Acrylic fabrication questions? I can help!

[dahenley]

some times, gluing a piece like you say in the corner will actually stress a joint....

also, what size tank it is? that can make a difference on how you fix it...

(when working with metal... we drill a hole at the end of the crack, to prevent them from spreading and also distributes the load 360 deg.)
im not sure if that practice would be liked in the tank world... but its what we do to metal....

 

[Floyd R Turbo]

actually I've seen that suggested several times. You need to stop the crack by drilling at the ends of it, then gussets. But still need better pics. that's one nasty looking crack and if it's through the bottom panel, you would have a hard time shoring it up without putting a new bottom panel over the old one or something like that.

Still it might be salvageable, but I would have left it and said *** give me my money back you silly tank dropper

 

[mmljarc]

At this point, I wish I had walked away. I had driven about 100 miles for it and was too jacked up about getting it, wasn't thinking clearly.

It is a 225 gallon tank - 72"x24"(width)x30"(height).

The crack does NOT go all the way through. It does not show up in the interior of the tank or the bottom of the tank it all. I can just catch a fingernail in the crack on the side of the tank near the bottom and the rear. I will be turning the tank onto it's face tonight and get some better, close up pictures.

thanks for the help -

 

[Floyd R Turbo]

mmljarc, I can see from the pics you posted that the crack does go through the bottom panel. it's in the corner, not in the open/inside the tank, but through the bottom panel to the underside. This creates a weak area in the corner. Also it looks like the crack is on the side panel and goes through to where it joins the back pane. Correct me if I'm wrong but it looks like the back panel is "inside" the side panel, that is, the back panel is bonded on all 4 edges (to the top/bottom and sides) versus the end panel being bonded on all 4 edges (to the top/bottom/sides)? nothing wrong with that, just not your usual construction. Most tanks are built with the front and back panel all the way across the front so that you don't see the edge of the side panel. Or are the front corners curved/bent maybe?

Anyways, the crack is definitely not limited to the side panel. But it appears that the crack terminates on the edge of the side panel right near the seam with the back (black) panel. So at least it didn't continue through the black panel, but if it did, it might not be easy to see and that could cause you a problem.

It's hard to catch this with a cheapo digital camera (versus an SLR) because of focus and flash so see what you can do to take focused pics of the crack from as many angles as possible.

 

[dahenley]

what is the thickness of the tank? just curious.

 

[mmljarc]

Thickness is 1/2". I was told it was a teneco...

 

[mmljarc]

My plan would be to use Weld-On 3 for the crack itself, then use 3 square rods of 6 inches each (1/2" acrylic) on the interior of the tank bracing the corner. I am building a stand for this also, and will butt this corner up as tightly as I can into the corner to reduce any outward flexing at this corner (realize that won't help much, but figure it may help a little, and sure won't hurt).

Think this would be sufficient?

 

[mmljarc]

Oh, and the front corners are curved on this tank - no joints there. I have checked all the other joints on the tank throughout - they look great - no bubbles or whiting out at all.

 

[Floyd R Turbo]

I don't know man. I do know that if you squeeze WO3 or 4 into the crack, it won't go all the way into it because there is not enough separation for capillary action to take it all the way through. It will also likely weaken the area more. Also, you can see in the 1st pic that the crack does extend into the black back panel.

I am going to defer to James on this one for repairability...

 

[Floyd R Turbo]

Response from James

...there is no way of effectively stopping the crack from growing into any of the 3 panels. It may work out fine for 10 years, but then again maybe not - no way of being absolutely certain. If it were me, I'd cut out the entire section and glue a block in using 40/42. It's actually in a good place as the 3 intersecting panels make this area extremely rigid, but as it is - there is no way of knowing what the future hold for it.

 

[dattack]

I have tried to use numerous different glue, even james concoction but I always get microbubbles inside the edge after glueing. Even when I put in the glue, I see it as a perfect seam but after letting it sit for 30 minutes, microbubbles start to form inside.

I am guessing it must be something wrong with my technique. I use shims and pins but I am not sure what else I need to do to get at least a near perfect seam.

 

[Floyd R Turbo]

What is your edge prep technique? Do you clean the joint with denatured alcohol before setting? Do you blow it off with air? How long is your soak time before pulling the pins? What is your solvent mixture?

 

[dattack]

What is your edge prep technique? Do you clean the joint with denatured alcohol before setting? Do you blow it off with air? How long is your soak time before pulling the pins? What is your solvent mixture?

I make sure all the edges are cleaned. Even with or without denatured alcohol i get the same problem. I am guessing that the shims when pushed in, changes the angle of the weld slightly. I use 99.99% methylene chloride, ethylene chloride and acetic acid. 80%, 15%, 5% .

Floyd, do you use the mdf with camper shell foam like James? I tried that in the past but it was hard to push the shim on the foam.

 

[Floyd R Turbo]

yes and I use it on both sides of a 4' wide strip of 3/4" MDF. For shims I use a pack of cedar shingles from Menards adn sift through them to find the super-thin ones or sand them down. If you use a flat enough table, you should be able to shim the joint only at the point where a pin won't self-hold after inserted. On a 75g sump build I did, I only needed 6 shims on a 9' seams. My test on those is that after i get them all snug, if I can blow the joint with canned air and not move any pins, I'm good.

I don't push the shims in after pulling the pins. IMO this is not necessary. Think about it. If you get the joint all lined up and pins in and they're all nice and snug, then you pull them and push in the shims more to "snug them up" then you have no frame of reference to tell which shims are not snug enough, which would leave an area or weaker pressure that you would not be able to 'see'. Plus shims are angled to you would tend to push up on the bottom piece of acrylic more in one area. So don't touch the shims after you're done pinning, just pull the pins and you're good.

Then I run the solvent, scoop bubbles if there are any, pull the pins, check for drift, and throw some weight on it. My fav weight is 12 packs of pop LOL.

I don't use EDC because of cost. It allows for longer soak time (or working time for long joints) without causing crazing IIRC.

Are your edges prepped with a router? Do you make sure all the 'pits' are trimmed off?

I'm thinking if you re-snug the shims significantly, this might be what's going on.

 

[dattack]

yes my edges are prep with a router that is an extension to my saw table. I think my problem must be not putting padding also. going to home depot today and get some mdf.

my other question is do I release the clamp after or pulling the pins?

 

[Floyd R Turbo]

Depends on when you applied the clamps.

What I do it set my piece in place, put the 90 degree jig on and clamp it to the vertical piece so that the joint is it the "final" position, then insert pins, solvent, pull pins. What happens is that the pins will lift the vertical piece and the jig, so when I pull the pins I don't need to release the clamps to let the piece fall into the final position. I will occasionally loosen the clamps momentarily while putting a little pressure on the vertical piece but I can't say that I have noticed that this makes any difference, but it's not a bad idea. I don't notice any additional squeeze out from doing this. With the EDC though you might get a little more bite and mash out the dissolved material a little more so it can't hurt.

 

[solRNY]

hi, i am building a overflow out of 1/2" black acrylic and am needing advice regarding which acrylic surface, rather it be sanded or flame polished, for best silicon adhesion glass?

thanks!

 

[kgross]

Sanded rough. Silicone does not stick to acrylic very well so the rougher the surface the better the hold.

 

[Floyd R Turbo]

Silicone will not form a structural bond with acrylic. Period.

 

[rrg1974]

Hello guys, I'm finally ready to start my tank, and I have a question. What are the first parts that I should connect, bottom and front, than sides??? If yes, how do I do with the pins on the vertical? Or should I start with all the sides, than at the end connect the bottom?? Thanks a lot for the help!