My Second Print! Still needs some work...

[jasay]

Get some blue painters tape. Lay it across the bed as flat as you can with minimal gaps between strips (or just use the 2"+ wide stuff for the small parts). Then you can print PLA with a cold (room temp) bed.

[Carrot_or_Stick]

What thickness of glass do you guys use? I'm using some 3/32" glass from Lowes which is just shy of 2.5mm

I'm thinking of picking up something thicker. Home Depot has 3.175mm glass (.125") which is a difference of .794mm so that may help along with setting my temp lower.

[Carrot_or_Stick]

I'll give it a shot and see if the issue goes away when printing on cold glass. Thanks for the help

Get some blue painters tape. Lay it across the bed as flat as you can with minimal gaps between strips (or just use the 2"+ wide stuff for the small parts). Then you can print PLA with a cold (room temp) bed.

[jasay]

From looking at my prints it seems that the layers will both expand and contract equally around the object. What I have noticed is that when I'm leveling the bed while it is heated that when the relay clicks on (begins heating) the glass will dip in the middle quite a bit (over 1mm), and when the relay clicks off (stops heating) the glass will come back up towards the nozzle. My nozzle is right at 0 in each of the 4 corners, its the middle that gives me issues.

A change in height of the bed could definitely cause layers to squish more or less depending on the direction of the height change. It's surprising that the glass would flex that much though. What is the temperature swing reported? Is the glass confined (perhaps by the screw heads) in such a way that it cannot expand in length/width and so has to bow instead when it reaches a certain temp?

[Carrot_or_Stick]

I didn't watch the temp reading very closely but what I recall is the swing would be + - 2C. The glass is clipped on the left and right sides towards the top and bottom corners with binder clips. The glass is also only 2.5mm thick window pane glass so it's quite thin.

I've actually watched the glass move almost a full millimeter when the relay is switching on and off. I should take a video sometime.

A change in height of the bed could definitely cause layers to squish more or less depending on the direction of the height change. It's surprising that the glass would flex that much though. What is the temperature swing reported? Is the glass confined (perhaps by the screw heads) in such a way that it cannot expand in length/width and so has to bow instead when it reaches a certain temp?

[jasay]

Tightening up the temperature swing might help. You can autotune the PID settings: http://reprap.org/wiki/PID_Tuning

Also make sure the sides of the glass are not touching anything so that it can expand. I'd still try the tape/cold bed first though just to make sure this is the root cause.

[Carrot_or_Stick]

Thanks for the info. I got some 1/4" glass from a glass supplier and that fixed all my issues. Turns out it WAS my glass flexing while being heated.

Tightening up the temperature swing might help. You can autotune the PID settings: http://reprap.org/wiki/PID_Tuning

Also make sure the sides of the glass are not touching anything so that it can expand. I'd still try the tape/cold bed first though just to make sure this is the root cause.