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Advice designing plastic bender using 0.035 nichrome coil?

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  • Advice designing plastic bender using 0.035 nichrome coil?

    I'm a bit snowed under making 500 face shields for the local hospitals to puzzle this one out, maybe someone with more resistance experience can help me out. I need to sharply bend 1" x 1/16" PETG, and I've been using a butane heat pen, which is not optimal for production. I was thinking a heat bending rig, with a heat element in a channel that you lay the plastic on for a few moments. Easy to jig for proper bend placement.

    I have a length of 0.035 wire .157 OD. I have some ceramic resistors, I also have a variac. I need about 300-400 deg. What voltage will work for such a short length, what common material for the bed that won't ignite? Would some 1/4" ceramic or porcelain tile work without cracking or do I need firebrick? What about Hardibacker? Any help appreciated. If anyone is interested in producing fast, cheap, reusable face shields I can post the design and jig details. I'm trying to make it producable by any home craftsman, basically there. Prototype below, I've since sourced better foam and film.

    Click image for larger version  Name:	mask prototype mark 2.PNG Views:	0 Size:	253.7 KB ID:	1866212
    Last edited by gellfex; 04-04-2020, 01:39 PM.
    Location: Jersey City NJ USA

  • #2
    I've done a bit of foam wing cutting using nichrome wire. Also I've robbed toasters and a couple of hair dryers for the heating elements. I've never seen any that were anything like .035 wire. It's always been quite a bit smaller.

    Speaking of toasters and the like why not rob a toaster of the flat elements with the carrier plates? Then use a simple suitable high power lamp dimmer to control the heat? Then some manner of plate to spread the heat evenly? Fire brick and ceramic tiles are not ideal for that because they are actually very good insulators for heat. I'm not sure what you need but it should be a better conductor than the ceramic or brick. Really you want something like aluminium that will conduct the heat rapidly so it spreads out very evenly.

    In fact I'm thinking that what you really want is just a range top coil run off a suitable high wattage lamp dimmer to set up the heat. And because those are nicely insulated then you can set up some heavy gauge aluminium angle with a spacer strip of steel along the base. The spacer also stops the plastic falling through onto the heating elements directly.

    This would create a long slot or trough for you to set the strip of plastic down into the slot and warm it evenly on both sides. And the flanges of the angle stock that form the feet would give a really good heat contact to the stove top elements.

    A meat or candy thermometer stuck into a drilled block of aluminium attached to one of the vertical flanges with pop rivets or the like would be your constant gauge for fine setting the power to the setup to reach a steady temperature. You'd have to watch it pretty closely for the first bit of time but after a few adjustments it should all even up and stay fairly constant.

    This should be something that would take a lot less time than trying to whip up something with nichrome wire or resistors that might blow out rapidly due to their use as purely heating elements. All the stuff I've mentioned could be picked up with one trip to a good big box hardware store. The toughest part would be finding a way to hold the heating elements. This assumes that you can't get away with using your own kitchen range top. If you could then go with that and just make up the aluminium heating trough and candy thermometer assembly and you're good to go.
    Chilliwack BC, Canada

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    • #3
      Originally posted by BCRider View Post
      I've done a bit of foam wing cutting using nichrome wire. Also I've robbed toasters and a couple of hair dryers for the heating elements. I've never seen any that were anything like .035 wire. It's always been quite a bit smaller.

      Speaking of toasters and the like why not rob a toaster of the flat elements with the carrier plates? Then use a simple suitable high power lamp dimmer to control the heat? Then some manner of plate to spread the heat evenly? Fire brick and ceramic tiles are not ideal for that because they are actually very good insulators for heat. I'm not sure what you need but it should be a better conductor than the ceramic or brick. Really you want something like aluminium that will conduct the heat rapidly so it spreads out very evenly.

      In fact I'm thinking that what you really want is just a range top coil run off a suitable high wattage lamp dimmer to set up the heat. And because those are nicely insulated then you can set up some heavy gauge aluminium angle with a spacer strip of steel along the base. The spacer also stops the plastic falling through onto the heating elements directly.

      This would create a long slot or trough for you to set the strip of plastic down into the slot and warm it evenly on both sides. And the flanges of the angle stock that form the feet would give a really good heat contact to the stove top elements.

      A meat or candy thermometer stuck into a drilled block of aluminium attached to one of the vertical flanges with pop rivets or the like would be your constant gauge for fine setting the power to the setup to reach a steady temperature. You'd have to watch it pretty closely for the first bit of time but after a few adjustments it should all even up and stay fairly constant.

      This should be something that would take a lot less time than trying to whip up something with nichrome wire or resistors that might blow out rapidly due to their use as purely heating elements. All the stuff I've mentioned could be picked up with one trip to a good big box hardware store. The toughest part would be finding a way to hold the heating elements. This assumes that you can't get away with using your own kitchen range top. If you could then go with that and just make up the aluminium heating trough and candy thermometer assembly and you're good to go.
      Thanks, but I'm afraid you misunderstood the goal. I want a very narrow strip of heat for a sharp bend, not spread widely. Most heat elements are too big. I guess perhaps salvaging the nichrome from a hair dryer might work. The stuff I have was from a heat element I misordered for my vac-former. It was too high wattage and I swapped the wire from the decaying old one onto it.
      Location: Jersey City NJ USA

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      • #4
        A possible alternative might be a hot air gun and suitable ducting.

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        • #5
          It seems that the easiest thing to do would be to string your nichrome wire between two points and use your variac. Start at zero and slowly ramp up a bit at a time. 300-400F is not all that hot really. Jig something quick up just to test the theory, even a couple of screws driven into a 2x4 and standing the wire up above the surface would work to test the concept. You likely won't need the wire to be glowing bright red.
          Last edited by alanganes; 04-04-2020, 05:26 PM.

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          • #6
            Sorry I misunderstood.

            What you're after still seems like it would be doable with the coiled spring like element from an old hair dryer. What I think I'd do is put the insulating qualities of thick ceramic tiles to work for you. Arrange three tiles or pieces of tiles so there's on as a base then two more (one tile split?) on top with a small gap to fit the coiled element loosely. Lay the plastic over the gap and heat the element to soften that area of the plastic.

            If you want a tighter affected area then do the same thing but work with the "V" groove with your heavier wire laid in the base of the "V". You may need to make the groove a bit deeper to get some clearance.

            I'm trying to keep these simple as you're doing good work and likely can't devote a lot of time to anything more fancy given the situation. Hope it helps. Or that one of the other posts hit the nail on the head.
            Chilliwack BC, Canada

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            • #7
              You mean like this? Built this 40 years ago when I was in College.
              Click image for larger version

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ID:	1866491Click image for larger version

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              • #8
                Yep! Not as neat and tidy perhaps given the rather rapid need for results. But yeah that's exactly the idea. Focuses the heat on the line to be bent and leaves the rest alone.
                Chilliwack BC, Canada

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                • #9
                  Is this an open source design or your design. I see there has been a call for face sheilds in my country (S Africa and the frame is a 3d printed frame. It seems a laboriously slow way to do it.I would think a strap of suitable size plastic could be cut by laser or even drilled out. Are you willing to share some more pics of what you are doing.?
                  Apologies .Please ignore my post
                  Last edited by plunger; 04-05-2020, 06:50 PM.

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                  • #10
                    Originally posted by plunger View Post
                    Is this an open source design or your design. I see there has been a call for face sheilds in my country (S Africa and the frame is a 3d printed frame. It seems a laboriously slow way to do it.I would think a strap of suitable size plastic could be cut by laser or even drilled out. Are you willing to share some more pics of what you are doing.?
                    Apologies .Please ignore my post
                    No problem, please feel free to ask any questions at all in the 'shield' thread I just started.

                    BCRider I did more or less exactly as you say with tiles but trying to use a heavy soldering iron as the heater. it was relatively slow. For this batch of 100 I gave up, and simply made a "sight jig" that you lay the clear plastic on and wand it on the line with the butane heat pencil. Works just fine, maybe next batch I'll work more on the nichrome device, after all I just destroyed a hair dryer for it! (was a freebie anyway)
                    Location: Jersey City NJ USA

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                    • #11
                      So I'm back messing with this. I took a 2" piece of coil from a hair dryer and it works quite nicely at 12v, pulling ~3.5A from the variac, 5 seconds for a bend in the plastic. But I'd like a simpler power supply, especially if folks like plunger want to tool up for this. I tried a dimmer, but it can't be subtle enough at that low 42 watts for 120v, it crisped the coil as I was turning it up. I have some bell transformers, but I think they're only about 20w. Any cute simple answers to powering this short piece of nichrome?
                      Location: Jersey City NJ USA

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                      • #12
                        Originally posted by gellfex View Post
                        So I'm back messing with this. I took a 2" piece of coil from a hair dryer and it works quite nicely at 12v, pulling ~3.5A from the variac, 5 seconds for a bend in the plastic. But I'd like a simpler power supply, especially if folks like plunger want to tool up for this. I tried a dimmer, but it can't be subtle enough at that low 42 watts for 120v, it crisped the coil as I was turning it up. I have some bell transformers, but I think they're only about 20w. Any cute simple answers to powering this short piece of nichrome?
                        What you want is a filament transformer. Go back 50 years and you'll find them.

                        -js
                        There are no stupid questions. But there are lots of stupid answers. This is the internet.

                        Location: SF Bay Area

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                        • #13
                          Originally posted by Jim Stewart View Post

                          What you want is a filament transformer. Go back 50 years and you'll find them.

                          -js
                          If my time machine prototype were working I'd only have to go back to January to head off this whole mess!
                          Location: Jersey City NJ USA

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                          • #14
                            We are making them with stamped out Mylar and gluing a 1” x 1” foam strip and a 1” elastic strap. No bending

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                            • #15
                              Originally posted by gellfex View Post

                              If my time machine prototype were working I'd only have to go back to January to head off this whole mess!
                              Battery charger transformer will work, or even a variac -- I've seen fosm cutting machines setup that way. All a filament transformer is, is about 6v at several amps.
                              25 miles north of Buffalo NY, USA

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