+ Reply to Thread
Page 2 of 5 FirstFirst 12345 LastLast
Results 16 to 30 of 64
Like Tree3Likes

Thread: hot wire cutting foam

  1. #16
    Registered User Jan Carlsson's Avatar
    Join Date
    Jan 2009
    Location
    Sweden
    Posts
    1,458

    Re: hot wire cutting foam

    She have time for that? isn't she looking after the constuction company in FL.
    Jan.

    A designer knows he has achieved perfection not when there is nothing left to add, but when there is nothing left to take away. Antoine de Saint-Exupery
    "Flight by machines heavier than air is unpractical and insignificant, if not utterly impossible." Simon Newcomb, 1902

  2. #17
    Registered User
    Join Date
    Aug 2006
    Location
    Toronto
    Posts
    129

    Re: hot wire cutting foam

    you guys are probably going to make a good cutter and don't need my help.

    I have had lots of success with the car charger (big amps with start feature). i have made my nichrome wire bow just the right length to control the resistance/heat for the foam i want to cut (40"). it is also good for charging my car!

    Make sure you have good ventilation!

    Cheers!
    Last edited by Woodenwings; January 18th, 2012 at 07:37 PM. Reason: spelling
    remember: Mother nature always wins.

  3. #18
    Registered User wsimpso1's Avatar
    Join Date
    Oct 2003
    Location
    Saline Michigan
    Posts
    2,539

    Re: hot wire cutting foam

    A variable system lets you adjust the heat level. You want a clean cut that is as close to the template as you can get. Too much heat remove more foam than just the template outline, and too little makes for wire lag. Also, different wires have different electrical resistance. Built a variable system. Then you can make saws in different sizes to suit.

    cammie - Please understand that we are talking about a saw that cuts polystyrene foam with a hot wire.

    Bill

  4. #19
    Registered User
    Join Date
    Oct 2011
    Location
    Springfield IL
    Posts
    281

    Re: hot wire cutting foam

    So a good car charger, some wire from my Mig welder and a pole to mount all this too. Do I have this correct?

    I can smell the foam burning now...

    Tony

  5. #20
    Registered User wsimpso1's Avatar
    Join Date
    Oct 2003
    Location
    Saline Michigan
    Posts
    2,539

    Re: hot wire cutting foam

    A car charger usually has two settings, both near 12 V. If it turns out that 12 V gives the right current for your length of hot wire and resistance of the rest of the system, you are good. If it is too much current or too little, you will find out pretty fast. I would do some test runs both to develop technique and to find out if you need to adjust power up or done some...

    Billski

  6. #21
    Registered User Jan Carlsson's Avatar
    Join Date
    Jan 2009
    Location
    Sweden
    Posts
    1,458

    Re: hot wire cutting foam

    The diameter and lenght of the wire change the need for power, when you have the right temp (and speed), you will get long treads from the foam, you don't want it to melt to much either, or get to much bend in the wire.
    Jan.

    A designer knows he has achieved perfection not when there is nothing left to add, but when there is nothing left to take away. Antoine de Saint-Exupery
    "Flight by machines heavier than air is unpractical and insignificant, if not utterly impossible." Simon Newcomb, 1902

  7. #22
    Registered User StarJar's Avatar
    Join Date
    Sep 2011
    Location
    Murrietta Ca.
    Posts
    583

    Re: hot wire cutting foam

    I've always used wire zig-zagged across a board. About 60'' of wire will make a big 'resistor'. Then it goes through the, approximately 52" of wire on the cutting bow. Just get brave, plug it into a wall recepticle, and blam; you have it!
    To adjust the heat, you change where you clip to the zig-zagged wire, before it goes to the cutting wire. The zig-zags are held by nails, down a 1"x12" piece of wood. One end goes to the wall socket plug, the other to the cutting bow/wire, and then through the cutting wire, back to wall socket plug, (to the other prong).
    Actually I learned this on Rutan's first Vari-Eze plan's and have used it on many projects.
    Making a bow, is also a bit of black magic. I use a 2"x2" piece of wood about 55" long. Then drill 2 holes 3/8" dia. near the ends. Then insert 3/8" 4130 tube (12" long) in each hole. The tubes need small holes drilled in them to string the cutting wire through. T
    he tubes are twisted with pliers the make the cutting wire tight. (not unlike a guitar). Large aligator clips and wires make the interconnections, between bow and the "Rutan" resistor board.
    Maybe I should just get a life and use a charger. But wait,, this is my life...

    Edit: I've had the wonderful experience of touching the wire on several occasions. It's just hot....NO SHOCK. because even though it is AC, you are not completing any circuit, if you touch it.

    Also the whole set up, mentioned above...about $15.
    Last edited by StarJar; October 27th, 2012 at 06:40 PM.
    oriol likes this.

  8. #23
    Registered User Head in the clouds's Avatar
    Join Date
    Mar 2012
    Location
    Gold Coast, East Coast of Australia
    Posts
    1,666

    Re: hot wire cutting foam

    Quote Originally Posted by StarJar View Post
    I've always used wire zig-zagged across a board. About 60'' of wire will make a big 'resistor'. Then it goes through the, approximately 52" of wire on the cutting bow. Just get brave, plug it into a wall recepticle, and blam; you have it!
    To adjust the heat, you change where you clip to the zig-zagged wire, before it goes to the cutting wire. The zig-zags are held by nails, down a 1"x12" piece of wood. One end goes to the wall socket plug, the other to the cutting bow/wire, and then through the cutting wire, back to wall socket plug, (to the other prong).
    Actually I learned this on Rutan's first Vari-Eze plan's and have used it on many projects.
    Making a bow, is also a bit of black magic. I use a 2"x2" piece of wood about 55" long. Then drill 2 holes 3/8" dia. near the ends. Then insert 3/8" 4130 tube (12" long) in each hole. The tubes need small holes drilled in them to string the cutting wire through. T
    he tubes are twisted with pliers the make the cutting wire tight. (not unlike a guitar). Large aligator clips and wires make the interconnections, between bow and the "Rutan" resistor board.
    Maybe I should just get a life and use a charger. But wait,, this is my life...

    Edit: I've had the wonderful experience of touching the wire on several occasions. It's just hot....NO SHOCK. because even though it is AC, you are not completing any circuit, if you touch it.

    Also the whole set up, mentioned above...about $15.
    Sheesh! It certainly is 'live' if one of the alligator clips fall off and you unthinkingly pick it up while holding the wrong bit of the bow.... maybe we're a bit more conservative over here since our mains is 240V.

    My custom made hot wire system is a transformer which puts out 70V and is controlled on the input side with a light dimmer, almost everything you could touch is insulated and it works great but still gives a good kick if you really work at not concentrating.

    Yours sounds like a cheap way of doing it if you know what you're about around high voltages though.

    But how do you adjust the wire tension as it heats and cools while cutting the foam? My bow is also rigid but has springs at each end which are constantly working in and out while cutting. I think the best bows I've seen (best in terms of keeping constant wire tension regardless of the wire temperature) are made just like an archery bow.

  9. #24
    Registered User StarJar's Avatar
    Join Date
    Sep 2011
    Location
    Murrietta Ca.
    Posts
    583

    Re: hot wire cutting foam

    Quote Originally Posted by Head in the clouds View Post
    Sheesh! It certainly is 'live' if one of the alligator clips fall off and you unthinkingly pick it up while holding the wrong bit of the bow.... maybe we're a bit more conservative over here since our mains is 240V.

    My custom made hot wire system is a transformer which puts out 70V and is controlled on the input side with a light dimmer, almost everything you could touch is insulated and it works great but still gives a good kick if you really work at not concentrating.

    Yours sounds like a cheap way of doing it if you know what you're about around high voltages though.

    But how do you adjust the wire tension as it heats and cools while cutting the foam? My bow is also rigid but has springs at each end which are constantly working in and out while cutting. I think the best bows I've seen (best in terms of keeping constant wire tension regardless of the wire temperature) are made just like an archery bow.
    Regarding 'live', ya I gues 240v can definately be more of a concern. To be honest I'm just real careful, and cognisant of all the wires, and have a plan if something happens; Basically break the circuit quickly, and then stop and assess what is happening.

    Don't forget, the only time the system is turned on, is while you are cutting, so it's not like you're going to put your hand on it while your drinking coffee or talking on the telephone.

    Regarding the bow, The 2" x 2" gives some spring, and the 3/8" tubes also bend to give some spring action. Unfortunately, I've never used one with springs, and so I can't compare it .

  10. #25
    Registered User SVSUSteve's Avatar
    Join Date
    Aug 2007
    Location
    Indianapolis, IN
    Posts
    2,438

    Re: hot wire cutting foam

    maybe we're a bit more conservative over here since our mains is 240V.
    This probably explains a lot but I inadvertently stepped on a live 240V electrical line while on a fire call several years ago. I learned several things that night:
    1. I can, as a point of fact, more or less do a backflip from a standing position.
    2. That I need to learn to watch where I step.
    3. That I really dislike the idea of working with high voltages.
    4. If you get electrocuted on a fire scene, you will be immediately and irrevocably nicknamed "Sparky" by your fellow volunteer firefighters.
    Head in the clouds likes this.
    "Unfortunately in science what you believe is irrelevant."- Orion

    Sport Aviation Association Member #2976

  11. #26
    Registered User timberwolf8199's Avatar
    Join Date
    Sep 2011
    Location
    Grand Rapids area, MI, USA
    Posts
    207

    Re: hot wire cutting foam

    Quote Originally Posted by SVSUSteve View Post
    This probably explains a lot but I inadvertently stepped on a live 240V electrical line while on a fire call several years ago. I learned several things that night:
    1. I can, as a point of fact, more or less do a backflip from a standing position.
    2. That I need to learn to watch where I step.
    3. That I really dislike the idea of working with high voltages.
    4. If you get electrocuted on a fire scene, you will be immediately and irrevocably nicknamed "Sparky" by your fellow volunteer firefighters.
    Thanks for sharing steve. Made my morning.

  12. #27
    Registered User SVSUSteve's Avatar
    Join Date
    Aug 2007
    Location
    Indianapolis, IN
    Posts
    2,438

    Re: hot wire cutting foam

    Quote Originally Posted by timberwolf8199 View Post
    Thanks for sharing steve. Made my morning.
    Glad to be of assistance. See, I'm not completely useless. I make a perfectly serviceable bad example.
    "Unfortunately in science what you believe is irrelevant."- Orion

    Sport Aviation Association Member #2976

  13. #28
    Moderator Topaz's Avatar
    Join Date
    Jul 2005
    Location
    Orange County, California
    Posts
    8,200

    Re: hot wire cutting foam

    I'm another that's using a automotive battery charger as my power source. To adjust the output, I use the "zig zag" wire setup as seen in Rutan's Homebuilt composites book. It's worked like a charm for me.
    "If you have built castles in the air, your work need not be lost; that is where they should be. Now put the foundations under them." - Henry James Thoreau
    Member of the Lake Elsinore Soaring Club.

  14. #29
    Registered User Jay Kempf's Avatar
    Join Date
    Apr 2009
    Location
    Warren, VT USA
    Posts
    2,269

    Re: hot wire cutting foam

    Quote Originally Posted by Topaz View Post
    I'm another that's using a automotive battery charger as my power source. To adjust the output, I use the "zig zag" wire setup as seen in Rutan's Homebuilt composites book. It's worked like a charm for me.
    I have a small transformer and a rheostat that I put in a little box with a dial I can write on for settings for different projects and a homemade bow. I use .032 stainless safety wire for the cutting wire because I can put a lot more tension on it than anything else so that it cuts really straight with not much lag. I have a system of springs that I use to maintain tension. I bought the original kit with rheostat and transformer from Aircraft Spruce but nearly any will do. That way you don't electrocute yourself on the primary voltage.

    Still cheap and dirty if you have surplus sources and no hokiness with zig zag bare wire Darwin award contender techniques. Mine has been working continuously for something like just short of 20 years I think.
    Jay K.

    VT USA

  15. #30
    Registered User
    Join Date
    Sep 2011
    Location
    Zagreb HR
    Posts
    680

    Re: hot wire cutting foam

    Quote Originally Posted by Head in the clouds View Post
    Sheesh! It certainly is 'live' if one of the alligator clips fall off and you unthinkingly pick it up while holding the wrong bit of the bow.... maybe we're a bit more conservative over here since our mains is 240V.

    My custom made hot wire system is a transformer which puts out 70V and is controlled on the input side with a light dimmer, almost everything you could touch is insulated and it works great but still gives a good kick if you really work at not concentrating.

    Yours sounds like a cheap way of doing it if you know what you're about around high voltages though.

    But how do you adjust the wire tension as it heats and cools while cutting the foam? My bow is also rigid but has springs at each end which are constantly working in and out while cutting. I think the best bows I've seen (best in terms of keeping constant wire tension regardless of the wire temperature) are made just like an archery bow.
    The voltage of 70V is a bit exaggerated for nichrome wire unless your wire is thick and long. The impedance of the wire (inner resistance) varies with the tension of the wire too, thus a variable voltage power source would be a better solution to have clean foam cuts.

    I see people use nichrome wire quite a lot but there is a better wire for foam cutting if smooth surfaces are needed. Nichrome has an inner specific resistance of 1.08 Ohm while Kanthal wire has 1.45 Ohm per mm2 per meter of length. The composition of nichrome wire is nickel and chrome while the Kanthal wire is iron, chrome, aluminum and cobalt. The aluminum part in the Kanthal wire allows to have smoother cuts because molten foam will not stick to the wire surface. This wire is less strong than the nichrome wire but it is intended for heating so has a better resistance to heat. Thus a Kanthal wire if the calculated resistance and voltage are met will almost never break and will cut smoothy. The thinner the wire the more resistance it has, so an optimum is to balance between resistance and voltage to get the right wire temperature. Tensioning the wire (be it nichrome or kanthal) impacts the thin structure of the walls and adds resistance to the wire. Basically, the higher the resistance the electricity 'does not want to go through' so you have to increase the voltage. As you increase the voltage in a high resistance wire the heat goes up. With a good Kanthal wire and a variable voltage power source you could make a foam cutter which could set an ideal temperature for the foam you intend to cut.

    The 0.5mm kanthal wire has an impedance of 6 Ohm while the 0.6mm wire has 0.4 Ohm. So you see the thinner you get the more voltage you will need. When tensioning with a spring the 0.6mm wire extends with the heat and it's resistance increases almost to the one of the 0.5mm wire. So, every spring that is put in a system might influence the heat of the foam cutter wire temperature and has to be taken into consideration.

+ Reply to Thread
Page 2 of 5 FirstFirst 12345 LastLast

Similar Threads

  1. Hot Rodding O 200?
    By 4trade in forum Firewall Forward / Props / Fuel system
    Replies: 13
    Last Post: November 14th, 2012, 02:13 PM
  2. CNC Foam cutting market research
    By Will Aldridge in forum Composites
    Replies: 9
    Last Post: November 20th, 2011, 11:41 PM
  3. How thin can you buy/hot wire foam sheeting?
    By HumanPoweredDesigner in forum The light stuff area
    Replies: 2
    Last Post: December 14th, 2010, 03:04 PM
  4. foam choices and method of cutting
    By drake in forum Composites
    Replies: 3
    Last Post: November 14th, 2008, 03:51 PM
  5. Foam cutting kit
    By Nilsen in forum Composites
    Replies: 5
    Last Post: June 19th, 2006, 04:35 AM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts