3D Printing - issues getting the bed flat

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I wondered if anyone has a good solution for setting up a flat bed for a 3D printer.

My Prusa clone is working great but for bigger prints the first layers are a problem because of height variations in different parts of the bed. I’m using ABL Expert in Octoprint for generating the bed leveling mesh. It always seems to result in over- or under compensation of Z axis offset.

I recently upgraded to a MK52 bed which seems flatter than my last one. I would prefer not to put PEI on it directly, as then the bed can’t be removed easily. I have a steel plate on top with clips, which is not flat. I’ve ordered some magnets to use with the MK52 bed so maybe that will help pull the steel plate down.

I’m thinking that a 3mm glass plate on top of the heated bed might be way to go. It would be truly flat, but would require a new sensor, and I don’t know if there are any which work with glass.

Any suggestions? @laurent_muchacho ?

An update on this for anyone who’s interested.

I realised that there was no point in using a glass plate without getting my autoleveling sorted out anyway. Even a completely flat surface will not present to the sensor at the exact same height all the way across, there are too many other variables.

The magnets for the bed came and I fitted them. Now the steel sheet is really tight to the bed and the variations in height across the bed are much less. It should also stay in position consistently.

I also changed my bed leveling mesh to be a 4 x 4 grid instead of 3 x 3.

With those changes I am now getting really good results. I am in the process of printing a featherboard for my homemade router table - it’s about 165 x 144 mm. The first layers went down really evenly. So it looks like printing larger items is now going to be possible. :smiley:

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