<p>I want to use magnets to hold the lid of a box down tight enough to keep it relatively airtight (along with a rubber seal etc.), but I am not sure what strength of magnet to use, that will still allow it to be opened without causing damage either by having to be pried open or by crushing the print layers. I cannot seem to find any guide to how magnets are used for 3d printing at various strengths and I cannot afford to buy too many types that I am not then going to use.</p>
<p>Any help that you can provide will be greatly appreciated.</p>

[{'answer_id': 18962, 'author': 'Henry Cabral', 'author_id': 20806, 'author_profile': 'https://3dprinting.stackexchange.com/users/20806', 'pm_score': 1, 'selected': False, 'text': "<p>I had a similar experience using magnets to hold two plates together. Currently also building a device (3d-printed) that clamps together with magnets. For both of these scenarios, I typically start by looking at what size and force you need. I would look into maybe 3 options of different magnets to start with. It could be in the range of 0.6 lbs, 4lbs and 6lbs. Do you know how much the &quot;opening force&quot; would be? As in what would keep it opening? If its substantial, I could see more the 6lbs but this is a very very very rough estimate that honestly would be best supported with trying a few ranges of magnets first. Try McMasterCarr if you're in the US. They have affordable sized magnets that I've worked with, ranging from different sizes, thicknesses and magnetic forces.</p>\n"}, {'answer_id': 18965, 'author': 'ChinchillaWafers', 'author_id': 27077, 'author_profile': 'https://3dprinting.stackexchange.com/users/27077', 'pm_score': 3, 'selected': True, 'text': '<p>You can vary the “strength” of the magnet by making a membrane of 3D printed plastic in between the magnets. The strength of the attraction is something like a logarithmic relationship to distance- small changes in thickness of material in between the magnets have a large effect on how strong they stick to each other. You could dial in your print by buying strong rare earth magnets and experimenting with attenuating the strength with the membrane. Could even use sheets of paper to get the right feel, then measure the thickness of the stack.</p>\n<p>If using an fdm printer, it could be helpful to insert the magnets with a pause in the printing, and print over the top, if there isn’t a good way to otherwise capture them.</p>\n'}]
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