[Lab] Plastic Bending Strips

Roman Gargulak roman at cncwings.com
Mon Jul 8 14:01:08 EDT 2013

We are talking about 250-300W of resistive load here so standard dimmer 
should do just fine.


On 7/8/2013 11:10 AM, Richard Sloan wrote:
> Just need a high power dimmer as the cheap dimmers are 300-500W
> Richard.
> On Sun, Jul 7, 2013 at 3:33 PM, Roman Gargulak <roman at cncwings.com 
> <mailto:roman at cncwings.com>> wrote:
>     Henri,
>     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.
>     Roman
>     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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