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I would like to add neodymium magnets during print. The model, which I would like to print, has fully enclosed holes made for placing magnets.

Hole prepared for magnet placing

I added pause on layer (M601) in slicer. Since, this is a very long print, I would like to avoid any problems. I read that the magnet can attach to the nozzle while printing. How can I avoid this, and what else should I watch out for? How should I prepare in advance for magnets placing?

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4 Answers 4

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Unless you are using a nozzle made of magnetic metal, the magnet will not attach to the nozzle. The heater blocks are usually aluminum, the nozzles are brass or copper, although some can be steel. Other portions of your extruder assembly could be a factor but I've not seen examples.

Pass the magnet under the nozzle area close enough to touch the nozzle. This will provide indication of which portions of the assembly might attract the magnet.

Consider to apply some super-glue-type adhesive and allowing sufficient time to cure (or use a thin layer of moisture on the magnet, or an accelerator) to provide additional security. Even a small segment of double-stick tape may provide the level of assurance you require.

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  • $\begingroup$ I didn't know, that the heater block is non-magnetic. I have to change the nozzle to brass, because my current one is stainless steel and it has too much force, so I don't think it will work. $\endgroup$
    – kosteklvp
    Jan 7 at 9:40
  • $\begingroup$ @kosteklvp Check your existing nozzle -- most stainless alloys are non-magnetic. $\endgroup$
    – Zeiss Ikon
    Jan 9 at 19:58
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    $\begingroup$ Some heater blocks have set screws (sometimes called grub screws). Those are magnetic if carbon steel and may be magnetic if stainless steel, depending on the particular SS alloy. $\endgroup$
    – allardjd
    Jan 10 at 19:31
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I've certainly had this happen. While it didn't attach directly to the head, it attached to the steel roller bearings that moved the head, as well as the BL touch probe!

The type of magnet matters as well. If you're just using a regular steel or ceramic magnet, you probably won't have a problem since they usually aren't strong enough to lift themselves the inch or two required. But if you're using a neodymium magnet, then those certainly are.

I've done three things to solve it:

  • Learned the tolerance of my machine so I know how large of an opening to make for the magnet so it ends up being a bit of a press fit (when designing my own stuff). It doesn't take much to offer just a little bit of resistance to prevent the magnet from lifting.
  • When printing multiple items at once (made some refrigerator magnets), I arranged them so the print head travel properly and not cross over the magnets of the other items
  • Used a glue stick to glue them in. I was a bit surprised this worked, but it was just sticky enough to solve the problem.

One of the best first prints I ever did was to create a cylinder, say 1" in diameter, with a hole in it (1/2" in diameter), then create the corresponding "pin" exactly 0.500". Then I'd create multiple cylinders with holes of varying tolerances, say 0.490, 0.495, 0.500, 0.505, 0.510.

Then I could compare the fit between the two items. Essentially if I needed to put a magnet into something, there's no way I can do a 0.500" hole. It's too tight. I've learned that with my printer, that if I oversize a hole by 0.01" diameter, then it's a nice fit with a little bit of resistance. Well worth taking a few minutes to do this.

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I'll share some experience, I got while printing with magnets:

  1. Firstly, check if the magnet can stick to something around the hotend, especially when using neodymium magnets. It may be necessary to replace the nozzle with a non-magnetic one.

  2. Apply a small amount of glue before placing the magnets. The magnet should be free of metal filings that may stick to the magnet, because the glue will not stick to the magnet properly. In this situation, the magnet will not stick to the print and may frivolously move around in the hole.

    I used a small amount of hot glue on the bottom and top of the magnet, completely surrounding it in the hole. Hot glue should be used carefully as it can deform the plastic surrounding it.

  3. Check magnets pole orientation. This one is important, if you want to use magnets in pairs, e.g. for parts that should connect and disconnect. Magnets should either attract or repel each other, depending on the application. Before placing the magnets, check that they are correctly positioned. You can also mark the poles first with a marker.

  4. Make sure the magnet fits in the hole. For this purpose, you can make a quick test print and check if the magnet fits correctly into the hole. This will save potential drilling in the printout and other unwanted problems.

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    $\begingroup$ Magnet pole won't matter if it's attaching to part of the printer, however. $\endgroup$
    – LarryBud
    Jan 11 at 15:43
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    $\begingroup$ Yes, but it is important if you want to use 2 magnets e.x. in a case and a lid. $\endgroup$
    – kosteklvp
    Jan 11 at 15:46
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You want the magnets to fit snugly in the holes for them so they can't jump out. Making the hole undersized is not a good way to achieve this, because forcibly inserting the magnet can then break or deform the partial part.

Instead, I like adding one or more very thin splines, like the ones Lego bricks have to interface with and grip the studs of another piece, in a slightly oversized hole. These splines can wedge against the magnet and deflect without deforming the rest of the part.

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    $\begingroup$ Do you have an image of the spline design technique? I think it would benefit the understanding of the answer. $\endgroup$
    – 0scar
    Jan 11 at 15:13

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