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

popgun pete

Well-Known Member
Jul 30, 2008
2,700
511
153
Australia
They work OK as I have the tri-cut and the pencil point of these three tips, but I don't have the arrowhead. As for streamlining they fold up into a small package, although they have more frontal area than just a round shaft with a tip ground into it.
jbl breakaway tri-cut folded.jpg

Bear in mind that these breakaway tips have been around almost since the beginning and I have Undersee Mako's with the same layout that I used on my big timber guns, but I only have one left of those as they stopped making them some decades ago. There is an Undersee Mako manufactured today, but it is a fat tri-cut point tip.
 
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Diving Gecko

Diving Gecko

shooter & shooter
Jun 24, 2008
1,234
301
138
Shanghai
What is the inner diameter of the barrel and what is the stroke of the piston?
What is the length and diameter of the harpoon?
Mostly traditional Italian sizes for the barrel and reservoir:
Shooting Barrel: 13x18mm (ID x OD)
Reservoir: 38x40.5mm (ID x OD)
Pumping barrel is 10x13mm (ID x OD).
Length of the gun: app. 140cm.
Shooting Barrel: 128cm (that's the full length, I am not sure what the working stroke is).
Shaft: 145cm
 
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Diving Gecko

Diving Gecko

shooter & shooter
Jun 24, 2008
1,234
301
138
Shanghai
no harpoon diameter
In this case, 8mm. But I have used 7mm and 7.5mm, too on a gun 20cm shorter. I am still not sure where the sweet spot is but on this trip, I am using 8mm as we may run into big dogtooth tuna that would need some proper penetration. I am also not running the gun at full pressure yet. I think I could run it at close to 40 bar which might be enough even for an 8.5mm shaft but I am running it around 28-33bar.

Honestly, this is all speculation until I find time to properly test this in a pool with different pressures and shaft thicknesses.
 

popgun pete

Well-Known Member
Jul 30, 2008
2,700
511
153
Australia
I think 8 mm shafts are best for that gun, if you want to use 7 mm then use them out of a regular "Cyrano" with the 11 mm barrel, or something similar. I found the "Mirage" 7 mm shaft was a waste of time as striking power was down compared to the 8 mm when using the "Mirage" tip. Shaft mass is 30% higher with the 8 mm shaft. A photo is attached with my "Black Sea" gun wearing the "Mirage" tip. The "Black Sea" is a hundred atmospheres gun.
Mirage spear tip.jpg
 
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popgun pete

Well-Known Member
Jul 30, 2008
2,700
511
153
Australia
I noticed that the newly arrived set of carbon calipers had a tiny bit of plastic at the top of one jaw keeping the jaws held open, so I cut it off as it was not meant to be there. Then with the jaws zeroed I measured a 7 mm diameter shaft and the reading came up as 6.7 mm! Thinking that could not be correct I used my digital metal calipers and got 6.99 mm, so these carbon calipers are junk! With their jaws closed you can see an opening on the knife edge lower section of the jaws when they should be closed tight as the top flat and wide section is. Note the shaft measurement was taken on the wide flat upper section of the carbon caliper jaws so the zero setting was correct. I only purchased them for their less knife like edges as the metal caliper jaws can scratch things such as bore diameters in parts that you cannot afford to be scratched. But for that purpose they are pretty useless, but then they were only 6 bucks and I have seen them since for about 2 bucks. Mock calipers would have been a better description.

 
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Diving Gecko

Diving Gecko

shooter & shooter
Jun 24, 2008
1,234
301
138
Shanghai
Setbacks in Indonesia - And a Warning!
So, I am still in Indonesia, chilling with local friends, spearing and doing a whole lot of repairs on the go...;-).
The gun has given me a fair bit of grief but honestly, I don't mind too much as long as I learn from it. This project was always a work in progress or proof of concept with the methods and materials I had available to me.
Anyways, enough of the disclaimer, let's get to the issues;-)

The gun worked fine for about three days or so when a small leak turned up in the nose cone (the newest carbon repaired version). As mentioned earlier, I changed the nose cone for the older version and the leak stopped. About a week later a bigger issue turned up. The Mirage bulkhead stopped working altogether. This meant, I couldn't load the gun at all. I dropped the pressure to about 20 bar and tried to use it as a "regular" gun but shooting 8mm shafts, 20 bar is far from enough power.
Back in the city I took the gun apart:
53686


Turned out a tiny piece of plastic had clogged a valve. I speculate that it could be from a thread I hadn't deburred properly and after a week of use, it had moved to the valve. Actually, it was sitting on top of the printed channel between the two valves, so I had to drill out the offending plastic.
Success, though!

For about a day... Then it turned out I hadn't managed to get all the new burrs from the drilling operation cleared out (again, speculation) and the valves got clogged again (what looks like grease to the left of this small o-ring is plastic debris):

53687


So, this time I spent quite a bit of time making sure everything was cleaned out and that the valves worked. I have a small pump that I use for my inflatable floats and I could attach that to the bulkhead and check the flow:
53688
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I am now fairly sure that if I use such an internal, printed air channel between the two valves in the future, it has to be much larger. A tiny piece of plastic clogged it as is probably only 2mm in diameter.

After this second bulkhead repair/service, I took the gun up to about 34 bar and went on another trip. But the spot had bad visibility, so I jumped in the water with my shorter Pathos 100 (yes, it's a bandgun...;-)) and never bothered to switch to the Evo Mirage. But unsupervised in the boat the gun snuck its way out into the sun and one of the fears I had a while back when I was printing these parts came true: After having baked in the tropical sun for hours, the plastic got soft enough that the pressure extruded the o-ring with an almost total loss of air as a result:
53690


So, I think it is fair to issue a warning. Do not use PLA plastic for parts under heavy loads that will be exposed to higher temps!

Once I took the gun apart, it was actually pretty fascinating to see how the plastic had moved around:
53691


At this point, I was ready to give up on the gun but after a few days of just leaving it in the corner, I set about making one last repair.
I filled up the front o-ring groove with epoxy glue and tried to repair the rear one as best I could with hand tools:
53692

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Then I put the gun back together again in preparation for another hunting trip and the nose cone repair worked - the gun held air:).
But the bulkhead, now serviced twice since the latest failure, was still acting up... It wasn't clogged like the two first times, but it was leaking. I could hear and feel that the pumping action worked, but the air didn't stay put in the forward chamber - it somehow made it back to the rear chamber.
This is the worst leak in a Mirage as it is so hard to troubleshoot. With my patience low at this point and out of extra o-rings (the big o-ring on the bulkhead is actually sanded down as I forgot the right ones at home) I decided to go a different route...
 
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Diving Gecko

Diving Gecko

shooter & shooter
Jun 24, 2008
1,234
301
138
Shanghai
No Magic in The Mirage but The Pulley Loader Saves The Day
With the Mirage bulkhead proving unstable as of late, I decided to pull it from the gun completely and have a go at using my Pulley Loader.
I took the pumping barrel out, too and used a plug I had brought with me to plug the hole in the nose cone where the pumping barrel would have gone. I didn't have to pull those parts out at all, but I wanted the improved airflow of not having the bulkhead in the gun - and I didn't mind the lighter gun from losing the pumping barrel, either (the gun now almost floats with the shaft in).

I should mention that a few weeks back, as the bulkhead first began acting up, I made a modification to my nose cone in anticipation of possibly having to use the pulley loader. In the pulley loader thread, I had talked about how it would be smart to have some hooks on the nose cone, but I didn't have that so I I made a dyneema "gooseneck" AKA a bridle instead:
53695


It has an eye splice on each end that goes around the shooting barrel and is held in place by the muzzle. But as I tightened down the muzzle, the force on the dyneema made it expand and squeeze the nose cone so much that it cracked a little. It's not an issue, there's no structural need for the plastic where it cracked, really. It's just not pretty.
I am attaching the line to the nose cone bridle with a slip knot which has worked fine but a hook system would certainly be faster.

As an aside, I have realized that I can keep the banana effect well under control by clamping down a lot on the nose cone. So far, up to 35 bar, I have seen zero banana effect, so that's a nice surprise.

The pulley loader is not yet perfect. I actually had the line slide through the cam cleat which really surprised me as I have used these on sailboats for years and never once had a line slide. Not sure what the issue is but I changed to some slightly thicker line and it seems to have become a little better. I am using Ronstan's smaller composite cleat but I think Harken's aluminum one in the same size would possibly have better bite.
Here's a pic with the newer line:
53698


And here one that shows how the sliding of the line ate into the teeth of the cleat!:-(
53699


Luckily, the cams are reversible, so you can swap them to the other side and use "fresh" teeth but as mentioned, maybe a metal Harken cleat would be better.

I first tried the pulley loader on the porch of the bungalow I was staying in the night before going spearing and managed to banana the shaft like crazy. Luckily, no permanent bend but I was nervous about using it the next day. But often, loading is easier in the water and it's the same with the pulley loader.
It's still early days with this gadget, but what works for me is twisting the line a few times around the shaft to keep it aligned with the shaft (same ideas as twisting the rubber on a polespear). That, and a hand on the middle of the shaft, seems to keep it from banana'ing.
53696


I am doing three twists so far, but will try to see if one or two is enough. As I load, the shaft does tend to untwist itself but it happens towards the end of the loading where most of the shaft is inside the barrel, so it's ok. But it does make a bit of a mess with the slip tip line and shooting line being wrapped around the shaft:
53697


As a stop gap measure the pulley loader is not half bad but it does take a while to load a gun like this. I have used it for two full days by now and have taken the gun from 24bar initially to 27bar on the second day. Both are more than I can load a regular gun at, so I am getting some bonus oomph. I haven't tried it with the regular shaft yet, only the slip tip shaft which is shorter so I guess less risky loading that one.

I store the loader by wrapping the line around the tube of the loader and just tugging the whole thing under the top of my wetsuit. It's actually a whole lot easier to do than I thought it would be.

Here's a pic of the loader next to some 1kg weights for a sense of scale. It also shows the loader in the "storable state":
53700


Also, I am finally getting fish. With the help of the pulley loader and the slip tip shaft I got four dogtooth, though nothing big yet. But I consider the whole Indonesia trip a stepping stone, learning to hunt tougher fish in more difficult environments - so I don't mind pacing myself.
53701


And it's always nice when you bump into a Mola Mola or some big eagle rays:
53702

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At some point, after this trip has come to an end, I will try to conclude on what can be learned from this Evo Mirage build. But for now, I am just going to enjoy my last few days here:)
 
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popgun pete

Well-Known Member
Jul 30, 2008
2,700
511
153
Australia
It seems to me that the “Mirage Evo” is a success, the problems lie with what are in a sense sintered parts as plastic bead layers are progressively fused together and if these were injection molded parts instead then there would be no problems. As for the pulley loader, the teeth on the cleats have a higher localized loading if they are biting on a thinner diameter cord as there is not enough cord cross-sectional area to distribute the load over more of the tooth surface.

Actually now I look closer the cord you are using is already pretty thick and anything larger may not go through the nip, so metal teeth may be the best option.
 
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Diving Gecko

Diving Gecko

shooter & shooter
Jun 24, 2008
1,234
301
138
Shanghai
It seems to me that the “Mirage Evo” is a success, the problems lie with what are in a sense sintered parts as plastic bead layers are progressively fused together and if these were injection molded parts instead then there would be no problems. As for the pulley loader, the teeth on the cleats have a higher localized loading if they are biting on a thinner diameter cord as there is not enough cord cross-sectional area to distribute the load over more of the tooth surface.

Actually now I look closer the cord you are using is already pretty thick and anything larger may not go through the nip, so metal teeth my be the best option.
I'll comment on the success (or not) a bit later when I have gathered my thoughts fully on the matter;-)
As for the cam cleat it was rated to take very thin line (perhaps 2-8mm) and the first one I used was 3mm, the white one is 4mm. I have used 3-4mm trim lines on sailing boats in similar cleats and not had any issues, hence why I am a bit perplexed. But yeah, if anyone feels like making one of these, as of now, my recommendation has to be to go for the smallest Harken cleat and possibly going to 5mm line, too. The latter will also make the pulling effort nicer on your hands.
 
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Diving Gecko

Diving Gecko

shooter & shooter
Jun 24, 2008
1,234
301
138
Shanghai
The Verdict - The Parts and Building Method
I have left Indonesia and had a bit of time to think about what worked and what didn't in this project.
I think I will do it like a Q&A but since I am doing both the Q and the A, I might miss some Qs, so just ask if I missed something.

Can You 3D Print Functional Speargun Parts?
Yes, I feel that you can. As this thread shows, there are special challenges when it comes to pneumatic guns as it is not easy printing perfectly airtight parts. Making them airtight took for some extra time consuming steps but I think this might change in a year or two as some of the more high end plastics which prints at very high temps make it to the consumer market. It might already be possible but it would take a lot of dialing in of the material and print settings.
For band gun parts, I think it would be fine as the parts can be a bit permeable. I would say you could definitely print e.g. a roller muzzle, though you obviously need to think about the forces a lot.

What About The Strength?
I printed in PLA which is one of the easiest materials to print but also not that strong. But the nose cones and bulkhead held up fine except for when I left the gun in the sun and the plastic softened so much so that the pressure extruded the o-rings - which is the downside of using PLA. There are already materials available with better resistance to higher temps (e.g. HIPS) but they are a little trickier to print and I didn't have time to dial those in.
I did break the sleeve for the CamWing, but that was because it took a big hit when I off loaded the gun (by shooting it) over the side of the boat and the recoil (not that much) slammed the CamWing into gunwhale. Entirely my own fault. But I could also have beefed up the sleeve itself and will likely do that on the next one.

Are The Tolerances and Precision Sufficient?
Yes. It took a while with dozens of testers and a fair bit of calibration but I got my printer to hold very nice tolerances, perhaps within 1/10mm on most parts. For some reason, internal bores and holes were harder to get right - but in practice, if you are designing your own parts, you can always go back and adjust a dimension in the CAD software to make up for most calibration issues in the printer.

What About Surface Finish - And O-ring Use?
The finish depends in large part on the resolution you decide to print in. Higher resolution means that the bead is thicker and you get more "stepping". This can be a problem as for an airgun you need a good surface for the o-rings to seal against. When I first set out to make these parts, the goal was not to have to do any secondary machining but to have the seals work straight on the printed part. That, I didn't succeed in at all. Every o-ring bore or groove has been machined on my mini lathe. This is obviously a problem if you don't have a lathe.
It might be possible to make the surface smooth enough with other materials or some of the more high tech ones coming out. E.g. HIPS can be sanded perfectly smooth whereas PLA and PETG doesn't really like to be sanded much.
Again, for a band gun this is much less of an issue as you don't need perfect sealing and I think you could use most parts straight off the printer.

Was The Build a Success?
How you answer that question depends on one's personality. I don't mind when things are not easy or work out right away - as long as I feel I learn something. Viewed like that, yes the build was a success. Not a resounding one as I had parts fail in use and ultimately had to dumb down the gun to make it work. But I had amazing days in the ocean and caught some very nice fish with a gun that had my homemade parts in it. On top of it, it might be one of very few guns in the world with 3D printed structural/functional parts and I find that a little bit cool. But most of all, I learned a lot and that's what I really like about the build.

Would I do it again And What Is Next?
Yes, I would - and I will:). But I am also beginning to really think of how to combine 3D printing with subsequent carbon fiber reinforcement. I actually think it is very doable to print a whole bandgun "blank" and reinforce it with CF. Perhaps even print a cuttlefish shaped airgun barrel, cover it with a CF laminate and get rid of the plastic mandrel/tooling. I have given this method a bit of thought and while it is still early days, I think there's a way to do it;-)
 
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