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Apply / find / create a stainless steel coating to apply to a PETG or PLA part to make it react to a magnet.

My goal is to make a small tubular and conical shapes that can be painted with a stainless steel coating and will react with a magnet.

I know I can buy iron filled PLA but these rust which I want to avoid. I'm trying to get the magnetic properties of stainless steel (no rusting / reacts to magnets)

I have found videos on how to coat with copper / silver / carbon but I'm looking for stainless steel no rust / magnetic properties.

I'm looking for a "low-cost" solution just for testing.

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    $\begingroup$ Beware some stainless steels are magnetic, and others are not, it depends on the micro-structure content. The company I work for used a company to clad metal onto the inside of composite cylinders so that they could be used with a piston for hydrophilic purposes, you could look into that, but I suspect that that is quite expensive and not what you are looking for. $\endgroup$
    – 0scar ♦
    Commented Feb 4, 2021 at 8:16
  • $\begingroup$ Thanks, but I'm looking for a "low" cost solution just for testing. $\endgroup$
    – Rick T
    Commented Feb 4, 2021 at 8:56
  • $\begingroup$ Leafmetal won't work... also "react with a magnet" is QUITE vague: do you want magnets to stick? Do you want to detect the print in a coil? Why you need the print to be magnetic all over? Would magnetism from some spots not suffice? $\endgroup$
    – Trish
    Commented Feb 4, 2021 at 10:17
  • $\begingroup$ @Trish if your talking about gold leaf type of materials I didn't know about a stainless steal magnetic leaf products if you know of one please share. Yes I do want magnets to stick to it (so the magnets may cause the metal leaf products it to rub off). Now that I think of it, only having the inside of the tubular / Conical shapes be magnetic would be fine. $\endgroup$
    – Rick T
    Commented Feb 4, 2021 at 12:50
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    $\begingroup$ @RickT that's why I said it won't work: there is no "stainless" type of that type. To stick a magnet, you need a considerable thickness. $\endgroup$
    – Trish
    Commented Feb 4, 2021 at 13:04

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The surface won't work

The only true-metallic surface treatments I know to be actual metal in large enough amounts to conduct electricity would be leafmetal, akin to leaf gold, and electroplating. However, you can't use the procedures for stainless steels, and even then, the thickness is in the tenth of a µm area and lower. Not only would that be far too thin to adhere a magnet to, it also would be super easy to damage with rubbing.

Filling?

PLA itself does not block magnetism - I have printed a PLA holder for a magnetic GPS device, into which I inserted a simple 0.5 mm steel plate for a magnetic surface with 0.5 mm of PLA acting as the container and seal against water.

If the prints can be done with one end open and no infill or have a dedicated area that a cheap piece of steel can be inserted into, this method can be used too. The only requirement is that there is a cavity on the inside that at some point is accessible. This also can be during the print.

This cavity could either take a piece of shaped steel sheet or be filled with a different magnetic filler, for example, simple iron powder. The powder could be bound in a non-oxidizing polymer, for example, epoxy resin. This method has been used to create cast stators for electro motors. It's not the most efficient, but might work in your application - if your walls are thin enough.

With the correct mixture, such a material can be used to coat or fill the inside with enough magnetic material to give the magnets something to stick to and not rust away - the shell and the resin together would shield the iron from any air that could rust it. Indeed, a quite stuffed Resin-Iron-mix and a strong magnet have been used in 2012 to create furniture by the name of "Gravity Stools" or other art pieces like in this video

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No rust but has magnetic properties? You could try varnishing the iron filled PLA.

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