Acrylic thickness and joining questions

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arnemetis

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Hi everyone,
I have just barely begun my work on my new pc, but an order to mcmaster would be wasted if you didn't save on shipping by getting everything you need. I will be finishing off my mod by giving the side panel of my stacker a custom window. This however is not your average window, I am completely insane and have decided to attempt to replicate a triangulated curtain wall design I came up with in my middle college days:


I would say each triangle's side would be between 3 and 5 inches long. As with the models, I will cut them as I go, fitting along previous pieces and creating the form freely. The side panel of the case would be cut in a jagged pattern, framing the points of contact for the triangles. I think I will want to find a balance between weight and strength with my selection of acrylic. Now finally, the questions:
1. What kind of acrylic would be best for this application, extruded or cast?
2. What thickness would be best?
3. What should I use for adhesive between the triangles? (The triangles will likely never meet flush, so I figure something with some thickness to it will be needed to fill in the joints)
4. What should I use for adhesive between the triangles and the metal case?
Thanks in advance to anyone who can help me out here. It's going to be a lot different working with this than it was when I was using hot glue to join triangles that were on average 3/4" to 1/4" per side.
 
Extruded or cast would be fine.

For thickness, I'd go 1/8" HOWEVER, I'd still have another straight sheet of 1/8" in the window, to support the structure... See what I mean? Have the normal pane and the curtain pain seperate, then glue them together.

Weldon 4 is your glue of choice!

As for adhesion to the case, see point 2 above... Adhere it to a straight panel, and fit it into the case, hold it with screws.
 
That assumes I won't have the triangles find their way into the case :eek: You aren't thinking three dimensionally enough. It will bulge out a bit, and it will creep inside as well at some points. I give you credit however, a supporting back piece sure would make things easy, and was quite the logical conclusion. But if I wanted easy, I would just go with a normal window, right? :p So let's try this again.
 
Hmmm. Well, the only prblem I see with that is your window bumping into the innards of your case, but so long as you measure everything out properly...

Weldon 4 is still your best bet. And for adhering it to the case, I'd still use screws somehow.
 
Hmm, don't know how screws will work directly, the triangles will not be meeting flush at the case. What if kind of like your idea of running an entire plate behind it, I run around the perimeter giving 1/4" or so of mating surface? Then the acrylic could be adhered to these pieces which are flat against the metal, and then these flat pieces can be screwed to the metal? (Let me know if this is unclear and I'll photochop something real quick) That will be a hell of a lot of screws, haha. I'm going to take a wild guess and say that using rivets would be a terrible idea? :p
 
Hmm, that sounds dangerous. During the construction phase, there needs to be a bit of play to adjust for minor changes to angles and to fit the next triangle in between the adjecant ones. Figure some spots of hot glue will hold it temporarily while I build it up, and I gradually use this ips stuff as I complete sections?
 
Yes this is powerful stuff, IPS Weld-on 16 actually chemically melts the 2 acrylic at the edge where you applied and bonds the 2 joined pieces for good, there's a reason why they call that stuff Weld-on acrylic cement. The hot glue idea just might work, just apply like a dab here and there just enough to hold it up, then once you're satisfied Weld-on the edges.
 
In order to bond the edges nicely with that kind of adhesive, you'll need to ensure that the edges meet with full contact - you will not be able to allow the two edges to each be square and then fill the resulting trough. That will require you to determine the edge angles with some degree of accuracy - if those drawings are from a CAD program, those angles can be determined from that (assuming it's a good one).

Without nice flush-fit edges, the design will look like crap, IMHO. With clean edges bonded nicely, the joints will be nice and sharp and the whole thing will look good. Thin acrylic or polycarbonate will give a better look than thick.

To screw the edges to the case, just use a flat sheet and cut the opening for the triangles. That will provide a small "flange" all around to attach the thing to the case and will provide a surface to bond the triangles to. If this is bonded nicely, you won't need a backing sheet.

As far as doing the trial fit, don't underestimate the value of transparent tape.

To make the edges fit nicely, cut them ever so slightly larger than needed and then sand them on a very flat surface - a sheet of thick glass with sandpaper on it will do. Use a fine grit to take it down nearly to size, then a finer grit. Finally, polish the edge on a flat surface with a plastic polish. If both triangle edges are clean, flat and polished where they meet, they joint will look clean.
 
Wow, that sounds like an insane amount of work.

In order to bond the edges nicely with that kind of adhesive, you'll need to ensure that the edges meet with full contact - you will not be able to allow the two edges to each be square and then fill the resulting trough. That will require you to determine the edge angles with some degree of accuracy - if those drawings are from a CAD program, those angles can be determined from that (assuming it's a good one).
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Those are old cad files, and don't really apply to the current project. I would have to create a new model and accurately model everything outside the case, this is not ideal. I planned on forming the triangles with the side panel in place, so I could see whereit's safe to go in the case and where I'd want to bulge out. It COULD be figured out, but wow that is an exceptional amount of work.

Without nice flush-fit edges, the design will look like crap, IMHO. With clean edges bonded nicely, the joints will be nice and sharp and the whole thing will look good. Thin acrylic or polycarbonate will give a better look than thick.
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I agree a flush edge would look much better, however I have become quite good with hot glue runs resulting in nice bubble-free lines, I was hoping to do soemthing similar here. However, you raise an excellent point - thinner material. If it is thin enough, even with one edge cut at 90, the piece that is fit in can be sanded to get the angle needed without much effort. So are we talking 1/16th acrylic now, or?

To screw the edges to the case, just use a flat sheet and cut the opening for the triangles. That will provide a small "flange" all around to attach the thing to the case and will provide a surface to bond the triangles to. If this is bonded nicely, you won't need a backing sheet.
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That's exactly what I was thinking. I think however I will not use an entire sheet and cut out the center, I will rather do it in several pieces (maybe a run along the top, then bottom, and each side)

To make the edges fit nicely, cut them ever so slightly larger than needed and then sand them on a very flat surface - a sheet of thick glass with sandpaper on it will do. Use a fine grit to take it down nearly to size, then a finer grit. Finally, polish the edge on a flat surface with a plastic polish. If both triangle edges are clean, flat and polished where they meet, they joint will look clean.
Click to expand...
I'll definetly use some sandpaper, but I don't know about polish, lol. I'll think about it after looking around for some. Do you have a recommendation? Thanks.
 
You could use four strips instead of one sheet to make the frame - a clean corner would be mostly hidden inside the case.

For polishing acrylic, I've used fiberglass polish - the stuff sold for boats. 3M makes some good quality stuff that's expensive - I used it because it was handy; only the finest grit is appropriate. You can buy various polishes at a number of shops that specialize in tools (polishing cutting tool edges) and metals (polishing metal surfaces). Probably the best choice is a plastics speciality dealer - they have polishing compounds specifically for things like acrylic and polycarbonate. Search this forum for "polishing" and you'll probably find the brands recommended; I've seen some posted in the past.
 
Fair enough. This part is already getting expensive as it is, if the polish is very expensive I will probably skip that phase, I mean it's only at the joints which will be glued anyway. At any rate, with these developments I still have some questions unanswered:
1. What thickness should I use? It seems thinner is better now, so, 1/16th?
2. Are rivets ok for joining the acrylic 'frame' to the case panel? Would it be ok if I added a washer so it doesn't crush the acrylic?
3. What kind of set time do I have with this Weld-on? I figure I'll have to apply it to two sides of the triangle then fit it into place, so I'll need a few minutes anyway...
Thanks for the help.
 
arnemetis said:
if the polish is very expensive I will probably skip that phase
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No - the 3M stuff for fiberglass boats is expensive ($20-$25 depending on grit). Many plastic polishes are pretty cheap - $5-$8. Novus is one of the brands others have used with success. There are plastic polishes in the auto section of any big box store - they are used to remove scratches from plastic lenses on cars.

1. What thickness should I use? It seems thinner is better now, so, 1/16th?
Click to expand...

The thickness will depend on the size of the biggest triangles - the bigger, the thicker, since thin will be flexible. I'd think 1/16 is on the thin side and tend to something thicker - 3/32' to 1/8".

2. Are rivets ok for joining the acrylic 'frame' to the case panel? Would it be ok if I added a washer so it doesn't crush the acrylic?
Click to expand...

Yes and yes, but bolts will likely look better than rivets. You can get some nice looking bolt heads and even get coloured plastic bolts (white nylon + dye), blackened steel, chrome-plated, painted, brass etc.

3. What kind of set time do I have with this Weld-on?
Click to expand...

I've never used this, sorry. Someone else can chime in.
 
I'll see if I can look into some of the plastic polishes at the local stores. So back to 1/8" acrylic with me - the triangles will all be between 3" and 5" per side. I think the rivets will look ok because I am getting black ones which will blend in with the black side panel. Maybe foxtrotniner will chime in again regarding the Weld-on. Thanks Michael!
 
SECONDS?!?! Ok, I need a new adhesive. With 5" sides, it would set before I'm even done applying it. If I'm making nice clean joints, and polishing them, I'll need a minute at least to apply and set in place. Any suggestions, Michael, anyone?
 
Google structural adhesives. That's what I do when I need something like that. There are some alternatives that will give you longer setup times. Some are industrial and can't be purchased in your friendly neighbourhood big box store - you'll have to buy off the web or at a supplier. Loctite and 3M make some good ones. They tend to be pricey.

Some fo the Loctite and 3M products that are in the big box stores are suitable. Be choosy.

You could try Hot Stuff Special T Cyanoacrylate - this is a gooey version of so-called "super glue" with a set up time of 30-50 seconds. Since it has the consistency of honey, it can fill gaps somewhat. Just make sure it's transparent - I'm not sure.

Epoxies are superb but you have to get the best quality stuff to be assured of a transparent, non-coloured adhesive. The bond is very strong and will set up in minutes to 24 hours depending on type. Marine epoxies like West System are good - the challenge is finding an affordable, small quantity. There are small repair packs (little envelopes of resin and hardener) sold for about $15 for a half dozen pairs.
 
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