Date: Sun, 4 Sep 1994 22:18:49 -1000 From: robert.pudlo@dbag.ulm.daimlerbenz.com (Robert Pudlo) Message-Id: <9409050818.AA12474@dagobert> Organization: Division of Applied Sciences, Harvard University Subject: Cutting ripstop with a "hot wire" Hi there, After deciding to build the Sputnik 4, I wondered whether there ain't an easier way to cut the profiles (37 of them required) than with a soldering iron. I dislike this way as my thumb and some other fingers are nearly falling off after cutting only 2 meters (maybe my cutter is underpowered). I realised that Styropor often is cut with a "hot wire" and decided to try it with ripstop, too. I bought several wires with different resistances. These wires are made of "Konstantan" (don't know the english expression for it), which consists of Cu and Ni and has a constant resistance nearly independent of temperature (correct me, if my memory of school-physics fools me). I tried several combinations of resistance, wire-length and voltage and finally found the following combination satisfying: - Use a voltage of +5V (DC) - Use about 10 cm (4 inch) of wire with a resistance of 63 ohm/meter (makes an effective resistance of 6.3 ohm) This combination requires a current of about 1 ampere (I = U/R = 5V / 6.3Ohm = 0.79 ampere, so 1 ampere should be on the safe side). I took a panel (plastic-covered wood), drilled a 3 mm hole in it and fixed one end of the wire at the underside of the panel. I stretched the wire by connecting the other end to the wire of the power supply, which (the wire) I fixed at the ceiling to ensure sufficient room to work. As the wire is very thin, tension shouldn't be too high. I tried this combination yesterday and cut 15 of the profiles without breaking the wire. Cutting is quite fast and not exhausting at all, but you have to concentrate on what you do as the ripstop follows every little move you make. As the wire is very thin, it is quite easy to cut nearly any figure you like, but straight lines are certainly better cut in the "old" way, as cutting with the hot wire is like sketching a line without a ruler. Though my english is not the best (especially considering technical terms), I hope you undersood what I did. If there is interest on this subject, I could drop a sketch of my "hot wire" to the archive. If there are any questions or comments, please don't hesitate to contact me. Is there anybody out there who has tried this before ? What were your experiences? Have a good time, Robert. = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Mon, 5 Sep 1994 07:55:01 -1000 From: swann_m@a1filton.filton.bso.mts.dec.com (Mike Swann) Message-Id: <55950150904991_1344017@FILTON> Organization: Division of Applied Sciences, Harvard University Subject: Re:cutting ripstop with a "hot wire" [This message is converted from WPS-PLUS to ASCII] > robert.pudlo@dbag.ulm.daimlerb > with different resistances. These wires are made of "Konstantan" >(don't know the english expression for it), which consists of >Cu and Ni and has a constant resistance nearly independent of I haven't used it for about 30 years, but back then in the UK it was called Konstantan. It's the stuff electrical heating elements for most domestic appliances are made with. Mike -- SWANN_M@FILTON.ENET.DEC.COM = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Mon, 5 Sep 1994 23:49:53 -1000 From: gilchgw@zoology.washington.edu (George W. Gilchrist) Message-Id: Organization: Dept. of Zoology, University of Washington Subject: Re: Cutting ripstop with a "hot wire" In article <9409050818.AA12474@dagobert> robert.pudlo@dbag.ulm.daimlerbenz.com (Robert Pudlo) writes: >... These wires are made of "Konstantan" >(don't know the english expression for it), which consists of >Cu and Ni and has a constant resistance nearly independent of >temperature (correct me, if my memory of school-physics fools me). We call it "constantan". We use copper-constantan thermocouples to measure temperature; joining two different metals, then heating them generates a small current that varies almost linearly with temperature. I'm unsure about the the temperature independence of resistance in constantan and a quick check of my reference materials on thermocouples has not provided any insight. Great idea with the cutting wire! George Gilchrist gilchgw@zoology.washington.edu = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Tue, 6 Sep 1994 12:14:21 -1000 From: mark@murder.demon.co.uk (Mark de Roussier) Message-Id: <778914861snx@murder.demon.co.uk> Organization: damage Subject: Re: Cutting ripstop with a "hot wire" In article <9409050818.AA12474@dagobert> robert.pudlo@dbag.ulm.daimlerbenz.com (Robert Pudlo) writes: [ details of hot wire cutting system deleted ] That sounds like quite an ambitious set up you're creating :). You get the same problem about keeping a smooth edge when you hot-cut on glass. Indeed, I think any system that does not rely on templates ( or industrial machinery ) has a potential problem here. [FX: grinding of gears as idle speculation mode starts....:)] Is there any way you could use a template to help ? You could not run the template against the wire itself, but the only function of the template in a system where the cutting point is fixed is to guide the movement of the fabric. Provided the fabric can be treated as a rigid sheet ( !:)) ), the template could be run against a guide which was fixed in relation to the hot wire, but which was not itself hot. It could not pass through the table, of course, so would need to sit either on the fabric or just above it. Thus in plan view : TABLE +-------------------------------+ ............................................. . . . . F . . A . . B . * . R . @@@@@@@@ . I . @@@@@ @ . C . @@@@ @ . . X@ TEMPLATE @ . . @@@@@@@@@@@@@@@@@@@@@@ . .............................................. +-------------------------------+ * - Hot Cut wire X - Template guide I can see several problems with this, not least of which is that the template has to pass between the wire and the guide. Fixing the template to the fabric is easy - use Spray Mount. But I can't help but feel that it should not be made this complicated unless you are going in for large scale production. -- Mark de Roussier ************************************ A nice man is a man of nasty ideas. Jonathon Swift. ************************************ = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Wed, 7 Sep 1994 20:43:49 -1000 From: andrew@tug.com (Andrew Beattie) Message-Id: Organization: /usr/lib/news/organisation Subject: Re: Cutting ripstop with a "hot wire" mark@murder.demon.co.uk (Mark de Roussier) writes: >Is there any way you could use a template to help ? You could not run the >template against the wire itself, but the only function of the template in >a system where the cutting point is fixed is to guide the movement of the >fabric. Provided the fabric can be treated as a rigid sheet ( !:)) ), the >template could be run against a guide which was fixed in relation to the hot >wire, but which was not itself hot. It could not pass through the table, of >course, so would need to sit either on the fabric or just above it. Sounds like what you really want is 2 templates, with the fabric sandwiched between, then just trim round the edge. Hmmm... I wonder if you could use a thin paper interleaf to separate (say) 10 layers of fabric, a very hot, very sharp knife and cut them all at once? Andrew -- Kite jumping is for morons. If you want to fly, get a hang-glider. Netiquette-of-the-day: Think twice before posting! You can FTP the kite FAQ's from ftp.hawaii.edu (directory /pub/rec/kites/faq) It is generally accepted that the ravings of Frank Kenisky should be ignored. = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Thu, 8 Sep 1994 21:19:37 -1000 From: andrewh@phoenix.harvard.edu (Andrew Hawken) Message-Id: <34p2a9$d4p@beta.qmw.ac.uk> Organization: Queen Mary & Westfield College, London, UK Subject: Re: Cutting ripstop with a "hot wire" Andrew Beattie (andrew@tug.com) wrote: : Sounds like what you really want is 2 templates, with the fabric sandwiched : between, then just trim round the edge. How do I get hold of several square meters of Fridge Magnet material ? That would make a pretty cool (hot) template for this technique. Andy -- ____________________________Andrew Hawken______________________________ "However many ways there may be of being alive, it is certain that there are vastly more ways of being dead" R Dawkins. Home : 0895 420110 QMW : 071 975 5542 AIIT : 0494 677045 Email : A.Hawken@QMW.AC.UK = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =