# Magnetic heatbed options - can I trim these to size?

I'm looking at options for removable heatbed surfaces for my Prusa Mk2 clone, which has a MK42 bed, 250x210mm

I have a removable spring steel plate at the moment, but it is not dependably flat - there are often issues with patchy filament adhesion or oversquashing, as it has bumps in it.

I'm looking at a magnetic solution instead.

Does anyone have experience of this type of stick-on magnetic surface?

1. Any drawbacks?
2. Can I trim it to size? I can't see any which are 250 x 210
• I have a spring steel plate but it is not dependably flat -> wouldn't that result in a bumpy magnetic plate when you stick it on?
– 0scar
Feb 20, 2019 at 14:36
• This magnetic surface would be in place of the spring steel plate, which is removable. I'll edit the question as that's not clear. Feb 20, 2019 at 15:20

## Adhesion and sizing

First of all, the product you link is very likely a BuildTak clone or a similar product. My Ender 3 came with a similar one and I have changed to a different one after I ripped it off accidentally to mount a similar one. I have yet to find a sheet of this material that you can't cut to size, as it is pretty much only a polymer with a strong tape on one side and a rough surface on the other. So trimming is not a problem at all.

## Mounting

To mount your new surface, you need to get a surface onto your heatbed that has

• good contact on all the area
• securely holds the bed in place
• is as flat as possible

So you surely want to get a metal sheet that is as flat as possible to mount your surface on. If your bed is heated, your mounting method needs to transfer the heat as good as possible, so a direct contact to the heated bed would be good. This, however, rules out most thin magnets, as these magnet sheets demagnetize under heat, limiting the usability for higher temperature materials, for example, ABS. The original Prusa uses a spring steel bed and high-temperature magnets embedded in the heating platform to work around this.

• OK, yes I'd forgotten about the PINDA probe - it needs a metal surface to sense proximity. In my heated bed there are 9 metal inserts for this. And obviously it wasn't a problem when using my metal sheet. Would this be a problem if I put BuildTak on my heated bed? If so perhaps I should be looking at a replacement removable metal sheet instead of this magnetic surface? Feb 20, 2019 at 16:38
• @Lemmy I don't see it making problems with sensing as it is usually less than 1mm thick, making no problems with the sensors Feb 20, 2019 at 18:15
• OK, thanks. I wonder if that is also the case with this kind of product, as it is in two pieces, one which adheres to the bed and another removable one which sticks to the first magnetically. I'm looking for a solution with a removable plate. If I want to print ABS it seems like I will need high temperature magnets. I've only used PLA so far but would like to have the option to use PLA in future. Feb 20, 2019 at 20:41