How to: Build a heater strip to bend acrylic for 30 bucks or less!
Here's my little contribution to mp3car.com, hopefully someone finds it useful:
So you want to bend acrylic to make that "gucci" computer case or amp mount, but don’t want to fork out a lot of dough to have someone with the equipment do it.
Understandable, and with proper units costing anywhere from 200 bucks to a couple thousand, what's a guy with the customizing bug to do?
I didn’t want to spend that much either so I started digging around and finally ended up building my own acrylic bending rig.
And it only cost about 30 bucks total! (Could be free if you're a good "dumpster diver" or have lots of junk hanging around)
So, here we go:
Saw (table saw, circular saw, or if you’re really energetic a hand saw)
Drill and bits
Measuring tools (tape measure, etc)
Hammer, screwdrivers, etc, etc…………the basic stuff.
Old hair dryer
16 gauge wire
Crimp on ring terminals
Wood nuts #10
Bolts #10 about 2” in length (adjust as required)
¾” sheet of mdf (2’x8’ is more than enough)
Wood glue (optional)
Deck screws or MDF screws (you only need 10 or so)
½ “aluminum channel
12 V power source capable of at least a 10 amp supply (I use a battery charger)
The how to:
(This is going to be kind of long, so settle in! You may want to print it if you're going to build one......)
What you will be building is this:
Making the heater strip:
Start by taking apart a hair dryer. I had an old one lying around, but you can pic one up anywhere for a couple bucks. What we’re after is the coiled wire in the nozzle of the dryer, this is the heating element. It's made of Nichrome and that's what we're after. It has a high resistance and that's what makes the heat when an electrical curent is passed throuh it. Same stuff is in toasters, toaster ovens, etc. Snip the end where it’s attached to the form and unwind it from the heat proof cardboard (mica or something like that) or whatever it is.
You want the biggest of the coils. Put the others away for another project (small ones are good for heater plastic cutters). I also saved the motor as it’s a 12v motor that can move a lot of air (never know where you’ll use one of those!).
Head out to the shop and clamp one end of the wire in the vice and use a pair of pliers to hold the other. Carefully pull the wire to straighten it as much as possible. Don’t pull too hard or you might break it. You’ll also be quite surprised about how long that sucker actually is!
Once you get it mostly straight (it will always have a twist in it so don’t sweat it if it isn’t bone straight), take the two ends and double the wire up.
Now take the two ends (or the looped end, doesn’t matter which) and clamp it in the vice again. We’re now going to twist the wires together. Take the free end and chuck it up in your cordless drill. Slowly turn the drill on and twist the whole length of the wire.
Congratulations, you just made your first “heater” strip!
Determining the heater strip length:
Once that is done, we need to know what length of the wire you can heat with the power supply you have on hand. The length of the wire you can heat depends on the thickness and resistance of the heating wire and the amps your PS can produce so everyone is going to be different. Mine is about 2 feet long which is just right for about any project you would want to do yourself.
Take one of your un-insulated ring terminals and insert the heater wire into it the normal way. Take a piece of your 16 gauge wire (about 10 feet we’ll cut it later), strip the end, and insert it into the ring terminal backwards. Crimp it down nice and tight. It should look like this when done:
*lost the pic somenow, I'll get another soon*
Clip your power supply to one end of your newly twisted wire.
*BE CAREFUL WITH THIS NEXT STEP. THE WIRE WILL GET HOT, POSSIBLY RED HOT, AND BURN YOUR TABLE OR YOU! NO FOOLING AROUND HERE GUYS. THE HEATED WIRE WILL CUT RIGHT INTO YOUR SKIN (AND DEEP) IN A BLINK IF YOU TOUCH IT!*
Turn on your power supply and touch the other end of the circuit (positive or negative ends if you prefer that terminology) to the heating element. Watch for the wire to get hot or even glow red hot. What you want here is to find a length that allows the wire to just barely get that “dull red” glow (It's so faint, you won't be able to see it unless the wire is in a slight shadow, it'll look pretty much normal in regular light). Any hotter and it may burn the acrylic, any less and it may not get hot enough to let it bend without cracking. As I said, mine is about 24 inches long. But if you find you want yours shorter, just clip your PS to the 16 gauge wire at different lengths (remember the 10 foot length?) until you find the right resistance. Look for that “dull red” color.
Now that you’ve determined the optimum length, cut your wire to length and crimp another ring terminal on it in the normal fashion.
Set your heater strip aside for now.
Construct your base:
Obviously, this is dependant on the length of your heater strip. You will want to cut your MDF at least 3 inches wider than the length of your strip.
Now cut a second piece of MDF the same size as your first.
Mark a centre line across your first piece. This is where your aluminum channel will go. Cut your channel a little bit shorter than the total length of your heater strip.
You can see the length here:
This will protect the MDF from the heat and direct the heat up to the desired bending area of your acrylic.
Now you need to cut your second piece of MDF in half. Place the aluminum channel on your center line and sandwich it between the two cut pieces of MDF. Make it nice and snug. You want the channel either flush with the top pieces or slightly recessed. You can use some wood glue to hold the halves to the base, but I just put a screw in each corner to hold it together.
Take another piece of 16 gauge wire and crimp a ring terminal on it. Drill a hole into the Mdf base, slip the ring terminal over the wood nut and insert the wood nut from below.
You can hammer it into the wood if you wish (recommended).
At the other end of the channel, drill another hole and insert another wood nut from below.
Your base is now done and it’s time for final assembly.
Take one of your #10 bolts and spin a nut on it. Slip the ring terminal on your heater strip on (the end without the 16 gauge wire). Spin 2 more nuts on the bolt. Push the bolt into the hole in the MDF at the end of the channel (the end with the wire on the wood nut) and spin it into the wood nut. Tighten the bottom nut down to tighten the bolt and keep it from turning.
Now take your small spring and attach it to the other ring terminal.
*lost pic, I'll get another soon*
The purpose of the spring is to keep the heater wire taught as it will get longer as it heats and not carry any of the electrical load (that’s why you crimped the 16 gauge wire backwards into this ring terminal). So you will want to have a little tension on the spring when you install it. It doesn’t take much! Spin a bolt into the wood nut (put a regular nut on the bolt first to secure it afterwards) at the end of the channel and slip the spring over the bolt.
Now adjust the height of the ring terminals on your bolts to have the heater strip below the top of the aluminum channel but not touching the sides or bottom. Once you get the height right, tighten the two nuts together on the plain ring terminal end to hold it there.
You can adjust the length of the spring also if needed (you may have to adjust the tension after you heat the wire also, remember it will get longer as it heats).
YOU’RE ALMOST DONE. STAY WITH ME NOW!
You want to mark some reference lines on you base so you can keep your acrylic lined up while heating. Use a tape measure and mark lines on the base parallel to the aluminum channel (I marked it every ¼ inch, but do as you wish).
Whew! The assembly part is done! A few adjustments and we’re ready to go.
Now, let’s give ‘er a test run.
Clip your power supply on either end of the heater strip by the 16 gauge wire. Again, you’re looking for that dull red glow. Make sure the heater wire doesn’t sag enough to touch the channel. If it does, shorten your spring slightly and try again until you get it just right.
Now take a piece of scrap plexi (or lexan, or whatever you need). Place it on the heater, line it up to where you want the bend and turn on the power supply.
Wait for about a minute or so, and then try to slowly bend up one side of the plexi. If it’s warm enough, it will bend in a perfectly straight line along the heated part. If it doesn’t move easily, let it warm a bit more.
With enough practice you can bend plexi to any angle you need. Here’s a scrap piece I bent to make sure the strip works:
As you can see, 90 degree bend and perfectly straight with a nice tight radius and no cracking!
Took me about 1.5 minutes.
You can bend to whatever angle you want or need.
You can make boxes, covers, etc. Clear, smoked, plexi, lexan - You’re only limited by your own imagination.
You can also light these things with led’s. Leave the plexi clear and it will appear “edge lit” or you can lightly sandblast the plexi to have the whole thing glow. You can get really fancy by sticking a logo on the plexi, sand blasting it, pull the logo off and it will glow around the logo!
Now, start creating some stuff out of acrylic! It’s marvelous stuff!
*Just so there's no confusion, the bulk of the "technical info" came out of a magazine I read recently, car audio something, but I can't rememeber which*