On 2023-02-01, Liz Tuddenham <liz@poppyrecords.invalid.invalid> wrote:> whit3rd <whit3rd@gmail.com> wrote: > >> On Tuesday, January 31, 2023 at 4:30:48 PM UTC-8, Don Y wrote: >> >> > I recall having a pair of electric *socks* as a kid. Powered >> > by D cells. Definitely not cherry red :> >> >> Maybe Nitinol? The flexibility (elastic range) is more important than >> other mechanical properties. For a hot-wire cutter, my experimenting >> with NiCr was dominated by the way the taut wire didn't hold its length. >> >> I suspect the familiar wave-surface foam slabs are cut with a straight >> (wire? knife?) as the foam was fed from a pair of very bumpy rollers. > > If you don't mind the increased power dissipation and poorer cut > definition, you could use a thicker wire. An adjustable mounting, that > allows you to shorten the length of wire in use, will reduce the > stresses when cutting thinner material.Cutting foam is interesting the faster you go the cooler the wire gets. but if you stop the wire inside the foam gets hotter than the wire that's in free air (because it's insulated). I expect that there's a cutting speed where the wire temperature is near uniform,> There ought not to be too much side load on a hot cutting wire unless > the machine is being over-worked, but if the force is mainly from one > direction, substituting a nichrome ribbon for the wire might give more > resistance to bending in that direction.Yes, but the wire only needs to emit heat in one direction and the ribbon is not facing that direction.> Rather than starting from the resistance of the wire, try looking for a > material that has the necessary hot strength/flexibility and then cut a > narrow strip of it from some sheet. Match the electrical supply to the > material, rather than the other way around.I've experimented with stainless steel in the past, but the thermal coefficient of resistance has the wrong sign leading to hot spots forming where the wire is doing the least work. nichrome at-least has a flat coefficient. -- Jasen. pǝsɹǝʌǝɹ sʇɥƃᴉɹ ll∀
Nichrome wire
Started by ●January 31, 2023
Reply by ●February 1, 20232023-02-01
Reply by ●February 1, 20232023-02-01
On 2/1/2023 1:52 AM, Liz Tuddenham wrote:> whit3rd <whit3rd@gmail.com> wrote: > >> On Tuesday, January 31, 2023 at 4:30:48 PM UTC-8, Don Y wrote: >> >>> I recall having a pair of electric *socks* as a kid. Powered >>> by D cells. Definitely not cherry red :> >> >> Maybe Nitinol? The flexibility (elastic range) is more important than >> other mechanical properties. For a hot-wire cutter, my experimenting >> with NiCr was dominated by the way the taut wire didn't hold its length. >> >> I suspect the familiar wave-surface foam slabs are cut with a straight >> (wire? knife?) as the foam was fed from a pair of very bumpy rollers. > > If you don't mind the increased power dissipation and poorer cut > definition, you could use a thicker wire. An adjustable mounting, that > allows you to shorten the length of wire in use, will reduce the > stresses when cutting thinner material. > > There ought not to be too much side load on a hot cutting wire unless > the machine is being over-worked, but if the force is mainly from one > direction, substituting a nichrome ribbon for the wire might give more > resistance to bending in that direction. > > Rather than starting from the resistance of the wire, try looking for a > material that has the necessary hot strength/flexibility and then cut a > narrow strip of it from some sheet. Match the electrical supply to the > material, rather than the other way around.Or, only apply the material in applications for which it is suited! That's the point of my question.
Reply by ●February 1, 20232023-02-01
On Wed, 1 Feb 2023 09:57:21 -0000 (UTC), Jasen Betts <usenet@revmaps.no-ip.org> wrote:>On 2023-02-01, Liz Tuddenham <liz@poppyrecords.invalid.invalid> wrote: >> whit3rd <whit3rd@gmail.com> wrote: >> >>> On Tuesday, January 31, 2023 at 4:30:48 PM UTC-8, Don Y wrote: >>> >>> > I recall having a pair of electric *socks* as a kid. Powered >>> > by D cells. Definitely not cherry red :> >>> >>> Maybe Nitinol? The flexibility (elastic range) is more important than >>> other mechanical properties. For a hot-wire cutter, my experimenting >>> with NiCr was dominated by the way the taut wire didn't hold its length. >>> >>> I suspect the familiar wave-surface foam slabs are cut with a straight >>> (wire? knife?) as the foam was fed from a pair of very bumpy rollers. >> >> If you don't mind the increased power dissipation and poorer cut >> definition, you could use a thicker wire. An adjustable mounting, that >> allows you to shorten the length of wire in use, will reduce the >> stresses when cutting thinner material. > >Cutting foam is interesting the faster you go the cooler the wire gets. >but if you stop the wire inside the foam gets hotter than the wire >that's in free air (because it's insulated). I expect that there's >a cutting speed where the wire temperature is near uniform,Given a wire with a decent tempco, one could servo the temperature.> >> There ought not to be too much side load on a hot cutting wire unless >> the machine is being over-worked, but if the force is mainly from one >> direction, substituting a nichrome ribbon for the wire might give more >> resistance to bending in that direction. > >Yes, but the wire only needs to emit heat in one direction and the >ribbon is not facing that direction. > >> Rather than starting from the resistance of the wire, try looking for a >> material that has the necessary hot strength/flexibility and then cut a >> narrow strip of it from some sheet. Match the electrical supply to the >> material, rather than the other way around. > >I've experimented with stainless steel in the past, but the thermal >coefficient of resistance has the wrong sign leading to hot spots >forming where the wire is doing the least work. nichrome at-least has >a flat coefficient.Constant current drive would do that to some extent. Constant voltage, the opposite. 304 has a pretty low positive tempco, about 850 ppm. Most metals are more like 4000.
Reply by ●February 1, 20232023-02-01
On Tuesday, January 31, 2023 at 8:58:31 PM UTC-5, Don Y wrote:> > But, I don't know what sort of mechanical load the wire "sees" as > it melts that stuff.That's because you're just an anonymous troll who doesn't know the first thing about science, engineering, or applied analysis.
Reply by ●February 1, 20232023-02-01
On 2/1/2023 2:57 AM, Jasen Betts wrote:> On 2023-02-01, Liz Tuddenham <liz@poppyrecords.invalid.invalid> wrote: >> Rather than starting from the resistance of the wire, try looking for a >> material that has the necessary hot strength/flexibility and then cut a >> narrow strip of it from some sheet. Match the electrical supply to the >> material, rather than the other way around. > > I've experimented with stainless steel in the past, but the thermal > coefficient of resistance has the wrong sign leading to hot spots > forming where the wire is doing the least work. nichrome at-least has > a flat coefficient.Yeah, in "cutting" applications you tend to end up with a "blade" that is longer than your longest cut will ever be. So, parts of the "blade" see different thermal loads. I'd imagine an industrial supplier would have their process set *to* the material they are making (they are unlikely to use a single cutter to address an unconstrained number of different sizes/applications. And, if you are using the wire just as a heat source, you likely don't have that sort of variation in "loads".
Reply by ●February 1, 20232023-02-01
On 02/02/23 06:08, Fred Bloggs wrote:> On Tuesday, January 31, 2023 at 8:58:31 PM UTC-5, Don Y wrote: > >> >> But, I don't know what sort of mechanical load the wire "sees" as >> it melts that stuff. > > That's because you're just an anonymous troll who doesn't know the first thing about science, engineering, or applied analysis. >Never mind, Don. It looks like Fred's been playing in the mirror again.
Reply by ●February 2, 20232023-02-02
Jasen Betts <usenet@revmaps.no-ip.org> wrote:> On 2023-02-01, Liz Tuddenham <liz@poppyrecords.invalid.invalid> wrote: > > whit3rd <whit3rd@gmail.com> wrote: > > > >> On Tuesday, January 31, 2023 at 4:30:48 PM UTC-8, Don Y wrote: > >> > >> > I recall having a pair of electric *socks* as a kid. Powered > >> > by D cells. Definitely not cherry red :> > >> > >> Maybe Nitinol? The flexibility (elastic range) is more important than > >> other mechanical properties. For a hot-wire cutter, my experimenting > >> with NiCr was dominated by the way the taut wire didn't hold its length. > >> > >> I suspect the familiar wave-surface foam slabs are cut with a straight > >> (wire? knife?) as the foam was fed from a pair of very bumpy rollers. > > > > If you don't mind the increased power dissipation and poorer cut > > definition, you could use a thicker wire. An adjustable mounting, that > > allows you to shorten the length of wire in use, will reduce the > > stresses when cutting thinner material. > > Cutting foam is interesting the faster you go the cooler the wire gets. > but if you stop the wire inside the foam gets hotter than the wire > that's in free air (because it's insulated). I expect that there's > a cutting speed where the wire temperature is near uniform, > > > There ought not to be too much side load on a hot cutting wire unless > > the machine is being over-worked, but if the force is mainly from one > > direction, substituting a nichrome ribbon for the wire might give more > > resistance to bending in that direction. > > Yes, but the wire only needs to emit heat in one direction and the > ribbon is not facing that direction. > > > Rather than starting from the resistance of the wire, try looking for a > > material that has the necessary hot strength/flexibility and then cut a > > narrow strip of it from some sheet. Match the electrical supply to the > > material, rather than the other way around. > > I've experimented with stainless steel in the past, but the thermal > coefficient of resistance has the wrong sign leading to hot spots > forming where the wire is doing the least work. nichrome at-least has > a flat coefficient.It sounds as though you need a composite wire: something like copper, with a large +ve temp coefficient, to carry the current and someting less conductive like nichrome or similar to give hot strength. As you presumably only need short lengths, there would be no need to search for a continous manufacturered product, you could make wires like this yourself in short lengths using a home-made batch creeler. For preliminary experiments you could hold one end of the wire bundle in a bench vice and the other end in a small hand drill; then turn the drill to twist the bundle. I expect the 'lay' will go all wrong, but it will give you a test piece that will prove the concept. I have put a sketch of a possible way of making these wires more professionally at: <http://www.poppyrecords.co.uk/other/Creeler.gif> You make a couple of tools as shown in the upper drawing, with a hollow stem for gripping in the vice or the drill chuck, and a disc with holes. Thread the copper wire through the central hole and 6 nichrome wires through the outer holes. When the chuck is rotated, the nichrome wires should wrap evenly around the central copper one but the whole assembly will shorten as they take up a helical shape. To prevent this buckling the copper wire, the latter is tensioned as shown in the lower drawing. Hope this helps. -- ~ Liz Tuddenham ~ (Remove the ".invalid"s and add ".co.uk" to reply) www.poppyrecords.co.uk
Reply by ●February 2, 20232023-02-02
On 1/31/2023 6:12 PM, Lasse Langwadt Christensen wrote:> onsdag den 1. februar 2023 kl. 02.06.41 UTC+1 skrev whit3rd: >> On Tuesday, January 31, 2023 at 4:30:48 PM UTC-8, Don Y wrote: >> >>> I recall having a pair of electric *socks* as a kid. Powered >>> by D cells. Definitely not cherry red :> >> Maybe Nitinol? The flexibility (elastic range) is more important than other mechanical >> properties. For a hot-wire cutter, my experimenting with NiCr was dominated >> by the way the taut wire didn't hold its length. >> >> I suspect the familiar wave-surface foam slabs are cut with a straight (wire? knife?) >> as the foam was fed from a pair of very bumpy rollers. > > the wire is spring loadedOr, adjusted by the user based on observations of the "current stretch": <https://hotwirefoamfactory.com/4-Foot-Compound-Bow-Cutter.html>
Reply by ●February 3, 20232023-02-03
On Tue, 31 Jan 2023 17:30:35 -0700, Don Y <blockedofcourse@foo.invalid> wrote: <snip>>I'm not sure what the heating elements in "glass cooktops" >look like "under the glass"... >It will depend on the mfr. some are visibly simple coils laid in a former. Have 'repaired' a few with zig-zag ribbons imbedded in filled insulator forms. These are brittle and very difficult to make a secure electromechanical joint at any point of failure. They're not meant to be fooled around with. A compression flat-fit, forcing-plates secured by offset screws with split washers, seemed to work. Don't know how long they lasted. Owner a fanatic for repair of esoteric brands. Glass cooktops are a joke, provoking the worst aspects of the electric stove top cooking w/r to delays, heat tranfer and loss. RL
Reply by ●February 3, 20232023-02-03
On 2/3/2023 1:21 PM, legg wrote:> On Tue, 31 Jan 2023 17:30:35 -0700, Don Y > <blockedofcourse@foo.invalid> wrote: > > <snip> >> I'm not sure what the heating elements in "glass cooktops" >> look like "under the glass"... > > It will depend on the mfr. some are visibly simple coils > laid in a former. > > Have 'repaired' a few with zig-zag ribbons imbedded in > filled insulator forms. These are brittle and very difficult > to make a secure electromechanical joint at any point of > failure. They're not meant to be fooled around with. > > A compression flat-fit, forcing-plates secured by offset > screws with split washers, seemed to work. Don't know how > long they lasted. Owner a fanatic for repair of esoteric > brands.Buy a spare appliance "for parts". :>> Glass cooktops are a joke, provoking the worst aspects > of the electric stove top cooking w/r to delays, heat tranfer > and loss.As well as maintenance. And, appearance (they show way too much dirt, dust, fingerprints, stains, etc. -- perhaps as an incentive for you to clean them often?) However, they seem to be the most readily offered varieties (induction and radiant). I've lobbied for gas simply because it is easier to keep clean. OTOH, I find electric better for REALLY slow cooking; it's near impossible for me to make a 16 qt pot of red sauce on a gas stove without the bottom layer of content getting scorched.
