Acrylic fabrication questions? I can help!

[Floyd R Turbo]

That should be easy enough to do, and the dims wouldn't have to be exact. The holes are probably a bit oversized for the bulkheads that slide through them, so you would have a bit of wiggle room. The issue is getting the surface clean on the inside while the tank is operating. But dropping in a couple vinegar soaked rags should do the trick to remove any surface gunk.

If you're going to go the patch route, have 2 made, one for each side. 1/4" should be fine.

 

[Chihuahua6]

I can actually reach into there to clean it out so that won't be a problem. Two 1/4" patches sound like the right way to go. I will look for someone to make the patches and post the progress. Thanks.

 

[Floyd R Turbo]

Sounds good. Also this is a good job for weldon #16. There are not many uses but this is one of them. #3 or #4 will also work if you can get in there and lay a bead down without making a total mess. It can be done - fill a 1/2 oz squeeze bottle 1/2 full, squeeze most of air out, release and invert and get down to application surface, apply solvent, release so that it starts sucking air again, and lay down the patch.

For the bottom part of the 'sandwich' it's pretty much #16. You can't keep that piece level while spreading the solvent on it and then getting it into place.

 

[Chihuahua6]

I will get Weldon 16 then. It's a shame it cracked in the first place but it could have been much worse. Thanks again.

 

[saintsnsinners]

What material should I use for a completely flat work surface? only need it to be 3' x 3'.

 

[Floyd R Turbo]

Flat surface is easy, consistent thickness material is the issue. That is the reason for using the pin/shim method in conjunction with foam-covered MDF strips. 1/100" may not seem like much but that can cause a bubble along a seam.

Use as flat of a table as you can get. Kitchen counter works fine in most cases, just do it while the wife is away haha

My process is:

Set MDF strips on surface
Place flat material on strips, make sure MDF/foam is under every area that will be joined (as best as possible)
Clean surfaces, blow with compressed/canned air
Dry-fit joint, including 90 degree brackets, clamps, etc (leave lip to be flush trimmed, will act as fillet)
examine joint "tightness". You will be able to see gaps.
shim under material until the gaps are all gone, as best possible
add pins every 6", roughly
During the pinning process you will likely end up with loose pins. adjust shims until all pins are tight. Go around one last time and tug on each pin, if one is loose, adjust shim, walk around again.
blow with canned air
apply solvent
pull pins (15-30 sec is all you need from the time you started applying solvent to pulling the first pin)
upon pulling last few pins, watch for float. Joint will slide. Adjust as needed for squareness and lining up joint. You have about 15-30 seconds of working time, so don't let go until it won't move/slide on you.
Add weight if possible
don't touch for 4 hours, 8 if you can. Don't route for 20.

 

[saintsnsinners]

So you've brought up a couple other things I'm wondering about....

first, I'm looking for a flat surface that I could around my garage, not just for tank building. so I was wondering if there was some I could get at the big box store that wouldn't warp. maybe melamine?

second, would you still do the pins method with a 2' x 2' frag tank made of 1/4"?

Third, can you please explain the mdf supports?

lastly, I want to build the frag tank with the bottom piece on the inside. what should the order of assembly be?

 

[Floyd R Turbo]

maybe melamine?

Whatever you use, you need some kind of support under it so that it won't bow under pressure. a 24x24" 1/4" frag tank doesn't weigh that much though so if this is a one time thing, it might be OK. Place it on a workbench on top of some quick framing, like 1x2s or something, should do in a pinch

second, would you still do the pins method with a 2' x 2' frag tank made of 1/4"?

Yes, I would. But that's me. The last thing you want is a bad joint popping a year down the road, which will usually happen while you are asleep or on vacation.

Third, can you please explain the mdf supports?

4" wide 3/4" MDF with 2 strips of "camper shell foam" which is 1" wide and about 3/16" thick, on a 30' roll at Menards, sticky-backed. Look in the weatherstripping section. Brand matters, home depot's stuff is junk (sticks to the project on the non-sticky side and tears apart, Menards brand doesn't)

here's a pic

lastly, I want to build the frag tank with the bottom piece on the inside. what should the order of assembly be?

Don't. Order is sides to front, then that assembly to the back (support in the middle between the front/back panes so they don't push out and mess up the joint) then top euro (if you have one) and then bottom. I would recommend at least some kind of top brace even for a 24" tank because that will box over time, depending on height.

 

[saintsnsinners]

Height is 8". it's actually 20" x 20". what type of brace would you recommend?

I'm glad you said don't do the bottom on the inside. I was trying to figure it out and it seemed like it would be a pain. I've done that style with glass before.

I should have clarified my question about the pin method - would you do this when assembling the front, back and sides? they're only 8" tall.

also, when I'm attaching the sides to the front, would I lay the front piece flat and have the sides sticking straight up in the air? how could I brace that at a right angle?

I don't think we have menards here in Phoenix, so I'll have to find the camper she'll someplace else.

 

[Floyd R Turbo]

Yes, pins method on all joints.

Use a 90 degree bracket (with the inside corner cut off so it doesn't bond to the joint)

Bond both sides to the front, then when the joints are cured (at least 8 hours) then you put the back panel on the foam/board and flip the whole assembly, and place a vertical support in the middle as the front will want to sag and push the sides out, meaning the next joint won't meet up right.

Lowe's used to carry a good foam. If you have to use the HD stuff that's not the end of the world but it just won't last for very many builds, that's all really. Make sure you leave the paper on the outside panels of else it will bond to the foam and you'll have to polish it out.

For an 8" tall tank you really don't need much, you could get away with a 2" wide brace. a one-piece perimeter brace is ideal, with 2" diameter inside corners, but you could piece one together also, it's just not as ideal, but for a smaller tank you could probably get away with it. It depends on if you want it to look nice or just function.

You could do it rimless but I would use 1/2" for the walls in that case. I've built a few 24x36 with 3/8" walls for frag/sale tanks and they bow easily with 7" of water in them so I make them out of 1/2" now and they can be used continuously.

 

[saintsnsinners]

Dang. I already bought the 1/4" and don't have enough for trim. can I lower the height and be ok tomless?

 

[bpaston]

So im looking to design my next tank and have decided to go with acrylic due to kids. Dont want any tanks shattering while kids were being dumb in the house while im at work....lol. So my tank is design is a drop off. I am looking at making it 84" - 96" long x 20" wide x 18" deep on the shallow side and 36" deep on the drop off. The shallow length of tank would be 60" and the drop off 24" - 36". Would 1" acrylic eurobraced with a 3" border and no crossbracing work? And will it also be strong enough to not have crazing issues due to excessive water motion in tank?

 

[Floyd R Turbo]

Drop off tanks are tricky. There are a lot of stress points to consider. Your stand has to be dead on or the tank is doomed. If you search enough in this thread you will find a discussion about a few.

Due to the nature of assembly of a drop off tank, I think the order changes. You would bond the bottom pieces and the vertical drop section together first, then bond these to the front, then to the back, and the put on the euro. That's the only way I can think of to make it work because of the inside corners on the front/back panel. Expert level build IMO.

But on the crossbracing question, without a doubt, you would need crossbraces every 24" on that tank, unless you built the thing with something like 2" walls. The stress points related to the drop off would tend to mandate an even sturdier euro than normal I would think.

 

[bpaston]

Drop off tanks are tricky. There are a lot of stress points to consider. Your stand has to be dead on or the tank is doomed. If you search enough in this thread you will find a discussion about a few.

Due to the nature of assembly of a drop off tank, I think the order changes. You would bond the bottom pieces and the vertical drop section together first, then bond these to the front, then to the back, and the put on the euro. That's the only way I can think of to make it work because of the inside corners on the front/back panel. Expert level build IMO.

But on the crossbracing question, without a doubt, you would need crossbraces every 24" on that tank, unless you built the thing with something like 2" walls. The stress points related to the drop off would tend to mandate an even sturdier euro than normal I would think.

What exactly do you mean by even sturdier than normal euros? As far as the stand goes I have that covered and is in the process of being built. I am going with two stands that connect and allow me to raise or lower the support under the drop to help with leveling and ensuring it has support. As I figured the weak link of the tank will be on the drop off side.

 

[Floyd R Turbo]

The way I see it, you need to make sure that there is really minimal bowing. Two things affect this, wall thickness (in relation to length and height of the wall) and the thickness and width of the eurobrace.

So if you want to minimize bowing, you would go with thicker walls and a thicker and wider eurobrace.

James will probably have to chime in and confirm all of this, but the wall thickness is going to be dictated by the deepest point. His general recommendation (i.e. how he builds his tank) has been

24" high, use 1/2" minimum
30" high, use 3/4" minimum
36" high, use 1" minimum

with these in mind, I recommend a 6" wide crossbrace every 24" of tank length. So a 48 x 24" will have 3" eurobrace and a 6" crossbrace. If the same tank were 72" long - just one more crossbrace. At 8' length, I recommend jumping up one material thickness to keep deflection down.

There are times when someone's lighting scheme doesn't match the above formula. Ie., if someone wants an 8' tank but only 3 cutouts in the top. In such cases, I recommend increasing the eurobrace width to 4.5" and increasing the width of the crossbraces to 8".

Iv'e been using this formula, 1.5" radius corners, and material thickness minimums above, for many years and I have *never* had a tank fail.

If someone doesn't want the crossbrace - they simply have to make the material thicker, and/or increase the width of eurobrace to maintain rigidity.

So as you can see, you would likely need to treat this as a 36" deep tank throughout and not cut a corner and justify a thinner wall because only part of the tank is 36" deep. You need that extra wall thickness to compensate for deflection causing problems with the dropoff. So you're now likely looking at 1.25" thick walls (and that's US, not the metric equivalent) and a 1.25" thick euro with 3" perimeter and 3x 6" crossbraces at 24" 48" and 72".

Again, that is my educated guess. There might be other things to consider related to the dropoff design, but I have not idea what they would be really.

 

[bpaston]

The way I see it, you need to make sure that there is really minimal bowing. Two things affect this, wall thickness (in relation to length and height of the wall) and the thickness and width of the eurobrace.

So if you want to minimize bowing, you would go with thicker walls and a thicker and wider eurobrace.

James will probably have to chime in and confirm all of this, but the wall thickness is going to be dictated by the deepest point. His general recommendation (i.e. how he builds his tank) has been



So as you can see, you would likely need to treat this as a 36" deep tank throughout and not cut a corner and justify a thinner wall because only part of the tank is 36" deep. You need that extra wall thickness to compensate for deflection causing problems with the dropoff. So you're now likely looking at 1.25" thick walls (and that's US, not the metric equivalent) and a 1.25" thick euro with 3" perimeter and 3x 6" crossbraces at 24" 48" and 72".

Again, that is my educated guess. There might be other things to consider related to the dropoff design, but I have not idea what they would be really.

I guess my goal in this project would be to avoid crossbracing at all costs. I like the look of perimeter bracing but not cross. I wonder if steping up to something along the lines of 1.5" with 3" - 4" perimeter bracing would work.

 

[fredej80]

Hello all, I've been browsing this thread for a while now trying to soak up some of the knowledge and now I have a reason to post. I'm looking for some advice on the possible repair of a large acrylic tank that is for sale near me. When I went to look at it and drained the remaining water out I discovered a crack in the bottom. The tank itself is 1.25" acrylic and roughly 90x32x52. It is set up peninsula style with an overflow wall at one end. The crack is in the bottom basically where the black overflow wall meets it. I'm just wondering how some of you might go about repairing this tank?
The picture isn't very good but you can kinda make out the crack.
<a href="https://www.flickr.com/photos/indiancreekclay/14713988475" title="image by fredej80, on Flickr"><img src="https://farm3.staticflickr.com/2898/14713988475_d495f30efa_s.jpg" width="75" height="75" alt="image"></a>

Anyway, let me know what you think.

 

[saintsnsinners]

So I'm getting ready to upgrade my table saw blade and flush router bit. I currently have a 60 teeth saw blade and cheap ryobi bits. these work fine for wood, but not so much for acrylic. what do you recommend?

 

[Floyd R Turbo]

I use the 80(?) tooth diablo triple chip blade ( got a Home Depot 3 yrs ago, still haven't sharpened or replaced) and for bits I use all Bosch and have had good luck. For the spiral up cut flush trim bits I use Amana, but that's just because I found them locally. Wicked expensive, esp the 1/2" one ($150?) but really good. I've read that whiteside brand is decent for router bits also

 

[Floyd R Turbo]

When I went to look at it and drained the remaining water out I discovered a crack in the bottom.

I would just walk away. I could give you a list of reasons, but it's been a long day.