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

popgun pete R said:

I just did a "quick and dirty" diagram to see how the "Saetta"View attachment 52369 handle would fit.

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I think the Saetta handle could be a very good option - but would need to confirm how large the offset really is. I think I know someone I can ask, just for the sake of knowing. As mentioned, when I tried to measure it on the drawing, I got a 4-4.5mm value which is very, very close to the Mirage. And it should give you that extra bit of space to beef up the thin walls.
I don't particularly like the line release but if that white grip is detachable, I think it would be easy to modify the grip of that handle, too if so inclined.

An Early Stab at A Bulkhead - Proto V1 (Non-functional)
I spent a bit more time calibrating the printer and a 40x40mm test piece printed at 40.03 x 40.03mm...! So, I feel like I have gotten the printer dialled in well enough that I can start printing real parts

I designed a bulkhead just to check the measurements and see how they correlate with the final part, which is being printed right now. No outer o-rings for now and there's a few other features missing. BTW, I don't think I will bother at all with an over pressure relief valve.

Here are some screen grabs from the CAD work:


From the CAD program (I use the amazing and free Fusion 360) you export an STL file which is then imported into the slicer of your choice (slicer is the 3D printing world's word for the CAM program which outputs G-code to run the printer). I am in between Cura and Simplify 3D, but here is a pic of how it looks when you drop your part into Cura:


Now, there are some really nifty features in these slicers. For example the option to look at each layer and how the "bead" is laid down. You can actually turn on a feature to see exactly how the extruder head moves. This is cool since it allows me to see exactly how it forms the inner walls and o-ring seats that need to be as smooth as possible.
That said, in this screen shot, that feature is turned off, but you can see how the layers are built and how many layers of bead a given wall is made up of:


You can also check the travels in free air of the print head. This relates to "retractions" which is a term used to describe when the printer has to leave a spot, stop printing and then move somewhere else to resume printing. The problem is that it's very hard to avoid slight amounts of filament oozing out of the nozzle during these travel moves, so it's interesting to see how exactly they are being done.
E.g. in the pic to the left, the printer actually stays away from any outer perimeters during the blue travel moves, so even if there's a bit of oozing it shouldn't end up on the walls of an o-ring bore. To the right, the printer chooses the shortest route but in that area, it's actually OK:


And finally a snap of the part being printed:

popgun pete R said:

If you have to 3D print the bulkhead boss separately then why not just glue it into the bulkhead?

Click to expand...

Oh, will edit the post about that part - I think I will turn it on the lathe in brass. That way, I can control all the tolerances and finish a whole lot better. One less thing to worry about.

popgun pete R said:

Can you machine that 3D printing stuff, say as in cutting the outer "O" ring grooves later in a lathe. I realize that you can print the necessary grooves in later editions, but maybe for some quick trials you could still use these blank outer versions without discarding them. Is the stuff porous, or does it need sealing, say with a thin coat of paint or lacquer?

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Stay tuned. Good news on that front;-)


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I'll elaborate on this a lot more later, but just a teaser and I'm really pleasantly surprised about this!



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An Early Stab at A Bulkhead - Proto V1, Continued...
Just a few posts above, you saw the CAD drawings of the bulkhead and the printer at work.
One hour and fifty minutes later, it was done:


in this next pic you can clearly see the layer lines:

The harsh lighting exaggerates it a bit but even though each of these layers are only 0.2mm tall, you still notice them. I actually think that as long as they are in the same direction as an o-ring you could still obtain a good seal.

But did it even fit on the gun?
Hell yeah, haha!




The Cyrano bulkhead sort of sleeves over the front of the handle and that "lip" is a little too thick in my printed part. If I reduce the diameter by 0.15mm it should be spot on. But the dimensions of the bores seem good.

And what about the outer dimensions, you ask?
Yup, fits as a foot in a sock (as the Danes say...):


BTW, Blue... Really Mares, blue...?. That grip will never see the ocean in my hands. And the angle is horrendous, too. Somewhere in between a Mirage handle and a Sten handle. If you get used to it - good. But for instinctive shooting it wont work for me.

And here's a funky brand conflict:

Yup, a Salvimar reservoir on the Mares handle. Why? Well, one reason is that Salvimar actually sell their spare parts at really reasonable prices.

BUT the main reason is this - drum roll....:


Kapow! This is the longest reservoir you can get off-the-shelf. Mares doesn't even make a gun that long anymore. And though I can't recall the precise numbers right now, a Salvi 130 is longer than a Mares 130 would be. I think something to the tune of it being a 137, if it was a Mares;-).
There's a doggie waiting somewhere in Indonesia for an 8-8.5mm shaft from a gun like this some day. At least I hope so, haha.

Machining Printed Parts
Pete asked if I could possibly machine these parts given that I have a lathe. And I was one very, very tiny step ahead of him as when he asked, I had just pulled the part off of the lathe;-).
I wasn't actually too hopeful on this matter as some weeks back, I had tried to clean up an o-ring groove on the very first grey nose cones which I showed earlier in this thread. They were made from a material which is supposedly a bit stronger and has better heat resistance but I couldn't get a good finish on it on the lathe. It was a bit too gummy and it seemed to melt more than cut.

So, given that the red material is supposed to have a lower melting point I didn't have high hopes. But it machines so much nicer than the grey nose cones did:


I cut this really slow, with a brand new, very sharp cutting insert and used a bit of WD-40 and I have to say this surface was far beyond my hopes. It is more than smooth enough for a good seal, I think.
As for why the material machines better, I think it is because it is actually stiffer - as in a bit more brittle. Whereas the other might be stronger because it is tougher and perhaps a bit more ductile (in case anyone wonders, the red material is PLA+ from Esun and the grey is a PETG but can't recall the manufacturer).

I faced it off, too and though the pic doesn't show it that well, it turned out quite OK, too:


I don't think I need to do more on these, as in coating them. When I cut them down, I felt I could actually see that the layers have bonded really well. The "separation" that you see in the earlier images is just the bulging edges of each layer (think about stacking sausages or the Michelin Man). Once I cut those bulges off, the plastic seemed to really have fused. Not porous, not about to split at all. I have tried my best with both hands to crush or crack this part - no dice!

Now, I don't think I will cut the full outer o-ring grooves this way (I still think deep cuts are risky in terms of heating the plastic and making it gummy) but there's another option. I could design all the features like the outer and inner o-ring grooves and bores a few 1/10s of a mm undersized and then put the part on the lathe afterwards to take it to final dimensions and a smoother finish. Since I have an independent four-jaw chuck for the lathe I can do all the off-centered bores, too. That, I think, is actually a very viable method.

Bulkhead - Proto V2
I drew up the next iteration of the bulkhead - largely based on the stock Cyrano 1.3 bulkhead and there are some funky solutions I haven't seen elsewhere.

Here's how my version looks, but the Mares one is very similar:


What I found strange when I first saw the Mares bulkhead is how the o-ring groove is at the front of the main body of the bulkhead. It's like Mares extended a lip forward pretty much only to have a place to put the o-ring groove. After having looked at the design and dimensions for a while, I think I know why. Since Mares made the air transfer bore (the one the power regulator bushing sits in) bigger in the Cyrano Evo I think they ran out of wall thickness between that bore and the bottom of the o-ring groove. So, they had to move the groove. They could possibly have moved it backwards where there's only the ø4mm rod of the power regular to contend with. But the groove needs to not get in the way of the bushing when it is being moved backwards as when the regualror is in the full power position. So, the groove would have to sit all the way at the back, but there - when the power regulator bushing is at its most rearward position - there's almost not enough space between the rear of the bushing and the front of the handle.
So, I think Mares moved it to the front out of necessity.

A handy side effect, if I am not mistaken is that there are less forces acting on the o-ring groove now (I think). The groove is now exposed to the pressure in the front part of the reservoir on both the inner and outer faces of the groove. As far as I can tell, there shouldn't be any force trying to push the outer walls of the groove inwards like there would be if it had the sometimes lower pressure of the rear part of the reservoir on its inside.
Anyways, let's move on;-)

I have mentioned that you can't really 3D print in free air - each layer should ideally be supported by the layer below it. But this new design violates that rule. This is why you sometimes have to use "supports". These are pillars that gets printed to support the parts of the print that would otherwise have to be printed in free air.
You see the wavy supports here:

(the part was printed with this face down on the build plate)

They should snap right out if pulled with pliers or otherwise helped along, but the surface on that first layer after supports aren't really something to write home about (perhaps I can dial in things a bit better in the printer slicer, though):


It doesn't really matter in this area of the print, and 1-2 layers deeper, the plastic is well fused again.

The part fits really well as I adjusted a few other dimensions by 1/10mm or so:


I then took it over the lathe to see how well I could clean up those inner bores. This is the first time I really used an independent four-jaw chuck but I bought it for exactly this application in mind. First up is the bore for the shooting barrel:


I used a boring bar and the same super sharp inserts as earlier. I think they are made for cutting alu. It cleaned up really nicely.
For the smaller bores I will be using reamers and I did a quick test on the bore for the pumping barrel bushing - it worked fine, too:


I didn't do the air transfer port as this was just to see if I could make this work and I think I can.

While I had printed one o-ring groove, I gave it a skim cut and then tried to cut one to full depth from "virgin" material. I was worried it wouldn't work, but it it did. So, as Pete suggested earlier, I might not even have to print the grooves. Though I think I will print them partially, at least to know where they should be placed when I turn them to depth on the lathe later.
The pic doesn't do a good job at showing the difference, but basically there is none (front one; printed + skim cut. Rear one; fully cut on the lathe):

ECK said:

If allowed by the administration, I can give a link to the topic on 3D printing.
I opened it, because I really liked the idea.
For the needs of underwater hunting and weapons print on the printer.
But for today I have refused it.
Because it turns out either bad or too expensive.

Click to expand...

I know there is a guy on spearboard.com who printed 1-2 functional guns. It wasn't cheap. But there is a way - and I think someone will do it soon - to make cheaper, cool guns incorporating this technology: You could just print the shell of a gun (bandgun) and then cover it in carbon fiber. If I was into band guns, this is what I would be using my printer for these days.
As for price. For the parts I have made so far in this thread, including all the ones for calibration and the early silver parts, I have probably spent less than USD 10...!;-)

popgun pete said:

I think the "O" ring positioning at the front of the partitioning bulkhead is more about assembling the gun at the factory. They drop the tank over the pre-assembled rear grip section and bulkhead and main barrel and the first thing is to wiggle the tank over the leading "O" ring, which is the bulkhead "O" ring. Then they push the tank on further until they hit the next body "O" ring. Thus the length of bulkhead helps line up the tank for that next "O" ring, as the bulkhead OD was a snug fit in the tank bore.

Click to expand...

[EDIT]
Haha, I guess you can disregard this post. I was wrong and it seems even the Sten guns have the o-ring forward on a lip like that;-). I only have one Sten but it's not with me now and haven't looked at it for years but I have been looking at the age-old Mirage bulkheads for too long...

But I will leave the original post up. Here it is:

Could be but I am not sure. They have been assemblying guns for 40 years with the o-ring in the usual place without problems;-).

I just had a quick look in the CAD to check this.

In the Cyrano bulkhead the groove sits about here:


But remember, Mares enlarged the air transfer bore a few years ago. If they had kept the o-ring groove next to it, in the normal way, this is how it would have looked:


Not a healthy tolerance...: