Foam cutter problems

B

bob Petritsch

Active member
Trying to cut the 12X12X19 foam blocks I got from tractor supply. First tried to just saw it with an old hand saw. Blade freezes up before it is all the way into the foam.
Built a foam cutter of kinfo from the Internet. Started to desiring an old banjo. The smallest string got hot enough to cut with a 1 amp output voltage converter. Put little pieces against the wire and it cut like butter. When I went to cut the block the wire snapped.
Go to the next larger string and the converter wasn't powerful to heat the wire. Went to a small" motorcycle" battery I use for lighte on the sneak box. Exact same problem, wire snapped about 4 inches into the block. This is about where I stopped pushing the wire and checked for square.
Went through the all four single wire strings on the banjo. Did not use the bass string as it is overwound.
Could I have created a hard spot when I stopped the wire moving forward. The wire is quite strong and I could not break it if I tried but they snapped very easily when heated.
Any suggestions would be appreciated. This was a test run and I did not use a spring to tension the wire. Once heated the wire really stretched and became loose.
 
What diameter wire are you using? Are you using a 3, 6 or 12 volt ac to dc stepdown transformer? Are you using a spring on the wire to allow for wire stretch when heated? Without these questions I will not be able to help.

Regards,
Kristan
 
The wires are.010, .012. And.016 inches.
I did not realize the 5th and first string are the same diameter. I think what might have happened was the transformer burned out with the first test. After that I used the battery from the sneak boat. I attached a 12 volt charger to it set a 2 amps.....the battery was dead. The wires are plain steel.
 
What kind of foam is it? plain old EPS? Or really high density stuff?
I have been using a bow saw (large aggressive teeth) on the foam blocks I am rough cutting. Takes hardly any effort.
I then use a coping saw and Sureform rasp for shaping
 
Did you try using a wedge of some sort to take the pressure off the sides of the blade of the saw once it plunges below the top of the blade? Might be a quicker and easier solution for you
 
A long time ago I remember a local surfboard shaper talking about using a wire hanger to shape foam and cut bevels. Can't remember if it was electric or if he was using a flame to heat.
 
I learned this from a buddy. If you have an electric filet knife it works real well on foam.

Mark W
 
Don't have a band saw, let alone one with a 12 inch opening. I only got a few inches through the block when I tried with the hand saw. The amount of static charged dust was awesome. The hot wire was so neat I really would like to continue with that method.
 
Your wire size should have been fine by the diameter except for the wire, you need a nickel chrome based wire or other super allow to handle stretch when heated. Typically steel based wiring will literally heat-up, start to melt and if under tension as it expands the wire becomes thinner then hotter which snaps. Not to get into too much detail but I do recommend using a step down transformer and a Rene wire or Nickel chrome wiring. Use the following site as a reference and to purchase. Jacobs-online.biz
I use a 50VA to 6/12 volt Step down transformer with 22 gauge "Rene" wiring which is around .014" cutting max thickness of around 12 inches. Since the transformer as the ability to go in-series you can get 12 volts out of the wire. Using a volt meter when I cut thicker materials at 12 inches I utilize around 10 volts of heat at 14 inch length (Meaning that my alligator clips placed on the wire are at 14" apart). I would recommend a 24 gauge if you use less than 12 inches per cut. My cutter I built out of PVC piping and a plexiglass table top. My top is 24" x 24" in an "U" frame configuration. For all electrical and materials to get it up and running was less than $80 bucks.
If you have any problems just give Jacob a call he will answer any questions.
Regard,
Kristan
 
Success at last. This morning I used the base string from the banjo. It is a wrapped string and contains some nichol. I set it up with a Molly bolt replacing one of the screws. The Molly bolt allows me to tension the wire before and after heating. I used a different block thinking there may have been an obstruction in the first one.
Same result. I even waited a long time to see if the wire would self fail before I attempted to cut the foam. I got further along this time.
Not one to give up I tried again. This time a just took off a corner of the block. I cut about two inches from the corner. It cut like it was going through air....for about 5 inches, then it slowed down. I moved the cutter to get a new section against the foam and again it cut like going through air then slowed down. I think the foam cooled the wire and caused it to not glide through the foam. I tried again to cut through the whole block but VERY slowly. Worked like a charm.
I was very happy to find that the melted foam did not refuse but parted without sticking together at all. And no statically charged foam balls all over the place.
Thanks Kristen for some great advise, wish I knew what you were talking about. Never can I understand electricity, it has been a mental block my whole life. I will order some of the nichol wire you mentioned. I am sure I will keep breaking banjo strings if I don't.
Now all I need is a good pattern to make some foam decoys. I will probably make some smaller one hand cutters to do some body shaping and reduce the amount of sanding . I know there is a bird inside there, just have to find it.
 
I have made a couple hot wire cutters. The most recent being a feather burner for arrow fetching. I had always used NiCrome wire before but was having trouble finding some for this project. Guitar strings were recommended to me but they were not thick enough to hold there shape. Unlike a normal hot wire cutter that is tensioned this needed to be bent to the shape of the fletching I wanted. What I found works well is plain Stainless steel fishing leader not the coated stuff. It is available in a variety of diameters and being solid instead of wrapped it may hold up a little better.Also being close to the coast you could probably pick it locally at a tackle shop.
 
Success didn't last long. Tried to cut another block and again the wire broke. Ordered a reel of wire from Jacob- will try again when I get the nichol wire.

On another not I shaped the first cut off. I finished cutting with a hack saw and a coping saw. A lot messier than the hot wire. Any suggestions on handling the result and snow storm of styrofoam dust.
I used a wood rasp, a surcoat rasp and a sanding pad. I used the coping saw to knock down chunks off the block.
 
You should try the electric knife. I used it quite a bit over the past couple of years to cut much denser foam than what you are going through. Super clean, very little dust and quick. You can buy a cheap I knife at Walkyworld for under $15

Mark W
 
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