Joing Acrylic Pieces

Suppose someone wanted to join some plexi or acrylic or something of that nature. Basically, I want to create a clear water reservoir of a custom size/shape.

1) Would it be possible to seal the seams so it was watertight?

2) Would screws or glue or both do a better job binding.

3) What type of corners should be cut into. Not too up on the terms for the different types of joins so a picture or something would probably help.

I know quite a few of you have build plexi cases and should know a fair bit about this subject.

Thanks

For joining, I suppose some sort of water-sealant like silicon may be a good choice. I'm sure screws wont hurt in holding it together as well.

Then again, I've never built anything like that, so... maybe someone else can confirm something!

I believe they have acrylic or plexi cement you can use to join them together most efficiently. What this stuff does is basically melt the surface the glue is on, then you stick them together and they get a nice strong bond together.

And, of course, I'd go with some silicon afterwards just to ensure a watertight seal.

Krusty said:

I believe they have acrylic or plexi cement you can use to join them together most efficiently. What this stuff does is basically melt the surface the glue is on, then you stick them together and they get a nice strong bond together.

And, of course, I'd go with some silicon afterwards just to ensure a watertight seal.

Click to expand...

Exactly, krusty.

Go to your local hardware store and ask for acrylic solvent cement. They even make an applicator for it to make a nice tight seam.

Does this cement stuff make some sort of chem. reaction with the acrylic that causes it to melt into the other piece? or is it just a type of glue that is transparent?

Iron Hawk said:

Does this cement stuff make some sort of chem. reaction with the acrylic that causes it to melt into the other piece? or is it just a type of glue that is transparent?

Click to expand...

No, it's not a glue. It really is a solvent. I'm not a chemist (I was in college, but that's another story ) so I can't explain exactly how it works. It is a very thin liquid and it actually melts, or "welds" the plastic together. The applicator is a small squeeze bottle with a long, thin, metal nozzle for applying the solvent where the two pieces join.

(I'll stop blabbering now)

So would I want to have straight edges, 45 edges, some sort of overlapping edge??

well...45° joints would give you more surface contact area for the seal and would probably be less noticeable as far as aesthetics. Straight joints on all surfaces would work just fine, though.

Whether or not you 45- the sides, I would just sit the 4 sides down flat on a bottom plate, not worrying about angles or such. Just depends on how much you want to worry with it...

Art...

The general concept of how Solvent welding works on Plexiglass in general is really kind of simple, even though I am no expert in the matter, I feel that I have a firm enough grasp on a concept of how it work. It has no fancy numbers or anything, but I feel that it adequately explains how the solvent welding works.

Pre solvent welding note: Check, with water, that the solvent will cover all of the connection point. So there are no areas, when you apply water just like you would solvent, that do not pull any water/solvent into them. A side that does not properly pull solvent into it will not form a good connection, or a seal. To correct this, lap the side that is not sucking up solvent.

How solvent welding works is as so. The solvent does exactly what all solvents do; it loosens the bonds between the molecules in the plastic. However, in the case of solvent welding it is put to a more “constructive” use then just breaking things down. When you fit the pieces together before applying the solvents you are preparing a place for the molecules to go when they are loosened. When you apply the solvent, it covers both the pieces of Plexiglass, causing molecules in both the pieces of Plexiglass to loosen. Because the solvents used are really quite strong, the molecules loosen and move enough that they soon become so intermingled that they are now, literally, a single piece of Plexiglass. During this time the solvent is slowly evaporating into the surrounding air(note: IT ATTACHES TO HAND OILS!!!) and leaves behind it hardened the now rebound molecules that the Plexiglass is made of. Just a little information for those who are wondering how it works.


About my note: the solvent evaporates just like superglue does, it attaches to anything it can. So if you leave fingerprints before you weld the Plexiglass they will be there forever, unless you buff them out of the Plexiglass which is a pain.

Weld-on acrylic solvent fuses similar plastics to eachother. You can buy it from most plastics shops for a few dollars. It's also much safer to work with than any other plastic-specific adhesive.
I haven't seen any online stores that sell it in sizes smaller than a pint.

you could always take a sheet of plexi measure out how large you want the box then use heat and form your own resevoir into whatever shape you want then use the solvent to glue only one edge of the piece and put some bottom and top pieces on and there you have it your very own custom shaped plexi resevoir...

Daewood said:

you could always take a sheet of plexi measure out how large you want the box then use heat and form your own resevoir into whatever shape you want then use the solvent to glue only one edge of the piece and put some bottom and top pieces on and there you have it your very own custom shaped plexi resevoir...

Click to expand...

This isn't easy to accomplish with sheets thicker than 1/8" and requires an even heatsource. Heating the sheets too much at the bend points will create bubbles.

that is why you use some kind of metal tube and heat it from the inside of the tube or whatever form you are going to use then use a heat gun to heat the outside and then wrap the plexi around the form...

but it would take alot of time and patience to complete this task but it would be really cool...

Plain old acetone does the trick nicely. It might very well be in some of the commercial plastic solvents, but you might have a container of acetone just sitting around the house...I know I did. =)

MEK is what I plan to use. I just need to find an applacator.

I was cutting some polycarbonate on the tablesaw yesterday (I use a chipped old carbide blade for nasty jobs like that) and got dredlocks - not snow - from the cutting. Sealed in a jar with a dollop of acetone, they melt. So now I have a milky, viscous, solvent-cement that should be perfect for that particular plastic. I just need to find a syringe (AKA applicator) to test it with. I'll try straight acetone too, for comparison.

EDIT: The local health units in many cities give out free clean syringes, no questions asked. That or buy a bulk bag at a medical supply or even drug store.

won't the syringes get solvent welded too? (aka, melt into oblivion)

sunrunner20 said:

won't the syringes get solvent welded too? (aka, melt into oblivion)

Click to expand...

I guessed they're vinyl, and I actually store acetone in a vinyl detergent bottle.

There's the rubber plunger part too. I'll just have to try it.

that is a good idea sean... put it in a bottle...

I'll be giving it a go too. And a small side note. do they give you just the applacator or the needle as well?