Acrylic fabrication questions? I can help!

[Floyd R Turbo]

James,

I've been working on a tank made of 3/4" Plex-G. We set the vertical joints with little issue. The top euro looked good except for right at the joints of the vertical panels in each corner where I forgot to scrape off the little bit of solvent that goos out when you pull the pins and then adjust the panels to be flush (oops). It's not horrible, but quite a few small bubbles right there on the corners. Much to worry about? Top is 1/2".

But, this is the real reason for my post below. We set the bottom joint and bubbles seemed to 'form' in a few spots as we ran the solvent in. As we filled it, the joint looked good and filled, then the bubbles would just form almost out of nowhere. Here's a few pictures. Tell me if this is really anything to worry about:

The tank is 48 x 19 x 30 H, 3/4 walls, 1/2 top/bottom, euro has 2.5" perimeter w/6" center, 2.5" radius corners. Used pins method, wiped both panels with denatured alcohol, blew off with air compressor, then canned air after pins, joint was still wet when be pulled the pins too so there was a nice fillet all around. Solvent was straight MC w/5% to 6% AA.

The only thing I can think of is maybe we should have shimmed the pins a little more aggressively all around to get them really tight. We really only needed to shim the corners and a little on the ends - table is a little crowned in the middle (maybe 1/8" higher), but the double-sided foam MDF boards seem to take care of a lot of that. Also I had one bad bubble (second pic) that seemed like the solvent didn't want to fill in, it was filling in at the inside and outside edges like a "U" then the solvent closed in around it making the bubble. Strangely this was over the crown in the table.

Could this be dust particles? I have noticed that it's kind of hard to clean the edges perfectly because of static. Even after wiping with alcohol and compressed air and canned air, I can't always get all the dust off. Is there a trick?

Is this joint doomed, or just unsightly?

Being the largest thing I've built to date, I am discovering that I may need to make some modifications to my table or technique, or both. I hope you can shed a little light on this...thanks in advance.

EDIT: PS the bubbles in Pic #3 are elongated because the joint floated after we pulled the pins, and we noticed it just in time to re-adjust it...

Bump on this one...could really use an opinion James...

Another thing we noticed today before drilling the holes was that the inside corner of the back bottom seam didn't have much of a fillet. If you look down along it, right in the middle for about 6 or 12 inches, it's almost non existent, or 'beaded' where you can see little bumps or dried solvent/acrylic, but the gusset isn't continuous. I think we were so concerned about the bubble in Pic #3 and aligning the tank after it floated that we check and go over the inside seams. There were no bubbles pulled into the seams near the area of the lack of fillet, but with this in combination with the bubble in pic #3, do we pretty much have to add a gusset along the back joint, just to be safe? Or just run over the seam with WO40 or even WO16?

Guess I'm still on the learning curve. Plenty of work with 3/8" and I can make seams that look like glass with beautiful fillets. So this is making me a bit nervous.

 

[ChadTheSpike]

Hi y'all, hopefully my question is just a quick/easy one

I have an acrylic fixture that I had built, however some of the exposed edges are not as polished as I would like them to be (router marks still visible on some)

I would like to polish the edges as best I can. What method do y'all recommend? Assembly is complete and there will be no further solvent use. I figure the top edges will probably take to a flame polish well, but I am worried about joints with adjoining, already polished, surfaces (see circled portions of the picture below).

Thanks all!!

 

[TheFishMan65]

If I know what Chad is talking about this for an LED fixture rather than a tank so strength is not a major concern. I don't know if this will affect the answer, but it may affect the answer.

Chadd - hope I am helping

 

[ChadTheSpike]

That is true, thanks for the clarification, Rob!

 

[Floyd R Turbo]

Yes flame polishing is very stressful on acrylic, but you're not talking about a pressure vessel. You just can't clean flame-polished acrylic with things like denatured alcohol because it will craze instantly. But for a device like you show in this pic, I wouldn't think it is not of concern.

 

[ChadTheSpike]

Do you think that flame polishing edges with adjoining polished surfaces would distort the already polished surface? (did that even make sense?)

It almost seems to be the perfect solution for my case.

(1/4" black acrylic, by the way)

 

[Floyd R Turbo]

for some reason, black acrylic does not flame polish as easily as clear, or maybe it just shows more because it's black. So was the material flame polished or hand/machine polished?

 

[ChadTheSpike]

Since the above pic I spent some time hand polishing the top edge (with sandpaper followed by a bolishing bob and rouge - it makes it black, but not very glossy), but the rest of the edges have a machine tooled finish (in other words not finished, I wish I would have specified that when I ordered it).

The router bit left a pretty clean finish, but it has a "greyed" out look to it rather than being black.

Can you put masking tape down to protect the surfaces not being flame polished?

Thank you very much for your help!

 

[Floyd R Turbo]

I know exactly what you're talking about. From looking at the pics, it looks like he made the staggered look by taking 1/4" and rounding off the edge, then bonding that to another piece that had the same done to it, then again. Sound right?

If that's the case, then you have a routered roundoff and that is the part that you are talking about. The first thing I would do it try to take off the router marks with a fine grit wet/dry sandpaper and this is where taping off the finished area around it will probably help. Start with 1200 or 1500 and a soft block to hold, keep the area you are sanding wet by spritzing with a spray bottle and also spray the sandpaper also. It helps to have a couple small buckets of water to dip the sandpaper into, one to get the dust/particles off mostly, and other to get the rest off (these can be small containers). This keeps the sanded particles from making more scratches.

You can probably go for 30 seconds to a minute between 'dips' depending on how fast you're working. you shouldn't need to work an area very hard to get the router marks mostly removed.

At this point, you can probably flame-polish it with MAPP gas and a flare nozzle, making passes as moderate, even speed (this takes some getting used to), but if you haven't done it before, practice on some scrap. If you mess up, you can sand again, etc, but eventually there might be no going back. Not to scare you, just sayin.

The other option is to buff it. Rinse the acrylic and use a buffing wheel with an arbor bit on a drill. You can get these at most hardware stores. Look for a 3-stitch wheel (it is a bunch of cotton circles stitched together with only 3 lines, others have many more stitch lines, you don't want those. Get some plastic polish, something like this

http://www.meguiarsdirect.com/product_detail.do?q=4729

http://www.meguiarsdirect.com/product_detail.do?q=4814

The first will take out the 1200 sanding marks, the second will polish to a mirror shine. You will want to use separate wheels for each compound.

This is what one company in CA uses (featured on LA fishguys recently) to polish tanks. You can get cheaper stuff, most 'final' car polish will work since this isn't in the tank.

Anyways, Spread a very thin layer of it on the acrylic (leave the tape on, or likely replace the tape) and let it dry a little, then run over it with the wheel at relatively high speed (2000-3000 RPM for a 4 or 6 inch wheel even). You won't need to press down on it, just get the wheel close enough to touch the acrylic. Oh yeah you will want to secure the piece to something sturdy before buffing. You will probably want to re-apply the polish several times as the wheel will soak it up. Anymore I drizzle it right on the wheel edge and even it out with a paper towel or cloth, but when you spin it up it will spray that stuff everywhere so be careful (eye protection).

After you get the hang of that, you'll probably be done with the ultra-cut step. It won't be finished yet, but it'll look a lot better, and you might be happy stopping there. It may still have a dull look to it yet. Go with the 205 (ultra finish) and you will likely get very close to a mirror finish. Then, if it's still not to your liking, a couple quick passes with the MAPP gas should make it shine up really nice.

HTH

Bud

 

[ChadTheSpike]

All of the edges are 90*, but other than that you have it right.

Bud, thank you very much for your help! I will go get some stuff to make it look purdy and report back.

Chad

 

[Acrylics]

Hello,

Just wanted some feedback on the thickness of a tank.

48"x36"x30"

Do I need 3/4" front and back and the sides and could I use 1/2" for the top and bottom?

Thanks for the help,

Need a good bit more info, but "need" is a relative term.. What are your bracing tolerances? deflection tolerances?
If you have a 3+" perimeter flange and a center-brace - 3/4" will do nicely with <.125" deflection. With no cross-brace - need thicker material or wider perimeter flange to achieve similar results.

You *can" make the entire tank from 1/2" as many companies do, but I wouldn't.. not in this lifetime..

And yes, you can use 1/2" for the top and bottom, just increase the bracing width a little..

This weekend I wet tested the tank I've been planning to use for my new (and 1st reef setup.) It held water with no leaks. It's a ~90g acrylic DT with a 120g sitting below it in the basement with an external beananimal on the acrylic DT. The acrylic DT was purchased used about a year ago.

I literally lost sleep last night over what I noticed...
A 1.5" long white area of the joint/seam along the vertical back left edge. The blue back is a single rectangular piece that spans the width of the tank, the sides and front are a single piece with curved edges that butt up to the back. It may or may not have been there before I purchased the tank, at this point I don't know.

1. Can I reinforce this by using a cut piece of acrylic and a weld-on a "lap" joint on the exterior?
2. Would I need to then to also weld-on a piece to the inside seam?

Personally, I'd just put one on the inside, omitting the outside. You can try it, but my guess is that you'd get some crazing in the area as the seam was most likely flame polished and you really don't want to introduce a secondary stressor to the area

Floyd,

Nothing I'd lose sleep over. Looks like what I'd consider a "loose joint" - meaning there is a slight gap between the bottom and the vertical panel and this was not shimmed up. Just unsightly.. while it's something you may not find aesthetically pleasing, in this case - not a worry IMO from what I can tell.

James

 

[triggers_150]

Acrylics - thank you for the comments.

I was planning a solid top with access holes in the top to give it about a 3-4" perimeter around the tank.

 

[sean04]

1. If I'm solvent welding a small piece 3/8" material of size 5" x 6" (sides of an external overflow) to the bottom piece do I need to use the pins method. I've been practicing on some scrap pieces and the pins make it difficult to get a straight edge.

2. Also, when I'm using the pins method for the larger front side (30" x 6") I'm putting the pins sticking out from the external and the plastic squares are placed on the inside. I'm having difficulty because the squares are in the way when I apply the solvent (weldon 3) from the inside. Is it ok to apply solvent up to a point and then pick it up and then continue from a different angle to get around the plastic squares. (These are plastic squares with the corners cut off.)

3. When I place the pins underneath the vertical piece, is it supposed to come out to the other side or is it just supposed to stick out from one side? Hopefully this makes sense. I guess my question is how far in should the wires go?

 

[madmike]

Also, when I'm using the pins method for the larger front side (30" x 6") I'm putting the pins sticking out from the external and the plastic squares are placed on the inside. I'm having difficulty because the squares are in the way when I apply the solvent (weldon 3) from the inside. Is it ok to apply solvent up to a point and then pick it up and then continue from a different angle to get around the plastic squares. (These are plastic squares with the corners cut off.)

apply the solvent from the outside, problem solved

When I place the pins underneath the vertical piece, is it supposed to come out to the other side or is it just supposed to stick out from one side? Hopefully this makes sense. I guess my question is how far in should the wires go?

I make sure the pins are at least in the depth of the acrylic, maybe a tad more.

 

[sean04]

apply the solvent from the outside, problem solved

I'll try but because I had these pieces cut I had them cut to be flush to the edge so it might be difficult. But, I'll give it a try with some scraps. Thanks.

 

[madmike]

I'll try but because I had these pieces cut I had them cut to be flush to the edge so it might be difficult. But, I'll give it a try with some scraps. Thanks.

Oh, thats makes it difficult then... In the future you should have them oversized a little and flush trim them with a router, makes for a much nicer looking result

 

[peppie]

James, I need some of your wisdom please

I was told by the plastic retailer, that I could use Weldon 3 to weld Polycarbonate. Is this true? Will it bond to Plexiglas-G. or just go strictly with the polycarbonate. Would it hold together a 25 gal tank?? 1/2'' polycarb.

Also is Plexiglas MC suitable for the building of a skimmer? and or a 40gal sump, 3/8 material?

Thanks James.

Peppie

 

[peppie]

Bump for Sunday!!

 

[BIG_KAHUNA]

As do I! Check out my thread and let me know what you think! Tank safe?
http://reefcentral.com/forums/showthread.php?t=2122409

 

[kaipo13]

I have a question. I'm currently assembling a sump with the dimensions 61" length x 12 " width x 15" height. I'm using 3/8" cast acrylic. Because of the narrow width of my sump I'd like to avoid putting on lengthwise supports(although I have 2 61"x2.5" pieces for this if need be,) so I can maximize access for skimmer, pumps, etc. I do have some baffles and support at the top width-wise.

With the limited info I have given does this sound okay? Just wanted a little confidence before I do my first fill test...

Thanks,
Kaipo