The Ultimate Travel Oleo? - A Custom-Sized Mirage 93

Fibonacci said:

Interesting project and some nice machining there Gecko
I've often wondered why there is not more cross-over between bow fishing gear and pneumatic spearguns... seems to me that there are several similar design requirements.
Some of the high performance solid 5/16" (~7.9mm) pulltruded fibreglass/carbon composite 32" bowfishing shafts could be adapted for a lightweight pneumatic travel gun... not sure how much performance you would lose with the lighter shaft mass vs stainless steel but increased velocity should enable a flatter trajectory as a trade-off?

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I think for skittish, fast fish at shorter distances, a light shaft might work, but not for bigger fish and might not for long distances either. Water is so much more dense than air and that could be the reason it is ok to go with mass over speed as a light shaft will loose inertia(?) way too fast. At least that seems to be the general consensus and since power seems to be going up in guns these days people are moving to even heavier shafts. That said, I don't have the real engineering knowledge at all to answer this.

Honestly, it does make me a little nervous drilling out this bore. The first time I did it, my fixture was not the best and I used a regular drill bit. But this time, I need to do my best to get it right and will probably use reamers.

The setup is quite rigid now and the handle in the right place to have the bore concentric with the drill/reamer:






I tried do get a pic of the inside of the bore to show the scratches but it's quite difficult to get and even more so now the bench drill is in the way

Sorry for letting you guys hang here, but will sleep on it and do the actually drilling tomorrow..

I finally managed to get a pic of the scratched bore. Sometimes things come out worse in pics that in real life, sometimes it is the other way around. For this one, I think it's a little less bad in real life but still not great:


Another trick I used when lining up the handle and bench drill was to color the tip of the brass "guide". Then I lowered it carefully into the handle and checked if any of the color had come off and moved the table accordingly:


I drilled the bore out to 9mm (from 8.6mm) and while the bore is definitely smoother now, it's still not 100% smooth all over. I'll end with a pic attempting to show how the bore looks now.
Parts of it are smoother than this, a few spots slightly worse:


I'm undecided as whether to order bigger reamers or try it as it is. A bit of real life work is coming up but that will also give me a few days to think this over.

Trigger Repair
Haven't made any progress on the trigger bushing except some Grade 5 titanium arrived (local Chinese stuff and cheap in small lengths) and to my surprise it machines quite OK on this little lathe. I'd say better than the 303 stainless that I also ordered which is supposed to be the most machinable of the stainless steels. So, if I need to make a new bushing for the enlarged bore, I will try to make it in titanium and reap the corrosion-free benefits. Also, of course, once you have titanium in the trigger mech, fish are bound to want to get shot out of sheer awe...

Palengas Line Release
Now, all this recent talk of the Palengas line release on another thread made me dig mine out again. My goal for the next trip is to have two Mirages with me. One 93ish and the longer 120. But only one of these two Mirage handles have an active release (Salvimar PredaThor style), the other one is still set up for a Palengas release. While the goal is to modify the second one for an active release, too I am not sure I will have time. So, I made a slightly improved insert for the Palengas release, just in case. The original Sten insert doesn't really work with Mirage handles so I had one made in a machine shop in Bangkok a few years ago and it has served me OK, but it was a bit too short and needed tools to tighten up nicely.

On the bottom, the insert I had made in Bangkok. On the top, my newer DIY one:


Besides pliers, I needed an allen key, too to tighten this thing up:


Needing tools for this job, especially the pliers, was annoying as I needed it every time I wanted to adjust the air pressure. So, for my own version, besides making it longer I wanted it to be "tool-less". Knurling the Delrin (POM) made it so:


The knurling on the insert itself is not that great. I think it's because I stopped a few times in the middle of the run to check it. But it wont effect the functionality. The knurled M8x1.25 screw turned out really nice, though:


Assembled:


Inserted in the pump valve of my first modified Mirage handle (the one without an active release):



(I might shorten the insert by another centimeter or so, just so it doesn't protrude rearwards of the handle).

As I mentioned on the other thread, my Palengas release only lasted one trip before the magnet rusted away. So, for the second trip, once I had given up on getting a replacement, I glued in a replacement magnet and sealed it in epoxy. That one also came apart pretty fast, so will have to insert a new one soon:


Just as an aside, instead of machining the male screw threads on the lathe with a cutting tool I made another die holder for the M8 die (it also holds dies down to M4, maybe even smaller). Well, I still use the lathe but just in a manual way to keep things concentric. The die holder sits on the tailstock so it should be pretty much 100% aligned with the part being held in the chuck:


I cut the front M14x1 male thread on the insert with a similar DYI die holder, just a bigger version.

Adventures in Titanium (or Trigger Repair Continued)...
I couldn't resist making yet another trigger bushing. For two reasons. First, the trigger bushing bore has now been reamed out to 9.0mm - as of the posts above and though it is still not as smooth as I would want it, I will try to see if I can make it seal before I enlarge it even more. Secondly, with the bigger bore, I should ideally up the dimensions of the o-ring groove a little to keep up the compression on the o-rings and that, of course, gave me the excuse trying my hand at machining titanium on my little machine...

This is the machine, placed in my apartment. I hung some PVC (originally intended for modifying an inflatable float but haven't gotten around to that project yet) on the wall to catch the oil splatter...:


The Chinese Grade 5 Titanium machines surprisingly nice. Somehow, it machines better with the alu cutting inserts than with the ones I have for steel. Actually, these inserts even cut hardened 17-4ph, so I am pretty impressed with them:


Now that I finally managed to get the tailstock into OK alignment I am not snapping these small drill bits at the rate I was before. I think this green one is a 1.5mm drill bit:


I mentioned above that I would make a simple and cheap DRO (Digital Read Out) for my tailstock and here it is:

It really does make life a whole lot easier when I have to hit specific depths for e.g. o-ring seats.

Speaking of those, I have settled for a 3.8mm diameter for the seat for a 1.4mm trigger pin with a 1.5x1.5mm (ID X W) o-ring. To make that seat, I pre-drill with a regular drill bit and then use a 3.8mm end mill. Works quite well in combination with the DRO on the tailstock:


The threading part is still a bit ghetto. The issue is that the o-ring seat sits just behind the thread and if I thread too deep, I ruin the o-ring seat. Unfortunately, my tailstock DRO doesn't yet work when threading, but I have some ideas on that front. For now, I painted/inked the taps and used my calipers to scratch mark the depth. It worked surprisingly well:


In this last pic, half of the bushing is a bit discolored. Titanium heats up like crazy when you machine it and I think an internal cut heated it up too much though the discoloration polished off later on. Also, the marks on the bigger part of the stock to the left are from shallow trial cuts when aligning the grooving tool perpendicular to the stock. Finally, there's a slight bit of chatter marks in the left most o-ring groove. The quick change tool post I got was too cheap to be any good and it's just not sturdy enough for parting and grooving operations. Need to get a better one...

Another Bushing Finished (Trigger Bushing V3Ti)
The new trigger bushing is in the same design as the previous one. Only difference is the material and that I updated the dimensions a little to reflect the bigger bore I had to make in the handle. I aim for 25% compression on the static seals and if I had kept the old bushing the compression would be around 17%. Also, the gap between the bushing and bore would be larger than ideal.

But without further ado, here's the result (L-R; Delrin dummy, brass V3 bushing and new titanium V3 bushing):


Some more:



And one for scale (AA battery):


Inserting these tiny o-rings and keeping them from sitting skewed in the o-ring seat was a challenge. So, I fashioned this little insertion tool from an off-cut from a 17-4ph shaft. (In an ideal world, I guess I should have used a softer material than the bushing for scratch protection but I also wanted to practice machining the hardened 17-4ph):


I honestly don't know if this will get rid of the last little leak at the bore or whether I need to enlarge the bore even more and thus make yet another bushing. But I don't mind the practice on the lathe and now I know I can machine titanium, too;-)

Third Assembly
Third time lucky, it seems...
Now, a still pic doesn't prove much in this instance, but on the earlier assemblies, I would have a steady stream or later - a slow trickle - of bubbles from the trigger and power regulator rod. Now, nothing.


I am not getting carried away just yet. The gun sits at 20 bar now, and I'll measure it again tomorrow.
As for the fixing, obviously, I just put in the new bushing from the two posts above. In regards to the power regulator, I unceremoniously chucked in an extra o-ring. There are already two in that seat but there's also an awful lot of empty space and it looked like the o-rings could easily get skewed in that seat before the pressure came up in the gun. I am not 100% sure if that is the issue, but the third ring seems to have done the trick. If it is, then I another possible remedy is to machine a new and longer Delrin bushing to keep the o-rings properly in place.

zmajmr said:

those drills which you snap on are made from carbide and are used for drilling very hard materials, for drilling stainless or titanium it is better to use HSS with cobalt , usually those carbide drills come in big range of sizes like 2 mm, 2.05, 2.1 mm and so on, so they are good for different size holes but unfortunately they break like glass in contact with stainless because it is chewy material. As I remember I used them to drill titanium also but you need to be very careful, look this video it might help you

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Thanks for the tip, Marko! Will check the video.
I guess the length and material makes the HSS drill bits much less brittle but they can also wander around more. I think I might just use the carbide ones to center drill for a few mm, and then switch to HSS. I think I already have the latter in 1.4, 1.5. 1.6mm sizes

[EDIT]
Oh, the video is from Joe Pieczynski. I have gobbled up most of his other videos. His one on threading towards the tail stock is awesome. As for this video, I saw someone else online make the same exact thing for very small taps for modelling machining. I just wasn't smart enough to realize it would work for drill bits, too, haha. I was thinking of making the tapping attachment anyways, but now with the double use it can offer, I certainly will. Thanks!

A Leak-free Update
It's a day later and the gun has held air at 20 bar.
Also, I did the pre-loading routine moving the air into the front chamber and it held air there for hours, too. This might not sound like a big deal but I have had small leaks internally before. This is frustrating as it is such a nice feature to be able to keep the gun in the pre-loaded stage, so that when you load it for real, it is super fast and effortless. E.g. in Thailand and Philippines, when spearing from boats, I noticed that sometimes fish would come right up to the boat for a quick check as we stopped on a new spot. But having to go through the full loading procedure on a Mirage would take too long and the chance would be lost. The alternative is keeping the gun loaded on the boat and I really, really don't like doing that.
I am taking the gun up to 30 bar now for another overnight check:


Next, I will cut down some Sigalsub shafts that arrived not too long ago. I ordered shafts in 7, 7.5 and 8mm with both single and double barbs (never tried the latter before):


As an aside, the 7.5mm shafts have their barbs placed 10mm neared the tip than the other shafts (70mm vs. 80mm). I talked to Sigalsub about it a while ago and they said the shorter distance is the old design, so I must have gotten those from an old batch. It's not a biggie at all:


Whether they are the new or old design, they are all a tad too long as I like to have minimum overhang on my airguns. Even if I didn't, then on this gun the limiting factor would the length of the fin bag;-). I have had a good run of ordering online in China but the M6 (and M4 and M5) threading dies I just received were lefties, haha (my own fault). New ones will be here in a day or two.

(Mis)Adventures in Titanium...
Hmmm... today I made a new part in titanium. It's another pump adapter with a quick coupling on the end. It'll work both for my ScubaFill adapter and the fridge compressor. The one I made a while ago in brass is fine, it's just a little short for one of my handles. So, here's the new one (above the shorter brass one):


I wanted to trim it down a whole lot and it does weigh 1/3 of what the brass one does. On this one, I wanted it to have a pin for opening the ball valve and I wanted the pin to be adjustable, too. The plan was to cut an M4 thread in the adapter and as on cue, a telescopic tap holder arrived with the courier. I know I said I wanted to make one myself for micro-drilling anyways, but I found one for 12 euros and it fits my MT2 tailstock perfectly. Just had to remove a pin and spring, so that it would rotate freely:


Still, despite my new gadget, disaster struck and I broke the tap in the part...:


I can't get the tap out, but the adapter actually still works, the air is happy to pass the broken tap - just that I can't easily take readings off of a gun without the pin feature:


I spent all day on this thing so I feel really bummed out. While I can machine this titanium it's just not easy to tap or thread. For the M14x1 thread I gave up using my die holder and cut it with a thread cutting tool instead. I did manage to cut the M5 internal thread in the trigger bushing but that wasn't easy either and this time, with the M4, I just couldn't make it work.
I did find one tapping chart that suggested bigger holes for steel than the ones normally given, so I will try that next time. Actually, I should, of course, have done a test first...

If I still want to make one of these in titanium, I will probably go up to M5 so the tap is a bit sturdier, pre-drill a little larger and do the threading as the very first operation. That way, I don't risk wasting a whole lot of time in case it doesn't work out.

To end on a slightly happier machinist note, I remembered how someone here recently mentioned the lack of caps for the pump. And I also remembered how there's always sand and dirt in my pump threads when I travel. Not a good thing to blow that stuff into your gun. So, I made some caps:

Fibonacci said:

Some nice machining there Gecko... didn't realise Titanium would cut so well!

Very frustrating re the broken tap... while EDM erosion is the industry standard to remove such stuck items its likely to be expensive.

You may have some luck just using a small diameter solid carbide or diamond impregnated ball cutter on a Dremel, aim the the core of the tap less sensitive to misalignment and if properly lubricated should cut through carbon steel very easily. You really only need to cut through one of the three lands to release tension between the tap and the material, it should then rotate out.

BTW great job on the end caps, I've had the same trouble trying to protect the threads on my Mares pump... looked high and low for a M14x1.0 plastic cap but the industry standard is M14x1.5... these are commonly available.
I can't believe the Mares pump doesn't have one as standard!

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Ah, yes, it must have been you who got my mind stirring about the pump caps. Actually, I just pulled out a Mares pump and the thread is full of sand from the latest trip so the caps are indeed a good idea! My Salvimar pump actually came with one. Not a screw-on one, but a nice tight fit of some softer type of rubber/plastic (PVC?). (I'll snap a pic a bit later and add here).

[EDIT] It was probably StefPix who talked about the lack of caps here.
But anyways, here are your pix of the soft cap that came on the Salvi pump:



You are right, the ti does machine surprisingly well on this tiny hobby machine so that's a sweet little bonus. I do have some cuts where I hadn't noticed the tool had dulled, which I think it does pretty fast on a small lathe that wont let me take deep cuts - I seem to generate tons of heat. But it's not a big issue. If I need to spend Euros 1.5 to make a part or two, I don't mind.

As for the broken tap, I have also seen a few examples of people using acid to dissolve broken taps. Might be worth a go. I do have a dremel-type tool so if I can get the bit, I will check that out, too.
I did read up on tapping titanium last night and the issue seems to be two-fold. My pre-drilled hole was made according to a 75% thread table which works fine in brass and alu, but for titanium I should have drilled larger (about 50%). Also, titanium has a lot more elasticity than SS so when you drill and tap, the material will actually give a little but then it will retract and grab the bits/taps. So, supposedly that's why taps tend to break on extraction. The deeper the hole, the worse it is. For this reason, there are specially designed ti-cutting taps with different relief angles. Finally, ti transfers heat badly and does actually work harden, so that doesn't exactly help.

But since none of these threads have to hold a whole lot, I will start with cutting larger holes and I will use a proper cutting fluid next time.

zmajmr said:

maybe you can find someone who have EDM machine so he can "eat" broken tap with it, I hate when that happens, probably would be less chance for braking tap if you had some more expensive /better quality one, also tapping liquid should help. You could eat broken tap with carbide endmill but you need to have for that rigid setup otherwise you will broke carbide endmill also. Knurl in titanium came out great , I never tried to knurl anything but your part looks really nice.

Click to expand...

I actually should have a contact or two with access to EDM machines. The issue would probably be that the machines are producing parts most of the time, but I will ask if they can put my thingy in for a little while;-)

Yeah, the knurl turned out way nicer than I had hoped for. Knurling is still very much black magic to me. But at least I found a nice online calculator to help me start with the right OD for a given knurl pitch.
Sometimes, the knurl looks great after 1-2 passes but then the next pass messes it up. I guess because my machine and knurling tool isn't stiff enough so the wheels might wander from one pass to the other. Anyways, when it works it looks really professional;-). And even when it is less than perfect, it is still good enough for me.

Play With Fire
Didn't get much done today, though I ordered a few more bits and bobs. Some more stock, a few more - and better - taps and some proper tapping oil.

Making the pump caps reminded me that I am missing a valve plug on one of my Mirage handles (the one without the Palengas release).
I normally don't bother with plugs but since I did think it was worthwhile making some for the pumps and pump adapters, it makes sense to take the plugs a tad more serious, too. So, I made two - and for some reason even put an o-ring in them...:


The red one was a bit too much on my very dark and subdued Mirage, so I think I will use the black one (don't worry - I will put the trigger guard back on before I put a spear in this thing):


While I can screw the plug in with my fingers, it might somehow end up too tight to unscrew so I fiddled around trying to make a sort of screw head, just in case.
Like all healthy boys, I turned to fire...:


I suspended a Philips head screwdriver with some pressure from the tailstock and heated it up with a small torch:


After taking off the worst burs, it actually worked out pretty alright:


I overdid it with the heat a bit with the black one - the delrin is also from a softer batch which caught me out. I ended up having to go in deeper and clear out the over-enlarged first attempt. But it's fine, now:


BTW, you just gotta love Youtube. It's where I learned to solder, curl my 14-y-o. niece's hair when her mom gave her an iron and no one knew how to use it, it's where I am learning to turn on my lathe and it's where I go for the oldies. Enjoy:

Pressure Gauge
I made an adapter for a pressure gauge today. Made it in alu which isn't really the best choice but felt like machining something easy today. I have ordered a more sturdy tool post but it will take a week or two before I get it. Then I might get back into the titanium game.

Here are some pics of the pressure gauge:






I made it with an adjustable pin so that I can dial it to that sweet spot where I don't loose any air when taking readings (well, except air lost to the dead air space in the pressure gauge and adapter itself):


It's half the weight of the Omer version (which I even slimmed down a bit on the lathe already) and a bit smaller, too:


Since I also made a plug for my scuba tank filling adapter so that it can be used as a standalone pressure gauge, I am not sure that the gauge I made today will see much use. Still good practice though


(I started a thread on the pressure gauge, too with more pics and the measurements here)

Rescues in Titanium
Remember the busted tap in my titanium pump adapter? Well, I was about to send it to South China to have the s@#* EDM'ed out of it but then I spent a bit of time reading up on this and someone somewhere online mentioned that diamond coated "dremel bits" should be able to cut a tap. ([EDIT] I just realized it was Fibonacci who said it just a few posts above. Thanks mate!)
So, I ordered some of those and they actually worked. Didn't bother to take pics of the action, so you will have to make do with a pic of the bits:

I got a ten-pack of 1mm (broke four of those) and and a pack of 1.5mm (broke none of those) and it cost less than shipping the part back and forth (which would still have been cheap).

With the broken tap out of the way, I set about boring out and re-tapping the titanium adapter. Again, not many pics, just this one of the tapping operation almost done:


I bored out for an M5 tap this time - instead of the M4 which broke. Earlier, I mentioned that I would pre-drill larger than normally, but I tried my luck at using the standard 4.2mm drill bit for an M5 thread, instead of suggested larger 4.5mm for harder steels. Also, I had some better taps and with some cutting fluid and it all worked out fine (thanks Marko). Actually, a HSS tap I already had on hand did the best job. When HSS is properly sharp, it just works...

I used a straight shank with an ER20 collet to hold the titanium adapter in the chuck. To not mar the knurl, I wrapped the part in some brown paper bag (highly recommended on a machinist forum). It worked a treat and was surprisingly close to being concentric:



Here's the finalized adapter with that fabled adjustable pin:

The pin itself turned out a lot better than last time. It is made from a titanium bolt, so corrosion shouldn't be an issue. The bore is 1.5mm and the OD of the pin is about 2.3mm. The wall ends up being a bit thin and a tad sharp. I was worried it could scratch the ball in the valve but I checked the hardness ratings; 316 (which I suspect the ball is made out of) is twice as hard as titanium, so it should be safe.

Now, I can use this on both my compressor pump or with my scuba filling adapter for when I travel:

The Saga Continues - The Elusive Mirage...
While my third assembly and subsequent kitchen sink dunk test showed no leaks I do have an internal leak between the chambers. Now, on a regular gun that wouldn't be a huge issue but on a Mirage, well... it means the Mirage Effect has gone with the wind, so to speak.
The whole idea with the Mirage design is to be able to move air from the rear chamber (which acts on the piston) to the front chamber by means of the smaller pumping barrel. If this function doesn't work then I can't load the gun... (If this goes bust on a trip, you can always lower the pressure and just use the gun as any regular air gun).

I did suspect this leak as I have had it before. But I did do a test where it held air alright but it was only at 20bar and it just failed at 30bar. A number of things could be leaking; the main bulkhead o-ring, the o-ring on the shooting barrel where the barrel goes through the bulkhead, the one-way valve at the rear of the pumping barrel, the over-pressure valve in the bulkhead or the power regulator bushing o-ring. Basically, unless I go all nerdy and only change one thing at a time I wont be able to fully diagnose which one it is. I think I will disassemble the gun in a day or two and service as many as I can in one go. My gut feeling is that is that the one-way valve is the culprit. As a joint second comes the over-pressure valve and the power regulator bushing o-ring. As for the latter, I actually didn't check how far forward the bushing sat in the bulkhead when I assembled it, so if I am lucky I just need to adjust that.