Acrylic fabrication questions? I can help!

[Floyd R Turbo]

Alarm bells sounding

Alarm bells sounding

Tell me if I have serious cause for alarm. Here is the situation. I took over maintenance of a tank back in December '09, it's a 125 acrylic tank, external dimensions are 66 L x 18 W x 24 H Ten e cor, all 3/8" except for the bottom which is 1/4", overflow on end.

After reading this thread and reading all the stories of problems with tanks, I started taking a closer look at this tank.

Here's it is:

The tank is supported by 2 steel square tubes that are probably not big enough, I think they're 1.5" or 2" square

This picture is slightly deceiving, because the back tube (right) is flush against the back of the cabinet, but the tank sits about 2" off the wall. The cabinet behind the tank is open to the drywall, so the back edge of the tank may or may not actually be directly over the tube. I'm guessing it's not.

So these pics are what led me to freak out today.

This first one is a close-up of the bottom of the tank, near the middle. The bottom is 1/4" material, so that gap is a little less than 1/8".

Here is a close-up of the bottom front joint. What you see here is not an optical illusion, this appears to be a seam failure in progress.

Here's the worst section, right about dead-center in the front.

I looked very closely at this from several angles. This crack appears to be vertical through the bottom panel, and parallel to the plane of the inside of the front panel.

When I shined my flashlight into the gap, it looked like the bottom of the tank was bowing and was in contact with the wood going further back. The engineer in my tells me that since the bottom of the tank is not properly supported, neither by the steel tubing (which appears to be deflecting) or the board (which is likely just laminated particle board or MDF), that the bowing of the bottom of the tank has caused a stress fracture at the joint, and the front of the tank is trying to pull away from the bottom.

This tank has been in this location for going on 3 years. What ticks me off is that neither the cabinet maker nor the LFS that moved the tank to this location (it was in another location for a couple of years) bothered to properly support the tank. It is also not known if the tank was completely empty during the move. They scraped the tank against the wall when they moved it and tore up some expensive wallpaper (which led to the severing of the relationship), which indicates to me that they probably left the rock in it and moved it quickly, because there's just no excuse for ruining a wall with an empty tank.

What really puzzles me is the front square beam. It appears that is it only in contact with the tank at the ends on the front, or at best, 1-2" at each end. Would this cause that much deflection? However, the 'why' is not nearly as important at this point as the 'what next'.

My gut tells me to empty the tank right now. I take a lot of pictures of this tank, and as I am pouring through the pictures, I can definitely see this fracturing in older pictures, but I haven't ever taken close-up photos of it, so I really don't have a true frame of reference to tell if it's getting worse or not. So I can't tell with any degree of certainty if it's getting worse, or if it has stopped progressing.

I can tell you that since taking over the tank, I've added plenty of live rock, probably between 50 and 100 pounds (offset by water weight, that probably doesn't factor in much). Most of the LR is stacked along the back of the tank as you can tell in the first picture, so I don't think this has added much. I did recently change the plumbing to allow for higher flow, and this resulted in an increase in the water level of the DT of about 1/2" or so.

So tell me honestly how much I should freak out.

Also, is this a repairable thing? Could I empty and clean the tank, run some #4 or DIY solvent weld into the crack, then add a gusset with #4/DIY or run a bead of #40 along the edge?

Or should I just ditch the tank and build one out of 1/2" like it should have been in the first place?

 

[CJBROWN]

Tell me if I have serious cause for alarm. >snip
So tell me honestly how much I should freak out.

Also, is this a repairable thing? Could I empty and clean the tank, run some #4 or DIY solvent weld into the crack, then add a gusset with #4/DIY or run a bead of #40 along the edge?

Or should I just ditch the tank and build one out of 1/2" like it should have been in the first place?

I would be freaking out. In fact, I'm freaking out now and it's not even my tank!!! When it lets go it's going to be a whoosh and then a drip, drip, drip. If it's in your house plan for replacement flooring, possible drywall repair. Might be time to call your insurance agent and ask some 'what-if' questions about coverage.

A proper stand with 3/4" plywood top, properly supported, will take care of the base. The DIY stand thread here on RC is a good one, makes a nice sturdy fully supporting structure for aquariums. Materials are cheap to buy, easy to get at lowes or depot, and easy to build.

Since it's holding water it is repairable. Apply/weld a triangle gusset to the inside. Ideally it would be cut from 3/4" material or even better, 1". The 1/4" bottom plate is rather light for that duty, but properly supported it should be fine. Of course to do this it has to be emptied out, cleaned out, sanded down, and material sourced. If you're a handy DIY'er it's do-able. Replacement for a 125 is fairly expensive, so might be worth saving it. I would do this today. Get a couple of barrels from depot and put your critters in them. Drain it out. Then you'll be able to see how extensive the damage is to the bottom panel, any evidence of further cracking and crazing that may be hidden now.

Perhaps James will have other suggestions besides just scrapping it.

 

[Floyd R Turbo]

I should have clarified, this tank is in a dentist's office, so the biggest concern here is what if I kid start banging on the tank and it gives way. That would be extremely bad.

I'm with you on the freaking out factor Chris. I tried to let the owner know the situation as calmly as possible. He's sunk thousands into this tank in the last year and a half to bring it back from the brink, here's what it looked like when I first saw it:

Compare that to how it looks now in the first pic above. This is very much my personal work of art and I would hate for something catastrophic to happen.

Lucky for me, I have a brand new empty 120 gallon tank sitting at home that I've been itching to make a stand for. I also have 2 x 45 gallon BRUTE cans and 20+ 5g Home Depot buckets. And a minivan.

James, any suggestions other than what Chris said?

 

[CJBROWN]

I couldn't tell if the dentist owner is a client or a friend, but I would imagine he would more than a little ****ed off if it blows. Expect an angry phone call at any moment.

That he has sunk a bunch of $$ in it already is irrelavent. If you have a 120 ready that you can setup for him DO IT. TODAY!!!!

 

[Floyd R Turbo]

Oh he knows who to be ticked off at if it does, this is directly attributable to the cabinetmaker and the LFS who moved the tank. Both of them should have known better.

 

[Acrylics]

Unless the tank is in imminent danger of failure, all you can do is talk to your client about it. tell him your thoughts on the matter and it really is up to him/her.

From the looks of the material at the bottom joint, it is in the process of failing - how long it has is anybody's guess. If it were me, the tank goes to recycling, I wouldn't try to repair it, or anything else. Material that has stressed to the point of failure is simply that - material that has stressed to failure. You can attempt to reinforce it all you wish, but IMO it won't make the tank viable, esp if you take the aesthetics in to consideration. And the addition of any solvent/40 could easily cause the material to fail immediately.

James

 

[Floyd R Turbo]

That's kind of what I was thinking. A 1" gusset would look pretty ugly.

As for the repair option, are you saying that the tank would fail after the repair was performed, or are you saying that the joint would simply break wide open once solvent was applied to the joint?

If a gusset was added, I would think that the joint would hold, are you saying that it might actually weaken the joint?

I was thinking that best case, this tank would make a good QT tank for me personally, so I might consider compensating him for it as it would make good practice also.

Thoughts?

 

[Acrylics]

are there multiple types of cell cast acrylic and is one better than the other? I am having to build my mantis tank after all and I found this cell cast acrylic locally at a plastics company. can someone (james) please take a look and let me know that it's ok? It doesnt list any of the brand names that are mentioned. Thanks

http://www.lairdplastics.com/content/view/886/71/

It doesn't list any brands because PMMA *is* acrylic. Laird sells Plexi-Glas G and Polycast and it's sister company (Port Plastics) sells Acrylite GP if you wanted that.

As for your question, yes there are multiple grades of cell cast and of varying quality

James

 

[gods child]

Floyd R turbo that is a good question I realy dont know, but next time iI see him I will ask .An I will let you know

 

[CJBROWN]

Unless the tank is in imminent danger of failure, all you can do is talk to your client about it. tell him your thoughts on the matter and it really is up to him/her.

From the looks of the material at the bottom joint, it is in the process of failing - how long it has is anybody's guess. If it were me, the tank goes to recycling, I wouldn't try to repair it, or anything else. Material that has stressed to the point of failure is simply that - material that has stressed to failure. You can attempt to reinforce it all you wish, but IMO it won't make the tank viable, esp if you take the aesthetics in to consideration. And the addition of any solvent/40 could easily cause the material to fail immediately.

James

FRT:
Based on Jame's reply I wanted to clarify that I made several assumptions in my assessment and may or may not have mentioned them all.
1. That the seam was definitely opening up indicating imminent failure.
2. That the seam failure was confined to just the seam. I have not heard good success with reapplying weld solvent to an old joint.
3. That if the failure was confined to just the seam then a triangle reinforcment would re-join the bottom and front panel.
4. That the stand trim would be made high enough to hide said repair.

Let us know what you decide and how it turns out.

 

[Floyd R Turbo]

Building my own stand for my 120 and pulling the tank ASAP. After I clean it up, I'll have a better idea of the damage.

 

[Acrylics]

That's kind of what I was thinking. A 1" gusset would look pretty ugly.

As for the repair option, are you saying that the tank would fail after the repair was performed, or are you saying that the joint would simply break wide open once solvent was applied to the joint?

neither, I'm say it *could* Solvents, 40, etc., all work by chemically bonding or breaking down the acrylic, as such - chemical stressors. Add a chemical stressor to material that is already stressed to the point of failure...could easily lead to real bad news. Exact same idea as to why you don't glue polished edges or put alcohol or Windex on a flame polished joint.

If a gusset was added, I would think that the joint would hold, are you saying that it might actually weaken the joint?

yup, very well could. But the surrounding material is obviously stressed, adding the chemical stressor to that material and the joint itself may become rather irrelevant.

If it were *just* the seam going, as in a bad glue joint, a gusset would make more sense to me. But it's not just the seam, at least from the appearance of the material in the pic. The material itself is stressed to the point of degradation. If this is, indeed, the case, the the material is now bad and IMO not worth anything, esp for a pressure vessel.

Go ahead and glue in gussets if you wish. May work for some time, may fail immediately. In either case *for me* the material is unreliable, therefore the tank is unreliable.

James

 

[Floyd R Turbo]

Gotcha, I knew that re-bonding would cause stress, but I didn't think about it not being the actual joint failing, which makes it a completely different issue. That's a bummer. I was hoping to be able to use it as a frag tank or something.

Do you suppose I could cut the bottom off and put a new one on? Eliminating the stresses material being the idea. Of course, that would present a whole new set of concerns, what with trying to get the cut-off bottom joint perfectly even all the way around. So just asking if that is do-able 'in theory'.

And just so you can see this clearly, yes the fracture is through the bottom panel so it is adjacent to the joint, but perpendicular to it. Here's some pics from today

And hi-res pics

Yesterday

Same 2 from today

I printed the last pic in color and then took an engineering scale to it. The fracture is just slightly more than 3/4 of the way though the bottom. That means 1/16" left of the joint. Ugh.

 

[Acrylics]

Gotcha, I knew that re-bonding would cause stress, but I didn't think about it not being the actual joint failing, which makes it a completely different issue. That's a bummer. I was hoping to be able to use it as a frag tank or something.

And you may be able to, just that *for me* not worth it

Do you suppose I could cut the bottom off and put a new one on? Eliminating the stresses material being the idea. Of course, that would present a whole new set of concerns, what with trying to get the cut-off bottom joint perfectly even all the way around. So just asking if that is do-able 'in theory'.

Doable in theory? yup

James

 

[Floyd R Turbo]

Hey James, there are several posts way back that reference pictures of tape blocks, and pictures in your album. But I think in the server transition back them they got lost or something. Do you have pictures of those that you can post again?

Thanks

 

[kaserpick]

Hey James, I have a 16" acrylic cube with two holes already drilled in the bottom. Here's a pic:

After running it this way with a pump and reactor, I want to change the setup. Here are things I want to change:

1. Glue acrylic sheet over the two holes
2. Drill a 1/2" x 4" cut-out at the top for an overflow
3. Glue a black external overflow on the back

Here's a pic:

Here are my questions:

1. Can I glue a sheet over the holes, and how thick of an acrylic does it need to be?
2. If I cut the groove out on the top, would it reduce the integrity to the point of risking a fracture? The tank is made out of 1/2" Acrylite GP. It holds under 15g.
3. Is it ok to add an external overflow like this, and how thick of a material should I use?

Thanks for any help!

 

[kaserpick]

I should note that the holes on the bottom are not that close to the edge of the tank. It's a good 1.5" away.

 

[Floyd R Turbo]

I think you could silicon a piece of acrylic over the holes, that way it's removeable. James has suggested this before. The silicone will seal OK and water pressure will keep it together. You just don't want to make a structural joint between acrylic and glass or acrylic an acrylic with silicone.

As for the overflow, I don't think a 1/2" cutout will be enough. I don't know what the flow rate would work out to be for a 4" wide 1/2" cross-section of water, but it's not that much and that would also mean that your tank would be completely full.

But, that's just my take...

 

[kaserpick]

I think you could silicon a piece of acrylic over the holes, that way it's removeable. James has suggested this before. The silicone will seal OK and water pressure will keep it together. You just don't want to make a structural joint between acrylic and glass or acrylic an acrylic with silicone.

As for the overflow, I don't think a 1/2" cutout will be enough. I don't know what the flow rate would work out to be for a 4" wide 1/2" cross-section of water, but it's not that much and that would also mean that your tank would be completely full.

But, that's just my take...

Thanks for the advice on the silicone Floyd! That sounds like a good idea.

Yeah, I was wondering about how deep I should make the groove. Do You think I should double it to 1" or go with 3/4". I want the water to be close to 1/2" from the top. I think it looks nice since the acrylic is 1/2". Thanks again!

 

[Floyd R Turbo]

I think it depends on your desired flow rate. If you want 1/2" from top, and a 4" wide slot, then you have to figure out what the flow rate for a weir 4" wide will be for varying depths. I'm an electrical engineer, not a mechanical engineer so I suck at fluid dynamics.