This is what I learned while using magnets seriously for the 1st time in a project…
One standard magnet size is 10×3mm, a snug hole is 10.3×3.1mm – of course this also depends on your printer’s calibration, and that the magnets are true to size.
Do a fitting test with your holes, in a draft print.
If you have 3 or more magnets, do not place all of them at the same height.
Make pairs of fitting magnets, mark them on the (future) inside faces (i.e. when stuck together, the outside ones). Do not use Edding, that weakens any glue adhesion (scratch them instead).
Use superglue sparingly, so it does not overflow or only a little – apply a tiny drop to the hole’s middle.
Apply with the magnet stuck to e.g. the nose of flat pliers, insert perpendicular and apply pressure with just a corner of the tool to the center of the magnet – that avoids any “tool stuck to the magnet or your object” situation.
Work pair by pair, so they really fit in the final assembly.
Take care that the scratched face goes INTO the hole.
Wipe glue overflow by turning a folded paper towel on the spot, no smearing glue around.
When I use magnets, I embed them into the model, no glue required, magnets are invisible and when attached to a metal part, it does not scratch the surface. For your example of 10x 3mm magnets make the hole 3.6 deep, pause printer when it reaches 3.2, insert the magnets and resume printing.
I guess I will try that out if there’s a need (you mentioned a few reasons), but I prefer to not needing the timed manual intervention for now. Maybe with a box / lid design where all the magnets go in at once, near the end.
Magnet should not be glued in…
The magnet is not flexible, the plastic is - not a great mix.
What glues the plastic well often won’t properly bond with the magnet and the other way around.
If there is no other options you can use then at least do it the best way possible:
Give the to the blued surfaces of the magnet a fine sanding, just a dull looking surface as otherwise the Nickel plating will make gluing a nightmare.
Use sticky tape to remove the dust - you won’t be able to wipe this Nickel dust off …
Then put gloves on and clean the magnets with Acetone - put them aside and WELL apart from each other.
As for hole(s) in the model - tight and snug fit or an oversized hole ?
Logical answer would be the first, correct answer is the later…
The hole should be about 0.2 to 0.5mm deeper than the magnet.
And there should be a similar sized gap, perhaps even more around the magnet.
The key is to combine superglue with baking soda.
Use the tip of a knife, a tiny spatula or just a tooth pick you flattened as a scoop.
Through trial and error determine how much VERY LOOSE baking powder you have drop into the hole so you push the magnet in to get it flush.
The powder should be pushed up the sides while the magnets it pushed and wiggled into place.
Grab another magnet to place it on the opposite side to hold things in place (if that’s an option).
Otherwise use a stack of smaller diameter magnets so you can hold the magnet in place or wiggle it a bit.
With a small needle push out channels around the magnet - like vent holes going all the way down, three to four will do fine.
Make sure those channels are wide enough!
At least 1.5 to 2mm as that is where you now drop the superglue in.
To get this last step right it is best to print some test fittings in a clear, transparent filament.
Thin bottom so are able to see whether or not the superglue will wet the entire bottom.
Don’t be tempted to use a needle applicator to get the glue all the way down - the baking powder will block them up and make a mess on the ouside.
Instead use a very thin and runny glue you quickly drip into the channel - one at a time.
Do it right and it will run down to the bottom before it sets.
If three channels are not enough to wet the entire bottom use more.
Once you worked out the timing and drop rate you can carefully break off most of the plastic and soak the magnets over night in acetone to break up the glue and use them again.
The mix goes almost glass hard almost instantly.
The process also creates quite a bit of heat, so the stuff will fuse even better with the filament.
And unlike superglue alone things cure without the need of being air tight.
Compared to suerglue alone the bond strength is increase by just over 500%…
When I’m modelling in fusion, just use an octagon (circumscribed polygon edited) at the magnet size. For Studio if I want to add a magnet, I’ve made up a set of octagonal-cylinders (eg. 10x3magnet.stl) and simply import via “add negative part > Load” and place where i want the magnet.
I have a lot of embedded magnets in a few existing models uploaded and in a series of new models all using magnets.
I use the PAUSE feature which gives you time to insert the magnet into the printed model and then print over it so it is embedded.
I add 0.4mm to the radius of cylinder magnets and no extra to the height. I learned adding a tolerance to the height even by 0.2mm allows the magnet room to move in the model and a gentle shake makes noise.
If you use small magnets, you should use an insertion tool, there are many here.
If you place a few magnets at a time, stack them up in the same direction you need them (north vs south) and plop them into the hole, slide to the next hole, plop and repeat. Even with minimal infill, this is easy to do and the slide and plop method means you will not accidentally flip the magnet pole direction and it greatly eases the process and speed of insertion.
I do a lot with 3x2, 6x2, 8x2, 10x2, 10x3, 15x3, 20x2 & 25x2mm.
It depends on the product, the model, the placement and most importantly, the distance from the matching magnet as the strength to close and open can affect the end model.
I have models that use press-fit that rarely need glue, but, those are usually smaller magnets 3x2mm ones, with only a drop of glue if the filament strength isn’t great. Magnets which are that small should not have a tolerance around them.
