How to make a good homemade plastic bender - DIY
A plastic bender, also known as an angle bender, is a focused heater that will allow you to make tight bends in all thermal plastics, including acrylic, ABS, PVC, etc. These benders are really simple to build. Anyone can build one at home with minimal tools. You can purchase a commercial unit, but they are usually very expensive, starting at $120 for a 12 inch and $210 for a 24 inch on the very low end.You can also purchase a strip heater for around $60, I considered these to be overpriced and do not work well. My goal is to give you everything you need to know to build a good bender for less than $40.
You can purchase everything you need from your local hardware store or may be found for free. Here are the basic materials:
- Heating Element
- Tinfoil or metal roll
- Extension cord
- Metal channels
The first thing you need to do is determine how long you want your plastic bender to be. I decided to build mine 25 inches so I can comfortably bend a 2 foot sheet.
Getting you Supplies
Finding an heating element is really easy. I selected a calrod (a electric stoves heating element) it was for a 6 inch burner with 3 loops. These elements can be found at a local hardware store, thrift store, internet, or you could make some calls to appliance stores and find a used one for free. I found mine off ebay for about $10. You can also use a oven element if you making a 36+ inch size bender. In certain sizes you can also buy them straight, but generally a lot cost more. Some other ideas are stainless steel wiring that can be purchases from a fish and tack store, toaster heat wire, hair dryer or electric clothes dryer heat coils. If you are using a single strand, you might want to make multiply pass (without the wires touching) to increase your resistance so you are not pulling too much current.
You need to know a few things while selecting your heat element: resistance, current and voltage you are going to be supplying to the element to determine the power (heat) your element is going to have. The rule of thumb here is between 100-200 watts per foot of your plastic bender.
How to calculate it?
We need to do some simple math, known as Ohms law. In the US we use 120 VAC and I wanted my 25 inch heater to run about 300 watts. So I used ohms law where I(amps) = E (volts) / R (ohms) and calculated power, where power (watts) = Current (amps) x Volts. You must remember as something gets hotter its resistance will increase, for a heat element figure about 10%. My heating element is about 34 Ohms cold, just about right to plug straight into the wall and get my 300 watts.
You do not have to get it perfect, anything close will do. Also you can use a variac or a phase fired controlled to decrease temperature and current (effectively you are dropping the voltage feeding into it.) I don’t recommend buying a variac ($99) unless you have a need for one for something else. A phased fired controller is basically a cheap PWM for AC that only operates on the line frequency. You can build one with limited electrical knowledge for around $10. You can also buy one, Harbor Freight sells a variable rotor speed controller (5 AMP max) for around $24 that will work great for this plastic bender.
You need two metal channels at least the length of your desired bender. I used a ¾ inch square aluminum tubing purchased from my local hardware store. You can dig around and probably find something for free if do not want to spend any money, water pipe steel or copper would work fine, but harder to attach.
The board will be used for your base, wood is the general choice. Any scrap piece large enough will do.
Any old cord will be fine, if you have a broken device or dig thru the trash you can probably find one free. I just purchased $1 extension cord from Harbor Freight.
Getting started building
First, cut your board into the shape of you base. I cut mine 7 inch by 37. I took some really light gauge aluminum (you can make tinfoil work) 25 inches by 7 inch and mounted it in the center of the base. The purpose of the aluminum is to to protect the wood from heat. Cut your channels to your desired length and mount them. Since my channels are square I screwed them in from the bottom. If you use a normal heating element it is electrically insulated already (so you don’t electrocute yourself while cooking) if you are using something not insulated (toaster, SS wire, hair dryer) you will need to insulate between the element and all metal, a sheet or two of fiberglass cloths will do fine.
If you are like me and used a heating element for a stove, you need to break it off and unbend it. It wasn’t hard to get off, just a pair of pliers did the job, if that doesn’t work try a Dremel. Straighten it out is a little bit of a challenge; I recommend two pairs for large pliers or vise grips and some clamps.
Place your heating element in the channel and make sure that you are not going to short anything out. Cut the top off your cord and wire it to each end of your element, make sure that the wires are not shorting themselves out across anything metal on your bender. I might recommend isolating your heat shields.
How to use
Plug it in and give it a minute to heat up. Mark your plastic where you want the center of the bend to be and align that mark in the center of the heat channel. Depending on the power and thickness of the plastic you are trying bend depends how long you need to wait; you want the plastic to bend easily so you do not stress the plastic. For 1/8 acrylic on mine it usually takes around 1 minute. For larger pieces you might have to flip them over and heat both sides. When it will easily bend, remove it and bend it. Be careful not burn yourself. A bending guide is a good idea, a square or protector or anything else that will help give you the perfect angle. Hold briefly and allow to cool and re-harden.
If you don't want to build your own, you can use a plastic strip heater instead. They are less costly than buy a normal plastic bender.