This is a general question for people who have made models using magnets AND people who have done prints using magnets, no matter what website the files came from or were uploaded to –
What is the most common magnet size used?
I am new to 3D printing, and want to stock up on materials, so that when I see something I want to print, I don’t have to wait a day or two for supplies for the printed part to get delivered from Amazon, or make a run to the store only to find they don’t stock what I’m looking for…
Obviously this answer will change because the size of the object changes… Generally you wouldn’t use a tiny magnet on a huge print, and I understand that… Relative to size aside, what are the most common sizes you find yourself using?
I use 4x6mm (DxH) cylinder magnets almost exclusively in my designs. It’s starting to cause stock troubles though. I’ve been starting to think about alternatives, but it seems hard to pinpoint what would be best. I’ve had different people request different sizes, so.
I like that size because they’re small enough to fit in the walls of the case designs I make, but deep enough that they can be friction fit.
I’ve been considering the magnets that Bambu carries through their Maker’s Supply. They are 4x2mm round magnets. Could prove as a replacement, but would need to be glued in. I requested they carry the 4x6mm magnets that I use
I often use magnets, which ones, depend very much on the application.
Smaller ones provide less magnetic strength but mean you can place them in smaller places.
I used 3x2mm magnets for this model. This allowed me to keep the case as small as possible, otherwise, the size of the case would have been dictated by the size of the magnet. I was able to place the magnets between the items stored within the case.
They are also press-fit as I spent time determining the perfect snug fit. Glue isn’t required to keep the magnets in place.
For this model, I used 6x2mm as they required more magnetic force given how they would be used. These required some glue as the bigger the magnet, the more they can yank themselves out of their housing when an attracting force is nearby.
You can also use rectangular magnets, they are less common though.
Start with a mix pack of cylinder magnets if you are unsure and you can do some testing.
I use the excellent Embedded Magnet Dispenser by Brian Dean, with this tool you can quickly and easily insert magnets (both north and south poled) into your prints and designs
I’ve gotten these twice, they’re 10x5x2mm. Once they were just $2! (For 120 magnets!) https://a.co/d/bkBF9sT (not affiliate) **Update: Currently like 50% off coupon **
One extra thing I’ll add is whatever size you go with for a project double check the actual size of them and don’t rely on the stated dimensions. I’ve had some that have been off as much as .4mm
I also design a magnet tolerance tester to print before printing the main model to test width and depth of the magnets to be inserted.
This will save you (and anyone who downloads your design) headaches with trying to get the magnets to fit.
There’s nothing worse than wasting a half a kilo of filament and 12 hours of printing when you find the magnets you have don’t quite fit correctly.
Sometimes you have to resize the holes in the model and other times you can just adjust the X - Y hole compensation in the slicer.
Either way, a magnet tolerance test piece will help flesh that out.
Oddly enough, I just posted on this in a semi-related topic. I’ve offered some recommendations in that post.
As others have posted, there is no such thing as “best size”. It all comes down to what the application calls for.
At the end of the day, you will have to experiment but here are some tips I can share.
First, let me make a broad statement based on my many failed experiments.
Forget about adhesive mounted magnets. Even the strongest adhesive tape will fail over time especially if exposed to temp extremes and/or chemicals. You will have better results if you learn how to design cavities inside your model and embed them. You will also more likely love the resulting appearance and you will never have to worry about the magnet ripping off. There are many posts and YouTube video explaining how to embed hardware in prints such as nuts and magnets.
You can find out for yourself but avoid ferro magnets like the plague. They are only good for gluing paper to a magnet or maybe holding something to a refrigerator whereby you’re only expecting to hold one piece of paper. Again, experiment and see for yourself if all you are doing is creating refrigerator magnets.
Rare earth magnets are what you want to use if you are going to embed inside of a model. They are expensive by a long short over ferro magnets but do the job better than anything else. Try both ferro and rare earth and judge for yourself.
Considerations:
Is this going to be a magnet that will have to be attached to a metal object or to another mating magnet?
Embedded magnets that are concealed inside the print will work really well. That’s my favorite because they look great; it’s almost magical when you have an ordinary-looking model that can stick to something with no visible magnet. For that, bar magnets are best.
If attaching a model to metal and desiring the concealed approach mentioned previously, then the question is: how thick is the intervening model wall? If you use 3mm thick magnets, you’ll be forced to make your model wall very thin if you want to go for the concealed look. My experience is that if you are doing metal-to-magnet attachment whereby the model is expected to stick on a metal surface, you’ll be forced to either make the wall thickness very thin or, as I recommend, go with a 5mm thickness magnet. Again, make test models to experiment.
If you’re making, let’s say, two models that are going to stick together, such as a box with a magnetic lid, then you can easily use two opposing magnets, one on each side of the print. This is exactly what Bambu does with the nozzle cover. In that case, you don’t need thicker magnets; two opposing magnets work very well and round magnets are very suitable to this purpose. I might also recommend saving on CAD time and using the cut model feature in the slicer in combination with dowels which will give you a perfect press fit. (let me know if there is interest and I can post a tutorial)
Round magnets are a great non-embedded alternative if you want to use a zero-thickness wall. In other words, the magnet will be exposed, similar to the magnets inside the Bambu lab nozzle cover. However, the trick here is to press-fit them into the hole and make sure the hole is slightly smaller than the magnet diameter so they don’t fall out. Again, as mentioned in the previous bullet, this can be more easily achieved with the cut tool and dowel feature.
And the last point, of course, is don’t forget that magnets will only stick to objects with a high iron content. Stainless steel will tend to be non-magnetic depending on the mix of Chromium, Nickle and Molybdenum content. So, you will want to test it against the surface you want to stick to. Some modern stainless steel refrigerators, for example, are designed specifically to not allow refrigerator magnets. I guess that’s to ensure a “clean” and “uncluttered” look. Clearly, those folks haven’t been in my kitchen.
Thank you for a very detailed and helpful post. If you are willing to post a tutorial, I would personally very much appreciate it. My specific intended application is figurines where 2 opposing magnets would be used to join parts (like arms, legs,etc) and the magnets do not need to “embedded” as they can be flush with the part.
My dilemma is often these are not models that I made so I would need to modify the parts myself. I know this should be easy but I just have not done it. Lastly (and I know asking a lot) would be a discussion of how to do this in the raw CAD file, ie not specific to Bambu, so the part could be printed on any printer. Maybe MeshMixer can do that?
The problem I’m currently running into is the filament not adhering to the magnet after placing them on the bed. Subsequent layers are clumping up on top. If the print is thick enough it typically corrects itself… eventually… but on this fidget slider I’m working on, its causing a decect all the way through the model. What’s the best way to combat this?
When you embed a magnet, you typically add a PAUSE command on the layer immediately above the magnet height.
So, if you have a magnet space start at two layers above the build plate (0.4mm) and the magnet thickness is 2mm, you would add a PAUSE command at 2.4mm.
This will then add a layer over the magnet.
As the magnet is metal and not a material that PLA will bind to, it will create a messy texture.
The next layer improves the look as some of the messy layer binds to the new layer, the third layer over the top typically ages it look reasonable.
You normally design with this issue in mind, there should always be at least three layers on top of the printed magnet to give a reasonable appearance. Depending on the filament being used, possibly more layers.
You could begin the printing over the magnet by purposely creating a void one layer taller than the true thickness of the magnet, this will create a icy better surface no contact will be made with the metal magnet, instead a bridge will be used to span over the single layer space above the magnet.
This obvious issue with this technique is the magnet has a tiny amount of space to move up and down in which will create a rattling noise when the model or part is moved up and down.
I think this model here is a perfect example of magnets in prints done right… I printed it and was shocked with how well it worked out, and how strong the cheap magnets were able to detect each other and bond thru several layers of plastic.
i embed sometimes as it’s cool, but to be honest i don’t mind seeing the magnets, i actually enjoy the look so i haven’t been going the embed route, you also need to be around for when the printer pauses, and i often need to be focused on other activities, which means the printer would be paused for quite a while which for me is innefficient
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