Foam cutter with plunge capability?

At work, I need to cut a lot of closed-cell polyethylene foam, in thicknesses from 0.25" to 1.5", to make custom Pelican case inserts… I’m currently doing it all by hand, using cardboard templates, but would like to reduce the amount of my time that it takes, and improve the neatness of the cuts. However, all of the commercial and DIY foam cutting solutions I’ve found are based on a stretched hot wire, which is fundamentally incapable of making interior cut-outs, a feature that I absolutely must have. So, I’m looking into the possibility of building something of my own, most likely based on an X-Carve (due to the extreme flexibility in ordering parts for them, and my experience with the original Shapeoko machine).

There are hand tools for making plunge cuts in foam, that look like this:

There’s even a CNC version of this tool, that has a mounting bracket instead of a handle, although I haven’t found any references to anyone actually using one. The problem with these tools is that the needle is really, really bendy - you have to move extremely slow (multiple seconds per inch of cut) to avoid damaging it.

As a proof-of-concept, I’ve tried a test cut with this hand tool jammed into the vacuum hose mounts of my old Shapeoko 1. (The machine is nowhere near big enough to do my actual cuts, which are about 22" x 17".)

Even with the feed rate slowed down to 5 IPM, the results aren’t great… here’s the top view:

And here’s a bottom view of the 1" thick foam, with even more deflection in the needle. All of those edges in the star are supposed to be straight!

Frankly, I can do a better and faster job by hand. Does anyone have any ideas on how to do this right?

I have three ideas, none of which I’m really happy with:

  1. Give up on the idea of heat-cutting, and use a normal spindle with a specialty foam cutting bit. I’m hesitant to spend the $50-$80 for the bit, when I have no idea how well it will work or how long it will last, and I expect that this would produce a tremendous mess (with heat cutting, you only need ventilation, there’s no swarf).

  2. Build the machine with two X gantries, one above and one below the foam, with carriages that move in unison. The top carriage has the usual Z axis mechanism, the bottom one simply has a hole (with a tapered lead-in) that receives the tip of the cutting tool when it is fully extended. That should brace it well enough to be able to cut at a reasonable speed - there would be some bowing in the middle of the needle, but I would expect it to be minimal. This is getting pretty complicated, and I have no idea how to mount the foam in the machine - the thinner sheets aren’t rigid enough to support themselves in the middle if held only at the edges.

  3. Somehow adapt the machine to use this style of foam cutter:

    which is what I use for hand-cutting in areas without any small, curved details. I don’t think a drag knife kind of setup would work (when hot, that blade will happily cut sideways about as well as it cuts along the proper direction), so an actual rotary axis would be needed. That rules out any sort of GRBL/G-Shield control system, and would probably require a completely custom CAM program - it seems unlikely that any off-the-shelf CAM solution (that doesn’t cost several fortunes) would know how to drive this. The necessary swivel mechanism is probably beyond my mechanical design & fabrication capabilities, anyway.

Did you try a laser cutter?

Maybe someone out there who has a foam cutting bit can give it try and post a pic? :smile_cat:

How did you secure your foam for the test? Tape?
My first thought is the foam, being flexible might be shifting a bit as it cut?

That plunge cut tool also seems pretty flexible. It might be worth contacting the hot wire guys and talk with them. You may not have been the first with this issue.
Maybe they have or would be willing to make a heaver gage version that wont flex as bad? It can’t hurt to ask. Or perhaps you can make your own. I am not sure how the plunge cut version works. I always assumed it was a loop of wire in a thin tube. It might be doable if you can source metal tubing small enough.
Lastly I would double check the mount. And make sure the cutter is not slipping up there as well. Some masking tape or tie wraps may be enough to clamp things down for a test at least.

I am interested in how this turns out because foam is one of the materials I want to eventual work with.

Hmmm, I would have thought this would have been way too great a depth for laser cutting, but I gave it a quick try on my little K40. It was a REALLY nice cut on the top surface, right at the laser’s focal length, but here’s how the cut looked from the back side:

I would obviously need something with a lot less beam divergence for this to produce usable results. I’m not sure that a laser with all the necessary safety covers, and a 22x17" bed, would be in my price range anyway. Thanks for the suggestion, though!

Have you done a test with just regular bits? Worth a try.

Here is a video I found of a specially foam cutting system. CNC wire and spindle
The wire looked incredibly slow to cut, you never see it actually move.
But I was impressed with the milling. Other than being extra long I am not sure what kind of bit was used.

[quote=“AaronMatthews, post:3, topic:21936”]
How did you secure your foam for the test? Tape?My first thought is the foam, being flexible might be shifting a bit as it cut?[/quote]
The foam was held in place with hat pins, going all the way through into a 1/2" layer of sacrificial foam, which itself was held against the frame of the machine with screws going into the wasteboard. There was no visible movement of the foam or the cutter during the job, but the flex of the needle was quite noticeable even at 12 seconds per inch.

[quote=“AaronMatthews, post:3, topic:21936”]
I am not sure how the plunge cut version works. I always assumed it was a loop of wire in a thin tube. It might be doable if you can source metal tubing small enough.[/quote]
The tool appears to be a metal tube, with an insulated wire running through it to provide electrical connection to the far end - in other words, the tube itself is the heating element. I would guess that the insulation is a bit exotic, to withstand the heat.

JTECH laser? Bolts on to X-Carve.

I’ve cut thinner closed cell foam with one but not tried anything that thick. If I can some I will give it a go.

Ok, here’s a try using a regular bit, the 1/8" 3-flute rotozip bit that came with my DeWalt DW660. That’s the only bit I own that was even close to long enough for this test with 1" foam; I’m not sure I’d be able to find a bit in a reasonable diameter that could handle my 1.5" foam.

This worked better than I expected, but the cut surfaces are incredibly fuzzy - covered with loose bits of foam that would easily rub off onto the equipment that will be stored in the Pelican cases, so this isn’t really an acceptable result. I would need some assurance that the specialty foam cutting bits produce a better surface finish before proceeding any further with that idea.

Looks pretty good compared to the first.

Do you have a heat gun? Maybe hitting the cut surface with a quick puff of heat to get it to tighten up would help with the shredded edges?

You should be able to get long bits, they make them. I have 1/8" end mill 4" long.

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@JasonHarper Have you tried piercing the foam up and down without moving side to side, making a perforated profile that you then pop out? It’s not the most elegant solution, but it does eliminate the side loads/bending of the wand.

BTW, I love Pelican cases!

A custom pick & pluck? I like that idea and would be a good way to add optional areas for equipment :slight_smile:

An early Shapeoko2 customer, I found this forum from an Inventables email I received and, looking through the threads, I found this one… and little, if any, info on anyone successfully piercing/perforating/cutting foam. I’m not really sure what foam(s) you are using, or how thick it is, but the link below describes a brushless motor foam needle cutter attachment for a CNC that I’ve developed to cut the sheet foam materials commonly used for scratchbuilding RC airplanes and might possibly meet your need.!

It is a very simple and inexpensive, easy-to-build, DIY project… a very-fast reciprocating needle – 0.025" music wire – that leaves a trail of closely spaced perforations through the foam that, as driven around on a 3-axis CNC toolhead, will result in an accurately and cleanly cut sheet of parts. The cutter can adjusted for a longer stroke but, as currently built, will cut most foam materials up to 1/2" thick.

There is a wealth of info/links on its development in lengthy threads on several RC scratchbuilding forums… including info on numerous user builds. If this cutter attachment or similar and/or the cutting method is of interest to anyone, just let me know and I’ll be happy to help and/or answer questions as I can.

– David “dkj4linux” Johnson

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The 660 is really fast (rpm) and wants to melt the foam. Single flute and move fast (feed rate), even if that means shallow cuts per pass.