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

[Diving Gecko]

Blowing O-rings Out Of Their Grooves

@Zahar mentioned this as being a risk and it has indeed happend to me on this very build. Back when I was using the original bushing which looked like this:

Looks like a perfect fit for an 8mm bore (or rather ~8.1mm), right?
Well, Mares designed the bulkhead for this gun to be 9mm...:

Which I think is a bit strange as that's an unneeded 0.5mm gap all around the bushing which is not healthy for the o-ring.
On top of that, as mentioned, the groove seems to not have any free space, either.

When I used this bushing in a Mirage system with a 9mm bore, the o-ring was blown off. But when I made my own bushing with a bigger OD resulting in taller walls around the o-ring, it stayed put. Not Mares' fault as it was never intended as a Mirage part but nonetheless, an 8mm bushing in a 9mm bore almost sounds like they decided to increase the bore to 9mm after having manufactured 1000s of 8mm bushings...

 

[tromic]

New Bulkhead In The Making - Part 2
I took yesterday off, but back in the workshop today. Last time around, at the end of Op 1 which are all the features I can reach from the front side, I hadn't programmed two of the chamfers perfectly. So, they stopped short when they were close to the filleted sealing lip for the power regulator valve.

I considered just finishing those chamfers in hand but I had a go at re-indicating the part in the vise and it went well
View attachment 60858View attachment 60859

The chamfers look almost perfect, just one little weirdness on the shooting barrel bore edge where it meets the sealing lip:
View attachment 60860

You can kinde see how it's ever so slightly higher, so maybe the Z-offset was not exactly the same. Anyhow, that little blemish can be ground and polished and overall, I think the finish looks great. Especially the inside bore walls come out very smooth.

I also engraved a version number on it so I can keep track of it down the line. But I got lazy and just used a 45d chamfer tool to do it. I have some tiny engraving tools, I have used to greater effect before.

OK, on to Op 2 which is all the remaining rear features.

David, I noticed that the lip edge may be too sharp, high, and could cut the rubber seal at a pressure of 35 bar...?
I tried to calculate the equivalent diameter of the air regulator opening, as if it were round, and I got 10 mm..?

I was also thinking about another problem. If the equivalent hole for the power regulator ID = 10 mm and if the shaft according to the picture is 6 mm then the total passge of the power regulator hole is the same as if the hole was 8 mm...? The Mirage has 9 mm with a different power regulator...
But I still like your design idea!

 

[Diving Gecko]

David, I noticed that the lip edge may be too sharp, high, and could cut the rubber seal at a pressure of 35 bar...?
I tried to calculate the equivalent diameter of the air regulator opening, as if it were round, and I got 10 mm..?

I was also thinking about another problem. If the equivalent hole for the power regulator ID = 10 mm and if the shaft according to the picture is 6 mm then the total passge of the power regulator hole is the same as if the hole was 8 mm...? The Mirage has 9 mm with a different power regulator...
But I still like your design idea!

View attachment 60898

Sorry, was "away" from this project for a few weeks.
I do have the numbers somewhere for cross area and yes, I do subtract the rod that's obstructing the transfer bore - but from memory it's equivalent to a cylindrical 9-10mm bore. Also, the rod at the rear is only 4mm, not 6mm.

Yes, I too have wondered about if the lip is too sharp or not. But I will try with this one. What I have noticed is that when you model small parts in CAD you sometimes get surprised how the features look in real life.
On that same note, I have been looking for some better rubber sheets as what I had is so fragile and just comes apart too easy. Turns out it's not that easy to find a good material, it's not like the sheets are generally the same quality as o-rings, but I think I may have found something, so that will soon be on the cargo ship to here.

[Edit]
Here's the exact number:

73.4mm2 not counting the rod, so equivalent to a ~9.7mm circular bore.

 

[Diving Gecko]

One Little Bit of Progress
As I mentioned, I have to put most of my time into another project these days. But actually, while that's also a passion project, I think if I work on that only, I will burn out. So, from now on, I am trying to schedule at least one day a week to play with other toys so to speak

So today, I almost finished one of the parts for the new valve - the rod:

I didn't make the internal bore and vent holes, yet as I am missing some tools for that but they will arrive in a few weeks. Nor did I make that domed front cap, yet.

Anyhow, last time I had a go at this I set out to make it mostly on the lathe, which is still a good plan, but the lathe was not in good shape and I have pulled the change gears off of the lathe, too so I can't single point thread and I can't actually find my M3 die so can't make threads on the lathe, right now. At least that gave me an excuse to use a threadmill on the CNC for an external thread for the first time.

First, the donor material on the left, a test piece in the middle and the almost final part to the right:

I used an old cut off from a shaft - so, it's hardened 17-4PH but it actually machines really nicely. I have cut threads on it on my mini lathe before when I have shortened my spears.

But here's the very first cut out of four for the external threadmilling for the M3 thread - it's slow compared to alu, but it works:

And the obligatory nut test as I don't have fancy go/no-go gauges:

I really need to add some lights on the machines and maybe bring a better camera because this old smartphone is crapping out when it comes to these small things in the dark corner of my workshop - so, not so many pics. But here's a bit more machining:

The o-ring groove was also done in the CNC using a T-slot cutter and it worked great.
Then I did a bit of work on the lathe, just taking the rod down to 4mm at the rear and machining the flange and its big chamfer but forgot to snap a pic of that, too.

After that, I put the part back in the CNC and drilled, chamfered and threadmilled the internal M3 hole at the rear of the part:

Threadmilling is like magic... It's totally handsoff and comes out perfect (well, except the first external M3 needed a bit of an adjustment in the CAM but that's the first one I have had to do that on - and now, it's saved in the software as a template so can be reused next time).

As mentioned, I still need to do the internal bore and vent holes but I don't have a 2mm drill long enough. As you can tell, it's a rather small part. The threads are M3, the part is only 1.85mm at the inner face of the o-ring groove, the front part is Ø3.5mm which is the part subjected to the highest pressure and the rear is Ø4mm - just since that's an old standard and also since I do need a bit of help from the pressure trying to push the whole valve rod "out through the handle" and thus help close it shut.

 

[tromic]

I've pretty well estimated the equivalent diameter from the photo. I calculated this based on the number of pixels in the image. 10 mm is close to your 9.7 mm. In this case and with 4 mm axle the equivalent airflow opening is about 8.8 mm. With 10 mm it would be 9,1 mm.

 

[Diving Gecko]

I've pretty well estimated the equivalent diameter from the photo. I calculated this based on the number of pixels in the image. 10 mm is close to your 9.7 mm. In this case and with 4 mm axle the equivalent airflow opening is about 8.8 mm. With 10 mm it would be 9,1 mm.

Yep, but the measurement from the CAD is excluding the area from the 4mm rod already
So, the equivalent really should be 9.7mm. Either way, it's big enough as per yours, Zahar's (and ChatGPT's) earlier comments on choking of airflow

But as you said, it's already 9mm in the upgraded "traditional" valve from earlier - but it just slams violently when you open it, so hoping I can solve that issue with this design. That's also why the rod I machined above is "only" 3.5mm and not 4mm where it enters the valve cap. I do have a 4mm version drawn up, too - but I wanna see if I can make the thinner one work first.