Acrylic fabrication questions? I can help!


So I'm a bit disheartened. I practiced building a fish trap using 3/8" scrap and basically just cut it with a circular saw and didn't really edge prep. I just wanted to see how to use the bottle/needle and it held water and didnt have many bubbles in the seam. Today I got some 1/2" extruded scrap that was cut at the distributor. I used a razer blade on the edges and tried the pin method. It's full of bubbles! What do you think? I didn't see the bubbles initially but they popped up not long after I removed the pins. I also used 3 pins along a 10" seam just to get the hang of pulling them out.
[IMG]http://[URL=http://s1211.photobucket.com/user/jcrunelle/media/Mobile%20Uploads/2014-11/572CC705-5BFF-47FA-8B43-AAA4AF35B9EE_zpski9hwuur.jpg.html][IMG]http://i1211.photobucket.com/albums/cc435/jcrunelle/Mobile%20Uploads/2014-11/572CC705-5BFF-47FA-8B43-AAA4AF35B9EE_zpski9hwuur.jpg[/URL][/IMG][/IMG]
 
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Hard to say for sure but a smooth circular saw cut is at least square, while hand-scraping leads to rounding. So the hand-scraped edge will not have full contact throughout the seam, and the solvent dries to a very thin profile, and as it dries if there is not full contact then air will intrude. If this is the case you will typically see the bubbles creep in from the edge. If bubbles are popping up in the middle of the joint, then this might mean that the edge had some pitting and air was trapped and as the solvent dried it created a vacuum in the cavity that was filled with solvent when it was liquid, revealing the bubble. Or it could have been a dust particle, same concept as the pitting, air clings to the dust particle and then allows for a cavity to form and a vacuum ensues.

These are the types of things you see with no edge prep. In this instance, your rough-cut table saw edge was probably a pretty good clean cut
 
And don't forget the brand name of the acrylic. i used some cast chinese stuff with perfect prepped edges and tons of bubble. Use spartech, plexiglas , or arkema brand.
 
I apologize if I'm posting this in the wrong spot but I've switched gears a bit. Instead of the acrylic build I got a lead on a 12'x3'x'2' out of 1" acrylic. It's on hold for me and I plan on making the official purchase this afternoon afternoon. Other than looking at the seems and for crazing or cracks is there anything else I should keep an eye out for?
It's painted on 3 sides. What is the procedure to polish that off?
I imagine new that's one expensive tank. I can't even find 144"x1" acrylic on the web. Any ideas of price on that?
 
Sorry for the late reply - long day yesterday!

The material alone for that tank would be several thousand.

yes you will want to watch for crazing and cracks obviously, I would pay attention to the radius on the eurobracing cutouts and the thickness of the top and bottom panels compared to the sides. Should be 3/4" or more on those, otherwise, they cut a corner making it.

As far as polishing off the paint, that's a tough one because you will need some kind of solvent to remove the paint, which would damage the acrylic. The other way to do it would be to sand it off and then polish the tank, that would be the way I would go. Start with as fine sandpaper as you can get. Like 1200 or higher.

I would say try doing wet sanding at first, but that might gunk up the paper quick. If it does, you might use a random orbital with dry paper but use high grit and once you see clear material, move on. Then go to the wet/dry and work the paint off. After all the paint is off, start with wet/dry at the lowest grit you used in any of the previous steps and make a full pass across all the surfaces.

Get yourself one of these

http://www.amazon.com/Time-Shaver-Tools-Preppin-Weapon-Sanding/dp/B001399URG

#1 timesaver for this job.

Then go through a few other stages of sanding. Usually I find the first 2 stages take the longest. The following stages, you can tell when you have taken off the prior pattern because the sound changes and the paper runs across smoother.

Then follow up with a power buffer and Meguiar's ultra-cut, then swirl free polish. Takes some practice but you can make it look like new - on the outside, at least.
 
This is right after I built it

DSC02594.jpg
 
thanks read through all of it. more questions.

1. what router do you use?
2. how much material do you take off each pass when you edge prep?
3. how do you change bits if you can't remove the router?
4. you said the aluminum plate wasn't needed and you could have just mounted directly to the MDF, right?
5. what size of table would you recommend if the widest piece I would route were 36"?
6. was James ever found and located?
 
1. Bosch, I think 1.75hp but I'm in bed right now so I'm not gonna check.

2. Depends. No more than 1/16 or you get pitting (using 3/4" straight cutter). Last pass is usually just enough to create some dust.

3. Base mounted to underside. Router is removable. Who said it wasn't?

4. If I had it to do over, I would mount to the top layer of MDF and not use the plate. Still 2 layers of MDF.

5. Depends on where you mount router head. 18" from edge + 36"...call it a 6' table.

6. James is "Acrylics" and yes he is fine and making tanks and posts here on occasion. Check the "low country reef" thread for one if his beautifully made tanks.
 
1. variable speed? is that even necessary with acrylic?
2. how do you measure from fence/guide to bit, to measure your cut depth?
3. I've only worked with routers that didn't have a detachable base. good to know.
7. are you using this for flush cutting too?

thanks.
 
1. Looked it up, 2.25 hp Bosch. Variable speed but I run it full out

2. I don't. You don't need to do this for tank building. Just run all the pieces through with the same fence setting and they will all be the same. Remember, for tank building, you are running the acrylic between the fence and the bit. Fence on left, bit on right. This is the only way (unless you have a sled) to get perfectly parallel opposing edges. Squaring requires a jig and double stick tape. Or a sled.

3. Um, ok. I didn't know that they made routers without a detachable base. I'm not a router expert tho.

7. Yes. And roundovers. Once I even used it to slice off the tip of my finger. I decided not to use it for that again.
 
2. I probably didn't word my question correctly. you said you take off 1/16" when edge prepping. what's the easiest way to measure that amount? if I understand you, a piece with the final dimensions of 24" x 36" would actually need to be rough cut to 24 1/8" x 36 1/8", then edge prep would take off 1/16" from all edges, resulting in a final size of 24" x 36". how do you ensure you're only taking off 1/16"?

3. me neither so I'll have to check mine tomorrow.
 
I'm getting the following tank built:
68 x 32 x 22 with a eurobrace and external overflow.

Is 1/2" acrylic strong enough? In my research, i read that tanks 24" and below can use 1/2" acrylic, as bowing is a matter of height and not length
 
usingthejohn said:
I'm getting the following tank built:
68 x 32 x 22 with a eurobrace and external overflow.

Is 1/2" acrylic strong enough? In my research, i read that tanks 24" and below can use 1/2" acrylic, as bowing is a matter of height and not length
Click to expand...

Probably OK. But James' recommendation of 1/2" for up to 24" tall is the minimum, and that is imperial thickness not the metric equivalent (i.e. polycast, not acrylite or plexiglas which are 0.472 - but still, you're probably OK at 22")

If you're going to go with 1/2" though, then you need to make sure the bottom and top panels are also 1/2", and that the euro is properly made to transfer the stresses across it without creating a focus point that could lead to a crack in the future. What I would recommend:

for 68" tank, have a 3" perimeter eurobrace with two 6" wide crossbraces at the 1/3 points of the tank basically at 22"-23" in from each end. All inner corners of the euro cutouts should be a minimum 2" radius cut to allow the stresses to spread out. Both sides of the cutouts on the top should be rounded over or at least knocked down with a razor blade to take the sharp edge off (the sharp edge actually focuses the stress, so removing it to avoid cutting yourself is not the only reason to do that).

Roundovers should be done on all the exterior corners for the same stress-focus removal reason.

And lastly - no flame polishing. None, not at all.
 
I don't know what an emerson guide is.

I used to just use a good quality metal 48" level and c-clamp it down to the table, then after each set of passes, I would loosen the front clamp enough to bump the level in a bit, make more passes, etc.

I wasn't perfectly happy with the level, so a while back I took 2 pieces of 1/2" black and bonded them together then ran them through over and over again until I had a nice edge on it. So now I basically have a 3" wide 1" thick 48" long fence. I call it the Black Mamba.
 
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