bending acrylic

[opengswede]

Ok, just got back after a two-week vacation with some modding attached.

My current idea is to build a skull-shaped case (sort of) in clear acrylic.
The first solution was to cast it in clear plastic, which turned out to be quite difficult since home-cast plastic always contain bubbles (I need a vacuum mould to handle that).

Then I saw a comment on the "tips and tricks with acrylic..." thread from tybrenis (are you still around?). The content was basically that you can shape acrylic to any form using a hot air gun and a wet cloth (and something to press against).

Trying this proved to be difficult though and hence my problem: the acrylic piece i use is 6mm thick and it took hours to get it warm enough to bend, but only slightly. That is, after heating the piece for approx. 1.5h i managed to bend the acrylic about 2mm. But when I apply pressure, using the wet cloth, the plastic cools and hardens, meaning another 1.5h of heating before I can start bending again.

Now my questions:
Should heating take this long (ie hours)?
Is the acrylic too thick (should I use a different thickness)?
Is there a more efficient way of doing this?

I'm moving this week, so there's not going to be much modding for me, but the next plan, if this isn't going to work, is to use something different (glue, or silicon) to do the case in and then reinforce it afterwards.

-.erik

[GT40_GearHead]

what are using for heating

[Cannibal23]

no it should not take long at all to heat this up. of course it does depend on what your useing to do the job though. personaly i have been useing the stove top element in the kitchen and or a heat gun / paint stripper gun. both of these methods dont take long to get a reasonably thin peice of plex warm enough to mold. i do however only usually heat up the part i wish to bend rather then the entire sheet if thats what your talking about. useing the wet cloth method i described in my tips secion that you have looked at, will work for some things but its not ment for large ammounts of work. in your case i would say casting is totaly the way to go if at all posable. i understand your concern about the bubbles, so here is something you might check out. maybe google for haloween props involveing clear skulls and see if anything suits you. as for bending it by hand i think that would be alot of work and probably painfull as you will most likely burn yourself doing it. sorry for the delay in responce, i didnt see this thread till just now.

[opengswede]

Yeah. I've been thinking about pre-fabricated stuff too, but usually they have a lot of crap on them. Plus, i'd lose the satisfaction of doing it myself.

The reason I had to heat the whole sheet is that in order to bend one part, the neighbouring parts hinder the bending process, I have to bend in 2 dimensions. Hence my thought of heating the whole thing. But appartenly it is a bad idea, and i'll try something different.

I gave it a shot and it didn't work, now back to reading on molding and casting methinks.

btw: I had an idea that I could cut the thing out from a large block of plexi, kind of like sculting. However, the price quote I got on that block was unbelievable, I mean eqvivalent of $1200US for a block of plastic, come on.

Thanks for the feedback.
-.erik

[chedabob]

you could try a vacuum mold. if you know somebody with a vacuum former, you could get a wooden model made, then mold it.

[Cannibal23]

thats exactly what i was about to suggest. as long as it dosent have to be solid that might work out for you. as an alternitive you may try takeing 2 seperate peices of plex and heat molding them one for the main body of the skull being the back and the part that curls over the top and then use the other one to mold the face and sides then glue them togeather.

[tybrenis]

You should be able to bend 6mm acrylic on something such as a line bender, for instance. A heat gun is pushing it, but maybe if you flipped it over halfway through, that would help you a little bit.

Ditch the wet cloth idea until you need to cool your acrylic.

[opengswede]

thanks for the tips guys.

I'm going to try all these ideas, starting with the last first, since I've got the setup for that already :)

Anyway, I'll see what works... right now we're in the middle of moving so everything is packed in a box that I can't locate...

thanks again guys.
-.erik

[Nox]

You also might try looking online for techniques on how to make Star wars stormtrooper armor. I saw an article where they took a sheet of plastic, stuck it in a clamp that was just a square but with an open center, and heated the plastic in a 400 degree oven until the center of the plastic sagged 2 inches from the frame, then they used a home made vacuum mold to suck the plastic around a mold of a stormtrooper helmet.
They even show how to make the vacuum mold out of household items and using a shop vac for the negative pressure.
I saw it, I know its out there - I'll look around today and if I find it again, I'll post a linky link.

*Edit*
Found the links to to the job, Mind you - they are using polystyrene, not acrylic.
You may have to modify your techniques or research some more on how the differences are between the two.
Working with plactics:
http://www.studiocreations.com/howto/vacuumforming/index.html

Building a vacuumform table and frame:
http://www.studiocreations.com/howto/vacuumtable/index.html

[tybrenis]

You also might try looking online for techniques on how to make Star wars stormtrooper armor. I saw an article where they took a sheet of plastic, stuck it in a clamp that was just a square but with an open center, and heated the plastic in a 400 degree oven until the center of the plastic sagged 2 inches from the frame, then they used a home made vacuum mold to suck the plastic around a mold of a stormtrooper helmet.
They even show how to make the vacuum mold out of household items and using a shop vac for the negative pressure.
I saw it, I know its out there - I'll look around today and if I find it again, I'll post a linky link.

*Edit*
Found the links to to the job, Mind you - they are using polystyrene, not acrylic.
You may have to modify your techniques or research some more on how the differences are between the two.
Working with plactics:
http://www.studiocreations.com/howto/vacuumforming/index.html

Building a vacuumform table and frame:
http://www.studiocreations.com/howto/vacuumtable/index.html

I have a vacuum former that I recently built. I could probably do a piece like this with the mold all ready made. I built my own using my own plans after reading about a home made machine online.

[opengswede]

cheers guys.
I'll look into this. It doesn't look implausible at all, now I just need to convince my gf that I need to use the oven for a while...

Perhaps I should build something custom for this... a more powerful heating element for instance.

-.erik

[tybrenis]

I built my vacuum forming oven using Nichrome wire and cement board.

[Cannibal23]

i just used the "wet rag" meathod again on the weekend. dont see what all the fuss is about. seems to work fine although requires some patients and a few trys to get it right. wish i had a vaccume former ..... (hint, share your plans Tybrenis lol)

[tybrenis]

i just used the "wet rag" meathod again on the weekend. dont see what all the fuss is about. seems to work fine although requires some patients and a few trys to get it right. wish i had a vaccume former ..... (hint, share your plans Tybrenis lol)

I'll be writing up a guide on how to build a vacuum former soon. I'm re-doing my oven.

Well, I don't have any pictures of the oven yet, but I do have pictures of the vacuum box being built. The thing was, I had one design with the oven built above the vacuum table, and that failed miserably. So now, I use a seperate oven and then the vacuum table. Here is the table from start to finish. Forget about those "posts" on the side on the last pics. Those are no longer there.

http://www.powerpackedpc.com/images/tbcs/DSC00989.jpg

http://www.powerpackedpc.com/images/tbcs/DSC00991.jpg

For this part, I will be using a shop vac for the suction. So, I bought a shop vac adaptor tube at home depot for like 5 bucks, and installed it on the bottom of the vacuum table. I then sealed the entire thing with silicon caulk for airtightness.
http://www.powerpackedpc.com/images/tbcs/DSC00997.jpg

I then used foam weather gasket tape on the rim of where the pegboard will go. This will create an airtight seal, if done right.


http://www.powerpackedpc.com/images/tbcs/DSC00999.jpg

My shop vac
http://www.powerpackedpc.com/images/tbcs/DSC01012.jpg

Shop vac attached to vacuum table. I used pegboard for the surface. The even distribution of holes will suck the plastic around whatever we're molding.
http://www.powerpackedpc.com/images/tbcs/DSC01013.jpg

Heres a quick video for you:

http://www.powerpackedpc.com/images/tbcs/MOV01016.MPG

[Cannibal23]

in that video its just plastic wrap right? thats not acrylic is it? looks a little thin

[tybrenis]

in that video its just plastic wrap right? thats not acrylic is it? looks a little thin

Lol yeah thats just plastic wrap, and the vacuum is much much more powerful when I am actually molding something, because I get an airtight seal that way.

[Cannibal23]

so do you have to cut your peice of plex to snugly fit the box, heat it up, form it cool it and cut the extra? or can you use any size plex? if you couldent tell im like drooling at the mouth looking at this.

[tybrenis]

so do you have to cut your peice of plex to snugly fit the box, heat it up, form it cool it and cut the extra? or can you use any size plex? if you couldent tell im like drooling at the mouth looking at this.

Lol, I built frames for different sizes. I have a frame for large, small, and medium sized forms. Basically, you choose what size you need, then clamp your plexi in the frame. Then you pull your frame (once the acrylic is hot enough) over the mold, and it creates an airtight seal (the vacuum surface has an outline of weather tape on it). Then you turn on your vacuum, and presto, you have vacuum formed plastic.

[opengswede]

what kind of heating element do you use in your oven? I found this (http://www.chemcastacrylics.com/technical/mx4.htm) page and they specify several options, electric oven, IR heater, gas, etc.

thanks for the layout though... that makes building it so much easier...

-.erik

[tybrenis]

what kind of heating element do you use in your oven? I found this (http://www.chemcastacrylics.com/technical/mx4.htm) page and they specify several options, electric oven, IR heater, gas, etc.

thanks for the layout though... that makes building it so much easier...

-.erik

I used nichrome wire, an electric heating element, conrolled by a variable transformer.

[opengswede]

beautiful, thanks.

-.erik