12-19V strip heater for bending plastics

[slowpoke]

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

[beanflying]

I looked at making one ages ago and decided to go pay someone at the time to do it for me 

There is plenty of videos on youtube including the one below but the key to it is control over the sheet when you have the bend area softened so some light clamping helps keep it nice. Also as per the video below the heat is controlled to a localized area by the channel which is fairly standard with the commercial units. Some Kapton or fiberglass tape to keep any bit of the acrylic away from the aluminium might be good too.

Ball park 0.8-0.9mm Nichrome or Stainless Mig wire will be fine somewhere between 12 and 20V. A 12V car battery way back when used to be my go to for Foam cutting at 900-100omm typical temps are similar to what Acrylic needs to soften but the shorter run you will be close at 12V and 600mm with an extra 300-400mm run and an alligator clip to adjust the temperature. You should also be under 5A so even a decent bench supply will cope.

[wizard69]

I haven't created a bender but at work we have a variety of heat seal tasks.   What your want covering the metal is PTFE tape.   The Tape is specially designed for such usage.

[beanflying]

Unlike the heatsealers the wire is below the surface of the table so you are better off without a cover for faster heat transfer to the acrylic. The bits that could do with some cover are the tops of the aluminium channel or just rebate them slightly below the surface like this should work. Hinges outside the 600mm for the OP and some sort of light clamp on the fixed surface to keep the sheet in place so the bend goes in the correct spot.

Quick and dirty model here https://a360.co/3fAZhCr

[slowpoke]

Mechanical part doesn't really bother me, i'm a maker Its the electrical part that i'm interested in.
My question arises from the need to make a strip heater on zero budget. I do have some unknown wire from heating elements of toasters and hair blowers, i also want to power it from something less than mains, for safety concerns.

I will dig out the heating wire today, just need to figure out how to measure/calculate/power it at length i need with atx(12v) or laptop(19v) power supplies.

[beanflying]

Hot and cold resistances vary a lot but a good way as you have 5V on the ATX start there with say 1m and take a current measurement. Your 600mm wide will soak up another 1-200mm getting off the surface then another 200mm as a slider resistance with an alligator clip to control it. You could add a buck convertor for control but the clip and extra wire is fine.

With your 5V info on a metre will give you a better idea of Ohms/metre. Then all things being well pump it to the 12V side of it and check again on the metre. I suspect if your wire is in the 0.8-1mm range your Laptop supply will run out of current and be to much voltage. If it is say 0.4 you will be out of or close to out of voltage.

"Maker" - CRINGE 

[slowpoke]

"Maker" - CRINGE 

Yeah, fairynuff, hate the word as well, but how else do you describe a "cheap/broke diy'er" ? (which i am).

Checked out simple commercial strip heaters/benders out there, 1200 quid for 500mm one ? thanks but no thanks...

[Ian.M]

You'll have a devil of a job unwinding a used toaster element and getting the wire straight.   The wire will be very brittle due to repeated cycling to bright red heat and oxidization.   The hair drier element probably didn't get as hot, but will be wound in a small diameter coil so is likely to be equally hard to straighten.  You *may* be able to use it still coiled if you support it with a tensioned glassfiber cord through it. 

Buying some 'virgin' Nichrome or stainless steel wire may well be your best option as you can then choose its diameter for a resistance per unit length appropriate for your desired heater power and supply voltage.  You should be able to get a 'feel' for the max heater power required from the specifications of the commercial units you've been looking at.

A 10A rated DC-DC buck converter module would give you a lot more flexibility so you can adjust the voltage for the temperature you require.  Assume a 1800W hairdrier.  At 240V its heating element draws 7.5A.   You probably don't need to drive the element so hard so a 5A buck module may well be sufficient - you wont know till you extract the element, see how many parallel sections it has at full power and try powering a length of it to get a feel for the max current and voltage required.  You probably need no more than 1/3 the current required to reach dull red heat.  Don't expect a 'chinesium' buck module to deliver more than 1/2 of its nominal rating for long. 1/3 is a safer bet.

[beanflying]

Really simply the word 'Hobbyist' it is what I started out doing in Electronics 40'ish years ago. I have spent 30+ years as an Aeromodeler as a Hobby at least 'so far' it has avoid the 'maker' tag. The word 'maker' used by others toward me in particular professionally who saw it in print or on youtube and as I spent my four years at Uni I have a small issue with it  Rant over now   

The commercial units to take your ideas from are a rail at 90 degrees to the element and a stop/clamp to control distance from an edge to your bend. The Aluminum under the element surrounded by MDF will make a fairly good oven of sorts even at circa 100W. If you were doing production bends and needed speed then a second wire run otherwise less will be more and easier to control.

[SmallCog]

With the issues around electrical and plant safety we bought rather than made the acrylic bender at work.

What I’ve learnt from it regarding making my own is that I won’t bother with the folding stuff, mine will just be a heated strip. I don’t tend to fold stuff in the machine at work I tend to do the folds outside of the machine (using jigs for repeatability)

There are calculators like this you may find handy - double check the results I’m not vouching for it

https://www.easycalculation.com/engineering/electrical/nichrome-wire-calculator.php

Here’s an Adam Savage video on strip heaters for anyone curious

https://youtu.be/iHAkCYwxUb0

[beanflying]

Good Calculator and seems about on the money for 0.8 or 0.9mm based on what I have done with it on foam cutting  12V @ 5A for about 1m to 300+C.

I had to run my own tests on some 0.2mm Titanium a week or so ago as all the vape crowd have little to zero idea and it varies a lot with Temp. Side note Kanthal is great too if you come across it for jobs like the OP's.

[slowpoke]

Bending out of the machine is a good advice and i was really planning on doing exactly that. I do have a large'ish laser cutter (900x600, 80W), been asked to do some bent acrylic stands and have no bender, hence checking what i can do on the cheap, as commercial heaters are stupid priced. If the job pans out and more orders roll in i might splash out for something fancy, but at the moment all my budget is going straight to materials for orders... (starting a business is a pain in the...well... there... )

Make a flat strip heater (with aligning bits, no bending bits like hinges), laser cut all the jigs i need out of ply, bob's your uncle. Never did foam cutters although i do RC, multirotors and cars mostly though, no foam involved. And what little is it's cut on a laser.

[beanflying]

If you have someone around you who does Mig welding and in particular Stainless work go hit them up for a few metres of 0.9 Stainless wire. I brought a 500g spool years ago for hot wire jobs and it was well under $20. Nichrome is cheap too but getting it locally is generally a specialty element maker or evilbay and wait.

I have all but the Tube assembled for a 1200x900 100W Laser build as my Toy one runs out of space way to often 

[SmallCog]

Laziness and having a bender at work have prevented me from making mine along with knowing that if I buy the materials I'll find them for free a few days later...

My intention is to use 3 rectangles of timber (probably concreters form ply or melamine from old kitchen cabinets) and a length of aluminium U channel

2 of the rectangles will be slightly smaller than half the size of the big one, the small rectangles will be attached to the big one (base piece) with the U channel between them.

https://www.bunnings.com.au/metal-mate-20-x-20-x-1-5mm-1m-aluminium-channel_p1079323

stretched across the U channel between some cup hooks will be my wire with a spring to keep it taught as it gets hot. U Channel will be slightly narrower than the with of the base board so the cup hooks can screw in.

https://www.altronics.com.au/p/w0435-9m-nichrome-resistance-wire/

I'll probably put a piece of right angle aluminium on it as a guide... If I haven't started work on 20 more things I've seen on youtube by then!

[Ian.M]

I don't like the cup hooks and croc clips approach.  Use the U channel as the ground return for the hot wire, so both connections can be to one end of it for convenience.  Then its simply a matter of bending up a tab at the far end to hold the spring, crimping the wire to the spring or using a single bare terminal from a terminal block to join them, and fitting a small ceramic two way terminal block at the near end, screwed to the base of the U (or on a bent-up tab) with one side cut to form a tab to go into one way for the ground connection. 

[beanflying]

What you like or don't about Crocodile clips and screws they work and have being for decades on model Aircraft Foam bows as a simply low tech adjustable resistor. Going back into that time a 5A variable power supply was a complete luxury item and not the sub $20 hunks of junk from China we have available now. These days I would just pull out my 0-15V 60A Manson and get to cooking. For the OP sounded like they didn't have a variable supply or to many spare $ so croc clips makes sense.

As to using the aluminium as a return has some good and a bad points. The worst one is if you tweak the wire physically wired as you suggest you can place a near dead short from wire to channel a lot easier this will get you molten Nichrome going sprong in a random direction due to the spring tension. Yep you can cover all that up or make guides close to the channel but to much complexity for a simple home made bender maybe 

Having a bit more look at the heat up time as youtube decided I needed to watch more videos about this I would be tempted to do two runs of 0.8-0.9 wire for about 10A @ 12V in the channel as toward 60 seconds seems to be the heat up time for thicker Acrylic.

[Ian.M]

Yes a short to the channel would be bad if the PSU wasn't current limited (or fused) below the fusing current of the resistance wire.  In that case, a separate fully insulated ground return would be a lot safer, leaving the channel floating.

[slowpoke]

Yes, i don't have variable psu. Should have, but dont. But have plenty of ATX power supplies in the box to use. Checked some of them out yesterday, 12V 20A rails on the 250W psu's.

I do have 15mm aluminium U channel kicking about, will be using opposite ends for powering and route the wiring neatly underneath.

Can't find the damn wire though. House moves suck, it takes time to organise your "order" of things (aka organised chaos ).

I must disclose that i never bent acrylic in this way. Heatguns usually, but bends come out too sloppy that way.

[SmallCog]

Once you’ve got the nack it’s great to work with

I’m thinking of grabbing a set of the hair straightener looking benders for doing smaller brackets and stuff, eg:

https://www.ebay.com.au/itm/Acrylic-Shape-Bender-Right-Angle-Bender-Bending-Electric-Iron-Tool-Kit-Hot-Sale-/224450681913?_trksid=p2349624.m46890.l49286] [url]https://www.ebay.com.au/itm/Acrylic-Shape-Bender-Right-Angle-Bender-Bending-Electric-Iron-Tool-Kit-Hot-Sale-/224450681913?_trksid=p2349624.m46890.l49286[/url]

[beanflying]

There is a few Indian or Pakistani (forgotten now) Youtube acrylic sign making channels I watched ages ago. Absolute magic skills making side walls on raised lettering dealing with long lengths of floppy plastic. 

Decided I am off to Bunnings tomorrow as I need to go to town and get some 12x1.5mm channel and I have the 18mm MDF already in the shack along with the Nichrome or Kanthal when I work out what works best at 600mm'ish.

[slowpoke]

I want to try this:



...but for that i need to upgrade my Z axis drive from dumb AC lift motor to stepper+driver. Would save me some headache with benders:D

[beanflying]

Interesting idea using out of focus energy to do the job. Lots of playing and funny shapes made along the way I suspect

Went to the hardware shop and grabbed some extra bits and pieces for a build. Few things not shown on the model screws, bolts etc. Laser cut 6mm Angle bracket on the left with a stop block fitted into the slot for easy repeat angles. Working on a maximum bend distance of 450mm and screwing the lot to a 600mm wide bit of MDF so it stays put.

Model is still here if anyone wants to pinch dimensions off it https://a360.co/3fAZhCr

[Jwillis]

Here's a place in the U.K. to get NiCr wire up to 3.25 mm .  wires.co.uk .  They have other wire as well. I got some  Manganin some time ago for sense resistors.

[Vincenzo]

I haven't created a bender but at work we have a variety of heat seal tasks.   What your want covering the metal is PTFE tape.   The Tape is specially designed for such usage.

Is that the same plumbers thread sealing white tape? Is that heat resistant?

[beanflying]

I haven't created a bender but at work we have a variety of heat seal tasks.   What your want covering the metal is PTFE tape.   The Tape is specially designed for such usage.

Is that the same plumbers thread sealing white tape? Is that heat resistant?

Nope not Teflon Tape for plumbing it is a Teflon encapsulated Fabric (likely fiberglass). Shot is of the jaw area of my double sided floor model sealer.