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

popgun pete said:

You could try coating them with paint from a spray can, just say two thin coats. Alternatively use a thin epoxy two-part type paint that cures rather than relies on solvent evaporation.

Click to expand...

Don't think it's gonna cut it. Not with 30bars of pressure coming at it. But I'm looking into vacuum impregnation. I actually have the gear needed for that. Alternatively, pushing the sealant into the pores with high pressure. Mulling it over right now.


Sent from my iPhone using Tapatalk

popgun pete said:

I think you will find paint will seal it as each '"pore" represents the area exposed to the pressure, their cross-sections are miniscule. Collectively they are large, but that is not how the pressure differentials work.

Click to expand...

Ah, that's a good point, the force acting on a particular small area of paint may not be much as the pores are so tiny. But I just tried something else. Stay tuned

Rescue Mission - Vacuum/Pressure Impregnation Part 1, The Setup
Annealing didn't work and switching to PETG filament didn't either. Next on the list of possible solutions is impregnating the part with epoxy under pressure or vacuum. It also happens to be the one idea I feel the most hopeful about.

Now, the challenge is that while air readily passes through these parts, liquids don't. When I tried pumping water through one of them, the resistance was massively higher, it almost wouldn't go through. And the thinnest epoxy I have has a viscosity rating about 200 times higher than water, so that might be an issue.

But, of course, I still want to give this a try. So, I went back to the red PLA material and printed a bunch of the test cylinders:


And then I got the vacuum pump and vacuum chamber out:


First, I degassed some epoxy . This is good practive as it gets rid of most of the air in the resin mix:


The first option of impregnation is to use high positive pressure and the most simple test I could think of was to pour degassed resin straight into the part, attach the pump and try to squeeze the resin through the porous walls:


I don't have a pressure gauge for the Salvi inlet valve but judging from the force I had to put into the pumping action, it think it's about the same as pumping a gun to 20 bar, maybe a tad less. After pressurizing the cylinder, I let it sit under pressure for a few minutes. I honestly didn't know how long the operation time of this epoxy was (I had never used this particular type before) and I had to have time to pour the epoxy out and clean up the part:


This part leaks in a long line along the surface (more on that in a later post) and I was very happy to see a bit of epoxy having made it through to the outside:


The part will now be curing overnight and then we will see if enough epoxy made it into the walls of the part to seal it properly.

Now, let's move on to the second method of impregnation which is to use vacuum but first, a bit about the differences. The advantage with using positive pressure over vacuum is that I can get a lot more force on the resin. 15-20 bar with a handful of strokes of the pump whereas with vacuum, I will only ever get 1 bar maximum.
Also, with the high positive pressure method, I would have to find ways of plugging the part to establish a pressure differential for the positive pressure to work against (I would need to design and build some pretty specific jigs).
On the other hand, with the vacuum method, it's a lot simpler as I can just drop the whole part into a resin bath and apply vacuum. The idea being that you suck out all the air in the cavities in the part - and in the resin itself - and then when you let the ambient air back in, the atmospheric pressure will exert 1bar of pressure on the resin and push it right back into all those little voids. But as mentioned, it's just 1 bar vs. the 20 bar from the hand pump and the resin might be too thick.

This pic shows the test part sitting submerged in resin under full vacuum (or rather as much as the pump can pull):


The good news is that it looks like the air bubbles are all coming from the part and not the resin. And it looks to be pulling quite a bit of air out.
It's more clear in this short video:

I think I pulled vacuum on it for about 5-8 minutes but now that I have a better idea of the working time of the resin, I can probably let it sit in the chamber for half an hour next time.

Like the first "positive pressure test" this vacuum one will now be left to cure and then I'll do leak tests on them in the morning.
Fingers crossed!

popgun pete said:

A friend of mine had some timber handles that he had carefully carved treated with a resin impregnation process. It made them much stronger in the thinner cross-section trigger finger-guard area, but also very heavy as they turned into solid resin blocks with a timber matrix.

Click to expand...

Interesting and it makes sense. Just yesterday, in my research for this method I saw some guys impregnate a block of wood to be used for a mallet. They cut it in half after the process and described it to have a hard plastic feel. But then again, wood is much, much more porous than this material. I did wonder if it would be a process for wood guns, but if it makes it too heavy, then it wont work.

But I will elaborate on that a bit later as I think I found out some things about the leak paths that I didn't know before.

Rescue Mission - Vacuum/Pressure Impregnation Part 2, Preliminary Test Results
It's been a day and the first results are in...
I decided to shoot this in video as the leaks are just so hard to show properly in still images. Apologies for the shabby audio - I actually intended to do a voice over in post but then just stuck to my original in-camera recording:

Honestly, I am really, really chuffed about the results.
Both the high pressure and the vacuum method seem to work and if the latter really works that's incredibly good news. As I mentioned, with the vacuum method, I can just drop the parts in a resin bath under vacuum. No need to think about pressure differential paths and making custom plugs and a high pressure tank (though the latter could actually just be a piece of normal 40mm reservoir).
Also, the clean up worked well, too. E.g. there was no epoxy stuck in the threads and the pump inlet valve went right in as before.
I weighed the part on a jeweler's scale before the impregnation process and the vacuumed part only took on 0.4g of epoxy. That's it. That was enough to plug the pores.

Next up, I'll do the vacuum impregnation process on the Apollo nose cone and put it back on the gun to have more of a real world test.

Rescue Mission - Vacuum Impregnation Part 3, Fixing Apollo
A few posts back, when I realized that the printed parts leaked, I made a "real" test cone. I chose to make it for a Predathor because it was a gun I had handy at home. The test cone leaked badly at 20 bar, so it makes sense I would try my newfound vacuum epoxy impregnation method on that part and see if it will work.

The setup was the same as yesterday's. I mixed and degassed the resin, then dropped the nose cone in (with a bit of a neck weight on this time):



I left some tissue in the vac chamber and used a water bottle for the resin bath, so the pic turned out pretty bad - but it bubbled steadily from the part:


I had planned to run vacuum on the part for about 20-30 mins or shorter if the steady trickle of small bubbles ceased - indicating there was no more air to be pulled out of the part. But 15 mins into it, the resin bath started almost boiling; much bigger bubbles rose to the top and over the edges of the cup at a faster and faster rate. It was a bit messy, so that's when I stopped pulling vacuum. It happened yesterday, too.
Normally, this "burst" happens much earlier on just once and I am am not really sure why this epoxy is so different. Perhaps something in the resin starts boiling off at that point. I don't think it is the part that is at fault. But next time I have some resin out, I will try to pull vacuum on it by itself for that long and see if the same thing happens. If it does, then I have some composite friends I can ask for advice. If it is a bad thing, then I will run the vacuum a little shorter and I will just drop the part in right at the start without degassing the epoxy first. This will result in the part being under vacuum for a longer time in total which should be a good thing.

Anyhow, the nose cone is now curing and I will try to put it back on the Predathor tomorrow.

Also, since I had so much epoxy left over from the impregnation procedure I had a bit of fun...:

Nothing too exciting, will reveal it in tomorrow's post;-)

Rescue Mission - Vacuum Impregnation Part 4, Fixing Apollo (Initial Result)
Yesterday, I vacuum impregnated the trial nose cone 'Apollo' to stop its leaks. And now, it's time to see if it worked.
Dressed up in nice flurocarbon double o-rings:

YES, after years of searching, I finally found an off-the-shelf alternative to the proprietary main seals used in all of my guns. So, I will stack up on these little green wonders.

And mounted on the Salvi Rocket:


Taking it up to pressure:



While the gauge reads 30 bar but that's not what's in the gun as this pump adapter doesn't have the little pin to open the valve and get a "real time reading". At least I think the spring force of the pump inlet valve has to be deducted from the reading on the pump. In this case, with this inlet valve it's a lot - about 8 bar (some of my other valves have less strong springs and the difference is about 5 bar).
Hence, we end up at 22bar (+/- 1 bar or so as I think these two gauges don't read exactly the same):


But the most important - no bubbles!:


The gun has been set aside now - I will take a reading on it later to see if it still holds the same 22 bar.

And as for the mysterious part in the vacuum bag, it was just the lid for my vac chamber being reinforced with chopped carbon fiber:


I am using a food storage vacuum jar and it was beginning to show a few stress cracks in the lid, so thought it better to try to reinforce it before it implodes on me and send epoxy resin all over the place...

Rescue Mission - Vacuum Impregnation Part 5, "Houston..."


So... Apollo actually didn't get fixed after all:-(
It looked great to start with but half a day under 22 bar was apparently too much for this nose cone and it has lost about 2 bar in these small leaks.
I was so happy yesterday when the testers held air and this morning when Apollo looked good, but now I am kinda back to being bummed out.

In the meantime, I have printed some more testers, really playing around with obscure settings in the slicing software and some of the testers are looking much less leaky which is kinda good news. I don't know if I can get to the "no leaks straight from the printer level" but it's worth at least getting as close as I can.
Also, there's always the high pressure impregnation method. Perhaps coupled with something like this:


I have two work trips coming up, so I wont get much more trouble shooting done for now. But I think it is OK to let this rest for now.
Just one more post on other stuff before I take a break from this project.

Finally Some Metal - But Not Enough of It!
I promise, no more - well, not too much more - plastic in this post!

It's time to check the shooting barrel. I know the Predathor barrels are 3mm longer aft of the sear pivot point than e.g. the Mirage and Hunter barrels so imagine my surprise when I realized that the Cyrano handle actually runs barrels that are even longer than the Predathor ones (I don't know if they are regular Sten dimensions, I don't have a Sten in China).
When I inserted the Predathor barrel in the handle there was a 4.7ish mm gap before the end of the barrel touched the rear wall:


I did my due diligence and checked that the trigger sear did indeed line up where it should. I "blued" the sear and then inserted the barrel into the handle (still short of the rear wall):


And then I pressed the trigger a few times and pulled the barrel back out:


Bar a mm or so, the trigger sits where it should. So, the barrel is indeed too short!
Even if I had known this, I would still have gotten this barrel. It's about 30cm longer than anything Mares makes these years. I just have to work around it.
I can think of two solutions. The first one would be to make my own, extended pump inlet valve. The current one only screws into the barrel two full revolutions and I don't trust that to be enough. And the second option is to move the pivot pin hole forward (and extend the slot for the trigger sear, too).

The second option, could look something like this:


Moving it by 7mm, gives me a 3mm wall between the old and the new hole. That should be more than fine as the force is not really in that direction.
Of course, I then need to cut off about 2.3mm of the end of the barrel to reach the 4.7mm offset and get the trigger pin to line up in the right spot on the sear.

I'll let this simmer while I am on the work trips, too though I am leaning very much towards working on the barrels rather than making an inlet valve. I don't really wanna cut stainless steel on my little lathe if I can avoid it and though Seac and Salvi actually have alu inlet valves, they are anodized and/or perhaps surface hardened/coated, too.

Also, not surprisingly, the combination of barrel, handle and reservoir results in a barrel that is a fair bit "too long" as it is. Here, I am just using a Mirage nose to show the difference:


I didn't expect it to line up at all, but since it's "only" about 16mm too long (after adjusting for the 7mm, I'll be shifting the barrel backwards) I am considering extending the nose cone instead of cutting a new thread on the barrel. That will also give me a little bit more real estate on the nose cone for a few improvements/features I have in mind. Again, perhaps it's not a bad thing that I have some time away now to think these things over.

popgun pete said:

Try painting them as you have nothing to lose by doing so now, hopefully it will work. I remember watching a TV program where part of an experiment evaluating the Archimedes screw as a water lifter required a large water tank being built into the ground. The water in the tank leaked fairly rapidly into the surrounding soil and all seemed lost until an old timer said “throw a handful of fine sand into the tank”. Jaws dropped when after a minute or so the water level in the tank stabilized as the fine particles swept into the cracks and sealed the tank.

Click to expand...

Will do

Meet The Humpback
Flying around China on different assignments these days, I found a bit of time to draw up a new nose cone:





It has a bit of a funny hump where the pumping barrel ends and it's a bit longer than the old one. It was either that or cutting down the barrel. While it does make the nose slightly heavier, at least, it also allows the fiber optic sight to grow a tad longer which should increase how much light it gathers and make the dot at the end of it brighter. As for the increase in weight - those cut outs should alleviate that somewhat.
I also carried over Pete's suggestion of the anti-banana bracket at the lower rear end of the nose.
I have a feature in mind I want to add to this nose cone so once that's done, I'll start printing it - I guess in a week's time when I am back from the road.

popgun pete said:

When everything works you may consider having some injection molding dies made in China and start up a business.

Click to expand...

That thought does pop up from time to time, but making 1-2 to prove the concept is where the real fun is. Anyways, there's a whole list of potential upgrades to the Mirage concept that I would want to incorporate before even feeling half good about having people spend their money on it. And then comes that whole question about whether you actually do want to become a manufacturer. You would have to take after sales services seriously, repairs, spare parts - all that stuff...
The one thing I could see me do, if one day I make a gun that makes me really, really proud, that is powerful, sturdy, well-built and with minimal maintenance requirements is to make a very limited batch of them and then sell them to people I know can deal with servicing them. I could always produce "how to" instructional videos or PDFs to help with that. And make sure there are no proprietary o-rings and such. But let's see. Baby steps

Ah, I got ahead of myself. Actually, if it is just an "upgrade kit" to a make the Cyrano into a Mirage, that might be doable. Two plastic parts and a pumping barrel with a PDF for assembly instructions. That does happen in many industries where 3rd party shops sell upgrades. It's happening in ours, too I guess with e.g. vacuum muzzles or replacement drop-in triggers and roller muzzles for the band boys. It's non-destructive and it's not the end of the world if one day, the customer wants to revert to stock setup.

popgun pete said:

At some stage a 14 mm ID inner barrel may be worth evaluating in thin wall stainless steel for a gun of this type.

Click to expand...

I've considered exactly that for awhile. But mostly to have a bigger pressure difference between the pumping and shooting barrel.


Sent from my iPhone using Tapatalk