Hot wire foam cutter - “MWLFC” - made with leftovers foam cutter

Things You've Made
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I finally made time to build a hot wire foam cutter - meet the “MWLFC” - i.e. “made with leftovers foam cutter.”

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Pardon the chaos on the LowRider table— I’ve got quite a few projects in the works.

I’ve ordered for this thing an affordable DC motor speed controller, aka PWM controller, so I can adjust the heat level. In the meantime I can cut with it briefly, but it gets too hot fast, so I’m holding off until the controller arrives.

However very little was bought expressly for this. Besides controller, the only other thing was the 22g nichrome (80%) wire, which I bought a year or two ago with this in mind …

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So, here’s the leftovers list:

  • Scrap 1/4” plywood
  • Aluminum extrusions that used to be an Ender 3 v2 — plus another bit of scrap from a different printer project
  • 12v power supply that used to power my LR3 router CNC
  • Switch that used to turn the LR3 on and off
  • Scrap of plywood so small you’d think it would never be useful (LOL)

I’m getting double duty from the rip fence that came with my VEVOR Bandsaw. I carefully checked the size and made sure it would work for this before I built it.

I used various other items already in hand in my shop, including wiring, screws, t-nuts, the spring, spacers, crimp-on connectors, some bits and bobbles.

Given the major use of leftovers & in-hand stuff, this is one of the lowest cost projects I can remember in a while.

Also, I found an affordable source for an ample supply of high density EVA foam that is 3/4” thick, and it is those interlocking floor tiles used for gymnasiums and people doing yoga exercises. The best price I could get on it was a package of four tiles, each 2‘ x 2‘, for only $20 from Target.

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Looks solid and nice (mine doesn’t). I would move the upper wire to this spot to prevent the top wheel from overheating and the plastic from melting.
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Thanks for the good advice. There is no plastic there though. It’s all metal.

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Very professional. What are you going to make with it? :slight_smile:

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My first thing will be some foam fingers for some printed feather boards for a rip fence. Think similar to bow, but DIY, so will be making several mods that improve over their design. The fingers are made of high density EVA foam. Same stuff as Bow uses, and same stuff as the gym mat flooring stuff is made of. And same thickness (3/4").

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Nice! I don’t have any of those featherboards but they look like they work well.

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To clarify, it’s the whole fence approach I’m talking about here. The feather boards themselves are not the direct target of the improvements.

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I’m slowly, slowly getting improvement regarding the mind fog. One of the biggest casualties of it is creativity and problem solving. Anything I do, and I mean anything, done while not free from the mind fog, is likely to be a not-good solution. Case in point, the way I was connecting the spring to the 2020 extrusion, and I will only show you all this on the condition that you promise not to shame me over it.

BEFORE (not good at all)

IMG_0128 - BEFORE (not good at all)
IMG_0128 - BEFORE (not good at all)1920×1440 165 KB

AFTER (way better):

IMG_0132 - AFTER (way better)
IMG_0132 - AFTER (way better)1920×1440 126 KB

Overall view - Hook for spring for 2020 extrusion - lower hook accommodates a spin-and-lock T-nut

IMG_0131 - hook for spring for 2020 extrusion - lower look accommodates a spin-and-lock T-nut
IMG_0131 - hook for spring for 2020 extrusion - lower look accommodates a spin-and-lock T-nut1920×1440 177 KB

I am currently getting only a few minutes in the morning before the mind fog returns. Making progress.

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I hope no one in the community goes down the shaming path. Be excellent to one another!

That said, this makes my electrical safety voice start screaming aloud in the back of my head:

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2 Likes
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Thank you. What should be done for improvement there? Several of the videos I saw showed clamping the electrical lead wire to the cutting wire using an alligator clip, but I don’t seem to have any alligator clips on hand.

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Shorter bolt, or have the nut on the top? Electrically insulate the connection between the wire and the spring? I’d be concerned that “as is” the threads on the bolt could wear through the aluminum coating and end up making the bar “live” when that wasn’t expected, and that the spring will always be “live” if touched, although it shouldn’t get hot if the nichrome is the path of least resistance under normal use…

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OK.

I currently have the electrified wire itself touching bare metal at the “pivot point” where it goes from vertical to horizontal, and that metal touches bare metal leading back to the aluminum frame itself. So even if I fix the spot where the wire connects to the spring, I still would not have prevented the issue. I will have to ponder on it after I’m not still dealing with mind fog.

Thanks for the input.

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I guess at this point I should be thankful it’s low voltage, the neutral wire there helps, and I’ve not used it much at all. Apparently in its current iteration, it’s a potential shock hazard.

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Would doing what @kockie-nl suggested…

… take care of the shock hazard, by having the neutral electrical wire connect before the cutting wire reaches the top of the metal frame?

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Any chance you could make the plates holding the pivot point out of a non-conductive material? There wouldn’t be current flowing through the roller that way, so it shouldn’t heat up much.

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I can indeed give that a try.

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I was wondering what you could use and the only thing I can think of so far is ceramic or glass beads with the hole in them.

I wonder if you can get Bakelite or ceramic stand offs somewhere.

Ooh, what about perfboard - pcb boards should be able to take some heat.

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What about putting the roller and spring under the table, so they’re not a touch hazard?

Another alternative (although more mechanically complex) would be to use the spring to pull down on the rear of a pivoting top beam. That way the wire could terminate at the roller and not need a connection to the spring.

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Using the frame itself to keep the wire tensioned, is the approach of at least one of the videos I saw. But the frame there was PVC pipe, bent using heat to give it a reverse bow shape, and the tension was similar to the way a bowstring is tensioned by a bow.

I currently have a few minutes each morning of clearheadedness and I will ponder on all this when I can think again.

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I think by its very nature, a hotwire cutter presents a shock (and burn) hazard. The whole wire is an exposed conductor.

Lots of stuff for low voltage is really dangerous for household AC voltages. The fuse box in my car would be terrifying if it ran 120V or 240V. A thin flammable plastic snap-in cover over fuses with exposed contacts? No thank you! But in the car, those exposed contacts are there to make finding blown fuses fast and easy.

I’ve seen much worse electrical joins in hotwire cutters, used without problem, but I’ve never seen a hotwire cutter sold commercially, so I’ve never seen one made to CSA or UL standards.

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