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Molding plexiglass?

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Old 05-15-06, 01:33 PM Thread Starter   #1
sno.lcn
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Molding plexiglass?


Can anyone tell me how to shape plexiglass and how hard it is to do? For my folding tower I want to have a giant clear plexiglass cylinder for the outside. Any ideas on how I would go about bending it? Or is there another material I could use?
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Old 05-15-06, 01:58 PM   #2
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I'd have to say something round to bend it around, a heatgun, and some weld-on adhesive should do it for you, and probably a lot of time. It just depends on how big it's gonna be and that will determine how difficult it's gonna be to bend.

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Old 05-15-06, 02:04 PM Thread Starter   #3
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Maybe 5-6ft tall and around a 2ft diameter. I'm thinking of suspending the mobos and such from wires going all the way down inside the case so I can get some nice cooling from a huge fan blowing up from the bottom.
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Old 05-15-06, 02:23 PM   #4
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From those dimensions it sounds like a somewhat thick bit of plastic... and a slightly tight curve to bend around. Yes that may be difficult - i STRONGLY sugest taking time in developing the jigs you will be using for this, they will make life much easier if planed out well.

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Old 05-17-06, 11:00 AM   #5
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ya heat will do it. ive done forming of plexiglass with ovens heat guns and stove tops. just remember to take it slow and be very patient. it you go to fast with the heat youll get bubbles and bends. and if you dont have enough heat it will crack on you. you can also do vacumn forming. its pretty simple you should look into it.
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Old 05-17-06, 04:28 PM   #6
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from the project log that I'll finish some time in 2020:
Quote:
Originally Posted by Vonkaar
So... yeah...

Originally, I was bending stuff with a hot-blower and a couple pieces of wood. This was more than a little barbaric, so I... constructed my bender. Total cost was about $50. If ya'll want another 'mini' update with pics on how this was done, let me know.

Anyway, the first set of bends looked like this:


You see how sloppy the corners are... it wasn't even square. Meaning, if I laid it flat like it is, one end pops up and it sort of rocks. I got a bunch of other bends to look a lot better with this method, but it became obvious that I'd have some serious trouble creating the 'truly' nice bends that I would eventually need.

So... I made the hot-strip bender and now I'm able to get perfectly square bends. I just made this thing for the 'mini' update:


You can see how much better the bends are looking... I'm able to make them perfectly square and can come up with all kinds of interesting shapes. Oh... the two 'imperfections' in the bend were intentional =p. You see the small fold in the 'boxy' part, that was slightly pressed forward for... er... flare. The second blemish is on the far lower-left. That's actually perfectly straight, the bent plexi distorted the image and makes it look odd. Otherwise, it's perfect! It's a perfect... er... thing.

My girlfriend walked in as I was finishing this and I tried to convince her that I made a recipe-book holder. She didn't buy it... nor did she cook for me. Anyway... the bender is great... I just wish I could chrome it or something because plywood is so 1994 Bob Vila =/
and about a year later...
Quote:
Originally Posted by Vonkaar

Howdy.

Alright... it's time. Back in the swing of things and such... from here on out, I have no excuses. Ninety-five percent of every single thing that I need to buy has been bought. The plastic people still have 3 or 4 other pieces to cut for me, but they are some of the 'last' pieces needed. Sooo... your 'hurry up, slacker' comments are now justified =p.

First, I said I'd talk about the bender a while ago. It's an incredibly useful tool and can be made for 1/10th the cost of a professional plexi-bender. I bought something called a "wire strip heater" from Tap plastics, although I've since found some local vendors that sell it for much cheaper. Anyway... this is the heating element that I use to bend the plastic.

Next, I bought a large piece of plywood from Home Depot. The idea is... you have a 3/4" to 1" wide channel to place the stripper into. You can do this with a router (which I don't own) or... the way I chose. The bender will be 24" long, so... I bought a piece of plywood that was 24"x24". I then had the sales guy cut the wood in half so I had two sections, 12x24" each. Then, I had the guy cut one of the pieces in half, leaving me with two 6x24" strips. Finally, I had him shave 1" off one of the 6" pieces, leaving me with my final assembly...
1 5x24" strip
1 6x24" strip
1 12x24" strip.

The 12" wide piece was the base for the bender. The two smaller pieces are then screwed onto the base, with a 1" space between them. If you go with heat resistant plywood, you don't need to insulate this... if not, it is reccomended that you place a layer of fibreglass in between the base and the two strips.

Next, a whole bunch of aluminum foil is bent around until I had a long U shaped channel... this is used both for heat insulation as well as reflection... a good portion of the heating depends on the aluminum foil. On one end, a grounding cable needs to be attached by a screw to the aluminum. The other end of this grounding cable should go to common ground.



Here we are.

Finally... when you have the aluminum foil channel secured in the path (using small tacks), you can place the wire-strip heating element inside the aluminum. When that's done... cong. You know have God-like powers over plexiglass. Little scrap pieces of acrylic bow down to your every whim. In fact, you might say... they'd bend over backwards HAHAHAHA!!! Villagers in Lexan-burg will sacrifice goats and cattle to appease you. You are PLEXI-MASTER. (too early in the morning... too much caffeine...)




Quick example of how easy it is to bend with this thing...

Step one: Heat it up for a few minutes, depending on the thickness and type of plastic. 1/4" lexan takes a bit longer than 1/8" acrylic.

Next... you can bend by hand, or use a wooden 'jig' to get your precise angles. I use a 90/45/45 carpenter's triangle and a long flat strip of wood. In this example, it's all by hand. You should take note that the only part of the plastic that heats up is at the bend... so... don't touch it with your hands. This is not only bad because of potential burns, but the fingerprints (and possibly flesh) will be permanently 'stuck' on the plastic. That sucks.

Now you can see how malleable the plastic has become. I've never had a fear of bending too quickly or pulling it apart like silly-putty... but it really DOES have the bend consistancy of... say... salt-water taffy. If you hold one end and flap at the joint, it WILL fly around. This gives you an idea on how easy it is to bend it precisely.

Once this piece is off the heat, it will start to dry and harden within 10-20 seconds. Plenty of time to get a precise angle. This time shortens if you are flapping it around the room shouting CAW! CAW! CAW! This took me several expensive pieces of plexi to figure out... it's either the airflow of the flappage, or there is some mystical connection between 'caw' and plexi-hardening time. Aaaanyway...

There you go. A perfectly rounded bend, with great optical clarity. Shine an LED into one end and the light follows to the other. Imagine the possibilities! And, yes... if you were wondering, that IS Stalin and Roosevelt sitting on their commodes.

So... I finished that plexi bender months ago... what is my excuse for so long in delaying the project? Well... a huge part were health problems. Headaches and then a few grand at the dentist (Damn you mountain dew!!!) prevented me from putting 'too high' a priority on this. But... that's all in the past! The project and I have renewed our vows of love and progress shall commence.
hope it helps... the bender was really useful and it only cost about $30 to build.

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Old 05-17-06, 07:30 PM Thread Starter   #7
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Awesome, thanks!
It's proving to be a little harder than I thought to get a perfect cylinder though. I'm using a 55 gallon drum as a jig and trying to make a perfect cylinder around it with the plexiglass, but it's not working out too well. If I use the cheap stuff with the blue wrapper on the back it fogs up a little and if I use the nicer stuff that comes with the green wrapper it doesn't retain the shape. I'm using a 500-1,000 degree heat gun. Do I nead a propane one or something? I'm thinking about switching over to fiberglass and just making plexiglass windows.
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Old 05-17-06, 07:54 PM   #8
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First off, please stop using the word plexiglass because it's not a material, but a very generic term for a diverse set of transparent plastics. Saying "plexiglas" is only slightly less generic than simply saying "plastic".
Quote:
Originally Posted by sno.lcn
If I use the cheap stuff with the blue wrapper on the back it fogs up a little and if I use the nicer stuff that comes with the green wrapper it doesn't retain the shape.
The first item you describe is probably lucite or another form of it meant for greenhouse windows and it cannot be heat-warped. I haven't come across anything with a green wrapper yet, but I doubt what you're trying to work with is acrylic.

You can really only safely heat-warp Acrylic for this purpose. Polycarbonate can be heat-warp, but is more resistant so you would need to work with lower thicknesses of it.
You have the right idea of needing to use a jig or form for the shape you want. They're vital because the sheets have the be held in the shape you want as they cool. You want to keep your operating temperatures below 300F and you want to do heating gradually. When working with such a large surface area you're going to need to use a strip heater in order to get uniform heating.

Call some local plastics shops and try to find one that sells their off-cuts. You should be able to buy what you need for a few dollars per pound.

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Last edited by Captain Slug; 05-17-06 at 08:00 PM.
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Old 05-17-06, 10:10 PM Thread Starter   #9
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Quote:
Originally Posted by Captain Slug
The first item you describe is probably lucite or another form of it meant for greenhouse windows and it cannot be heat-warped. I haven't come across anything with a green wrapper yet, but I doubt what you're trying to work with is acrylic.
I think the green one is lexan.
Quote:
Originally Posted by Captain Slug

Call some local plastics shops and try to find one that sells their off-cuts. You should be able to buy what you need for a few dollars per pound.
Thanks for the tip, I've been paying like $50 a sheet for this stuff and I keep messing it up.
Quote:
Originally Posted by Captain Slug
First off, please stop using the word plexiglass because it's not a material, but a very generic term for a diverse set of transparent plastics. Saying "plexiglas" is only slightly less generic than simply saying "plastic".
Sorry, I didn't know what else to call it.
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Old 05-17-06, 10:39 PM   #10
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GE Lexan is usually packaged in blue/white or a brown paper if it's a special order product. Polycarbonates such as lexan (and there are 5 other brands) require higher temps in a narrower range in order to be heat-warped without bubbling or carmelization. With polycarbonates you also have to forge the shape by either over-warping it or using a mold. Unless you need your case to have superior impact resistance it will be best to go with acrylic.

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