Plastic bender

[elib]

Hello everyone,

Introduction:
I'm currently working on a project about food growing. In order to do it I need a bench to bend plastic (acrylic) easly to make the main structure. The goal is to bend plastic and also being able to make precise curvy bends.
I have seen some DIY project that propose to heat up a wire of nichrome from a batteryy/variac and other..

Here are some examples :

- http://www.wa4dsy.com/robot/hot-wire-plastic-bender
- http://www.instructables.com/id/How-to-build-a-Plastic-Heat-Bender/
-

Project:
Here are some picture of where the project is a this moment.

Picture 1: whole structure made of agglomerated wood, aluminium beams and small other pieces.

Picture 2: show hoz the structure is going to bend the plastic

Picture 3: it's the area where the wire is going to stand and heat up the plastic



Next:
I'm novice in electronics and I need to find the best and safest solution to heat up the wire.
Some possibilities:
- Use a Variac : expensive but easly customable, electricity could be dangerous
- Use a 12V battery 7mAh: less expensive but how long os the battery gonna last? Less dangerous with electricity as I would be playing with 12V
- Use a voltage variator: look also dangerous because I would be playing with hight voltage. But cheap
(http://www.befr.ebay.be/itm/REGOLAT...172918?hash=item33b3a38fb6:g:kMwAAOSwMORW6-KO)

What would you do?
What nichrome would you use?

Thanks in advance for your answer, I'm gonna give you the result as soon as possible!

 

[Mr Random Guy]

Do you have an old microwave lying around? Saw a great video of some guy that rewound the secondary of the transformer in it with a very small number of windings so that the voltage was very low (5v or something stupid so no shock risk) but the current insanely high because power = current * voltage and power stays the same. Run that through that nichrome wire stuff and it will heat up very quickly. And I believe the primary just runs of mains so no batteries

He did use a VERY thick guage wire though to handle the current though

 

[KTW]

Could you use an old iron for pressing clothes?

 

[shrtrnd]

This may not be practical for your application, but I'll throw it out for consideration.
Your project looks like it may be too large for this:
When I was younger, I used to make a lot of wood art-type things, and got into integrating Plexiglas into the wood
designs. A leaping antelope with a wooden body and horns, but Plexiglas legs and neck. Same with a horse, and some other wall-art.
Anyway. I cut the Plexiglas to the size and shape I wanted, then put the sheet into the conventional kitchen oven.
It didn't take long, we're talking minutes, and I could remove the Plexiglas sheet from the oven, and had FULL ability to bend and shape the plexiglas to any shape I wanted for about 20 to 30 seconds while the pliexiglas cooled.
It looks like your acrylic may be too large for an oven, and you may think this idea not practical for your application, but you asked for opinions/options, and that's mine.
The remarkable thing about the method I used, was that the Plexiglas molded to any shape I wanted, remaining completely clear at the bends. Not an imperfection to be seen anywhere on the sheet.
If you heated a Plexiglas sheet, removed it from the oven and quickly placed it on your hinged, folding shaper with a
straight-edge secured on the top of the sheet where the fold will occur, it's an idea to consider.
Your nichrome wire for one straight fold SOUNDS easy, if it works well for you.
Just thought I'd submit a different idea to consider if needed.
The reason I bring this up is primarily aesthetic value. There are many different types of acrytic sheets, some are very brittle and others not. It seems to me heating the entire sheet allows you to make bends with clear results. Depending on the acrylic, making a bend at the heat source with cooler areas adjacent to the heated Plexiglas area, might allow for the white krinkle-type imperfections in the Plexiglas you usually see in stress points the plexiglas is subjected to. In this case thermal stress where the cold meets the hot.
If your nichrome wire works well, congratulations on your project.

 

[elib]

Thanks for your answers.

@Mr Random Guy : I might have one. The process look more complicated that what I'm doing but It could be a good solution if I don't achieve mine.

@KTW : old iron? Definately not what I'm looking for.

@shrtrnd : the oven technic look cool but unfortunately mine is too small and the number of parts to bend is too big. I'll keep it in mind if I have to make more original bending.


After some research here is the solution I suggest:
- Nichrome wire 0,5mm - 5,551ohms/meter (I use 40cm, 2,2204ohms)
- 12v 7amps power supply

0,5mm nichrome wire with 6A heat up to 760°c (http://hotwirefoamcutterinfo.com/_NiChromeData_files/1_Amperage.jpg)
U = 2,2204 * 6 = 13,3224v

So I could use this kind of power supply (12v):
https://www.amazon.fr/Bloc-daliment...ie=UTF8&qid=1463613101&sr=8-1&keywords=6a+12v

What do you think about this solution?

Some questions:
- 12v power supply while needing 13,3v what's the matter? Is it better to target 649°c with 5amp and needing 11,102v or even ?
- Do you think 760° or 649°c is enough?

 

[duke37]

A Variac will be good to vary output but must NOT be used direct since it is not isolated. You could use a Variac to drive a transformer or old style battery charger. I know of a lamp dimmer being used instead of the Variac but you may get trouble from transformer saturation. A series bulb in the primary will protect against this.

I am not clear on what the wire is doing, if it is heating the acrylic by radiation, then a high temperature is required but if in close contact, then a low temprature is necessary. Some time will be needed to diffuse the heat throughout the thickness of the sheet.

 

[elib]

The wire is there to heat the acrylic. What do you think of my proposition. A simple power supply well calculated isn't a good choice?

 

[Mr Random Guy]

The wire is there to heat the acrylic. What do you think of my proposition. A simple power supply well calculated isn't a good choice?

I think the PSU idea will be fine, just wondering how long the wire will have to be in contact with the acrylic before it will bend