[Lab] Plastic Bending Strips

Roman Gargulak roman at cncwings.com
Sun Jul 7 15:33:28 EDT 2013


The dimmer switch is a crude idea for this kind of regulation, but it 
may work, you will need to try it. It worked for me when I needed to cut 
6ft long wing halves on my cutter.
I would strongly advise against using dimmer switch directly, without 
isolation transformer as you will be dealing with mains voltage and can 
electrocute yourself.
Your 5V transformer will not work unfortunately with 8ft of wire, it 
will not provide not enough voltage to push required current through.

1000°C sounds rather high, I think nichrome wire should not be used 
above 800°C-900°C. If it is that hot (1000°C) it may break easily.
You will need close to 50V (that's dangerous level already), I have a 
1:2 step down transformer with a dimmer switch that you can borrow if 
you want.
Also, I have plenty of 0.009" stainless steel wire, but I am not sure if 
it can sustain that high temperature without breaking, on top of it, 
it's resistance is higher than nichrome (about 10ohms/ft) so you will 
need really high voltage to heat up 8 feet of it.

In my opinion, your best bet is a guitar string (G), maybe run two in 
parallel to reduce resistance.


On 7/7/2013 12:52 PM, Henri Kuschkowitz wrote:
> Hey guys,
> It might be good to clarify what I want/need. After some more research 
> I think I also have a better understanding in general of my 
> requirements. I (will) have various cuts of acrylic, max 7' long, 1/8" 
> thick that I need to bend at a straight angle. As such I require 
> evenly distributed temperature. I similar idea to Roman's foam cutter 
> is probably to closest example. Just to be sure, I am trying to have a 
> setup with a max 1000deg C heat wire. The video I posted earlier seems 
> to do the trick easily if i use 22 gauge Nichrome wire across 8ft and 
> just a dimmer switch for 110V and 15Amps (12Amps). I do have access to 
> a 5V 60Amp transformer,  but with my limited skill set I am worried 
> about breaking it. Could someone give me some pointers how I would 
> calculate if I can reach the temperature I am looking for?
> I have used the formula on this 
> <http://www.heatersplus.com/nichrome.html> page to get some details 
> about what I would need for my setup and am currently looking through 
> some more. I am trying to see if I can use the "G" string idea Roman 
> pointed out since Nichrome wire is nowhere to be found in the area and 
> shipping will take a bit too long for my taste.
> Cheers all,
> Henri
> On 2013-07-04, at 10:36 PM, Roman Gargulak <roman at cncwings.com 
> <mailto:roman at cncwings.com>> wrote:
>> I do not think that particular PID controller will work with this 
>> application as it is not meant for fast switching, it is meant for 
>> relatively slow processes.
>> The wire itself has very little mass so slow switching will not work 
>> as wire will cool off quickly.
>> You really do not need closed loop with feedback for this, the variac 
>> is good solution but maybe a bit overkill, if your heated wire is 
>> only 3-4 feet long.
>> On my CNC foam cutter I use 0.009" wire which has quite high 
>> resistance and I need only about 18-20V to heat it up.
>> With 20AWG wire (which has over 0.030" diameter) you will need lower 
>> voltage and higher amperage, which variac will provide, just be 
>> cautious and treat it as mains as someone wisely pointed out already.
>> If you can not find wire, you can always use steel guitar strings, 
>> "e" string is 0.009", "G" string is 0.016" (talking about guitar G 
>> string here, just to be clear ;-) )
>> If you can not find variac, you can always try to use regular step 
>> down transformer and dimmer switch on the primary side.
>> Or since you will need low voltage, you can try just regular bench 
>> top power supply.
>> Roman
>> On 7/4/2013 4:25 PM, Michael Grant wrote:
>>> That power supply is also known as an autotransformer.
>>> https://en.wikipedia.org/wiki/Autotransformer
>>> Care should be taken with an autotransformer, while the voltage can 
>>> be set low, there is no, none, zero galvanic isolation.
>>> Meaning the full current of the service is available (20amps). Treat 
>>> the output as you would treat 120VAC direct from a receptacle...
>>> I've never seen one in the lab, but they do have a variable  DC 
>>> supply that is maybe 3amps and 30v max.
>>> Depending on the load, the heating element, you might be able to use 
>>> one of those twisty things for lights...
>>> Alternatively, an AC thermostat for bang bang control with hysteria 
>>> should also work if you keep the thermal loop tight.
>>> The last and best option would be a ~$14 PID controller from ebay, 
>>> that would give the best thermal regulation.
>>> Sometimes they come in a kit with an SSR (solid state relay) and a 
>>> thermocouple for a little more dough...
>>> Here's one kit for $24...
>>> http://www.ebay.ca/itm/100-240V-Digital-PID-Temperature-Controller-max-40A-SSR-K-Thermocouple-Probe-/290825156892?pt=LH_DefaultDomain_0&hash=item43b687b91c
>>> Michael
>>> --
>>> http://krazatchu.ca/
>>> On Thu, Jul 4, 2013 at 4:07 PM, Henri Kuschkowitz 
>>> <henri.kuschkowitz at gmail.com <mailto:henri.kuschkowitz at gmail.com>> 
>>> wrote:
>>>     So, I am still getting some more costs tomorrow, but I think I
>>>     might go with this quick/dirty setup:
>>>     http://www.youtube.com/watch?v=wVEf7PfuKxo
>>>     What do you guys think? This leads me to my next question, would
>>>     anybody know if the lab has an item similar to this:
>>>     http://www.temcoindustrialpower.com/products/Variable_Transformers/TVT001.html?utm_source=temcotransformer.com&utm_medium=Banner%2BAd&utm_campaign=Variac%2BTVT001
>>>     <http://www.temcoindustrialpower.com/products/Variable_Transformers/TVT001.html?utm_source=temcotransformer.com&utm_medium=Banner+Ad&utm_campaign=Variac+TVT001>
>>>     Cheers all,
>>>     Henri
>>>     On 2013-07-04, at 7:54 AM, Alex <alexbarbour at bell.net
>>>     <mailto:alexbarbour at bell.net>> wrote:
>>>>     Henri
>>>>     Angle iron is a common name applied to steel angles. some are
>>>>     extruded in the heavier sections and have a sharp outside corner.
>>>>     Some are bent from flat stock and have a radiused corner.
>>>>     These are better for use as formers for plastics.
>>>>     Home depot. Hardware dept.
>>>>     CTC ect.
>>>>         ----- Original Message -----
>>>>         *From:* Henri Kuschkowitz <mailto:henri.kuschkowitz at gmail.com>
>>>>         *To:* Alex <mailto:alexbarbour at bell.net>
>>>>         *Sent:* Wednesday, July 03, 2013 9:12 AM
>>>>         *Subject:* Re: [Lab] Plastic Bending Strips
>>>>         Hey Alex,
>>>>         I have a very particular type of acrylic we are going to be
>>>>         using that I doubt comes 'bendable'. Angle iron? I haven't
>>>>         seen those before. Got a reference or suggestion?
>>>>         Cheers,
>>>>         Henri
>>>>         On 2013-07-03, at 8:03, Alex <alexbarbour at bell.net
>>>>         <mailto:alexbarbour at bell.net>> wrote:
>>>>>         On the other hand they do produce an acrylic sheet that
>>>>>         can be bent cold .
>>>>>         Have done small pieces by hand. For larger OR thicker (
>>>>>         say 1/8 inch + )one needs a former for the edge. Angle
>>>>>         iron with a round egde serves well.
>>>>>         Alex B
>>>>>             ----- Original Message -----
>>>>>             *From:* Henri Kuschkowitz
>>>>>             <mailto:henri.kuschkowitz at gmail.com>
>>>>>             *To:* lab <mailto:lab at artengine.ca>
>>>>>             *Sent:* Tuesday, July 02, 2013 3:09 PM
>>>>>             *Subject:* [Lab] Plastic Bending Strips
>>>>>             Hey guys,
>>>>>             I figured it's a good time to start asking the
>>>>>             collective for some feedback. We are planing on
>>>>>             bending larger sheets of acrylic (they will definitely
>>>>>             not fit into the laser cutter) and I am looking at
>>>>>             bending strip heaters
>>>>>             <http://www.briskheat.com/p-152-rh-plastic-bending-strip-heater.aspx> to
>>>>>             build a custom heating element for our purposes.
>>>>>             Before I go ahead ordering the pieces I was wondering
>>>>>             if anyone had ever used such a thing and/or knows of a
>>>>>             good local source? For saving some money, I wonder if
>>>>>             reusing a baseboard heater could do the trick :P
>>>>>             Cheers all,
>>>>>             Henri
>>>>>             ------------------------------------------------------------------------
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