Acrylic Tank Design Question

  • We are currently upgrading MFK. thanks! -neo
Phixer said:
Yeah, thats the whole reason I decided to go with 1.5" and limit the height to 36". I dont care much for the bowing either. Will probably either sell the 1.25" panels if I do decide to go with 1.5 for the top. Im still thinking about using thicker for the top as you mentioned but Polycast only comes in 120 X 72 at that length so Id be left with an extra 120 X 36 after cutting it down, not to mention the material for cut outs.
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I"m definitely no expert, but from what I've seen, I think 1.25" for the top is plenty thick.

Are you sure you only want the access holes to be 12" wide? I like the 40" long part, but 12" wide seems pretty narrow...kinda limits your options in regards to aquascaping with large driftwood, large boulders/rock etc.
 
Phixer said:
Feeling a lot better about using the #40 now. Yeah I thought about how hard it's going to be to move, my basement may end up looking like a shipyard with all lifting and pushing methods Ive devised. The latest is a rotisserie jig made by modifying two engine stands with cross member and sections of removable steel square tubing to flip it when necessary. Looks kind of like a chassis jig with a cage in the middle.

Today I heard back from a tank MFG that dosent anneal either. Am finding that most do not. He said that if you can prevent the acrylic from heating up to much during machining then you dont need to anneal it. Annealing is mostly done to prevent crazing.

He even goes to the extent of wiping the edges with alcohol prior to bonding them with the 2 part cement (which I though alcohol & acrylic was a big no no). He does this because if the panel was over heated during machining process it will instantly show up as crazing after the alcohol hits it and then can shave off the crazing with a router. A pretty good preliminary test actually. Im going to test this out on some scrap material.

The moral of the story he wanted to impart was to keep the acrylic cool when machined.
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I've always felt there was some sort of trade secret when it comes to bonding acrylic. When you go to the huge public aquarium displays and look at where they have joined these massive sheets of acrylic the seam is almost invisible/perfect. It's the same with cylindrical tanks...the seam is always almost invisible. It looks nothing like the seams on standard mass produced acrylic tanks. I think it just takes quite a bit more time to heat the seem and do it right and that's why you see alot of acrylic tanks with sloppy seams. I'm not sure how they would anneal these enormous panels...do they really have ovens that can accommodate a 30'+ panel?

In any case, I have also heard that wiping down with alcohol is always a good idea.
 
Doubht anyone has an oven for a 30' sheet lol...my thoughts on crystal vs. Shotty seams is all in what glue was used. Its almost impossible to make a seam look bad with #40 due to the consistency and the way its applied generously so to speak. With thinner solvent glues, applicators can be tricky. Bubbles and dry spots are eaisly "trapped" in your seams and are impossible to remove unless you start over with new material. The way to make seams dissapear like the pros is extensive sanding and polishing. You can even bond two sheets side by side with 40 and make the seam almost invisible. For example my local mall has a 16' long tank with two 8' sheets clearly fused together for the front window. If you look at it right you can see the "wave" where the two sheets meet. Finishing aspects to acrylic are just as if not more important than bonding it. Pretty amazing feat to join 2 sheets side by side imo. If youve ever seen a racetrack (rounded end tank) this is using the same concept of adheision for sheets side by side.

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Will probably go with wider access openings in the top. Was thinking of small access holes only if I do end up using the 1.25" stuff for the top since it's thinner I wanted to keep the access holes smaller to keep it rigid under pressure and prevent to much bowing.

Ironic that you mentioned how the seams are joined for the large public aquariums. Im learning a lot of trade secrets by piecing together bits of information over the years on how these tanks are made. Today I went by the Dubai mall and looked at that one. There is also a tunnel underneath it and they offer small glass bottom boat rides. Mostly stingrays a few groupers and a lot of tuna in there. The corals are all fake. Back to the point...sorry.

The panels for that tank are humoungous and are on several levels. I believe they are joined together using the 2 part stuff and a v groove, then clamped together and polished smooth, no annealing. The second floor panels appeared to be anywhere from 6-8" thick not a scratch on any of them either with the ammount of traffic and kids hanging all over them. The second floor panels measured about 12ft X 12ft. The ones on the main floor are much, much larger and the seams were nearly invisible I could only see them from looking down and at an angle. At one point in time (video on you tube) this tank had a rupture on one of those seams. The tank held together but you can hear the commotion of the crowd as it was pouring water out. There is no crazing on any of these seams.

Sorry for the long post, I did also learn that as long as the material and bit is kept cool when machining then the panels are less likely to craze therby eliminating the need for annealing. Also if they do craze when wiped by alcohol before bonding they will require reshaving the surface to eliminate the crazing, normally about .050 gets taken off.

Your right, it really is an art making those seams look invisible. I just cant see someone solvent cementing 8" thick acrylic, or annealing panels 2 stories high.
 
What do you think about using both solvent and #40?

I know the 2 part stuff is strong but what concerns me is getting it to bite into the acrylic. An example was given with steel, it would be a strong joint but you would be able to pull it apart easily. If I scuff sand it then I can basically forget solvent.

Thinking of solvent cementing the joint and then casting an inside and outside fillet like the pics earlier using #40 or #42. Really no way for me to prepare the edges perfectly on panels this big and heavy for solvent cementing which is the whole reason to use #40 in the first place. Id probably get a crappy joint but it may still be the best of both methods.

Any ideas or should I stick with one or the other. At this point Im leaning towards the 2 part stuff with an edge bevel and a small gap for the cement to flow under.
 
Like this:

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Now were talkin :) all depends on ur applicator skills for the solvent. Maybe a special applicator aswell. The small ones may not hold enough for a 8ft. Seam at 1.50". I believe with that much 40 on the inside it should b plenty strong with solvent on the bottom like that.

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Thats what I was thinking. Since there is so much area to solvent cement there's a good chance of getting at least a few bubbles no matter how hard I try not to. Too many variables with material this size. And since you only get one shot with solvent, combining the benefits of both to keep from getting a bad joint makes some sense. #40 would structurally beef it up a little and may compensate for minor solvent irregularites. Best of both IMO.

Maybe solvent bonding using pins method with .008 stainless suture wire. A bunch of full needle applicators standing by ready to go and someone to yank pins shortly thereafter. Will be using MC Bond solvent instead of #4.

Here's the thing.

1). If water pressure is pushing outwards, wouldnt I want an outside gusset/fillet as well to act as a wedge... like a door stop? Normally these get trimmed off with a router upon finishing but Im thinking it would strengthen the joint more if I left the extra material and just covered the overhang with notched wood trim. Emphasis is more on strength then aesthetics.

2). If I outside bevel the bottom edge (maybe 15 degrees) to benefit the #40 method then I forfit any advantage of a solvent bond as it wont have anything for the solvent to grab on to. Would definitely have to keep the bottom flat if using hybrid method.

Will need to do some practice samples.
 
Good ol MS Paint for doodling.
 
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