determines the drag). But this could very well be the main problem.
(That the width of the o-ring groove is narrower than the o-ring itself also makes very little sense to me).

I did some calculations on the stretch and compression of the original o-ring and some alternative ones to see if I could just swap the o-ring for another one. My idea is that though it is not ideal, I could increase the stretch of the o-ring and make it sit tighter that way:


The original design actually puts very little compression on the o-ring and 10% stretch which I felt was not enough for my particular use.
But if I kept the original bushing (and just widened the groove a bit) I could double or triple the stretch by just changing the o-rings. So, I hurried up and put an order in online for yet more small, green and black pieces of rubber.

Normally, it takes about two days until I get my o-rings delivered, so I kept thinking about that original bushing design where the shoulder is substantially smaller than the bore it sits in. I even checked the older Mirage power regulator bushing which (not surprisingly) is the same size as the bore. Suffice to say, I figured I had to test this so went about making a quick and dirty new power regulator bushing...;-)

A few pics of the process:





The whole idea of the new bushing is to maximize the size of the shoulder sitting behind the o-ring. I didn't do a perfect job, but at least it's a lot bigger than before (remember, the Evo air transfer bore is 9mm):

(And yes... I drilled all the way through, too. But the Loctite thread locker should seal that, haha).

Here's the new one next to the "old" one:


The reason the new bushing is longer than the original is that I used a spare ø4mm rod from my Seac gun which is a few mm shorter than the Evo rod.

Time to assemble the gun again and see what, if any, improvements I made...

2nd Assembly - Dolphins?
I just put the gun back together after swapping o-rings and springs in the check valves and making a new - and hopefully improved - power regulator bushing.
The results were encouraging though not perfect.

First, I put 20 bar of pressure in the gun and the Mirage Loading worked perfectly. The check valve opens with a funky dolphin sound as the air hisses through.
I did three "sets" of loading, waiting and opening the valve. After each waiting period I would insert the shaft again to see if I could feel any increased resistance pointing to a leak between the front and rear part of the reservoir.

1. Wait time: 10 mins. Result: No leak
2. Wait time: 60 mins. Result: No leak
3. Wait time: 40 mins. Result: Very, very slight leak or no leak (judging from feel)

So, those are the encouraging news but... I then took the gun up to 33 bar and something gave up the ghost after a few pump strokes and the Mirage left the gun. I had a long day and not in the mood to take the gun apart just now but will get back on it tomorrow.

At least, I don't think I killed the power regulator this time - it feels like the o-ring is still where it should be and it would be cool to have solved this problem. I just hope it's not structural damage to the bulkhead - the pressure differential between the front and rear is quite intense at the end of the loading phase and I might not have beefed up the bulkhead enough in the design phase.

BTW, next time, I might use a pressure gauge to see if there's a leak during the waiting time (gun pre-pumped but power regulator still in the closed position).

Bling, Bling, Bad Trigger or Arrrrghhh, Mares!
Man, I am getting tired of these fancy pants companies making bling for the frikkin sake of bling and certainly not checking the real world implications.
No pics right now, maybe later.

Anyways, here's the deal. That oh-so-pretty stainless steel trigger never really impressed me. I am not kidding you, just the sheer mass of it makes the trigger feel like walking in knee-deep mud. The metal clanging sound is unpleasant, too but I can live with that.
But the real issue is how it engages with the line release.
With the gun taken up to (only) 20 bar for the leak test, I did a rough test to measure the trigger pull (no piston hooked to the trigger) and it was somewhere around 600-700g. But then I dummy rigged three loops of shooting line at about as taut as in real life rigging scenarios and the trigger pull jumped to 2-2.5kg just from the friction between the line release and the trigger! 2.5kg! That's just crazy and will likely impact the ability to take an accurate shot.

Maybe I need to put that stupidly strong resetting spring back on the line release to alleviate some of this but I think that with it on there's a real risk the line release will slam back before all the shooting line has cleared it. At the very least I will try to polish this turd (trigger)...

(Sorry for the tone of this post, but besides heavy guns the one other thing I really don't like is a heavy inconsistent trigger pull. Imagine spending five months on/off on this gun just to find out a did trigger makes you spray shots all over the place... Besides that, I just hate when big brand name companies think they don't have to switch their brains on).

Air Transfer Bore Sizes/Power Regulator Bulkhead - A Standard To Be Found?

popgun pete said:

Instead of relying on memory I measured my "Mirage" (Version 1) brass piston plug at 6.96 mm OD and the rear entrance of the transfer port at 7.52 mm ID. My digital Vernier calliper jaws are unnecessarily sharp as razor blades, so I did not push them into the front side for fear of scratching the bore. I have a plastic set of callipers which don’t scratch, but they are about as accurate as measuring with a kid’s wooden school ruler (now made of plastic these days, but you will get the idea).

Another check on the sizes are the "O" rings used and I recall I listed them here: https://forums.deeperblue.com/threa...for-older-mares-pneumatics.91719/#post-853873

Click to expand...

Yeah, I always thought that video and its mentioning of a 6mm bore was weird. I think it would be 7mm.
Yesterday, I checked the original Mirage bulkhead (V2) bore with differently sized rods and 7.0mm fit spot on with no play (the front of the bore has a bit of a lip and is slightly smaller though. Normally, with this method, even 0.1mm of gap translates into a bit of a wiggle.
If I was to hazard a guess right now, I'd stay the old "standard" would be 7mm.
I'll check the Seac bulkhead later on and I think I have a Sten taken apart I can check at my friend's place in a week or so.

[EDIT]
I measured the Seac Hunter bulkhead and the air transfer bore is 7.0mm, too.
Turns out some parts of my Sten are here, some are in Thailand and whilst the bulkhead is not here, the power regulator assembly is. I measured the OD of the o-ring as it sat on the plug to be 7.35mm, so I think that points to the bore likely being 7.0mm, too. The plug itself is larger than 6mm so for sure, the bore is not 6mm.

I have been working on a spreadsheet for all the various o-ring sizes I come across in my guns but it's turning into a monster as I have also added the ones I have been using in my own parts and various experiments.
But consulting it just now, I can see that the o-ring for the Mirage, Sten and Seac power regulator plug is a standard AS568-007 ring with the dimensions of 3.68mm x 1.78mm (ID x W) or 7.24mm x 1.78mm (OD x W). (I think actually this is one of the rings that Mares specified to be of a harder compound in some of the diagrams).

As for backing the regulator plug out of the bulkhead I have been alluding to a modification on that front, too. Hope to get around to it in a day or two;-)

Now, I need to decide between Cohen and CCR for today's workshop soundtrack. Choices, choices, choices...;-)