Installing magnets in heated bed
-
I'm wondering what experiences the collective has had with installing magnets in their heated beds?
I've just upgraded my bed to 10mm MIC6 cast aluminium.
It's 300x300 with a 250x250 240v AC heater.
I would like to start using a PEI coated spring steel plate for easy removal etc.
I've sourced some 9.5mm x 3.2mm N42SH magnets rated up to 150C
As I print a fair bit of ABS and Nylon I typically run 80-100C bed temps.
I was hoping to use 8 of these magnets around the outer edge to hold the plate.
I'd rather not use them over the entire bed as I'm unsure how that will affect distortion.
I found some interesting info here which suggests I'd have been better off using longer magnets for heat resistance, but naturally didn't read it till after I'd ordered the 3.2mm units
https://www.kjmagnetics.com/blog.asp?p=temperature-and-neodymium-magnetsHas anyone used magnets just around the edges?
Any issues with the steel buckling or lifting in the middle causing uneven surface or temperature? -
@OwenD for better heat resistance, choose samarium-cobalt magnets.
-
In my exeprience you will want to use more magnets. Warping is an issue there if your metal sheet is not really well "sticked" by the magnets, you will notice warping on the metal sheet when you print some medium size ABS/nylon part. I have a bed with 36 samarium-cobal magnets, 15x3mm, en even that amount sometimes cause me tropubles wuth a little big nylon prints: the nylon is attached to the bed... but the bed lifts from the magnets! Real problem is that the spring steel is not really magnetic, at least not as magnetic as pure ferrous materials.
-
@Tinchus
So you're saying the tension from shrinking of the part when cooling is lifting the build plate?What effect is that having on the print?
Do you find having magnets across the entire bed causes warping due to irregular thickness?
I've always use stick on PEI surfaces and can continue to do so.
I was hoping to go to the steel build plate for convenience, but the whole point of the new bed is to fix the terrible lack of flatness my old bed had, hence my reluctance to drill holes all over it. -
@OwenD Yes. But also I have to say that it depends a lot on the material your spring steel is made of. I have found some of them to be thin and way less magnetic than others.
And it depnds alot also on the size of your printbed: my print bed is 400X400mm, so in that size the metal sheet is way more prone to flex than the same sheet but in a 200X200 mm size.
Taske into consideration that even when these magnets are meant to be used on high temperatures, that doesnt mean that they hold the same magnetic force at room temperature than at 80 or 90 degrees celsius. At high temeprature they are weaker. The advance is that they dont loose its magnetcs propteries along the time as "nortmal" neodimium magnets.
Regarding flatness: it is not an issue. I have drilled 3.25 mm holes (mgnets are 3mm -+ 0.1mm) apply some silicone glue, put the magnet insive and then I use a ruler to press the magnet to it flush with the bed. After that, the beatifull 100 probe points mesh thae duet3 gives me , asures me a perfect first layer.And about the results: this warping happens almost all the time when the ABS print gets to the border of the bed, specially near the corners, and with some geometries. When in dounbs I use a strong hair clip on corners to be sure the spring sheet is not going to detach from magnet there. And when it happends... it depends. There have been some times where the warping has made the nozzle to crash and motors loose steps. Other times is just continue printing and I can see the part warped.
-
@Tinchus
Thanks for your detailed reply.
I received the spring steel sheet today and it has a curve typical of anything that came off a coli of sheet.
So my plans of securing just around the perimeter are dashed with this one.
It can be pressed flat easily enough, but won't sit flat under its own weight. -
@OwenD said in Installing magnets in heated bed:
I've sourced some 9.5mm x 3.2mm N42SH magnets rated up to 150C
As I print a fair bit of ABS and Nylon I typically run 80-100C bed temps.
I was hoping to use 8 of these magnets around the outer edge to hold the plate.I think you'll need more magnets.
I used 32 number 9mm diameter 3mm thick samarium-cobalt magnets in a 300 diameter bed. Your magnets may be stronger than mine (mine were nominally 1kg pull when in contact with a large steel plate 3mm thick), but not that much stronger.
As others have noted, it does depend on the spring steel plate - I use circular with PEI one side only plate from aliexpress, and I'd like it to be about 50% grippier, but if I put a genuine Prusa spring steel plate on it's plenty grippy enough.
There's pictures and more description of what I did at https://forum.duet3d.com/post/300128
