Page 1 of 2 12 LastLast
Results 1 to 15 of 22

Thread: Hot wire foam cutter

  1. #1
    Nay sayer Domestic Engineer Mr Ed's Avatar
    Join Date
    May 2006
    Location
    ACT
    Posts
    624

    Default Hot wire foam cutter

    I need to make some stuff out of polystyrene so Im gonna knock one of these up hot wire cutters tonight. Theyre a pretty simple thing but Im trying to make it using stuff I already have lying about.

    Ive got a bunch of bits of wood, steel, plenty of spare electrical wire and guitar strings to use as the cutting wire.....what Im trying to figure out is what to use as the power supply.

    I have a bunch of random transformers from random old appliances (the black box type that plugs into the wall with a 12v lead connecting to the printer/wateva)....but Im guessing these might not supply enough current for the job.

    I have a bunch of car batteries that could be used, but Im guessing that these might supply too much current. (Maybe I could whack a variable resistor in series with a battery??)

    I know a bit about electronics but I have no idea what range of voltage/current I should be aiming for. Any tips?

    Or am I best to just to go buy a transformer from jaycar thats more suited to this sort of task?
    I used to eat alot of natural foods. That was until I learned that most people died of natural causes.

  2. #2
    Junior Member Too Much Toyota oldcorollas's Avatar
    Join Date
    Aug 2005
    Location
    sydney
    Posts
    12,496

    Default Re: Hot wire foam cutter

    "I'm a Teaspoon, not a mechanic"
    "There is hardly anything in the world that a man can not make a little worse and sell a little cheaper" - John Ruskin (1819 - 1900)

    AU$TRALIA... come and stay and PAY and PAY!!! The moral high horse of the world!

  3. #3
    Nay sayer Domestic Engineer Mr Ed's Avatar
    Join Date
    May 2006
    Location
    ACT
    Posts
    624

    Default Re: Hot wire foam cutter

    Gonna give this a go with a car battery and see how it goes. I ducked out and bought some nichrome wire ($5 for 4m at jaycar) at lunch time and the idea is that I just hook the power up the the wire at different points to vary the current.

    Will post up how I go.
    I used to eat alot of natural foods. That was until I learned that most people died of natural causes.

  4. #4
    Junior Member Too Much Toyota
    Join Date
    Sep 2005
    Location
    Qld
    Posts
    5,590

    Default Re: Hot wire foam cutter

    jaycar power supply would be better - you'll want to vary the amps somehow.

    Edit: a power brick for a printer/scanner will toast itself pretty quickly - most are under 1amp output rated.
    ------------------------------
    ST185 road barge / MZ11 forest barge / RA65 garage barge

  5. #5
    Nay sayer Domestic Engineer Mr Ed's Avatar
    Join Date
    May 2006
    Location
    ACT
    Posts
    624

    Default Re: Hot wire foam cutter

    If theres too much current I guess I could loop the cutting wire round so theres two long resistors in paralell, then move the position at which they join for finer adjustment.

    My physics is a little shaky these days though.

    Some guy on PF says he uses and battery and it works. I figure its worth giving it a go. I could put a 10amp fuse or something on it if Im really worried.
    I used to eat alot of natural foods. That was until I learned that most people died of natural causes.

  6. #6
    Junior Member Too Much Toyota oldcorollas's Avatar
    Join Date
    Aug 2005
    Location
    sydney
    Posts
    12,496

    Default Re: Hot wire foam cutter

    got the resistance for the nichrome?

    Power = voltage x current.

    but yeah, hook it up at different lengths and see when it melts

    when makign furnaces, i'd use abotu 10metres of kanthal wire (similar.. ish.. sorta..) and with a 100V/10A supply, it would toast itself if the power was not controlled (i think 1400-1500C was highest accidental temp...

    hmm... got an injector or fuel pump resistor lying around? that will reduce current.
    "I'm a Teaspoon, not a mechanic"
    "There is hardly anything in the world that a man can not make a little worse and sell a little cheaper" - John Ruskin (1819 - 1900)

    AU$TRALIA... come and stay and PAY and PAY!!! The moral high horse of the world!

  7. #7
    Junior Member Too Much Toyota
    Join Date
    Sep 2005
    Location
    Qld
    Posts
    5,590

    Default Re: Hot wire foam cutter

    find the Race magazine issue that had Nero and mate doing the foam core for a rear wing. It talked bout the volts/amps used by his form cutter
    ------------------------------
    ST185 road barge / MZ11 forest barge / RA65 garage barge

  8. #8
    Nay sayer Domestic Engineer Mr Ed's Avatar
    Join Date
    May 2006
    Location
    ACT
    Posts
    624

    Default Re: Hot wire foam cutter

    It should be 13.77ohms/m, the bow will be roughly 1300mm and I have 4m of wire so that gives me a resistance range of 18-55ohms.

    Ok so here my attempt at some physics on the thing, I used to know this stuff a bit better....but I havent really thought about it in 10yrs.

    Say my battery is 12v and 400amp.... this gives me P = 12x400 = 4800w

    I=√(P/R)

    Max current = √ (4800/18) = 16.3amps
    Min current = √ (4800/55) = 9.3amps

    This seems a bit high, say I want to aim for a maximum of 6amps.....R=P/I²

    Max current (6amp); R = 4800/6² = 133.3 ohms
    minus resistance of bow (18ohms)
    = 115ohm resistor req'd

    Before I get too carried away....how do those figures sound?
    I used to eat alot of natural foods. That was until I learned that most people died of natural causes.

  9. #9
    Nay sayer Domestic Engineer Mr Ed's Avatar
    Join Date
    May 2006
    Location
    ACT
    Posts
    624

    Default Re: Hot wire foam cutter

    Quote Originally Posted by thechuckster View Post
    find the Race magazine issue that had Nero and mate doing the foam core for a rear wing. It talked bout the volts/amps used by his form cutter
    Yeah Ive actually got a copy of that issue but I lost it somewhere in the midst of moving from Brisbane.
    I used to eat alot of natural foods. That was until I learned that most people died of natural causes.

  10. #10
    Junior Member Too Much Toyota oldcorollas's Avatar
    Join Date
    Aug 2005
    Location
    sydney
    Posts
    12,496

    Default Re: Hot wire foam cutter

    umm V=IR=12

    if you want 6 amps, you need 2 ohms total

    133ohm and 6 amps... = 800V battery

    battery is voltage fixed, not power fixed
    "I'm a Teaspoon, not a mechanic"
    "There is hardly anything in the world that a man can not make a little worse and sell a little cheaper" - John Ruskin (1819 - 1900)

    AU$TRALIA... come and stay and PAY and PAY!!! The moral high horse of the world!

  11. #11
    Junior Member Grease Monkey
    Join Date
    Aug 2010
    Location
    SA
    Posts
    95

    Default Re: Hot wire foam cutter

    How much power do you need to cut through the foam? Need that first before you can really work anything out. Also you'll have trouble finding an accurate value for the internal resistance of a battery, so it could be significantly out. I wouldn't really bother too much trying to calculate it.

    Personally I'd avoid looping back the wire, as you'll make cleaner cuts using a single piece. If you need to reduce the current, use a resistor.

    Battery charger is probably a decent start. 10amps isn't going to do too much damage but should be enough to cut. If it's not enough, then you've got a baseline to work from.

  12. #12
    Nay sayer Domestic Engineer Mr Ed's Avatar
    Join Date
    May 2006
    Location
    ACT
    Posts
    624

    Default Re: Hot wire foam cutter

    Cheers...I thought I must be doing something wrong.

    Well Ive got minimum resistance of 18ohms for a 1.3m bow, which will only give me 0.667amps. From what Ive read I dont think that will be enough.

    Sounds like I'll either need to find a different wire or use a smaller bow. Perhaps this is why people recommend using guitar strings?

    Sounds like I should make my bow only 150mm or so wide, which I can get away with this time. I'll make a bigger one another day.
    I used to eat alot of natural foods. That was until I learned that most people died of natural causes.

  13. #13
    Nay sayer Domestic Engineer Mr Ed's Avatar
    Join Date
    May 2006
    Location
    ACT
    Posts
    624

    Default Re: Hot wire foam cutter

    Quote Originally Posted by banana_socks View Post
    How much power do you need to cut through the foam? Need that first before you can really work anything out. Also you'll have trouble finding an accurate value for the internal resistance of a battery, so it could be significantly out. I wouldn't really bother too much trying to calculate it.

    Personally I'd avoid looping back the wire, as you'll make cleaner cuts using a single piece. If you need to reduce the current, use a resistor.

    Battery charger is probably a decent start. 10amps isn't going to do too much damage but should be enough to cut. If it's not enough, then you've got a baseline to work from.
    By loop the wire, I meant having the loop out of the way of the cutting wire, but it sounds like I wont need to bother.

    I need to do some testing but google seems to suggest somewhere between 2 and 4amps will work.
    I used to eat alot of natural foods. That was until I learned that most people died of natural causes.

  14. #14
    Junior Member Too Much Toyota
    Join Date
    Sep 2005
    Location
    Qld
    Posts
    5,590

    Default Re: Hot wire foam cutter

    post a query on the race magazine forums?
    ------------------------------
    ST185 road barge / MZ11 forest barge / RA65 garage barge

  15. #15
    Nay sayer Domestic Engineer Mr Ed's Avatar
    Join Date
    May 2006
    Location
    ACT
    Posts
    624

    Default Re: Hot wire foam cutter

    I didnt realise there was one. Will check it out.
    I used to eat alot of natural foods. That was until I learned that most people died of natural causes.

Similar Threads

  1. tacho signal wire for 1jzgte
    By 88cameron88 in forum Tech and Conversions
    Replies: 5
    Last Post: 18-11-2009, 03:17 PM
  2. Oxygen Sensor - 1 Wire to 4 Wire conversion?
    By AndyTTR in forum Tech and Conversions
    Replies: 4
    Last Post: 11-07-2009, 10:03 PM
  3. AE86/Sprinter Fuse Box - Wiring Help
    By xXxPigeonKickerxXx in forum Tech and Conversions
    Replies: 13
    Last Post: 15-11-2008, 09:46 AM
  4. 4AGE 100kw into AE92 (where 4AFC used to live)
    By Grega in forum Engine & Driveline Conversions
    Replies: 6
    Last Post: 24-07-2008, 05:53 PM
  5. Identifying AFM wire on 2JZGTE ECU
    By infotechplus in forum Tech and Conversions
    Replies: 13
    Last Post: 10-06-2008, 05:41 AM

Bookmarks

Posting Permissions

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