Submitted by friggityfrogg t3_y3b8xe in DIY
i bought a styrofoam material poster and tried cutting it down in size with an xacto knife, but it came out very rough and uneven. i googled how to trim styrofoam and the options are an xacto knife or tools that i dont have. is there an easy way to trim or sand the edges down to make it smooth?
I've made a hot wire from a guitar string and a soldering gun. It worked really well actually.
I replaced the heating element (tip) with the guitar string and tensioned it with some screws driven into wood. I've seen this sort of setup used in scenic shops with lengths of 1x to hold the wire out so they could cut into huge styrofoam pieces that were as big as a car.
For a one off, I just use a blow torch to heat up some bailing wire with the ends wrapped around scrap wood pieces. If op doesn't have a blowtorch, they should anyway.
I have 2 blowtorches, but i wouldn't have figured that out.
Do you have any other Maker secrets?
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Like this? https://youtu.be/-QbFvDIyy1k?t=374
The only other option??? What about a hot knife? Made specially for cutting foam.
>tools that i dont have.
The OP specifically mentioned that they didn't have specialty tools. So I offered the only options that are readily available to them.
However, if you have a knife, and presumably some way to heat it up, you could have a hot knife
This is true.
Hot knife = wire with electrical current. They sell these.
How is this so low down in the comments? As a sailor who has to cut everything from foam to rope, this is absolutely the best answer, and they cost like $20.
I think it's important to note that you need ventilation or do it outside. My friend just burst into the room saying that his eyes sting after cutting styrofoam with a heated knife.
Though he suspects his is faulty and probably gets way too hot, over the suggested temp.
I cut Styrofoam for an hour once... for the next few hours I came down with an intense flu that eventually went away.
Hopefully I didn't fry anything terribly important.
Teflon Flu
Incredibly important to ventilate. Those fumes are very bad for your lungs.
Yeah, he decided that plugging an extender into an extender and finishing this outside is still better than fire regulations
Excellent call out. Styrofoam fumes are bad for the earth and the body.
https://www.harborfreight.com/30-watt-5-in-1-hobby-woodburner-63850.html
Hey, look at that, $10 for a heated x-acto holder.
Metal ruler as your edge guide, multiple shallow cuts. Plan to make 10 passes. Slow and steady, starting with a fresh blade edge. Get zen about it - trying to power through the seemingly soft material in one go will just shred it.
This is literally it. Everyone treats x-actos like they are one and done knives, but even on posterboard you want multiple repeated passes.
This right here.
Take it to a custom framing store and ask if they'll trim it for you.
Someone felt like this should be down voted, but I did framing for years and trimming foam board for people was something we did frequently. OP, if you aren't in the mood to play with wire and a battery, this is your next best option for a clean trim.
Although, the fact you've already cut it down means there might not be space to make fresh cuts.
One of those motorized Black and decker turkey knife cutters or hot knife. Hot knife reduces the size as it melts.
I've had reasonable success heating up an xacto knife blade and then carefully cutting with that. Basically same idea as a hot wire cutter.
Electric carving knife
This works amazing well, a little messy though.
Foam core board only needs to be cut with a sharp xacto blade, a metal straight edge for guidance, and a slow, light touch. No heat required.
When cutting the 1" purple foam I've been using the big snap blades, where the razor is scored so you can break off sections for a new edge. Extended all the way out so you can get a nice shallow angle on the pull
I do the same. It makes surprisingly good cuts.
Score it first before you attempt to cut it to full depth.
Hot wire, and use a fine sandpaper after. Wear a mask, that shit is awful for your lungs.
Hot knife / foam cutter
Easy way?
Get an old knife you don't care about. An old butter or steak knife will work. Heat it on a stove element. Cut the styrofoam with hot knife.
Warning - do this in a very well ventilated area and preferably with a respirator with a VOC filter. A hot knife cutting plastic will throw off some pretty nasty chemical vapors.
Just remember to slice, and use a sharp knife!
If you press, it'll break into an uneven edge.
Heating a wire/knife and then using that will melt/cut through it but make sure you have a place for the fumes to go if you do.
(You can use a butter knife and a cigarette lighter, the amount of heat needed is pretty low)
Electric meat carving knife
Do you actually mean Styrofoam (dense, closed-cell foam, often pink, blue or black) or expanded polystyrene (white squishy beads pressed together)? The latter stuff is widely and incorrectly called Styrofoam, but the two things are quite different and advice for one doesn't always work for the other.
Expanded polystyrene (EPS) is virtually impossible to cut really cleanly without a hot blade or wire - the beads will tear out and the edges will snap.
Actual Styrofoam (XPS) can be cut nicely with knives etc. but if you have confused the two materials this could explain why you are having trouble.
I have not tried it myself but I’ve been told to use a powered drill but run it backwards. Pretend it’s a jig saw. Don’t know it the bit diameter matters.
Adam savage from mythbusters has some YouTube videos. I believe he just uses sandpaper after cutting.
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You could also just heat your knife on the stove for a cleaner cut. Obviously be carful, it doesn't need to be glowing red or anything.
Bread knife.
Exacto knife blade is a little small, and gets dull fast cutting through both the paper and the foam inside. A snap knife, the kind with extendable blade that you can snap off sections might work better. Use a pair of pliers to snap of the end pieces of the knife as it gets dull. That or a razor blade knife might be better. The hot wire cutters are great for just foam, but would do nothing for the cardboard on both sides.
I’ve used a q-tip and nail polish remover. I used a pencil and ruler to “draw” a straight line and then went over that line with the q-tip.
Find an old thin knife. Heat it up on the stove and cut the foam. There will be some shrinkage so make sure to cut carefully. Should give a nice smooth edge.
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Dental floss
Electric knife that you might carve a turkey with always works good. Works good on foam too.
I cut a bunch of insulation board with a sawzall medal blade. Might be overkill
I've used an oscillating tool, cuts like butter and leaves a clean cut.
Don't use an exacto knife. Go to the hardware store and buy a pack of extra razorblades. You can get them in quantities like 25 or 50. They go dull decently quick, but theyre easier to handle since the blades a lot wider. I've cut tons of foam boards by hand with just the blades.
Use a heat gun on it lightly after you cut it. It will tighten it up a bit.
Buy a hotwire cutter. The handheld tools are pretty cheap.
Hot knifes give you NO control. They start superhot and melt away a ton of material, then cool down and you get stuck or pull it out, coated with styrene. Its BS. Invest 10 bucks and do it the right way. Most of them come with at least 2 different tips plus the hotwire.
hacksaw - fine tooth.
Sharp knife (I like Olfa brand), metal ruler, a surface underneath like a cutting mat so you can press down hard, and one clean long cut. I find doing multiple passes leads to worse outcomes though.
Also, practice!
I was able to cut smoothly through 2" EPS foam board with this $2 utility knife. I had to change blades frequently as they had to be very sharp otherwise it would tear the material too. https://www.harborfreight.com/snap-blade-utility-knife-97068.html
Most people are saying fresh xacto blade, and they are correct. But it also may require multiple fresh blades. A blade gets duller every inch/mm/hot dog it is used. So some projects and some materials may require multiple fresh blades for a quality cut. Then you save the slightly used blades for projects that don't require as perfect a cut, or for materials that are more forgiving to the blade.
I’ve used a fine tooth blade on a saber saw. Go slow and it makes a smooth cut.
I used a very sharp steak knife Just go slow Try one with the little cut outs on blade so it doesn’t stick as much
9 volt and a bent paper clip
Heat up some long knife to burn through it.
Yeah because its super easy to control....no. Get a hotwire cutter...
Dude, how do you cut your meat and chop the veggies?
Are you special or just talking out of your ass? A HOT KNIFE cools down as you are "cutting" with it. You compare that to veggies and meat? Pull your head out of your ass and stop giving useless advice! What a donut...
A lot of people know.
Glad i could help.
strangebutalsogood t1_is7mwii wrote
A heated wire is the best way, there are instructions online to make a basic one with a 9V battery and some wire.
The only other option is to use a VERY sharp long knife, xacto blades get dull fast so make sure you're using a very fresh blade extended out long, any burrs on the knife blade will cause jagged cuts.