Hot wire knives need not have all the fancy electronics. I do a merit badge course every winter with the local council's STEM U. One of the projects I have them construct a "cooler" out of the blue construction foam insulation board using glue/tape/other means to assemble pieces of cut foam. Before starting, I have them construct "cutters using 2 large pop sticks covered in aluminum foil and a piece of welding wire strung between. For a power source its a D cell battery. The assembled knife is the battery in the palm of their hand with the sticks on each pole.
Every year I say, DO NOT TOUCH THE WIRE - IT GETS HOT! Invariably, one scout has to "touch it". It does not get real hot - probably up to 350 F depending on the strength of the battery used. I usually have to keep the kids on track because they become fascinated with "carving" the foam with this simple tool. bg On Wed, Apr 5, 2017 at 10:16 AM, Gene Heskett <[email protected]> wrote: > On Wednesday 05 April 2017 03:13:07 Erik Christiansen wrote: > > > On 04.04.17 12:29, Gene Heskett wrote: > > > On Tuesday 04 April 2017 06:04:50 Erik Christiansen wrote: > > > > On 04.04.17 05:00, Gene Heskett wrote: > > > > > > Those scraps of that blueish foam have all been binned or used years > > > ago. And Lowes no longer carries that same board in 2" R22 > > > thickness. The current product the last time I looked is a white, > > > larger cell product and only about R20 because of that, but its the > > > same $35 & tax a 4x8 foot sheet. How it would cut with a hot wire > > > would be TBD. > > > > Should be good. It's when resorting to a cold sharp knife that the > > "melded bean bag fill" crummy foam crumbles. > > > > ... > > > > > How hot does the hot wire need to be? > > > > Just go by feel. This one suggests 600°F (that's 315°C, which sounds > > like a good starting point): > > https://www.youtube.com/watch?v=3GWzHb4Hd8Y > > > > but with a 555 & MOSFET, you can PWM your way to happy cutting from > > 12v with most bits of recycled nichrome wire even a foot long. > > > > Some make the frame from wood - that'd be more rigid than his. > > (I've welded a couple of small bits of RHS together, added a baseplate > > to screw to an old chipboard kitchen sink cutout (melamine topped), > > and need to rout a slot from the edge to the base of the wire, for an > > Al T-slot, so I can slide a vertical pin back & forth for setting > > radii for cutting disks, rings, and cylinders. > > > > > Seeing as how thats best jiggered up as a wire support frame I could > > > stick in a vise on the g0704's table and rig some sort of a sheet > > > gripper leaving a cutaway, for the hot wire to move within, attached > > > to the chip pan, if I get it rigid enough to keep its place as the > > > wire moves, I could probably just write gcode to drive the cutters > > > path. Where it needs a lid like the outside face of a belt cover, > > > just cut the outline out and glue it on. > > > > Takes a while to build, though. Sketching the outline on the back of a > > cornflakes packet, cutting it out with scissors, running around it > > with a ballpoint pen on the foam, then carefully following it by hand > > with the hot-wire cutter, is quicker. (I don't know of a good > > temporary adhesive for sticking the template on the foam without > > tearout on removal.) > > > > > But, I think buying the printer would get me a nicer looking belt > > > cover. > > > > The printed product could perhaps be used directly, instead of then > > making a casting, and machining it where necessary? > > > > Erik > > That would be the intention. Barring an errant hammer blow to break it, > probably loose by snapping off a mounting tab, a lot of swarf could even > be hot enough to stick to it, but would brush off when cooled. > > Without the spindle turning but the motor running at 30hz, it has set out > there and run all night, no joint errors. So I next write an infinite > loop, moving each axis back and forth half an inch at about 20 ipm. I > have got to find the source of the joint errors. They hit random joint > numbers, often both joints when only one joint is moving. I am convinced > its a comm error as I have seen the tach dial jump to 400 or 500 rpms > when its not turning. Not often but thats also a joint error for both > joints. > > And since rockhopper is the only tool I know of that will output the > signal path so that can be compared to the addf order, I just tried to > install that, but apt couldn't find it in the pi's repo's. :( > > Time to print out the hal file and trace thru it, putting a number at > each addf as the signals make their way thru the modules loaded. Thats > getting complex as the hal file, with all these jog-wheel additions, is > 19 landscape printed pages now. In the finished trace, the numbers in > each thread should be in order. I suspect the servo-thread is not in > order so I'll trace that first. And the spi buss is so timing critical I > can't even hang a 10x scope probe on the clock signal while lcnc is > booting up. > > I bought 3 of those 40 to 26 pin boardsfrom OSHPark, but according to the > xray printouts, the 4 pins of the spi buss, 3 with the term r's are the > only pins cross connected! No other pins are connected to anything > except the data return from the 7i90! So I haven't built that, but made > my own on perf-board, connecting all the other ground pins etc that need > connection. Maybe thats a ground loop? But I figured with all the other > stuffs plugged into the pi that are grounded to it, it needed a good > solid interconnecting ground to the 7i90. > > Whatever, the comm link, using the rpspi.ko driver is certainly being a > problem child. > > So today I will cut off the long power cord for the pi, which bypasses > the 7i90 power plug and goes past it about 7" to a terminal strip I > mounted as a 5 volt distribution point and make the pi powered as an > extension of the power rail driving the 7i90, which will shrink the size > of the ground loop by half or more. And I am not impressed with the > molded on ferrite choke, so that will get removed in an effort to reduce > the impedance of the ground between them. I can always add it back as I > have a small bag of them yet. > > > ---------------------------------------------------------------------- > >-------- Check out the vibrant tech community on one of the world's > > most engaging tech sites, Slashdot.org! http://sdm.link/slashdot > > _______________________________________________ > > Emc-users mailing list > > [email protected] > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > Cheers, Gene Heskett > -- > "There are four boxes to be used in defense of liberty: > soap, ballot, jury, and ammo. Please use in that order." > -Ed Howdershelt (Author) > Genes Web page <http://geneslinuxbox.net:6309/gene> > > ------------------------------------------------------------ > ------------------ > Check out the vibrant tech community on one of the world's most > engaging tech sites, Slashdot.org! http://sdm.link/slashdot > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users > ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
