# 12-19V strip heater for bending plastics, help needed

#### baronpork

Joined Apr 16, 2013
67
I need an acrylic sheet bender. Checked out prices of the machinery and noped out real quick.
Heatgun bending is not an option as pretty precise and neat bends are required.

Can someone help me figure out how to go about making one ? I've seen some videos of people making them but usually all electrical bits explanation is missing.

Ideally i need something that can strip heat a length of about 600mm, powered by 12V (ATX power supply?) or 19V (laptop power brick, beefier one, over 3 amps? ).

How to go about calculating the nichrome wire i need, gauge and power requirements to achieve needed temps. Don't need the wire to glow white, just to keep to ~200-250 C. (I have some dead toaster heating element wire unwound somewhere in the parts bin...)

Don't want to go full mains voltage (240V) for safety considerations.

Anyone here constructed such a contraption ? Need input

#### LowQCab

Joined Nov 6, 2012
2,171
If You are tight on Money, I would suggest picking up a used "Toaster-Oven" at a Thrift-Store.
Some of them have very nice Tubular Ceramic Heating Elements,
which will "probably" provide the Temps that you need with around ~50 volts, AC or DC.

The trick with any DIY project like this one is accurate Temperature-Control.
That's why the commercial units cost as much as they do.

You "might" be able to get away with using a very high-power Lighting-Dimmer to
have "some" basic control over the temperature,
but if you require actual contact of the Acrylic to the Heating Element,
Accurate Temp control will be very difficult.

And You MUST HAVE Accurate and Repeatable, Temp-Control.

Low Voltage operation will usually require
an expensive Power-Supply Transformer, (~$150.oo, ~$200.oo),
but you may be able to create your own High-Current Transformer from
a used "MOT" (Microwave-Oven-Transformer),
but then there is still the problem of accurate-Temp-Control.

250-C may require a "Thermocouple" to sense the Temperature accurately,
the output of which will then need to be amplified and used to control
a PWM Power Supply Regulator.

I estimate that you will spend more Money and time getting a DIY unit to
consistently produce the results you are looking for,
than it will cost to purchase a Commercial unit.

I would use Hot-Air, blown from narrow-slots,
on the top-side, AND on the bottom-side of the Bend,
to transfer the Heat to the Acrylic Sheet.
The Temperature of the Air is easier to control and direct,
and will provide more even heating, with no hot-spots, or cool spots,
and a much reduced chance of melting.
.
.
.

#### shortbus

Joined Sep 30, 2009
9,441
Or switch from acrylic to polycarbonate/Lexan that can be bent cold in a brake.

#### MrChips

Joined Oct 2, 2009
26,512
I would straighten the heater wire from an electric space heater and use a light dimmer to adjust the power.

#### baronpork

Joined Apr 16, 2013
67
Or switch from acrylic to polycarbonate/Lexan...
...and die of fire and smoke while laser cutting parts needing to be bent in the process
PC cant be cut neatly with CO2 lasers, which makes it a useless material to me...

#### shortbus

Joined Sep 30, 2009
9,441
...and die of fire and smoke while laser cutting parts needing to be bent in the process
PC cant be cut neatly with CO2 lasers, which makes it a useless material to me...
And from your question how was the method of cutting known?

#### baronpork

Joined Apr 16, 2013
67
Well, i did state "acrylic" in my initial post. I didnt state cutting method as its irrelevant to my question, but i do apologise for that.
Having a laser cutter one quiclky learns differences between plastics where it becomes second nature and so obvious i'm forgetting to mention it

#### MisterBill2

Joined Jan 23, 2018
12,431
My experience with bending plastic is that in general it conducts heat rather poorly, and so it takes a while for the heat to soften all the way through. It is also subject to damage if the temperature is too hot, and so the applied heat needs to be carefully controlled. This means that an open nichrome element will not be suitable. You need to duplicate the commercially sold devices more closely to achieve the results you require.

#### shortbus

Joined Sep 30, 2009
9,441
Well, i did state "acrylic" in my initial post. I didnt state cutting method as its irrelevant to my question, but i do apologise for that.
I was putting the Lexan out there from having to remake many machine guards over the years. Ones that were originally Plexi and made in glued pieces that could be made in one piece by cold bending the Lexan. This the switch from Plexi to Lexan was because the Plexi is no longer legal for machine guards.

#### Sensacell

Joined Jun 19, 2012
3,011
You will need more power than you might expect.

If the wire touches the plastic- burn/stink/fail. This means an air gap.

You need the IR radiation + some air convection to heat the material, it's gotta be much hotter than 250C.

#### MisterBill2

Joined Jan 23, 2018
12,431
Lexan iis much tronger, but I have accidentally shattered a piece one time, cleaning up a sawed edge using a fly cutter in a mill, spinning fast and feeding a bit too fat and all at one. The cutter was sharp enough and the setup was correct, just took too big a bite at one point.
Why was an EE running a mill? Because I knew how, and was allowed to do personal projects during lunch breaks. And I was totally accepted by the shop folks.

#### Lo_volt

Joined Apr 3, 2014
268
Years ago I put together a heater for bending plastic sheets. I don't recall whether it was acrylic or polycaronate. It's too long ago, but I'm leaning toward it having been acrylic.

We used nichrome wire for the heating element and a Variac to vary the temperature. It took some experimentation to come up with the right setting.

We created a wooden trough about 2 feet long and about 1 inch wide and deep which we lined with ceramic tiles. The width will determine the heated area and therefore the maximum bend radius. We placed the nichrome wire deep in the trough stretching it from one end to the other with some tension to hold it tight.

It was clunky and we certainly didn't bend to any great precision. I think it's possible to improve on that by heating from the top and the bottom of the sheet. I'm not sure but some experimentation may be in order.

If you want better control of the temperature it may be possible to use an SCR to control it with feedback from a resistive temperature sensor or a thermocouple.

#### MrSalts

Joined Apr 2, 2020
1,841
Lexan iis much tronger, but I have accidentally shattered a piece one time, cleaning up a sawed edge using a fly cutter in a mill, spinning fast and feeding a bit too fat and all at one. The cutter was sharp enough and the setup was correct, just took too big a bite at one point.
Why was an EE running a mill? Because I knew how, and was allowed to do personal projects during lunch breaks. And I was totally accepted by the shop folks.
polycarbonate often shatters when you get binding between cutter and fence - binding is caused by high CLTE and total linear movement of PC before it softens. At some point, it has no place to go and you get catistrophic failure if (and only if) you have a high speed cutting tool on one edge.