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Products: Best hot knife/wire cutter for cutting EPS

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  1.  
    • CommentAuthorShevek
    • CommentTimeMay 4th 2013 edited
     
    What's the best hot knife/wire cutter on the market for cutting EPS? (need to cut 100 mm, 160 mm and 250 mm thick)
    • CommentAuthorShevek
    • CommentTimeMay 4th 2013 edited
     
    Anyone used one of these?

    Hot Wire Foam Factory Hot Wire Polystyrene Cutter PRO BOW CUTTER 2 - 4FT
    http://www.ekmpowershop23.com/ekmps/shops/terrascenic/hwff-hot-wire-polystyrene-cutter-pro-bow-cutter-2---4ft-517-p.asp

    Can you cut in straight lines with these things?
  3.  
    Have you had a look on ebay.co.uk? lots of choice.
    • CommentAuthorShevek
    • CommentTimeMay 4th 2013 edited
     
    Yeah this one looks pretty good. A lot cheaper too:
    http://www.ebay.co.uk/itm/Polystyrene-DEPRON-HOT-WIRE-FOAM-CUTTER-TWO-IN-ONE-WITH-POWER-NEW-/261199392447

    Edit: oh hang on, it only cuts 150 thick.
    • CommentAuthorShevek
    • CommentTimeMay 4th 2013
     
    Thinking it might be simpler if we just use a saw and vacuum cleaner.
    • CommentAuthorEd Davies
    • CommentTimeMay 4th 2013 edited
     
    Amazon.co.uk do nichrome wire.

    E.g., http://www.amazon.co.uk/Brimal-Nichrome-Nickel-Chrome-CB928/dp/B0071KZKBQ/ref=pd_sim_sbs_ce_5

    There are also one or two metre lengths available but probably worth having some spare in hand.

    Web search this afternoon found a site which seemed to be saying you want about 40 W/m (watts per metre) for thin wire (0.4 mm) up to 70 W/m for thicker (1.6 mm) (working back from the quoted currents, resistances and AWG wire sizes).

    http://hotwirefoamcutterinfo.com/_NiChromeData.html

    That 22 SWG wire on Amazon is 0.71 mm diameter and 2.7 ohm/m. 13 volts across a 1 metre length would give a current of 4.8 amps and a power of 62 W/m. Slightly longer length - less current, less power and even less power per metre. Slightly shorter length - bit more current, bit more power and quite a bit more power per metre.
  7.  
    Posted By: ShevekThinking it might be simpler if we just use a saw and vacuum cleaner.


    Yep, got the T-shirt on that one
    • CommentAuthorSprocket
    • CommentTimeMay 4th 2013
     
    Best place used to be "Scientific Wires" but they seem to have divided:-
    This looks like the stuff I have:-

    http://www.wires.co.uk/acatalog/cn_bare.html

    They sell a lot of other interesting stuff, for example Kanthal.
    • CommentAuthorCWatters
    • CommentTimeMay 5th 2013
     
    Posted By: ShevekCan you cut in straight lines with these things?


    Not with just a freehand bow. You either need to fix guide(s) to the eps or fix the bow to a table with a guide (bit like a band saw set up).

    There are lots of vids on youtube showing home made hot wire cutters in action.
    •  
      CommentAuthorfostertom
    • CommentTimeMay 6th 2013
     
    Reinventing the wheel! There was a thread on GBF quite recently that gave the full recipe, pics, electrical details, experience, results - search for it.
  11.  
    Posted By: ShevekThinking it might be simpler if we just use a saw and vacuum cleaner.


    As you don't have a massive amount of insulation to fit then this may be the best way forward, if you don't have nichrome/batteries/car battery chargers/lab packs etc lying around then it will take as long to get the stuff and throw it together to make a hot wire cutter than it will to just cut the EPS with a normal saw. I have a hot wire bow cutter (bit of bent mdpe water pipe, lab pack PSU) for 300mm xps, it does the cut ok but is a two man job to get it to follow the line both sides.
    • CommentAuthorEd Davies
    • CommentTimeMay 6th 2013
     
    http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=9565#Comment_156314

    an02ew used 22 SWG. Sprocket's source supplies that at 1.24 ohms/m. So 400 mm is roughly 0.5 ohm. A 10 A, 12 V charger will pull down to about 5 V if it current limits accurately so 50 W or 125 W/m - a bit higher than the source I linked above was suggesting.

    Note that a 12 V battery instead of a battery charger will produce a lot more current and power as its voltage will not be pulled down anything like as much (it won't current limit). You'd need a bit more than a metre of nichrome wire to deal with it.
  13.  
    Posted By: Ed Davies
    Note that a 12 V battery instead of a battery charger will produce a lot more current and power as its voltage will not be pulled down anything like as much (it won't current limit). You'd need a bit more than a metre of nichrome wire to deal with it.


    Batteries work in practice although you have to keep an eye on things. Old UPS/motorbike ones are a handy size. They will burn the nichrome out if just left on, but if you are cutting, especially thick stuff then the heat is taken out of the wire and you effectively just get a much faster cut.
    •  
      CommentAuthorSteamyTea
    • CommentTimeMay 6th 2013
     
    I found that the wire tended to wander a bit and it did not produce a good cut, so turned up the juice and it then melted the material without actually touching it, this lead to an inaccurate and varying cut.
    Using a bench circular saw is a great way to get the neighbours involved :bigsmile:
  15.  
    Handy hint using wie cutters, I got some aluminium 'L' shaped profile from DIY store, drill some holes and insert small nails, these will then stick in the EPS 150 we were cutting great. Insert one on each end of the insulation down the line of the cut and the you can push the hot wire against the metals tracks as it melts through giving a perfect cut every time.
    • CommentAuthorShevek
    • CommentTimeJul 17th 2013 edited
     
    Bought one of these German Jago AG knifes (£63):
    http://www.ebay.co.uk/itm/221255272831

    And a 250 mm blade (£37):
    http://www.ebay.co.uk/itm/221255269306
    •  
      CommentAuthorfostertom
    • CommentTimeJul 24th 2013
     
    The hot wire/hot knife fumes are stinky and make you feel sick after a while - but claimed to be non toxic. What's the truth?
  18.  
    No expert, but if something makes you feel sick , I'd put it down as toxic
    • CommentAuthorShevek
    • CommentTimeJul 24th 2013
     
    If I was doing this all the time I'd probably wear a mask of some sort but I think a one-off self-build is probably okay to just do it outside.
    •  
      CommentAuthorSteamyTea
    • CommentTimeJul 24th 2013
     
    Posted By: jamesingramNo expert, but if something makes you feel sick , I'd put it down as toxic
    Thankfully my Malboro are full of vitamins an minerals.
  21.  
    Tell that to the Malboro man :confused:
    • CommentAuthorTimSmall
    • CommentTimeJul 25th 2013
     
    Posted By: SteamyTeaI found that the wire tended to wander a bit and it did not produce a good cut


    Need more tension in the wire... I hung a half-brick off the end of the wire I think, but you could use a long-ish spring instead (the wire elongates with length, so the tensioner needs to maintain a similar the tension over a few mm of travel).
    •  
      CommentAuthorSteamyTea
    • CommentTimeJul 25th 2013
     
    I used a spring and it just broke the wire in the end. May have had the wire too hot too.
    • CommentAuthorMikeRumney
    • CommentTimeJul 30th 2013
     
    Posted By: ShevekThinking it might be simpler if we just use a saw and vacuum cleaner.


    'swat we did ... even for curves :cool:
    • CommentAuthorShevek
    • CommentTimeJul 31st 2013
     
    The hot knife has turned out to be next to useless, at least with 150 kPa EPS. To get through without it burning you need to apply pressure, but that amount of pressure not only buckles the blade as you cut (so you end up effectively cutting with two blades) but it also damages it by bending the blade at the base.
    •  
      CommentAuthordjh
    • CommentTimeJul 31st 2013
     
    Thanks for the feedback. Just as useful as success stories!

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