Heat bed sagging

I've been fighting with my printer lately to try to get it to print some object that span a larger area of the bed.

Despite manually leveling the bed and also running ABL, the bed does sag closer to the middle.

Any suggestions? It's an i3v 10" and I am using the aluminum heat bed mount.

Thanks,
Matt

How much is the sag?

I assume you have glass on top of the heater. Have you tried flipping the glass over to see if the sag remains or turns into a hump?

Keep in mind that what we're dealing with here is the distance between the nozzle and the print surface. A variance could be in the print surface, or in the vertical location of the nozzle as the carriage moves in X and Y. What has been done to rule out a height variation in X Y movements of the carriage? This can be tough to do, but people ALWAYS assume the print bed is the problem (and maybe it usually is), but it can be more than that.

I had a similar issue today and a few weeks ago where it would print above the glass, I watched it print and the ABS slowly falling down to the glass. I spent a few hours weeks ago and about 3 hours today trying to figure out the issue.

I gave up and switched back to an old Slic3r basic from Makerfarm with a few tweaks and the damn thing put down a near perfect first layer. It came up a few layers later so I tweaked again and its about 6mm up and still going. So I have to say it could be settings. Im still not sure why the Slic3r expert was printing way to high and using very little filament(nearly hair thin).

Hi

This is really boring stuff to do ... sorry about that.

You need to start from a flat / fairly level surface. The table in front of me is neither flat or level. It's not as easy a thing to find as you might think.

Check the base of the printer for flat, then for square (measure diagonals). Next check for tightness on *all* the screws (I said it was boring).

Move up to the vertical structure and check it for square and flat ( more diagonals and some triangle math).

Next check the bed the same way. If it is way out to start, ABL will only do just so well. Make sure it and the tracks are level and square.

Finally the X carriage, same drill.

Yes, you did this just a while ago, It is still needed.

Now, check the heated bed PCB for flat (cold). A straight edge should do the trick. Heat it up and check it again. If it is out of flat cold, check the aluminum bed for flat. Check the screw holes in the pc board to see if they bind. Check your insulation to see if it is pushing on the pc board.

So now the pc board should be ok. Put the glass on, check it for flat with a straight edge cold. Check it again hot. If it is bowing hot, unclamp it and see if it drops back. If it checks out as flat, check the X carriage when things are hot ...

Yes, that's only part of the drill. It should get you to the point that you have a mechanically correct printer and a pretty good idea where the issue is.

Bob

Thanks for the quick replies! Sorry this is late. I finally had a chance to test it again and everything seems close enough now. Just to clarify, I was seeing the sag at the middle of the bed (center along the y-axis). I could barely slide a sheet of paper between the nozzle and the left and right side of the bed, but could easily slide the sheet between the nozzle and the middle with room to spare. When printing in that middle area the filament wasn't sticking to the bed and was getting stuck to the nozzle and being dragged.

I was suspicious of the 10" bed maybe being too wide to only be supported at the corners. Doesn't sound like it's a concern though.

Thanks again,
Matt