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

popgun pete

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Jul 30, 2008
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I recommend using a metal piston and shock absorber anvil in any uprated “Mirage” type speargun as the plastic versions will not be up to the job.
Mirage original piston R.jpg
 
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Diving Gecko

Diving Gecko

shooter & shooter
Jun 24, 2008
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Yeah, that's one solution but actually, Dima's improved parts have been up the task (plastic piston, metal shock absorber). It's just funny since Salvimar's Vuoto is basically a clone of Dima's design yet, I haven't busted a single o-ring on Dima's muzzles. I think the Italians overdid it on the tolerances. My gut feeling (haven't measured it yet) is that the shoulder/flange the o-rings bang against is less wide and/or the gap between the absorber and the inner wall of the muzzle is too big.


Sent from my iPhone using Tapatalk
 
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Diving Gecko

Diving Gecko

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Jun 24, 2008
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Back at It
Some real work came up so this project was set aside for a few weeks. But I am slowly getting back to it.
Exactly a month back I dropped a 3D printed part in a cup of gun oil to see if there were any compatibility issues. I was supposed to fish it out after a few days, but since I was busy with work I let it sit there until now.
The part seems totally fine. No dimensional changes at all and it seems to scratch the same as the other parts - which is the best I can do to test any changes to the material itself:


I will also be testing Pete's advice on spray painting the leaky nose cone. Here's 'Apollo' after a few primer layers and light sanding:


And after having had fun with a rattle can of grey paint:



"Dummy mounted" on a barrel:


I haven't had a chance to test it yet. The rest of the Predathor has been in South China (where I did some pool testing) but the parts just got returned to me, so will test it soon.

The one thing about this possible spray paint solution that I am not too fond of is that it's not the most sturdy of paints. Two-component car paint would probably be better, but let's see. Perhaps this will work.
But still, I couldn't let go of my idea of impregnating the nose cones with epoxy and since the vacuum method didn't seem to do the job fully, I kept thinking about the positive pressure method (forcing resin through the tiny holes in the part under high pressure).

So, I built a small chamber to do exactly that and here are two pics showing how it will go together:



The barrel is a cut-off of a very old Mirage barrel I had and I am 3D printing the end caps. The one in the pics above is for nose cones where the barrel sits centered in the reservoir but here's one for the Evo Mirage:


These end caps will leak, too so I will need to give them the same primer and paint treatment as the Apollo nose cone:


Basically the idea is to pour in a bit of epoxy and then pressurize the chamber until epoxy starts seeping out of the nose cone. And then, before the epoxy cures, take the whole thing apart and clean up the parts nicely. It will be more messy than the vacuum impregnation but hopefully not too bad.
Once the nose cone has cured, I will also be able to use the chamber assembly to test for air leaks. It's simpler, faster and more handy to use this little chamber rather than assembling a whole gun.
 
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popgun pete

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Jul 30, 2008
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Provided the paint does not chip off then it should be OK to seal the 3D printed parts as to leak the air pressure would have to drive paint particles through the matrix of microscopic interconnected holes.
 
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Diving Gecko

Diving Gecko

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Jun 24, 2008
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Belt and Suspenders
Not much progress lately, though I did resin impregnate one nose cone. As most often is the case when I work with epoxy, I don't get to shoot many pics - it's just too messy.
I actually did both the vacuum and the high pressure impregnation. First, I vacuum impregnated the part - by letting it sit in a jar of epoxy for about 10 mins while vacuum was being pulled. The idea being, as stated previously, that you "suck all the air out" of the small cavities in the part and then once you let the ambient pressure back in (turn off the vac pump and open the valve), the resin should be sucked into all those tiny gaps and occupy the spaces where there was air before. After the vac procedure, it was time for the high pressure treatment so I assembled the small pressure chamber:



I plugged the pumping barrel bore with a black Delrin "dummy piston":


Then I poured in a bit of the degassed resin, put the end cap on and added about 20 bar of pressure.

Here it is before being hooked up the the pump:


(This pressure gauge is a bit of a dud. First, it came with what I suspect was moisture inside the glycerin leading to a foggy dial and then later, I accidentally tore the little rubber plug off and the glycerin leaked out. Not a biggie, can fix it at some point).

As mentioned, there's a tad of cleanup work needed after the high pressure procedure:


After letting it cure overnight, I actually went and did it all again. Well, the high pressure procedure, not the vacuum one. I am not sure it was needed as not much resin came through - only a bit from the pumping barrel but I blame that on a leaking plug.
 
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Diving Gecko

Diving Gecko

shooter & shooter
Jun 24, 2008
1,234
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Shanghai
Work Holding #1 -Sleeve Fixture
Since I added the anti-banana'ing feature to the rear of the nose cone, it's been a challenge holding the cone in the lathe chuck. It's actually almost enough of a reason to dump it again. But I'll keep it for now, so needed a solution. But first a rendering to remind you how the rear of the nose looks:


And the solution, for now, is this:


For lack of a better idea, let's call this one a sleeve fixture. Printed out and in real use cutting the o-ring grooves:


Not much else to report on it - it works as intended:)
 
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Diving Gecko

Diving Gecko

shooter & shooter
Jun 24, 2008
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Did you test the painted version for gas permeability?
Yes and no, I haven't bothered to put the painted nose cone on a gun yet but the painted end caps for the impregnation chamber leak a little through the paint, so lost a little hope for the painted nose. I'll probably test it in anger next week.

More urgently, I need to service the lathe a little and make an upgrade or two. I was beginning to get some chatter on the lathe, so time to adjust the gibs. Also, I need to drill and tap some holes in the carriage so I can mount a traveling steady - which would have come in handy when I cut the reservoir down to make the impregnation chamber. I have had one for months, just not been able to mount it, yet. Finally, I might make some 3D printed parts to hold the DRO scale in place - now, the alu angles are just stuck on with (strong) double sided tape.
 
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Diving Gecko

Diving Gecko

shooter & shooter
Jun 24, 2008
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Work Holding #2
As mentioned in the post just above, I had to spend a little time getting the lathe back in shape. Now, that I have had it for a while I feel like I know its ins and outs, quirks and whatnot, so it didn't take too long. It was also long over due that I drilled and tapped two holes for mounting the travel steady.
Now, I can do something like this:


"This" is cutting down e.g. a long shooting barrel to a reduced diameter in order to save some weight. It's something I've wanted to do pretty much as long as I can remember but I haven't even been able to get paid machine shops to do it. It's really not that hard, but you do need a traveling steady rest to do it.
I might upgrade the steady rest a little down the line. I have seen people add bearings to the brass fingers but for now, this simple steady rest will do the job nicely:


One bummer, though. The steady rest "bore" is actually not big enough for a 40mm reservoir...
 
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Diving Gecko

Diving Gecko

shooter & shooter
Jun 24, 2008
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Nose Cone - Prototype V12, Testing
Keeping with naming of the parts in compliance with the CAD program, I am up to V12 on this latest nose. This is the one I have already vacuum impregnated in epoxy resin and high pressure impregnated twice to boot.
When I did the resin impregnation, I had a small leak at the pumping barrel bore so now that the lathe is back together, I cut a new plug with slightly shallower o-ring grooves to get a bit more compression on those seals. (There's no need to use a real pumping barrel for this dip and dunk test and I haven't finalized the bulkhead design anyways - hence the plug).
Then I assembled the parts and since the long 130 is too unwieldy I just used the 85 barrel and reservoir.

No leaks so far, but the vac impregnated Apollo nose cone didn't show any leaks for the first few hours either:


I have this up to 31bar:


And I am using the Evo handle. I guess this is actually the first time I have a pressurized gun together using that handle and my DIY nose cone:


I guess that's an accomplishment of sorts, perhaps there's now light at the end of the tunnel:).
 
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Diving Gecko

Diving Gecko

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Jun 24, 2008
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Nose Cone - Prototype V12, Test Result - Success!
I think it works! I forgot to snap any pics when I put the pressure gauge back on the gun after it has been sitting almost a full day but there was zero loss of pressure:). This was at 31bar, so that bodes well for the high pressure epoxy resin impregnation method.
Well, I guess I can show one more pic of the V12 nose cone:


Also, since I had the proper cam out, I shot the pumping barrel bore plug which I mentioned earlier:


In regards to the impregnation of this cone, I did kinda break one of my rules of only changing one parameter at a time when I did both the vacuum and the high pressure impregnation. But given that the vacuum-only procedure didn't work on the Apollo nose cone, I am assuming it was the high pressure method that worked this time around. If this is indeed the case, despite the high pressure procedure being more work and more messy, it does hold one advantage over its vacuum counterpart: It uses way less epoxy. Probably about 4-5 times less and honestly, it was feeling slightly frustrating mixing two cups of epoxy and just have the part suck up a few grams of that and then ditching the rest of it.

I have modified the latest nose cone design slightly. All the important dimensions are the same but in V14 (bottom of pic) I have made bigger cut outs on the side as the nose was beginning to get quite heavy:


These two cones are both printed from the same material. I think the discoloration of V12 on the top is from the epoxy reacting with the water in the sink. This epoxy turns a little hazy when exposed to water.
 
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Diving Gecko

Diving Gecko

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Jun 24, 2008
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Work Holding #3 - Expansion Arbors/Mandrels
For some machining operations on the lathe it's tricky holding the part in place. I've now made a few 'expansion arbors'. A few have been printed and one I made in alu:


The 3D printed one may just be a tad too flexible - even though the screw is the full length of the arbor itself. So, I might have to make that one in alu, too. It inserts into the pumping barrel bore for cutting the small front bore to size:


But that front bore is not a super critical dimension. It just has to be big enough for the tail end to slide through and not much bigger. Also, it doesn't actually have to be as smooth as the bores where o-rings have to seal. I can just print the front bore to size and live with the slight rippling from the layers.
Then, for turning the inside of the pumping barrel smooth and to size, I needed an arbor to insert from the front:


Now, don't think I came up with this all by myself. It's a pretty established work holding idea in the metal machining world. Probably best explained/shown by the cool Joe Pieczynski in this video.
Apart from the 3D printed arbor perhaps being slightly too flexible, they both do an OK job, though admittedly, if I added counter balances they would probably be even better.
 
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Diving Gecko

Diving Gecko

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Jun 24, 2008
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Apollo Relaunched, Meh...
I made a new end cap, this time in POM/Delrin. It's just so easy to work in and honestly, as was proposed earlier I have thought about making the nose cone out of it, too (more on that later).

Apollo mounted on the pressure chamber and hooked up the pump:


Taken up to about 40 bar:


And it kinda almost holds air...:


I know you can't really say that as it either holds air or it doesn't. But while it leaks a bit out the front and at the reservoir flange, it's not by a huge amount. One could be forgiven for thinking it's just bad o-rings but I don't think so. The dimensions on the bores are giving ideal compression, the surface smooth on account of the paint and the o-rings brand new. I tend to think the air is somehow going under the rings, through the material and just coming out in those two places.

So, depending on how you look at it, this could be a glass half full scenario. You could argue that with a lick more paint, it should work out. But I will say, it's more like a glass quite empty given that this nose cone actually had a full resin vacuum impregnation treating before the sanding, primer and paint job. So, my thinking right now is that if it was just painted - like the end caps for the pressure chamber - it would perhaps leak a whole lot more.
Well, I might actually test that at some point. I guess I need to try it for real before we bust or confirm that this could be a solution.

Now, back to the Delrin which I mentioned is super easy to work in. It holds air, machines so easily and you can get an amazing surface finish on it (not that I cared when I cut down the OD as you might notice in the first pic). Many posts back it was proposed that I give up on this whole 3D printing adventure and given that I have a four jaw chuck, just get on with it and make a nose cone on the lathe. I have indeed thought about that many times before. It was one of the reasons, I started thinking about that chuck in the first place but where's the fun in that;-). Also, I can't get swank shapes and undercuts on it on the lathe, but one possible option would be a combination. Basically make the rear part that needs to seal 100% in Delrin and then a "sexier" 3D printed front part which is not under any pressure. The 3D printed front could incorporate the shooting line holder, the fiber optic sights and just look overall better than a circular nose made exclusively on the lathe.
 
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popgun pete

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Jul 30, 2008
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There may an uneven microtexture on the surface causing the leaks. Once I had a nose "O' ring, the one that sits behind the main barrel thread, leak despite me changing it as It seemed to leak on the barrel tube itself due to a slightly scuffed appearance there but with no visible scratches. I spun the barrel in the lathe, put light oil on the tube and polished the surface with fine grade (800 then 1200) emery paper. The "O" ring sealed perfectly afterwards as the barrel had a fine microtexture which I completely smoothed out rather than take a skimming cut with the lathe tool as the tool may not pick up on the tube evenly despite the centering action of a three jaw chuck.
 
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Diving Gecko

Diving Gecko

shooter & shooter
Jun 24, 2008
1,234
301
138
Shanghai
Nose Cone - Prototype V12, A Bit More Testing, A New End Cap and Updated Results
A few posts above I tested the epoxy impregnated V12 nose cone and it held air. But since the printed end cap for the pressure chamber setup was leaking I had to assemble a gun to test the nose cone. It seemed a bit silly, so today I made a new end cap in Delrin:


Assembling just the little pressure chamber for testing these DIY nose cones is a lot easier than assembling a whole gun, so even though the nose cone held air the first time around, I saw no harm in trying again:


This time, I pressurized it to 40bar (I stopped at 30bar the first time):


And as the next two pics prove, there was zero banana effect:



Actually, there was a bit of banana'ing going on when I tested the nose cone on the gun setup the other day - but I hadn't tightened the muzzle more than finger tight. This time, I tightened it a whole lot more. Not fully sure what I can conclude on this matter. The fit of the nose cone in the reservoirs is extremely snug, so perhaps the anti-banana feature doesn't really do much - perhaps, what makes a much bigger difference is how tight you screw the gun together.

Oh, the results!
Well, the first time I dunked this assembly, it was leaking badly. Turned out I had not only forgot to add the pumping barrel bore plug but I had also not put a main o-ring on the nose itself, haha. Second time, it still leaked at the pumping barrel and I found out that the bore was chewing up the o-rings of the plug on insertion. I guess I just got lucky the other day as it didn't lead to a leak. But I think the epoxy impregnation left a few tiny sharp edges or blobs of resin. It was an easy fix, I just wet sanded it with #400, #800 and finally, some #1200 grit sand paper. You can sand this material if you go slow and keep it cool.
In the end, there are no leaks at 40 bar though I am leaving it pressurized over night, so I should have a final verdict some time tomorrow.

[EDIT]
It's been a full day, give or take a bit, and the nose cone has held air perfectly so I will consider the epoxy impregnation a success.

Next up is to finalize the nose cone design. The overall dimensions, the bores and o-ring grooves are good now and the V14 shown a few posts above would do the job OK (as would this present one). But it could still loose a bit of weight and I'm considering adding a feature to hold a slip tip line taut, just not sure how best to do that yet...
 
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Diving Gecko

Diving Gecko

shooter & shooter
Jun 24, 2008
1,234
301
138
Shanghai
There may an uneven microtexture on the surface causing the leaks. Once I had a nose "O' ring, the one that sits behind the main barrel thread, leak despite me changing it as It seemed to leak on the barrel tube itself due to a slightly scuffed appearance there but with no visible scratches. I spun the barrel in the lathe, put light oil on the tube and polished the surface with fine grade (800 then 1200) emery paper. The "O" ring sealed perfectly afterwards as the barrel had a fine microtexture which I completely smoothed out rather than take a skimming cut with the lathe tool as the tool may not pick up on the tube evenly despite the centering action of a three jaw chuck.
Yeah, a few years back, I had that issue on a few of the carbon fiber barrels that were a little bit "resin starved" leaving the inner wall just a tad too rough. I solved that issue by giving it a layer of epoxy and then wet sanding it back down.
But I don't think the wall surface of the reservoir is the issue here - though, I waited to reply to you until I could confirm it. But since I just used the same reservoir on the latest Evo Mirage nose cone test without a leak the reservoir should be fine:).
If I find the time, I will try to make one final test on the paint (with no epoxy impregnation) solution. Honestly, for now, I just feel the epoxy method is a more sturdy treatment. Even if it gets nicked, scratched and abused it should still seal as the epoxy is inside the part and not just on the surface. But you are right in that it's more work.
 
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Diving Gecko

Diving Gecko

shooter & shooter
Jun 24, 2008
1,234
301
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Shanghai
Work Holding #4 & Nose Cone V14 - The Pumping Barrel Bore
I was setting out to bore out the pumping barrel bore on the newest nose cone, but when the part was on the expansion arbor it did actually have a bit more vibration than I thought when I first used it. With the boring bar, I just couldn't seem to get a good surface.
So, I went back to Fusion 360 and a few hours later, this gadget came off the printer:


I had mentioned that one way to improve the use of the expanding arbors would be to use counter weights to balance the part on the arbor. So, I took the sleeve fixture design and added a way to add weights to it.

I used to have some thin lead sheet lying around and the idea was to just wrap it around that long peg, but I couldn't actually find that lead sheet.
Instead, I had some small weights, that I think are used to balance car wheels, so I used those and just super glued them on:


To do the balancing itself, I used two ball bearings mounted in the chuck jaws but since they were just from the odd parts bin they weren't big enough for my arbor, so made an adapter out of Delrin:


The balancing sleeve works a treat, I can now spin this part to 2000rpm with no vibration where I had noticeable shakes starting at around 400-500 without it.

But strangely enough this didn't solve the issue with the boring bars giving a less than OK surface finish when cutting the bore. I even have brand new cutter inserts in them. I thought I used the same arbor when I cut the bore on the last cone, but maybe I didn't. Maybe I used a much thicker press fit mandrel stuck in the shooting barrel bore and then mounted it offset in the four jaw chuck... So, maybe this thin alu arbor is just not stiff enough after all.

But then I remembered, that before I fell in love with my new thin boring bars, I actually did order a 13mm reamer, so I gave that a shot instead:


And here's the same pic just heavily cropped to show that the reamer left a really nice surface finish:


(The jagged, thin, white lines which look like cracks of sorts are just lint left over from using cotton buds to fish out the plastic shavings)
 
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Diving Gecko

Diving Gecko

shooter & shooter
Jun 24, 2008
1,234
301
138
Shanghai
Younger and (Almost) Slimmer
It turns out, the 3D printed nose cones are not that heavy after all. I always felt the plastic in the Mirage seemed pretty heavy so we are not too far off:


The original Mirage nose is about four grams lighter:



I could probably shave off that weight difference on the 3D printed ones in future versions if need be. But I might not bother as I should really get back to work on the bulkhead and handle.

BTW, looking at these pics, it only now dawns on me that I don't have an anchor point in the muzzle for a shooting line bungee... But there's a reason for that - I simply forgot because I never use it and wont either on this nose cone. I use reels or breakaway. I don't know what it is, but I just don't like to let go of the gun and see a fish swim away with it - even if attached to a float line.
 
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popgun pete

Well-Known Member
Jul 30, 2008
2,700
511
153
Australia
You can get chatter with the boring bar if the speed is too high or you take too big or ironically too small a cut. There will be an optimum depth of cut and speed, you just have to find it in terms of chuck rotational speed and lead screw feed speed. Leave as little boring bar unsupported as you can get away with.
 

popgun pete

Well-Known Member
Jul 30, 2008
2,700
511
153
Australia
It would be interesting to be a fly on the wall in the Mares boardroom when they realize that while asleep at the wheel they have missed the opportunity to create a new gun that they should have done themselves.