I'd like a flatter bed

I have a PLA version that has performed pretty well for me.

I have modified it to allow leveling of the bed in the y direction.

However, I have considerable sag in the center of my bed: it is about 10-15 mil (~.3 mm) lower than the corners. I'd like to add a (glass?) plate on top that is considerably flatter than this. Recommendations?

On a related note, can I get advice on the feasibility of upgrading to a heated bed?

Thanks,
Craig

 

Check it out.
Take your bed bolts out and flip then as my picture shows.
Tighten the Bold to the regular nut HARD and make sure u get it as centered in there as u can.
This setup for me was much better then the original it came with in the box.

Slide bed back and worth, find which corner is higher or lower and place a piece of paper betwin spacer and the bed to create more height.

Using my method, i nearly perfected the bed.
It does how ever have small warping at one end of it, but u can compensate for that by making a RAFT by 2 layers at the bottom of your model. It will create leveled surface to build on as well as provide better grip to what ever tape u print on.

Good luck.