Acrylic fabrication questions? I can help!

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I have an acrylic question--

I just purchased a used 135 gallon glass (3/8" thickness I think) tank (72x18x24)-- one of the previous owners of this tank cut out both of the cross braces at the top of the tank (I'm pretty sure because they blocked his 2 MH lights)-- I did see the tank full of water with the braces cut-- I did not measure it for bowing in the middle section.

The tank is currently empty but I want to get it up sometime in the next week.

My question is on adding 3 or 4 cross braces made of 1/4" acrylic--
I was thinking of cutting out (2) 1 1/2" wide strips and running these on the outside of the tank rim (flush with the top) and then running 1 1/2" wide pieces across the top of the tank and using "weldon" to bond them to the pieces on the outside of the tank rim and therefore hold the rim from pulling out if the glass tries to bow some-- I have a table saw to cut the acrylic.

Does anyone think this will help at all and will this small of a "joint" be strong enough to help me at all??

I would kind of like to use acrylic since it won't block the light (other then a little bit from salt creep)-- I plan on staggering these so as not to be near my MH lights when i add them-- would be under my VHO tubes though.

On a related note-- should I run a single piece along the front an back or use several short pieces (each short piece bonded to a cross brace).

Alternately-- would using weldon "bond" the acryic to my existing tank rim (instead of running the pieces along the front an back) looks to just be black plastic??-- this would be much easier to do if the acrylic will bond to it.

Any help/opinions would be appreciated...(I've done very little acrylic work so far)

Thanks alot...

ps

an alternative to this would be using pieces of glass as cross braces and some silicone caulk to bond this to the plastic rim of my tank.

I've even considered building a steel frame to fit over the top of the tank (welded angle iron) although this would probably be my last resort. I just don't want to come home to a busted seam.

If anyone has any alternate suggestions-- I'm all ears.....
 
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Spuds Your thinking makes sense to me if I am following you correctly. Basically you are building a new top frame to slip over the existing plastic frame. I would use a 1"-1 1/2" verticle piece that runs horiziontal along the front and back and extends past the sides by whatever thickness acrylic you are using. I would use a 1"-1 1/2" verticle piece that runs horiziontal along the sides between the front and back pieces making a band that wraps around the tank frame. Then do the same thing only in the horizontal plane so that the top front and back overlap the side pieces so the joints are staggered. Then do the same thing in the horizontal plane so that the side pieces fit between the front and back and overhang the side band piece. Then glue your cross braces to the horizontal band where ever you want them. Just make sure they extend all the way across the top front to back to mazimize the amount off surface to be bonded. Hope this make sense. John
 
Definitely give IPS a call, and see what they have to say. Ask again about the "percent bonded" for their calculations to double check that if you get a chance.

I like to cure at least a weak with good air flow for tanks, and prefer several weeks. The thicker the acrylic, the longer you should let it cure.

I suspect that you would be fine with a month, but don't have experience with that thick of acrylic.

Zeph
 
Bowman said:
Spuds Your thinking makes sense to me if I am following you correctly. Basically you are building a new top frame to slip over the existing plastic frame. I would use a 1"-1 1/2" verticle piece that runs horiziontal along the front and back and extends past the sides by whatever thickness acrylic you are using. I would use a 1"-1 1/2" verticle piece that runs horiziontal along the sides between the front and back pieces making a band that wraps around the tank frame. Then do the same thing only in the horizontal plane so that the top front and back overlap the side pieces so the joints are staggered. Then do the same thing in the horizontal plane so that the side pieces fit between the front and back and overhang the side band piece. Then glue your cross braces to the horizontal band where ever you want them. Just make sure they extend all the way across the top front to back to mazimize the amount off surface to be bonded. Hope this make sense. John
Click to expand...

I had to read it a few times.. :)

Thanks for the advice/input.

I think I get it-- you seem to be concerned about the strength of just bonding the vertical (front & back pieces) and horizontal (braces) at 1 point (a corner)-- so having me build a frame to fit over the entire thing (at right angles) and make it so the braces have a larger area to bond to since the horizontal braces would be parallel to the top of the rim piece bonded to the outer section distributing the force more.

Do you really think I need to wrap the entire tank though??? I can maybe understand doing it this way if I were removing the existing rim...

Also, I know this would make it stronger (like a big sump rim)-- I'm just trying to avoid buying an 8 foot long sheet of acrylic....

What about making 2 right angle pieces to fit over maybe the middle 1/3 or middle 1/2 of the tank on the front and back and just have cross pieces bonded to these overlapping (like how you described)-- do you think this just won't be rigid enough??? angle would try to twist if force put on it.

This is kind of how I was going to frame it if I used angle iron (steel) like I described in my original post as a last resort....

I hope I made this clear...lemme make a drawing of it in case I'm not being clear.
//edit//
Top and side view (middle section of tank)-- excuse the quality-- was trying to get it up fast.
spuds725-BRACE.JPG
 
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I was concerned for a couple reasons one of which is the depth of the tank 24" top to bottom. The other is the fact that you are using flat sheet stock cut into strips to fabricate your top tank frame. When those plastic framesare made, they are made in one piece and you have structural integrity throughout the whole frame. When you use flat stock to make dimensional shapes you are relying on the glue joint for structural reliablity so the more surface area for the bonding the lesser chance of glue joint joint failure. Your going to make a significant investment in your tank, due you really want to cheap out for the few bucks it would cost. Also if you talk to your supplier they may have some shorts or scrap you could get for reduced price or even free and only have to buy your 72" pieces. HTH John
 
Why don't you just use nylon screws to join the bracing piece with the 90 deg. angle piece instead of weldon? It'll drill easily, the nylon screws won't rust and I think you might get a better result. JMO

Russ
 
Nylon screws give nowhere near the strength and flex tolerance that actually gluing the pieces together would. JMO as well. Also, nylon tends to get pretty brittle when in contact with saltwater for long periods of time, IME. Knurled head screws on skimmers are one thing, but underwater, or where they will be exposed to salt spray, screw heads break off if they are old....
 
Bowman said:
I was concerned for a couple reasons one of which is the depth of the tank 24" top to bottom. The other is the fact that you are using flat sheet stock cut into strips to fabricate your top tank frame. When those plastic framesare made, they are made in one piece and you have structural integrity throughout the whole frame. When you use flat stock to make dimensional shapes you are relying on the glue joint for structural reliablity so the more surface area for the bonding the lesser chance of glue joint joint failure. Your going to make a significant investment in your tank, due you really want to cheap out for the few bucks it would cost. Also if you talk to your supplier they may have some shorts or scrap you could get for reduced price or even free and only have to buy your 72" pieces. HTH John
Click to expand...

But I'm cheap :lol:

Of course you make perfect sense-- my question is more of the strength of the acrylic and joints as I'd never worked with building any joints and if doing it the way I described would work or not.

I'm not even sure if its needed or not as I don't know if the tank "bows" when filled-- If it does bow and the "joints" fail I think I would be in worse shape as the tank seams would be shockloaded by the glass bowing quickly then slowly like when it is filled--

I was and am exploring alternatives but your plan sounds like the most sound and safest.

If I go this way, I will likely put 3 cross braces across the middle section and between where my MH lights would be and on each out side of where the MH lights would be (5 total) in addition to the ones at the end-- does that sound like it will be strong enough??

This will be my last question on structure-- thanks for the help btw.

Spuds
 
AQUAN8TOR said:
I appreciate the response, Zeph. I was kindof thinking the same thing about the bonding. I'm more than a little afraid that I'm going to end up squishing out too much glue, even if beveling the joint edge.
Click to expand...
I thought the solvents were simply there to melt the stock and pretty much evaporated away. The weld-on 4 leaves no residue
 
Right; They don't leave residue, but they change the surface of the acrylic. What I was talking about was squishing out too much of the Weld-On 40, which isn't a solvent, but an acrylic epoxy.
 
whats a good buffing kit/process i have a few spots on the front of my 300 and i tried to get them out using this kit i got from an lfs but it seemed to make it worse.

someone said to get a buffing pad and rouge to get the whole front buffed but im not sure.

can anyone help me here please i dont want to wreck anymore than i seem to have done well not wreck but its just not as clear as it could be.

the tank is empty right now also. and my lights havent arrived yet
 
anyone else care to post links or let me know what they use? i really dont want to do anymore harm than done already even tho its not bad. there is like a scuff mark i wasnt able to get rid of i think mostly because i did too large an area at 1 time. i got the scratch i was aiming for out but there is a hue to where i was working and its not completely clear.
 
ok so those are all hand sand ones. i know there is a trick to doing this. should i wet the acrylic as im sanding it some? do i just take a small spot and sand it and then try to match the whole area or can i re-sand the whole area and hope to get the whole scuff/haze out of the front. i havent dont this before and was trying to follow the instructions to the T on the kit i got but it took the deep scratch out but now i have a haze/scuff kind of look and its not completely clear. im trying to figure out how to clear the haze out.
 
AQUAN8TOR,

Sorry for the late response - just been swamped.

Check your material to make sure it isn't AR coated as WO40/42 nor solvent will penetrate it. Banks commonly use the AR material in BR applications.

I would ask that you revisit the idea of using some bracing on the top of your tank, CYRO's thickness calculator is invalid (in my *personal* opinion) regarding tanks with no top. I have built tanks such as these specifically for the chief tech rep from Cyro, had him visit my shop and concede there are flaws in their formula but will not change it. For tanks without tops, the formula (according to me) should read 2.5x normal thickness rather than 1.5X to achieve similar deflection rates.

As for joint strength with 40/42; it would be a rare occurance than 2800psi is ever reached in a hobbyist aquarium - ever. 2800psi is the rating for solvent bonded joints (using WO4 IIRC) and roughly 4200psi for WO 40/42 joints (non-annealed 7 day joint), the problem with this is simple - it does not take the material being glued into account. Differences in various brands and various batches of acrylic (cell cast or not) can & will have vastly different physical properties, more specifically - molecular chain length which, for our purposes, is the material's ability to handle stress. There exists an inverse relationship between this stress handling property and solubility which is required for acrylic solvents and resins (such as 40/42) to "bite" into the acrylic. WO 40/42 do need to bite into the acrylic, they don't just stick to it as a glue.
One of the nicest things about solvents is you know immediately whether the joint is strong. With 40/42 - you can't tell until you actually stress the joint. I've seen more than a few tanks that had beautiful "cast" joints that literally fell apart upon first fill that used #40. While the "bond" intself *may* have been very strong - this has little to do with how well the agent sticks to the acrylic. WO 40/42 can yield perfect looking joints in stainless steel - will this yield a strong joint? nope. While this may border on hyperbole, it's just to demontrate that bond strength and actual joint strength are two totally different things.

This much said, WO 40/42 are great things but IMO take much practice to work with and the material used has to be of highest quality and consistency.

Personally, I use solvents for everything up to about 2.5" as I have the capability of machining material accurately up to this point. After that, cutters flex too much to get the accuracy and consistency needed. It is at this point where #40/42 becomes fantastic products. Casting sheets together in series such as bullnose tanks and extra long panels are other great situations for these resins but are usually done in shops very familiar with working with thicker materials.

I'll stop rambling for now :)

James
 
Hmm.....I get 1.44 using the 2.5x normal thickness value instead of 1.5x Do you think that I could get away with it if I use triangular 3/4" corner piece bracing?? ----putting a piece of acrylic 3/4" on a side in each side joint to strengthen it??
 
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