Do you bring a knife, or router bit, to a fight with magnetic sheets?

Curious if, and how, anyone’s used their CNC to drag knife cut, or router bit cut shapes out of magnetic sheets? e.g.

Was imagining…

But web/youtube info seems straight forward. Saw warnings against using laser.


Was imagining…

Now I have that image stuck in my head :open_mouth:

That looks like an A.I. created image.

if you take a search, i know there has been some talk of drag knife. I am not sure If I saw the completed solution. There are alot of different types on Printables, and all those other websites.

Quick google search shows that a Cricut can cut magnetic sheets so I don’t see why you couldn’t do it with the LR3 and a drag knife.

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Have you links for the guidance to not use lasers?
Curious if it’s because it’s not safe or it’s not effective.

They’re just ground up ferrite magnet powder in a polymer binder, so it likely depends on what that polymer binder actually is, which could be difficult to find out definitively, depending on your source. The laser isn’t going to do squat to the ferrite itself so I can’t imagine it’d cut cleanly, anyway.

We’ve briefly played with similar materials (semi-flexible ferrite loaded polymers, although not magnetic ferrite) and cut it with a knife or guillotine. It might be pretty rough on the blade depending on what the ferrite to polymer ratio is. Ours was pretty high, something like 80% by volume.


I only know you don’t want to let it get hot. The magnets will demagnetize if they get hot.

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Which is pretty interesting for sheets that go in heated beds on printers. Maybe an M&P person can weigh in- but my understanding is that the magnetic particles can be chosen from (more expensive) rare earth types and those have much better resistance to thermal de-magnetization than the cheaper ferrite magnet materials.

ferromagnetic materials have a curie temperature that you need to stay below so you don’t randomize the domains and destroy your magnet. Iron oxide / magnetite is 580 °C. Nickel, cobalt, and rare earths would be different. My friend google tells me that cobalt is higher, nickel is lower.

And yet, I have a cheap Amazon sourced magnetic adhesive sheet that has nearly completely lost its’ magnetism despite ‘only’ ever seeing 105 C. I know others with similar stories.

There are some magnets that lose their magnetism at much much lower temperatures, so your mileage may vary depending on what particles were used to make it.

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I ruined some rare earth magnets trying to get them embedded in a 3D print. I used a soldering iron somewhere in the 250C range. I ended up gluing the next set.

If your 3d printer heats steel red hot… your printing experience is more interesting than mine.

Not at 105C it doesn’t… :wink:

I was wondering about the warnings because you definitely can cut it with a laser so were the warnings about fumes?

I can’t imagine there’d be many other reasons. There are a limited number of options. Either it won’t work, will do something that’s bad for you or do something that’s bad for the machine.

I’d guess it’s a fumes/byproduct concern. Some plastics get pretty nasty to cut. The laser cutter at the uni had a large warning on it to never cut PVC and the vendor of our original laser cutter said the warranty would be void if corrosive damage from PVC fumes was found.

I know that vinyl is deadly creates a toxic gas when burnt, is there anything to that? Do the magnet sheets share any common properties to vinyl? If they say it is unsafe, probably better to side on caution, then ease of cutting!

The answer is a big NO . The powerful laser beam acts to quickly melt vinyl which results in the production of several toxic gases and chemical fumes. Among them, Vinyl dioxin and Vinyl chloride are the most common. These gases can severely damage human health and may even damage expensive laser machines.

quick google search shows some of those sheets are made with PVC, so yeah, if you do not get sick, etc, it can kill your laser, I would not cut with laser.

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The polyvinylchloride (PVC) is a carbon chain with chlorine atoms attached. Lasering this gives off (in addition to the vinyl species mentioned) chlorine gas, hydrochloric acid fumes, and CO2 (greenhouse gas) and water when combined with air. This moist fume can effectively coat your exhaust/fume extraction tract and allow the acid to slowly dissolve your machine over prolonged exposure and isn’t great for you, but isn’t likely going to get you immediately. Plus pumping it all outside next to where you are cutting it isn’t doing anyone else any favors, though dilution is the solution to pollution.

With respect to lasering sintered particles in a polymer matrix/binder, I would just mention that the laser won’t cut/melt/vaporize the embedded ceramics, just the polymer binder, so if your percent solids are high enough in the matrix, your laser may not make it through and just brown the surface, which is probably another reason to not laser the stuff. My 60W CO2 won’t make it through some 1/4" plywood when there is too much glue, so lasering metals or metal-oxide particles with it or with the 455 nm blue light diode laser seems to be a waste of time.