Model Boat Mayhem
The Shipyard ( Dry Dock ): Builds & Questions => Submarines => Topic started by: bbdave on October 21, 2012, 03:30:16 pm
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After lots of thinking and brain storming pawing over John Lamberts i have made a start. I have decided to build in two halves top and bottom using 1/16 balsa which will then be filled sanded then clad in glass and cloth i'm not 100% on the dive system yet but as this will be all inside a WTC tube it isn't a huge problem whilst building the hull.
I have enlarged the plan by around 1.5 giving a final hull of L 813mm x W 127mm i think/hope {:-{.
The top half frames have been layed and lined up not all are integral some are dummies which cross fingers will remain on the board when the hull is removed the permanent frames are the cut out ones from 6mm ply.
(http://s13.postimage.org/7rg2zbt77/003.jpg) (http://postimage.org/image/7rg2zbt77/)
(http://s8.postimage.org/qjpyysklt/002.jpg) (http://postimage.org/image/qjpyysklt/)
(http://s9.postimage.org/anysj47fv/004.jpg) (http://postimage.org/image/anysj47fv/)
(http://s8.postimage.org/adyo99lqp/006.jpg) (http://postimage.org/image/adyo99lqp/)
Dave
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Great stuff. Action man scale!
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Will have to dig eagle eyes out of the loft %) I need to get some FG ordered not sure what to get as yet but the balsa planking will be quite fragile till i get it glassed.
Dave
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Are you making a mould, or will the wooden hull be part of the finished boat. If the former, polyester or epoxy will do the job depending on your preference and depth of pocket.
If the latter I would use epoxy resin, it tends to soak into wood better I find, possibly becuase it tends to be thinner. You can thin polyester with a small amount of styrene, but it weakens it a bit. Cloth is easier to fill than CSM, with epoxy you can use the small sponge rollers you use for decorating to get a really nice finish. Order some colloidal silica to thicken the resin, which will make it easier to sand and will fill the weave quicker.
I highly recommend Reactive resins for epoxy, and CFS fibreglass supplies for polyester (they sell epoxy too, but it's West Systems, so a bit pricey).
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Looking good and it's so nice to see someone actually do some scratch building!
You are still at the stage where you can do a one off or use it as a plug for a female mould. (I can't help feeing that you are best making a female mould but I have seen the glass coated hulls being used very successfully at Barrow.)
Regarding the final mould finish have a look at the Nigel's builds on the AMS forum. (He has used aluminium Duct tape or tinplate.)
Glasplies in Southport are a good, reliable supplier (call in or mail order), certainly for polyester.
David
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I think i will go the polyester route mainly due to cost and just build the one for now i have a contact who makes boats so may ask him at a later date about making a mould if this works ok
Dave
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If you make a mould, you can crank out a few more hulls. Even if you only make one extra hull, and sell that, you'll most likely recoup the material cost of producing the boat.
Epoxy resin works out about three times the cost, but do bear in mind that if you are making tools, you will need to purchase both laminating and gelcoat resins, and as the minimum quanity you can purchase these in is usually 1kg, you will find that the overall cost works out about the same if you're only going to produce one hull. With epoxy resin you use the same resin for laminating and gelcoat, you just add a filler into the resin (colloidal silica) to thicken it for gelcoating.
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At the moment poly will only cost me around £25 resin and cloth so not a major outlay if it all goes wrong
Dave
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Have you done any GRP work before?
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I have done some boat repairs built an outboard well etc. with west systems unfortunately non left or it would have been done in that. I've not used polyester rein before but i guess not much difference in use or am i wrong? i do have plenty of colloidal silica left.
Dave
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Not a great deal of difference, apart from the pong of the styrene. I find polyester tends to give you less time to work than epoxy, however you do have adequate time to complete the lay-up.
If you're just laying glass over wood, you don't really need gelcoat. Chopped strand matt is easier to work with than cloth, but will result in a heavier laminate. CSM does produce stiffer laminates though, which I think is an advantage for submarines. Apparently laminators often mix a layer of CSM in with cloth lay-ups to add a bit of extra stiffness. If using CSM with epoxy it must be powder bound, which tends to be more expensive than styrene bound. Polyester can use either powder or styrene bound, with most people using the latter, because it's the cheapest. I use 300gram matt and usually use two layers with tissue. If just lining a wooden hull, one layer of 300gram is sufficient. A layer of tissue will improve the surface finish, but you will still have to sand back and fill a bit if you're going with a lined hull.
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Basically what i was planning was to coat the wood with resin lay CSM adding colloidal silica to the resin when cured add second coat i can add around 1mm maybe 2mm depending on sanding back to the wood to keep scale but we'll see how that turns out. I willl add a layer to the inside when off the board.
Dave
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The approach I would take is this- Give the wood a coat of rein, thinned 10% with styrene. This should help the resin penetrate the grain of the wood. Let that dry off for a few hours until tacky, then apply a a layer of CSM with normal unthinned resin, and no colloidal silica. Lay one layer of glass tissue over the matt, and ensure then ensure the matt and tissue is fully consolidated with the resin (I like to use a washer roller). Let that dry off overnight, then carefully sand back, taking care not to break through the thin coating. Fill any dips with polyester filler, and work until it is smooth.
Then you can prime and stopper the hull until you have your desired finish.
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Ok makes more sense i presume the CSM and tissue are applied on the same application of resin?
Planking so far not pretty so no close ups. This is the first time i've used gorilla glue so it's a learning curve but as it's 100% waterproof i thought a better option than PVA
(http://s7.postimage.org/ygk557eh3/IMAG0060.jpg) (http://postimage.org/image/ygk557eh3/)
(http://s12.postimage.org/ggf181nix/IMAG0061.jpg) (http://postimage.org/image/ggf181nix/)
Dave
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That's the way I apply it.
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Planking on the top done ready for filling sanding and glassing. Not sure yet if i'll joint the top and bottom then cut the access or to have the break through the equator.
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Progress so far i have now glassed the top half and removed it from the dummy frames ready for the next set of frames for the lower half which hopefully will get planked up this week and glassed next weekend
Dave
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Very nice. Looks like it came out well.
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Coming along. Something I should have mentioned before, but it slipped my mind at the time. It's not a bad idea to add a bit of tint (something dark) to the resin. This helps show up any areas you may have missed- especially important when using wood in a submarine.
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I have made sure the outside had a good coating plus i'm planning to do extra resin coats inside and out to make sure it's fully encased the balsa.
I still havn't decided if to cut a hatch or continue with it splitting on the equator line, but plenty to think about on that and other bits i'm just trying to get the dirty work done first.
Dave
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Have you considered glassing the two halves together and splitting it radially?
All the controls on a Welman are mounted aft, so you need no access forward of that. Will keep the hull nice and taught too.
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I had thought of that but not sure how to achieve it and maintain access to linkages etc. i did it with a bayonet ring on my u47 but the removable deck allowed access. Any ideas?
Dave
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The usual solution is to cut in a small access hatch somewhere near where the linkages hook-up.
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I see Norbert does different size bayonet rings so i will seriously consider it as i had no problems with my u47 it worked faultlessly. I'll get the main hull made then decide whats best there are some complicated linkages so i'll have to sort what access i need.
Dave
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Just a thought from someone who knows nothing about this boat. From what has been said all the gear is near the stern - prop, rudder, planes, yes? Why not split the hull radially just forward of, say, the planes with a tray for the motors, etc running forward from and attached to that stern-most section? The linkages should then be reachable - perhaps {:-{
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I thought that is what I suggested in reply 20?
Anyway, you don't need aluminium bayonet rings, you can make a radial separation and just have the WTC slide in.
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I see so just join the hull with magnets or the like over a wtc could be a plan that
Dave
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I thought that is what I suggested in reply 20?
Sorry, with his reply in #21 I thought it was a radial split in the middle of the hull being considered.
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Magnets are an option. Not keen on them personally for this kind of thing, too weak and the two parts might separate, too strong, and you might end up a source of amusment for spectators wrestling with a wet hulled boat- akin to trying to grab a greased pig!
I favour either a machine screw fixing ( one will be adequate) or a simple bayonet locking mechanism. Have a look at a lightbulb fixing or those round tubs blank CD's are supplied in. That should provide you with a bit of inspiration for a simple latching design that you can fabricate inexpensively.
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Made some progress this week finished planking the bottom half it has been glassed and taken off the formers both halves sanded and dry fitted not the best join but not the worst i've seen but some side bulges will be added later so by the time it's all joined and filled it should all come good. It needs plenty of resin coats inside and out to make sure the wood is sealed and to give me some sacrificial layers to sand down externally.
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Looking ahead I am toying with the idea of using the Thunder Tiger dive system buying off the chap on ebay the control unit and the pressure switch.
I presume any 12v roll pump will work and any bladder? or are the TT ones ok i will need a motor for the pump unit i guess
Dave
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Some of the peristaltic pumps are painfully slow, leading to long dive times. The Welman shouldn't need a large dive tank if the conning tower is freeflood, but all the same, I wouldn't go for anything too ponderous.
The Neptune pump has a fairly good flow rate. Not sure about efficiency though mind you- the pump is directly driven, and as I recall relies on slippage of the motor spindle to slow it down.
An alternative is to use the switcher, ballast bag and pressure switch, but use a small geared pump instead. With a bag system the pump is working against very low pressures, which helps the life of the pump. These will give you a good flow rate, but are not self sealing, so you will need to make a pinch valve or fit a solenoid controlled valve. Pinch valve is easy to make and cheap.
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Just to clarify this is The controller
http://www.ebay.co.uk/itm/390315372150?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649
Dave
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Yes, it's a just a basic relay switcher, with a built in failsafe. Think it also has a water detector, hook-up for the pressure switch and also a voltage checker (for a 12 volt system). Relay contacts are rated for 10A, so more than enough for any pump system you're likely to fit in the Welman.
You can use ordinary ESC's for pump control too.
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Tonight has been spent sanding some foam to mould the front dome planning to do this on Saturday as i have to go to work so i'll have use of the workshop.
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Had a busy morning this morning i have joined the two halves using CSM and tissue to make the joint strong i covered my mould in plastic and gave it the same CSM and tissue you can see from the mould how much heat a small amount of resin produces but as it only needed to make one this wasn't a problem i'm happy with the result
While waiting for this to cure i made up a stand.
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Are you going to make the detacheable mine for the bow too?
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I will be making it when i've finished the rest of the sub as an add on as it only screws on via a threaded rod.
Dave
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The story so far the shape is getting there plenty of filling and sanding to do to achieve an acceptable finish then i'll be cutting the hatch and making all the side bulges keel rudder etc then the WTC to make
Dave
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Now you need a big tub of filler!
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I had a productive afternoon making a mould for vac forming the side blisters which hopefully will get done tomorrow
Dave
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Vacuum forming looks an interesting technique.
What material and thickness can you use it for?
Can you suggest any more information on the method?
David
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I got the vac form done today which seems to have been successfull we used 2mm sheet i had it done at work and think i'll be finding some more jobs to do on the machine.
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Looks good.
It has to be a useful technique for submarine superstructure - reasonable strength with low displacement.
But not feasible for home construction, I take it?
David
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Looks good.
It has to be a useful technique for submarine superstructure - reasonable strength with low displacement.
But not feasible for home construction, I take it?
David
Very usefull method for repeat pieces i dare say a simple vac-former can be made and used in the home oven then the vacuum cleaner attached i could use it for the superstructure but there's as much work involved making the mould than to make it from styrene sheet so i'll be doing the later method i think.
Dave
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Update so far i have been mostly sanding adding filler and resin and sanding i then gave the hull a spray of yellow primer then wet and dried it all off i have just glued the side tanks on not sure yet if to put a layer of glass tissue over them when the glue has set to make sure they are in place for good.
The plan is to cut the hull out from behind when the hatch has been made making them free flooding?draining also a possible location for battery packs.
It's not as perfect as it would have been if i had used tube for the hull but it has more of the home made appearance hopefully matt black may work wonders %)
Dave
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If you have flaws, just means a little more work with the putty and sandpaper. Don't spoil the boat for hapeth of tar.
Matt black will show every mark. I've only seen a couple of colour pictures of these craft, one was painted black, the other was a mid grey. I thought the latter was more in keeping with these craft, but it's your boat so paint it how you like.
If you glass the vac formed pods from the inside, they should be very strong.
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Last time I saw the one at Gosport it was painted in a sort of sea grey colour.
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The finish will be smooth no divets scratches etc it's just not dead flat i.e. if i lay straight edge along it doesn't follow exactly %) . i've sat pondering this afternoon building up courage to cut the hatch it's all marked up i just need to take the plunge excuse the pun.
Dave
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Last night i bit the bullet and cut the hatch with no problems so my nerves can now settle :-)
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Well done! When I built my Gato, the song "The First Cut is the Deepest" kept playing in my head. Look forward to your next posting, keep up the great work.
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The past couple of days have been spent on building up the keel it's hollow to allow for the rudder and plane linkages bit of build and design this i'm sure i'll fathom it with plenty of bits of brass.
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All is on hold now for 6months or so as the in laws have moved in so i'll be concentrating on making small bits linkages etc so i have it all ready to go when i can work on the main hull again.
dave
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the in laws have moved in
You have my sympathies.
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I'm looking at WTC materials i have a couple of choices the usual acrylic tube 3mm wall or aluminium with 1.6mm wall both 90mm O.D. are there any issues with reception using ali? the price is roughly the same give or take £1 or £2
Dave
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You will have to run the aerial externally to avoid it being shielded. The aluminium tube will be a bit heavier too, as it's about three times denser than water whereas PMMA is about 1.2-1.5 times depending on if it's been glass filled.
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Ok so no real problems then I might go for Ali a nice polished WTC could look good wander if I can find some turned Ali end caps
Dave
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You'll have to make them. Anodizing the tube would be the best way to keep it looking slick. If you polish it it'll probably tranish quickly unless you lacquer it- I found aluminium is very corrosive in water.
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It would be specialy if brass is present but I'll deffinatley look into it
Dave
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If I make the end caps when I create the groove for the o ring how much does the o ring need to depress to form a seal?
Dave
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Have you got Norberts book? Tells you in the back appendix the right dimensions for the sizes you are likely to use in a sub.
In case you haven't, assuming the bore is fairly decent you should aim for about 12-15% compression of the o-ring thickness e.g. a 4mm thick o-ring will be squished down about 0.5mm, which would give you 1mm of compression over the diameter, as the ring is compressed on both sides. Maximum compression for an o-ring is generally about 25% of the thickness, but you'll find it very difficult to push the seal home with that level, and you certainly shouldn't require more than 20% unless your bore is very poorly toleranced.
You also need to make the o-ring gap wider so the o-ring can squish into it (the rubber doesn't technically compress it extrudes). So for our 4mm o-ring we would want at least a 4.5mm gap assuming 0.5mm compression, as the ring will expand 0.5mm width wise as it forms an ellipse when squeezed.
You can use Nitrile or silicone o-rings. The latter are softer, but they can be more fragile than nitrile, and they're typically more expensive and a little harder to get hold of.
Does that make sense, or sound like double dutch?
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No that makes sense i must get hold of Norberts book
Cheers
Dave
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EXCELLENT explanation!. :-))
I must say I didn't know how much is going to compresss the O-rings as percentage.I guest make theproperr adjustments several times until I consider is OK,and then tested in the water.So THANK YOU. :-))
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I have received my acrylic tube today and now trying to figure how to fit everything in if i get a ballast bag of 65mm x 200mm and wrap it round inside the 90mm tube will it fill fully or does it need to be layed flat in the tube?
Dave
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Some leave the bag loose in the cylinder, the Thundertiger neptune is a good example, as is Norbert Bruggens Delta sub.
Some other modellers fit the bag inside a a small cylinder of its own, or in a sealed off section of the main wtc pipe. This helps constrain the bag, plus it can't chafe against other bits and bobs inside the cylinder.
Both systems seem to work well enough, your choice.
Andy
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Thanks i meant if i fold the bag will it still fill ok?.
Dave
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I see. Yes no problem at all.
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Ok this is the sixth attempt to post so hopefully the Internal error wont rear it's ugly head this time >>:-( . For the last week or so i have been busy with the hacksaw and file making bits to operate the rudder/dive plane it's all a little Heath Robbinson at the moment but it does seem to work the only thing that needs changing is the UJ from tube type to conventional as the tube allows to much flex which i thought might happen but it was worth a bash but apart from that by jove i think it works.
First off was setting the rudder tube and making the rudder/dive plane
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I hope these pictures explain the controls easier than words the rudder and plane move at the same time turning and diving/surfacing the bottom pivot needed to move in and out in both directions as the arc prevents solid linkages
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That looks good. Perhaps a stiffer piece of tube will remove or at least cut down on the flex. The only other way I can think of would be a crude type of CV joint or a cardan joint of some type.
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That's the next plan i can get one the right length but it'll be 2mm wider so hopefully shouldn't look to out of place
Dave
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Well the six months are up we have moved out from the in laws and got sorted in a place of our own so I have resurrected the build and started wet and dry sanding in earnest so not much to show for a bit while this goes on but more time spent now will fingers crossed save hassle later
Dave
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Ok I'm in the process of measuring up the end caps the disc that will hold the o ring works out to be around 77.94 the o rings I can get are either 75.79 or 78.97 which would be a better size to order?
Dave
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You always want a bit of 'snap' on o-rings so that you stretch them slightly to fit. Between 1-5% stretch of the o-ring diameter with about 2% being optimum, but don't sweat too much if you can't get it spot on. So the 75.79 o-rings are your best bet.
Odd sizes- are you buying imperial o-rings?
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Dave..........mmmmm 75.79 x 3.53 section is a standard 2-234 series o-ring
Technically it should fit a shaft of 76.2 or a bore of 82.55....however these are listed for 250 Bar hydraulic applications and your use is very low in pressure....1 to 1.5 Bar? so the o-rings will not be pressure energised
O-rings are forgiving and will stretch..........but it is the cavity sizing that should provide approx. 10% crush for these low pressure applications.....
Generous angled & smooth lead in chamfers + white petroleum jelly will also help in ensuring you don't shave or shear the o-ring during installation.....Derek
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Cheers chaps where can I buy just a few o rings as the place I was looking has a minimum 10 quid order I may aswell buy the end caps ready made if that's the case plus I don't need over 100 of the things!
Dave
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I have found these people to be very good:
http://simplybearings.co.uk/shop/index.html (http://simplybearings.co.uk/shop/index.html)
Good delivery etc. I am told that you can buy O rings cheaper but they are very convenient and reliable. (Driving down to the shops can cost you a bit anyway.)
David
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Thanks that's better i'll have a think it still works out about 7 quid but I do fancy making the end caps .
Dave
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I go on ebay for small quanitites of o-rings e.g. http://stores.ebay.co.uk/FitPrice/_i.html?_nkw=75mm+o-ring&submit=Search&_sid=799700493 (http://stores.ebay.co.uk/FitPrice/_i.html?_nkw=75mm+o-ring&submit=Search&_sid=799700493)
Bear in mind quite a few vendors quote external o-ring diameter, which isn't technically correct. This can catch you out, so check the spec carefully (ask me how I know!).
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Bbdave.
Have you tried your local bearing suppliers, they stock o rings too.
at mine you can order what you want and if not in they get them the next day.
Last time I wtd 4 of different size cost me "
£1.00.
regards sub.
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That's assuming you have a local bearing supplier. Used to have one, but they disappeared along with most of the small industry in London.
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Hi.
Seek and ye shall find.....
But comming from a good old northern engineering district certainly helps, we even built some of the x craft...and that company is still very much alive...unlike that german ship.
Up north we have a long engineering standing, still alive I am glad to say.
Regards to all.
Sub.
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High rents have pushed pretty much all industry out of the capital. Seek all you like, but it's going to be mail order I'm afraid.
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Thanks Davy1 I ordered the rings yesterday afternoon they arrived today :}
Dave
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I have just been testing my pump and a 500ml I.v. Bag it will fill to 500ml in 24 seconds I got just under 700ml in but will keep the max to 600 ml if needed the bag is still mailable at that.
It does need to lie flat in the WTC other wise it fills unevenly causing high pressure spots and risk of the bag bursting sending 500ml of water across the kitchen %) {:-{ .
Dave
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That's a good pumping speed for a peristaltic, more than a match for a geared pump in fact. Some put the bag in a small vented cylinder of it's own, which helps constrain the proportions, and prevents it moving and/or chafing against other items inside the boat.
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I have a geared pump a Kavan pump at least I think it's geared
Dave
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Oh right. Sorry thought you were using the TT neptune pump. Fair enough.
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Hi just testing the app. for resizing pictures hopefully this works should be a picture of my test tank :}
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As that seemed to work here's where i am at the moment I'm waiting for some bits for the wtc to be made and a couple of bits to be delivered. the hull is coming on not to much detail but what there is its big.
Dave
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Looking good. Been busy with the old filler and sand paper. Have you substituted the earlier aluminium rudder, rear hydroplane for brass?
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I changed to a brass rudder because it made soldering it all together alot easier the hydroplane is still Ali
Dave
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This sub looks great. I like the way it is shaping up!
I asked myself what sub is this, but duh, it is in the title of the build.
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I have my endcap bits now laser cut by a chum at work i'm not sure if i get enough seal though so my need to get the centre disc made slightly bigger if i install the cap and add a little water then blow into the other end as hard as u can i get a few drips out through the seal not sure what pressure i can blow at though.
A quick Google search shows about 2psi is this sufficient for a model sub? max depth would be 1.8m.
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You'll be a bit over 2 psi at 1.8m (0.1 bar or 1.47psi per metre).
Sounds like you've gone a bit too low on your o-ring compression. I see you've gone for radial seal compression, which is a bit more tricky, bearing in mind the differences in internal pipe tolerance, which tend to be fairly sloppy. I turn them to fit each end, if you have to go down the laser cutting route, it's better to measure your pipe carefully, and either go for a higher o-ring compression or use a larger o-ring cross section.
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I think I'll get a couple more discs done as it is free just a fraction bigger these ones give about 12% compression so 15% may prove better. the discs are 4mm so a 3.53 ring has space to squish into, a 4mm would be unable to compress in a 4mm groove, right?.
Dave
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Hi.
Just a thought....why dont you put an o ring on the shoulder and go for axial compression on that one as well as what you have.
A friend of mine went your route with radial
Compression and after a short time they actually cracked the acrylic tube.
As sub culture quiet rightly says getting it just right is tricky, as the tube dimensions leave a lot to be desired if you did you will have a double seal one internally and one external.
Just a thought for the small price of the o rings.
Regards sub.
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A friend of mine went your route with radial compression and after a short time they actually cracked the acrylic tube.
I agree that acrylic is finicky stuff compared with other plastics, and extruded acrylic tubing is full of stresses unless normalized (not really very practical for the hobbyist) but in all honesty I've never found that it's so fragile it can't take the compression of an o-ring. Perhaps something else may have been wrong with that tube, maybe it got dropped or came into contact with some chemicals that interacted with the plastic.
12% compression is too low for the inside bore of extruded tubing. I would aim for 15%, and go towards 20% if it's really Himalayan like.
Quite correct about the width of the groove, you must allow a good gap for the o-ring to extrude, too much is better than too little.
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Just another couple of points.
1. Why are you using Acrylic for the end caps? Any of the thermoplastic or thermosets for that matter would do.
2. Have you consulted one of the Tinternet suppliers of "O" rings technical tables for the correct groove dimensions?
You can use the wet finger "It looks right" technique but the manufacturers charts give guaranteed results.
Regards Ian.
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Acrylic laser cuts well, unlike most other thermoplastics. however i think the discussion was centred more around acrylic tubing, and that tends to get used because people like transparent cylinders, and also you can get it in a wide range of sizes. Polycarbonate is a better alternative, but costs a good deal more. PVC tubing is available transparent, but tends to be very expensive compared with the opaque plumbing stuff, and offers no other advantage.
Datasheets can be a bit misleading, as they tend to give slightly higher compression percentages than we need for models. 15-20% of the o-ring cross section is more than adequate
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I will get some discs cut these ones are 77.7mm i think I'll round up to 78mm and dress them down if needed the reason for using acrylic is it's free and i can get it cut free plus it does the job :-))
Dave
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Only mentioned it for the end caps, not the main body. Laser cutting? haven't seen an o-ring groove cut using that. Given that many need to be told what length their "Scale" model is, percentage compression is a whole new ball game. {-) and percentage of what dimension?At least manufacturers figures give a starting point and don't forget, in this application, if the fit is too tight, you can machine the groove a bit deeper to give a slacker seal, hard to put it back on if too slack.
In the case of Axial seal, as Subdriver has stated, limiting factor is how much you swing on the spanner.
Regards Ian
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Ok the % is the C.S. of the o ring which in my case is 3.53mm so %20=.706mm the I.D. of the tube is 84mm minus 2x3.53 plus 2x.706mm which= 78.352 for the middle disc i think {:-{
Dave
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You got it, Dave. 78.4mm will be sufficient. Bear in mind that tubing varies in diameter even along the length.
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Bingo looks like a spot on fit this time will the friction be enough to hold them in or is it best to hold them in mechanicaly?
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As you are pressurizing the internal cylinder you will need some means of retain the caps to prevent them popping off.
Various ways of doing that, a good way is to take a leaf out of Robbe's book and use the tech rack to keep things buttoned up.
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I take it you can remove/replace the cap easily? With firm hand pressure.
(The photo makes it look a little tight - thats all.)
What ballast system are you planning to use? (To help assess any overpressure)
David
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I may wet and dry them a little but i'd rather a good seal but any reduction will be tiny but I'll make sure they are easy enough to remove specialy the battery end.
Dave
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If you think the seal is a little tight, you can file gently around the circumference of the inner disc with a small square file.
You do have quite a bit of tolerance with these seals, especially as you're using a seal on the fatter side.