There have been many verified reports of strong magnets adversely affecting the performance of the air assist fan, FWIW.
You bring up a good point, I should probably clarify the magnets I use. I use ceramic magnets, which have a significantly lower BHmax then Neodymium magnets.
It is the size of the field that is critical, shielded magnets or tiny magnets do work. If you wave a screwdriver at the height of the laser and can feel the pull the field can interfere.
If you embed 1/8x1/8 Neodymium magnets 1/2" apart in a piece of wood, the field will not reach the fan, but it will hold paper very well.
Its not as much an issue of having no magnetic field hit the fan, after all if the goal is for there to be zero magnetic field then it would be best to never power on the GF, let alone let the laser beam touch a surface of a material. Basically, have no electrons move and yes, you will not have any magnetic field.
But I believe the caution with the magnet in a GF topic issue is broadly making sure that the fan does not enter a strong magnetic field. Because “strong magnetic field” is a rather relative term, I choose to scope it to “a magnetic field greater then the specs of the components in the print head and what the components were tested to”. I do not know those specific specs of the GF system but I feel I am within the acceptable range and accept the risk of any possible overshoot. I choose to mitigate the risk by using ceramic magnets and only use enough to complete the task.
I am just offering up the solution I use (which is ceramic magnets) and I purposely avoid ever saying my solutions/recommendations are the “right way” or even the “only way”. I do agree that I could have done better at stating all factors in my decision making and the risks when I first suggested the use of magnets.
I was really guilty of messing up my first machine with Neo magnets, never realizing the effect of the head moving quickly through a strong field, much less with the spinning fan. As soon as I thought about it for a moment it was really obvious. I was slow to catch on I think as some were shielded and did not cause the problem.
Your basic fridge magnets (ceramic rubber etc.) never did much of a job, holding down as much as an equal sized lump of lead.
I was guilty of letting condensation in my glowforge when I first got it because I left the vent connected to the window Now the first thing I tell new glowforges is to make sure and watch how you vent. So I can certainly see where caution with magnets can come from. For projects where my ceramic ones do not cut it, I just use tape. Thankfully, at least the fabrics I work with in my GF, are light weight enough where I don’t need too much.
My thesis was on controlling EMI in high speed PCB designs, specifically signal integrity. I now work on systems with the purpose of creating extremely large magnetic fields. So I completely agree magnetic fields can create some big issues and should be taken into account in decision making. Magnets can really screw stuff up for sure.
You would have been handy to have about when we were figuring how to make a motorhome work with an MRI. Had one with a fixed magnet in an 18 wheeler and managed to not only not have passing cars jump off the road and stick to the sides but were able to actually do MRIs driving in traffic.