Science, yo. Lately I've been asked (and seen some shady marketing shit, who's surprised?) about magnetics by the people wishing to build their own buildplates and include the right magnets for the job. You can get involved in the discussion and design practices by joining in on our forums and if you are already here you're in the right place... Making your own isn't difficult, just like anything else though there are considerations when doing so or buying a system from a 3rd party. Our own plates for the Artillery 3D printers use all of this culminated experience, just to be clear I don't take making something that works well lightly and want to give everyone choices. The ones you make are up to you, just be informed. Learning something is what this is supposed to be about right?
Our plates for Artillery and other printers will be available soon. Keep up to date by joining our community.
I started pouring over some textbooks hoping to get consolidated information I have tucked away in that 80's rock and roll god still having orgasmic seizures brain of mine and broke down knowing someone has it out there. Well, I found it (after rereading and checking for validity) so, for credit purposes I'm going to use a bit of well constructed information from articles written by K&J. At the bottom I'll also include links (no affiliate bullshit here) so you can source them yourself if you wish. They aren't the least expensive out there, but a majority of them are reasonable for you retail folks.
Now a word about imported magnets- as with anything there's always the "cheaper Asian" suppliers to get all excited about but be warned, you will not always get reliable or consistent quality most of the time and the possibility of getting lower grades than what you are paying for is common. Certifications don't mean shit when they come from a geography or trade system that doesn't police it's own dealings reliably. For my own uses and adventures over the years its why I stick to my guns on buying from reputable suppliers in the USA, mainly because in the engineering and science fields there is hell to pay for those practices and we love reliable results that can reproduced.
Fortunately for this purpose you can get away with a bit of a grade range, the caveat being you might be getting ripped off by marketing to justify higher costs being passed on to you, which can translate (google that shit if you don't understand the concept) into higher profit margins for them and a skinnier wallet for you. It's your money, do what you want with it.
Lets break the types down a bit and you'll understand why I have the attitudes I do about some of the currently available systems out there. The sciencey meat will be towards the bottom of this article so bounce around if you wish.
Flex Plate With Magnetic Sheet
This was a funny response to the early magnetic beds that had actual magnets built in. It's something any garage monkey would try after looking at that fridge magnet business card and going "Hmmm?" We all did back then. But if you put the beer down and remember your science you leave it on the fridge.
The magnetic sheet, in layman's terms are basically a flexible plastic with magnetic ferrite infused. Ferrite magnets are low grade to begin with and rely on surface area to do the work to compensate for its low holding properties. Problems arise when they are subjected to high temperature cycles, its magnetism diminishes, the sheets can and do bubble, add considerable weight and add another layer of resistance for heat transfer. You can expand the range of problems by just taking those few into consideration and thinking them through what you do with your printer. You will never get me to say they are anything other than pure shit for our needs except in a temporary capacity- personally I don't like replacing things or wasting time and money.
Ever have a part lift off the bed and leave you with a spaghetti art piece in the morning, and you cant figure out why? The sheet's properties can allow for bubbling underneath during heat, lose its magnetism strength over time and if your part starts to warp but your adhesion is good on the surface guess what can give? I've seen it happen, and Homey don't play that.
Magnetic Bed With Magnets
This is the logical approach, but years of profit margin emphasis (instead of reliability) has introduced bad examples in a otherwise excellent design choice and Ill explain why- if you are going to use removable flex sheets (which are a whole different discussion on why most of them out there are also pure consumable shit) you have to build it right. The magnets must be of a higher grade and strength to do the job over time. Ever wonder why some of the plate designs look like a pinwheel with what seems like dozens of pockets and a army of magnets underneath? Lower cost and higher profits for them, higher cost for you. They need so many of them because of the pull strength and the flex sheet is thin enough to bow if that warping situation I mentioned earlier arises. Not just one poor design choice, but two with bonuses you wont realize until its time to replace it. That's another discussion again.
Ok, the stage has been set with a few things to ponder. On to the differences magnets make, and alot of referencing to the K&J article(s) I mentioned. This information is widely available from many sources, so fact check to your hearts content, I always do and so should you.
The big one is temperature. We routinely cycle the beds anywhere from an average 50c to 80c, sometimes higher for exotics. Those who stay in that common range wont have to over spend but let me ask you this- if you think you might toy with some of the higher temperature filaments that require 90c+ bed temps why not spend the extra few dollars (and its not that much more) and preplan for that possibility? We already know the "ferrite sheet" is below our needs, and most bed systems out there usually use N40/42 neodymium magnets for cost savings. They are adequate for the common range but only barely. You lose out on the possibility of reliable magnetism retaining over time. As you can see in the reference material neodymium magnets have ranges for safe working temperatures.
So let's look at the different types and consider the ranges we really want to think about.
You'll quickly determine that NM, NH, and NSH fall well into the operating ranges we use. Remember me mentioning N40/42+ ranges being used in most systems? They are produced alot more frequently and often used or in some cases snuck in along the way. I've seen it firsthand and thats why I prefer reliable sources. The costs scale a little bit but its not breaking the bank to move up where you should be, although some marketing shills will over emphasize quality to justify exorbitant costs. Its bullshit.
On to Magnet Strength
Besides the use of lower quality/range magnets for cost and heat cycle reliability, the pull force and surface field properties should also be considered in the design. there are many choices here and I'll try to summarize it a bit. Still, it wont kill you to read the charts and take them into account when determining your choices.
Now you know why in some cases the bottom of a 3rd party buildplate looks like a starburst of exploding magnets. Weaker or cheaper magnets need to bring friends, sometimes many of them. The downside to this is they add production cost (in different ways), and need that friend convention to account for losing magnetism over time. They also add weight for little return, just more pocket cash for the seller in the long run. Choose stronger magnets of a higher grade and you'll find yourself with a reliable plate that wont let you down when things need to be sticky.
Mounting those little buggers isn't as much of a challenge as you'd think. There are potential problems if done wrong, from warping from machining to coming loose/dropping out to poor heat transfer (naming just a few). You can faithfully get away with just kapton tape IF you have a bed heater that is a good flexible silicone and not think twice about it. The bed mat will gleefully transfer heat properly because they do conform to the surfaces. Its actually a better choice over the common glue-in-the-channel method because all of those rtv plugs contribute to a wider swing in heat transfer over the whole bed, which can lead to warping too if the pattern is funky.
If you are going the machined route, aside from proper heat dissipation during the machining process (cheap shops or cost cutters don't bother with cooling more often than you think) you have to do it RIGHT. That's again why we fabricate here ourselves in the USA because we don't like surprises in the form of a warped bed you bought hoping to solve the problem of... bed warping. The bed material itself is a consideration but not as much IF you know what the hell you are doing so don't get bullshitted into the "premium" marketing again. Aluminum has pretty easy properties to deal with but it takes experience and that experience shouldn't be passed on to you- it should be a badge of honor for the fabricator because doing it right does NOT cost more than doing it wrong. Period.
In summary, less is definitely better but you have to do it right and I hope with this knowledge you gain some reliability and confidence in your choices.
Articles referenced, Main Sites: