Plastic Bending Strip Heater

I'd like to propose for discussion at tomorrow's meeting that the Hive consider obtaining a plastic bending strip heater. These can be incredibly fun and useful, particularly when used in combination with the laser cutter. Acrylic flat patterns can be cut on the laser, CNC, or in the wood shop then folded along lines to make stands, boxes, covers, cases, etc. these can be used to bend up to 1/2" acrylic, which even opens up the possibility of making acrylic furniture. These can also be used to heat smaller pieces over larger areas by moving them around over the heater to make freeform shapes by hand bending, twisting, and shaping.

48" X 1/2" strip heater, $295, 4.3 out of 5 star from 14 ratings

24" X 1/2" strip heater, $215, 5 out of 5 star from 7 ratings

Just google search "bent acrylic" for some examples of possibilities.

I personally have a few phone/tablet stands and charging stations that I'd like to make using one of these (that I already have the material for) and plans for some future computer/electronics enclosures.

Interestingly, making a strip heater came up in a side conversation yesterday. We have a transformer and voltage control lashup. I have a bunch of nichrome salvaged from an old dryer. Along with some hardy backer board strips, we could lashup a strip heater. Probably a better one that I’ve used in the past.

That said, in my experience, heat is only one element of the process. The often overlooked piece is the form. Once heated the plastic is - plastic - until cool.
A shape with the right angle and radius to lay the sheet over until it freezes into position. Good thing we have a saw and router to shape forms.

I personally have only ever done freehand bending, and it is definitely possible to get good results, but I am sure some MDF forms/brakes would make it more consistent.

I’d strongly advocate building. In this case, the result are quite good, the project is easy and fast, and the machine is more versatile.

Nichrome works great. But, for durability, simplicity, and safety I often get silicone or kapton heaters:

https://www.aliexpress.com/store/709519?spm=2114.10010108.0.0.24377282r5Usq9

A 400mm (13") strip is $10. They make them in any custom dimension you ask for for the same price level. So, a one meter heater would be about $20. Very nice, even heat. It’s such a simple technology. A machine “prints” wires on kapton or rubber, and the resistance heats it up.

Look up PTFE (non-brand name for teflon) coated fiberglass or foil tape. It’s used on the jaws of machines that thermoform and seal plastics. It’s as cheap as $10 a roll. PTFE coated aluminum bar is easily obtained too. There are plenty of us who can help with machining, wood forms, etc.

Heck, we have a vacuuform. If you’re doing a bunch, vacuform over a form you carve or scuplt or 3d print, then cast in the mold created with fiberglass or cement or plaster or cement or whatever. You could have a production quality mold & form.

L

Last night we discussed building a strip heater. I promised the attached sketch, such as it is.
We can make this from parts we have in the HIVE or at home. While definitely not UL approved, it can be made safe enough to use. Given that the user is wise enough not to stick a fork into a toaster. If we add one of my spare GFI’s then, it’s as safe as you can make a heater.

If there is interest in a build, I’ll contribute a 4 ft x 18 inch sheet of concrete board and the skill saw blade to cut it. The board is smooth, though it could be dressed up with PTFE tape. Long ago, I made a heater with drywall as the frame. Though it scorched the drywall paper, it also bent plastic.
I’ve also got a bag of nichrome wire to use. Brad volunteered the heater core of a kitchen appliance.

The online videos using heat guns and torches are crude and hand formed. You get better results with a form to drape or lay the softened sheet against. It’s also the way to control the bend radius.

Strip Heater Sketch.pdf (644 KB)

I’m down. I can contribute misc hacker skills. Also, I have all sorts of kapton tape and film (which is useful for electricity + heat), as well as some ptfe and latex materials. I’ll look around.

I also just threw together a calibrated VOC sensor. So, it might be fun to measure the parts per billion of toxic plastic fumes emitted during operation. This is a personal project, though. Hive is on its own…

Lorin

Looks simple and usable! if we want to up the safety just a bit, we could enclose the heating wire in a fused quartz tube, they are not terribly expensive in the size and length we would need for this.

Today, I brought the concrete board and some salvaged nichrome wire down to make a test set up using a transformer
and dimmer to demo that it will work. The concrete board is cut into 60" long strips, I tested 48 inches of nichrome.
Let’s discuss and figure out what the length should be then cut it to length.

While hot, the wire grows in length and moves a bit. That might be the best reason to use a quartz tube.

The parts assembled so far are on the electronics bench.

I picked up some heavy copper terminal lugs, (cause the heat fried the wire nuts used in the test.)
a gang electrical box and a spare GFI from my house rehabbing leftovers. I’ll bring them in tomorrow.

Dave

Was nicrome wire the stuff called ‘muscle wire’?

Nope. There’s a shape-memory wire alloy called nitinol aka muscle wire – similar name, different stuff.

Nicrome is the wire in toasters that gets red hot when electricity is applied. It’s also cheap (muscle wire is not).

Lorin



From: Raven Abird
Sent: Tuesday, April 24, 2018 6:34 AM
To: cincihackerspace@googlegroups.com
Reply To: cincihackerspace@googlegroups.com
Subject: Re: [CHP] Re: Plastic Bending Strip Heater

Was nicrome wire the stuff called ‘muscle wire’?