Renovating and Modifying a Mares Mirage

I got my hands on a sample of 6K braided CF sleeve which is a bit thinner and thus more pliable than the 12K which was what I used in the last posts.
I like the 6K for this handle layup and it is probably the best compromise between pliability and building up laminate thickness without having to do too many layers.
But unfortunately my local CF pusher misquoted me, so when I went ahead to order from him, the minimum order quantity turned out to be three times higher than I was first told. I don't have need for 40m of this sleeve...!:-(
So, I will likely order it from a shop in the US where I can buy it by the feet and have it shipped here.

I laid it up yesterday, pulled it from the bag today and then post cured it in the oven at 80C for four hours. The latter serves two purposes. Post-curing at an elevated temperature, for some resins, makes the epoxy and laminate stronger and also it melts out the wax core in the process. Two birds...

I was a bit sloppy when I bagged the handle, so once again, I had some minor shifts in the laminate, but it's nothing too major - mostly cosmetic.




Now, there's still some wax residue left on the inside which of course is not ideal since I need the bond between this grip and the original handle to be as strong as possible so I need to figure out how to get rid of that.


The handle, before final trimming, weighs about 39 grams.


It is very strong. I can't make it wobble or flex with the force of my fingers and hands. That actually surprised me a bit. I think the thickness of the laminate should be about 1.2-1.5mm but I am not sure on this yet.

Now, I f'ed up a bit and made a proper beginner's mistake not taking into account that the bottom part of what is left of the original handle is actually thicker than the top part... This means, I can't just slide this CF handle onto the stub of the original handle as the opening in the top of the CF handle is too small... Yeah, stupid.
So, I will need to make a smart cut somewhere to make this a two-part handle. But from glancing at it now, I think I can get it done without losing much structural integrity.

For filling the handle once it has been glued in place, I have mentioned two-part polyurethane (PU) foam before in conjunction with using an epoxy mixed with fibers for the glue points. But I think I will forgo the PU foam.
Thing is, though it is supposed to be a closed-cell structure and though I can probably get it in a dense enough version to withstand any compression, I am still not sure how well it will hold up to any kind of water intrusion. I have seen PU foam rot away before. For two-part foam, it might be less susceptible to rot, but I don't think it is totally without risk.

Instead, I am thinking that the safer choice is to mix up some syntactic foam, which is a fancy name for epoxy filled with microballoons/microspheres. Though this mix is brittle, it has great compression strength and water should really not be able to do it much harm.
I did a very dry mix of this as a test (lots of filler, not much epoxy) and it came out with a density of 0.46g/ml. I will make it a bit wetter so it flows out better, but I think I can still get a more buoyant handle in the end than the original.

The glue joints will be made with chopped carbon fiber and epoxy.

foxfish said:

To make a two construction seems a bit like going backwards, cant you trim the handle fixing?
You can but a super light fairing powder that might work for you.

Click to expand...

I thought of trimming the stub further, but there's a risk it will become too weak or bendy. It would be the easier way, though.
I'll let it all simmer for a day or two before I decide.

I can't add fairing or filler to the upper part of the stub to make it the same size as the bottom either, as that means the CF grip wont fit on the top at all. (Though that would be the way I would go if I had to start over.)
If you mean a fairing powder for the internal core, then that is pretty much what I have. Microspheres/Microballoons are about the lightest filler you can get for epoxy;-)

Even if I have to chop up the grip, it will be fine. I have identified a place where I think I can make the cut without risking the grip breaking off later on.

Just a test fit, I haven't epoxied it in place yet:




I went with Foxfish's suggestion and just trimmed down the stub of the Mirage handle some more. Combined with opening up the CF grip a tad, it did the trick and I can now slide the grip onto the handle. (The Mirage handle seems as sturdy as before.)

But with the opening of the CF grip it doesn't mate as well to the Mirage handle as it was meant to. There's a 1-2mm gap around the top but that will be be filled with epoxy thickened with chopped CF. It is mostly an aesthetic issue - which I don't care that much about on this gun. If I did, then I would not even use this first grip but try to do a better (prettier) one.

I have been pondering different solutions for attaching a float line to the handle.
I thought about making a tube from the underside to the orginal Mirage stub, and thread some Dyneema through there. Or attach a sort of stringer to the stub and let it exit at the bottom of the handle.
I also sourced a few SS eyebolts and I could get a U-bolt and fix either one on the flat underside of the grip.

But I think I will drop all these ideas and go even simpler.
As mentioned earlier, I am positively surprised by the strength of the CF grip. I put 70kg on it - by standing on it - and I did not notice any flex.
So, the plan now is to just drill a hole straight through the rear, lower part of the handle. The inside here would also be filled with chopped CF and epoxy.
I don't see the grip breaking in two even with a strong pull on the float line - the risk is the whole grip coming off the stub. But with the shape of the stub as it is, and perhaps a few strategically drilled holes in it, I am pretty sure, the grip will lock in firmly once the epoxy glue joints and core has cured.

Hey guys,
Another update.

For this (first) prolonged Mirage, I have settled on a 130cm model. Take that in for a second, will you.
(There really can't be many of those around, though I have actually come across one in my countless hours online. One...)

The deciding factor was the last remaining 100cm carbon fiber tank I had left. Using this in it's full length will get me a Mirage 130.

To prolong one of my existing Mirages, I obviously also needed a longer shooting barrel and a pre-loading barrel, too.
For the shooting barrel I bought a spare for the longest Asso model which is still a tad longer than I need.

As I write this, the Asso barrel has has been cut down and a local machinist has had on it on his lathe to make a new "Mares muzzle thread", new o-ring grooves and I guess on the mill, for the notches at the back for the plastic stubs in the handle.

Before I handed the barrels over, I spent a long, long time measuring the original barrels and then made technical drawings in hand.
But here's the catch - I suck at drawing. Big time.
So, I really hope the machinist still got it right. I couldn't be there to look him over the shoulder and I haven't seen the barrel yet. It's actually in another province, but good machinist are hard to come by here. This was the result of a friend of a friend calling in a favor. Very Chinese
It should be alright - he had the original Mirage barrels plus my drawings to go by.

For the pre-loading barrel I sourced some 14x10mm 6061 alu tube. Before sending it off to the machinist just a few days back, I ran did a quick polishing of the inside.
(Have a look at my polishing setup here).
Tolerances seemed to be good and once the inside had been polished a bit, I got the piston to slide pretty nicely. I think it will work. Yes, I know it is not anodized but this will be fine for now. It will anodize a bit by itself eventually;-)

Unfortunately, my hand drawing for the pre-loading barrel was even worse and I got really worried about the machinist being able to decipher it. But since I had a bit of time waiting for the tube to arrive from the vendor and then shipping it onwards - I had a go at a new and pretty easy to use software for tech drawing (check out onshape.com. Free and awesome. I truly feel it is an example of "If I can do it, so can you!").
I still don't know all the proper rules of drawing but at least this, combined with some screenshots of the 3D renderings, should make it much easier for the machinist.

I'll probably draw up the shooting barrel as well at some point as it is good to have these measurements saved digitally.

Here are some screen shots:



And here is a jpeg of the tech drawing (yeah, a diameter of the "rubber hose valve" holes and a few other views are missing, but the important stuff is there:


Fingers crossed for one-two more weeks - then I'll get both the barrels back.
I will also receive a very, very modified trigger pin bushing for one of my Mirage handles. One of them is completely bust, the thread in the handle can't hold the bushing in place when pressurized. So some pretty extreme measures had to be taken there - but that's for another post/thread

PS.
I am super psyched about the prospect of a 130cm Mirage! So much so, that I am already considering going all in on a 140-145cm for the next one.
The limitation will be the longest 13mm spare barrel I can source (which looks to be a Salvimar Predathor).

The more I have been reading about bandguns lately end especially shaft mass and power, the more I realize how short my guns are. There could be plenty more power to harvest while still having a maneuverable gun.

So, I mentioned that one of my Mirage handles are bust.
The thread in the handle is in such bad shape that that it can't hold the trigger bushing in place. When I first got it, the gun leaked by the bushing so I cleaned the o-ring and o-ring seat and obviously, wasn't too thrilled to see the state of the threads. With crossed fingers, I took the gun up to 30 bar, only to have the whole bushing pop right out.
Here is an attempt at taking a picture of the sad, sad threads in the handle (this was even before it popped out, just before I cleaned it up and changed the o-ring):


The first repair idea was to enlarge the thread and use a threaded metal insert with an inner thread suited for the original bushing.
Here is a pic of two types of threaded inserts (helicoil to the left and what I call 'solid' to the right):


But two things made me drop that idea.
First of all, you have to make quite a big hole to accommodate these inserts and that is an issue the way the handle is made and also, I think the o-ring seat itself is scratched. So, even if I used a threaded insert to hold the original bushing in place, I still don't know if I would stop the leak.

So, after a lot of thinking, I am doing something a bit upside down, so to speak. I am making a whole new trigger assembly which installs from inside the handle and relies on a flange and not a thread to hold it in place.
This way, I need only drill an 8.3mm hole where the old bushing was and all the way through to the inner reservoir. I chose 8.3mm as it should be enough to clean up the mess there is now and leave me with clean sidewalls for the new bushing to seal against - and I don't want to go much larger as the handle runs out of material quite fast on one of the four sides.

Obviously, it's more hassle installing and servicing it, but if I did my o-ring calculations properly and the machinist gets it all right, then I think this is a better solution than anything else out there.
Also, the trigger bushing is taller than the original one and will offer more support for the thin 1.4mm trigger pin, I will be using.

The machinist has already made one of these, but I need to modify it slightly in hand, when I get it. I need to hand tap it and trim the sides of the flanges a bit. I just wanted to make it easy for him.

When done, it should look something like this:

Hey Pete,
Sure, this is definitely the last resort, so it is easy to be brave, haha. And it's no secret that I would be very happy if this worked out!

Yeah, there is just about enough room - the schematic is not 100% correct. There was about 2mm of room underneath the barrel if I recall correctly, but I chiseled away a bit of the plastic and got to 3.2mm. Actually, I don't think that was needed as the flange would probably have been plenty strong at, say, 1.5mm thickness.

Yes, to your comment on the pressure acting on the bushing, too. I do think that the o-ring was still leaking as I pressurized the gun, so the force was acting on the whole area of the original bushing and not just the pin.
I know, that it will be a lot more force now, but as you say - there's nothing to loose.
The new bushing bore will be 8.3mm in diameter which gives it a cross area of app. 0.54cm2 so at 30bar, if my calculations are not wrong there should be 16.2kgf on the bushing. Hard to say if that is a lot or a little, but my feeling is that it should be fine - there is actually more material in that area in eg. the top of the handle.

I will make a jig for the handle for when I need to drill the hole for the bushing. Nothing too extreme. I am thinking of just using some Polymorph or polyclay. I still have some left of both.

A note on the support for the thinner, custom pins. They are actually not that well supported as the hole in the top of the handle is +3mm to accommodate the old Ø3mm pin. The support through the o-ring seat depends on the design of the top part of the two-part bushing for the thinner pins and how much it is allowed to wiggle in that area. If you screw the bushing in tight, you can get the top of the bushing to sit quite firm, but that often means squeezing the o-ring too much which could lead to an early leak.
In mine, it seems that when the compression on the o-ring is "healthy" the top of the bushing has some wiggle room.
Add to this that the lower part of the bushing is only 5mm tall and you can start to see why I feel that in this department, my "rescue design" actually should have the upper hand.
In total, there is app. 13 mm from the underside of the bushing to the underside of the sear and now, a thinner pin is only properly supported for possibly less than half its length.
Mine will be supported for around 10-11mm, so that's double what I have now;-)
Come to think about it - the best way to get the most support out of a two-part bushing is to make sure the OD of the top part matches nicely to the ID of the bore through to the reservoir. Then the top part would sit snugly in place.

Hope this drawing explains things a bit more clearly:



(The red area (chiseled) should be extended towards the back, but you get the idea. But as said, there was already about 2mm of space there).

The main issue was the area in yellow. The threaded inserts which can hold an 8mm bushing are 10 or 12mm OD depending on the type (the helicoils are smaller, the solid machined ones bigger). With the 12mm ones, you even start running out of material in the sidewalls. Tapping the thread by hand and not scratching the o-ring seat could be a challenge, too. (Hard to use bottom taps w.o. taper in hand.)

On other handles with busted threads, a threaded insert might be an option though. But on the other hand, replacement handles for a lot of the traditional guns are not difficult to come by and are even quite affordable as brand new spares.

That's actually how it is now;-)
I specified the bushing without a thread to have the option. I just felt maybe it was actually easier to have a threaded insert than having to get the right amount of "press-fit" in a non-threaded insert. I don't want the insert to move up and down with the pin and if it gets stuck the "up position" it could get in the way of extracting the barrel from the handle. And if the press-fit is too tight it might be a hassle to get the insert out if I need to change the o-ring.
I even thought of having a set screw hold the insert in place, haha.

I will get it all tomorrow and then figure out what to do for the insert.

I got my barrels and trigger bushing back
Actually, one of the barrels might be 1-2mm too long but it remains to see if it will be an issue in sealing or if I have to have it modified again. (The machinist who did this is used to working on much bigger pieces for a power plant! And since this was a favor, I can't really bitch about it, haha).

Friend of a friend brought the parts back from the machinist:


I had said, that brass would have been more than fine for the bushing but the machinist is used to working in stainless, so that's even better. (Sorry about the blurred pics):


I forgot to do as TV chefs and prepare in advance so I can't put it all together just yet. Thing is, I hadn't yet epoxy coated the inside of the CF tank at the ends as I have done with the rest of the tanks in the past.
The coating helps the o-rings seal and protect the unidirectional fiber on the inside from being scratched and gorged when sliding the barrels, handle and nose cone in and out.

But lately I have had a few issues with my epoxy where, when using it for coating, it would fish eye or bead up and not flow into a film. I read a bit about it and normally it is caused by contamination especially from silicone. This was puzzling as I used acetone for cleaning.
But it might be a silicone or something else on my latex gloves that caused it. And I actually came across a Aussie speargun builder saying he has had the same issues when using cheaper acetone.

So, yesterday, after sanding the inside I used hot water and a bit of soap to clean with. Rinsed off well and left to dry under the AC. Furthermore, I used a very thin layer of glassfibre on the inside where normally, I have just used the resin on its own.
This time, the epoxy flowed nicely and didn't bead at all. I guess the fiber could possibly also have given the resin something to "hold onto" as well.

Tomorrow, I will assemble it all - using the healthy handle for now - and hopefully, I will have a leak-free Mirage 130...!

Here's the carbon fiber tank with the thin layer of glassfibre. It is thinner than it looks, probably around 0.05mm thick and 50g/m².


It looks wavy here but in reality, the resin laid down nice and even.

Good thoughts and I have been considering a lot of things over the past few months. My dream gun is actually one that uses the Mirage tech but not the handle and bulkhead, as there are improvements to be had in the handle design;-)
But that is for the future and it is an uncertain one at that.
One modification that Jegwan and I had pondered was to simply move the whole power regulator bulkhead a few inches forward. If I am not mistaken, this should mean that a shot on the loading setting will be more like a regular low power shot on normal guns. Maybe the residual pressure in the shooting barrel after having done the pre-loading pumps would be higher (?) but that would be OK, as long as it would still be manageable.

Yup, you could pump more times, or just stop at app. 5 and your loading effort will be a tad harder, but still should be easy enough. I think, that is how I would make a modern Mirage. And as you pointed out earlier - only two settings needed, then.

It would not be too hard a mod to make either - you need a spacer insert that also holds the return valve in the right manner and it should work.

I did a quick assembly of the 130 yesterday and it seems to hold air - except by the trigger. This is not the busted trigger but a thin trigger assembly, but it is quite sensitive to how far in you screw the bushing. A quarter of a turn, literally, makes the difference between a leak or no leak.
Luckily it came with an installation tool that has a pin the size of the trigger pin go into the assembly as you screw it in. This is cool because you can use this, under low pressure, to fine tune how far in you screw the bushing. Listen for the hissing and turn until it stops.
I actually wonder if the outer o-ring is slightly too small as it seems it might be depending on extra compression from the assembly being screwed in a bit tight. I will investigate that next and if possibly change to an o-ring which has more "natural compression" on its own. It's either that or that the bottom of the seat is not sealing well - meaning the o-ring has to be moved up into a more healthy portion of the seat by the bushing being screwed in more.

But this is actually another advantage in my own "rescue design" from an earlier post above. Speaking of which, the machinist unfortunately made an error reading the drawing and the diameter of the o-ring seat was made to be 6.5mm when 6.05mm was specified. But I just did some new calculations and it seems I can make it work by switching o-rings from 1.5mm to 1.2mm section width. So, I just need to order those now.
Good thing is that I can buy o-rings easily online in China and they start at 0.002 USD/ring. So, I am nice and tend to order at least 25 of each ring each time, haha.

Back to the handle itself - I still needed to glue the new CF grip in place.
Unfortunately I skipped the pic taking a bit on this step.

But what I did was to drill a few holes in the stub of the handle and make a few cut-outs along the edge of the stub. The idea being that the "glue" would flow into these and better lock the grip in place.

As you can see on the picture of a quick test, I used molten lava for the glue:


Nah, not entirely, but the epoxy mixed with chopped carbon fiber that will be used as glue is rock solid, literally.

I proceeded to glue the stub to the inside front of the hollow grip and then let it cure. I do most of my curing at room temp for about 24H and then 4H elevated at 80C to get the most out of the type of resin I am using. The elevated cure also makes it less prone to being effected by heat later on. (Room temp cure epoxy can go soft if left in the sun, even after fully cured).

With the grip secured to the stub of the handle I still had a void behind the stub and and all the way from top to bottom of the hollow CF grip. I decided to fill half of the grip with 'syntatic foam' which is a fancy word for resin mixed with microspheres or micro balloons. This mix is less dense than water, so will give me a bit of buoyancy but has very good compression strength on account of the tiny little glass bubbles.
The idea is that even if the grip wanted to move in relation to the stub or break off from the "glue line", it would not be able to as there is simply no empty space in that area.

I heated the epoxy in a water bath to make it less viscous so that I could pack more microspheres into it while still having it flow just enough to fill in the voids.


I poured just enough that the rigid syntactic foam levels off where the end of the stub is. Anymore would just be a waste. You can just about make out the chopped CF "glue" at the bottom of the pic next to the two little white "rivers":


I still have about 50% of space in the handle that I can fill with two-pack PU foam. I should win a few grams of buoyancy that way as it is quite light;-)

In the end, this handle will be heavier than I had hoped for, but it's OK, I have some plans where it might actually have to have some lead in it... I still have an idea of making a custom tank for the next long Mirage pushing a lot of volume just in front of the handle and having a very thin first half of the tank. As such, I might need the handle to actually be negative to keep the gun in horizontal balance.
Also, I think I will succeed in resurrecting the other handle with a blown trigger bushing thread, so if I want to go lightweight on that, I still can.

Back to the issue with my other Mirage handle, where the trigger bushing thread had been blown out.
As mentioned above, I have designed a new bushing which inserts from the top down - from inside the handle.

Next week, I should get the o-rings for it, and I will need to fashion an insert to keep the pin from wiggling but so far, so good - the shooting barrel slides in place over the bushing now (I needed to file the bushing down just a tad):



Hard to tell from this pic, but notice the little step over the bushing - sort of a ramp where the wall of plastic disappears abruptly. This is the reason it was not really an option to go with anything much bigger in diameter than this solution: