Build plate glass variability - using a scraper

[ColinH 0]

I am noticing that my build plate, with fine Z layer settings <=0.08mm, results in brims that reveal what looks like variations in the glass surface. Some parts of the brim are almost transparent. Others are striated thicker. (see the pics).

NOTE:

1) 'Initial Layer Thickness' has been set to zero. if I do anything else the print fails every time because the brim is too thick and never adheres. As it is all prints warp from the thickened brim points, which is the first place the print lifts.

2) It's not affected by atomic cleaning of the extruder and the effect is repeatable although it varies a little from print run to print run.

3) It's not affected by washing the glass.

Brim 1

Brim 2 (to the left of Brim 1

Brim 3 (same position as Brim 1 and same everything except performed later)

Q1. Is what I am seeing actually glass surface variation of the order of the same size as the layer thickness, or is it systematic error in the extruder head positioning?

Note: I have been using this implement to scrape clean the glass.

Q2. Is this OK? Am I damaging the glass?

Cheers

Colin Hales

[owen 19]

Hi Colin

Try flipping your glass and print on the other side and see if you get the variations in the same place to determine if the variations are in the glass or maybe your XY rods. Generally you will always get a bit of variation which is why being dead level and starting with a thick first layer (0.3mm for a 0.4mm nozzle) usually works.

You also need to do all the other stuff like

Having the right bed temperature for the filament you are using.

Printing a slow first layer and using glue stick or similar.

Not having the fans on for the first layer.

No cold drafts blowing through.

If you ever use window glass you will see very high variations.

Hope this helps.

Owen

[ColinH 0]

Hi Owen,

I am using a 0.25mm nozzle. I need machine-quality reproducibility. The UM2+ machine is new and I wouldn't expect the XY rods or drive train to degrade that quickly.

Glue stick and hair spray make it worse (looser on the plate)

Fans on/off makes no difference.

I built an acrylic hood and a door. They did nothing obvious.

No two print runs are ever the same. I have done literally dozens of trials. Very frustrating. I don't mind exploring when the exploration space is systematic. This is random and unpatterned ... I learn very little from the trials.

I am starting to think that a major part redesign is required if I need to do it in ABS. Maybe that is the lesson: If you must have ABS for material property reasons, then the design has to be started with ABS printing limitations in mind.

For the moment I have actually given up trying to do this particular part in ABS. It's an OK workaround, but I have had a disappointing introduction (Ultimaker newby) to ABS.

Will try the glass flip. Sounds like a good idea. It might give an insight!

cheers

Colin