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Cutting Styrofoam

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  • Cutting Styrofoam

    I need to cut some 1.25â€‌ diameter x 4" deep (preferably blind) holes in 8x8 Styrofoam blocks. I will also have to cut some 3â€‌ x 2â€‌ deep holes.

    I was hoping someone could offer some insight on an easy and efficient way of making clean holes in this material. I haven’t done any experimenting yet, but I am guessing that sharp woodworking tools will probably be my best bet. A shop vac should help cut down the expected mess. I could make a punch or hole saw out of thin wall pipe, but they won’t be through holes. Using heat is another option.

    Thanks.

  • #2


    After making the hole twist out the plug with a butter knife.

    [This message has been edited by Evan (edited 06-23-2004).]
    Free software for calculating bolt circles and similar: Click Here

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    • #3
      I've seen people use a hot wire to do the cutting. Just connect some thin, steel wire to an appropriate holder (a bent coat hanger w/ insulation is OK) and connect the ends to a battery. Make sure you use enough juice to heat the wire w/o going red hot. GOOD LUCK!

      OOPS. Misread. You want holes. How's about heating a thin walled pipe?

      [This message has been edited by tonydacrow (edited 06-23-2004).]

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      • #4
        THE WIRE IS NI-CHROME. AS FOR A BLIND HOLE, WOW,THATS A TOUGH ONE.

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        • #5
          Why not use a heated tube with a wire stretched along the diameter of the tube? The tube could make the hole sides, and twisting it would cut out a nice clean bottom with the wire. Getting the wire hot enough could be a bit of a problem, but insulated uh, ni-chrome or whatever it's called could work. Just insulate where it touches the tube and run an electrical current through it.

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          • #6
            You could cut completely through it and then put a plug back in with glue.

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            • #7
              A router with a guide bushing riding on a plywood template and a Foredom brand carbide wood rasp,might need a VS router or a speed control.You might get by with a sharp HHS router bit too.

              What would happen I wonder if you used a cutter like Evan's,to make the circular cut,and instead of removing the plug in the middle you just used a round chunk of plywood or metal to compress the styro in the area to a thinner size?

              It just hit me,what about a good sharp forstner bit?Spun up in a drill press it should wippit out in nothing flat,plus since the rim has a razor edge and cuts first it should be slicker than snot on a bed post.Heck,I got to try that myself

              [This message has been edited by wierdscience (edited 06-23-2004).]
              I just need one more tool,just one!

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              • #8
                RobDee has it. That's how I'd make a core box.

                Dave

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                • #9
                  I wouldn't want to spring for a 3" forstner.

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                  • #10
                    I had to try it,1-3/4" spun up at 2,000,hand held and wow!Hope this helps-
                    I just need one more tool,just one!

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                    • #11
                      Foam is easy to cut with hot wire. I use stainless safety wire. top held by a shelf bracket, passed through a hole in work table and weight on the bottom. 12 volt transformer run from a variac to adjustthe heat. Works on styrofoam and the much more durable poly stuff that will not dissolve in oils.

                      Made me a close spaced socket set holder by putting sockets in a toaster oven and when they got hot enough to melt the foam just let them melt down as far as you need them to go. Not a precise fit but "good nuff". The final use was to put in a a small tin tool box. got every size from 1" to 3/16 in the box plus ratchet, adapters, extensions etc. The ratchets and extensions lay loose, the sockets are "shadowbox" holes. Wonderful in RV- use little room, self inventorying and very handy when trouble occurs at night. Lasted ten plus years and no sign of deteriorating.

                      The sockets are mostly "blind holes".

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                      • #12
                        Grizzly has the 3" for $29.95 last I saw,if you catch the Homier tool truck,they have the 24pc sets for about $26 the last time they came around,also the smaller sizes 2" and less can be had at Homedepot or Lowe's for cheap and they have the solid edge insted of the sawtooth,although it did cut that chinese tv box foam smooth
                        I just need one more tool,just one!

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                        • #13
                          Don't get me started on saw tooth "forstner" bits. That's a lot better price than I thought you'd have to pay for a 3". Thanks

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                          • #14
                            The hot-wire "trick" is the way even the pros do it for profiling foam, though not much good for blind holes.

                            I just wanted to say that the way we did it in shop class (jeez that was so long ago, I'm sure feelin' old!!!) was using a transformer (as Doc mentioned) from an electric train set-variable and adjustable heat.

                            We had a similar bracket with hole in table rig only it had a bottom bracket beneath the hole in the table.


                            Also that was the same transfomer that we used to separate the tops from bottles that were cut--make cut with glass cutter in bottle cutting jig than wrap the wire hooked to transformer around bottle at the cut mark,
                            apply power till the wire glowed, count to 5 (seconds) then hold bottle under slow running cold water, the top pops right off!

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                            • #15
                              Use the hot wire method. Make a square loop about 1/8 inch narrower than the wanted diameter of the hole, and attach the loop to the edge of a piece of mdf with some screws and washers. The ammount of loop sticking out is the depth of the hole. Plunge the loop, and twist at the same time, until you have gone a full circle at full depth. The mdf is your handle, and for a few seconds, ten or so, there won't be enough burning to worry about. Feeding the right current to the wire loop is the trick. Use dryer element wire if that is obtainable, and use a variac and a filament transformer to power it. If you need to use a car battery because it's the only current source available to you, then also wire in series with the loop a good length of some #18 speaker wire. That becomes your limiting resistor, and you can adjust the length of that to get the right speed to be cutting the foam at. The right speed is about 1 or 2 inches per second. Know that it will start cutting quickly at first plunge, slowing as the heat dissipates into the foam. Don't linger with the loop in any one position, as the foam will melt away from the wire, overcutting the hole. This is all best done outside.

                              [This message has been edited by darryl (edited 06-23-2004).]
                              I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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