First layer adhesion question

[mikey 0]

http://www.youtube.com/watch?v=rpi39ISmedk

As you hopefully can see in the video sometimes on the first layer it seems like the pla does not want to stick at all to the bed in some spots. Is this from a dirty plate or would something else be the cause? Sorry if this is a dumb question It just seems odd because I have pretty good adhesion most of the time.

Thanks Mike

 

[illuminarti 16]

It could be due to the bed being slightly off-level, so that in some parts the head is a touch too close to the bed; the plastic can't escape properly, so pressure builds up, and then it escapes in a blob when the pressure is high enough.

Are you using any adhesive on the bed, or just printing straight onto the glass?

 

[mikey 0]

It could be due to the bed being slightly off-level, so that in some parts the head is a touch too close to the bed; the plastic can't escape properly, so pressure builds up, and then it escapes in a blob when the pressure is high enough.

Are you using any adhesive on the bed, or just printing straight onto the glass?

 

Straight on the glass, I have had a lot of problems actually getting the correct bed level. Not only have I had trouble keeping the bed even but I also had trouble with how close I was. Do you have any tips?

 

[gr5 1,071]

If you print straight on the glass you need to heat to at around 40 or 50C (or hotter - 70C is recommended but 50C is fine).

Are you using a piece of paper during levelling? It should just barely touch the paper enough to be slightly tighter than completely loose. In other words once it is tight enough that you notice restriction in movement then you are close enough. Also it is best to level with a hot nozzle and a hot bed for two reasons:

1) hot things expand so you want to level with same conditions as printing

2) sometimes there is a tiny tiny blob of pla on the end of the nozzle. If that is hot then it shouldn't hurt your leveling procedure.

I have only levelled my UM2 once about a month ago and haven't messed with the levelling since then!

 

[IRobertI 434]

I have seen the same behaviour. I don't think it's due to pressure building up. If you look very closely as the head is laying down the plastic you can see that it exits the nozzle without any issues but in some spots it immediately disconnects from the surface of the glass. It looks sort of like if you would take a piece of tape, clean off the adhesive in a spot near the edge and then stick it down. The part without adhesive will lift slightly from the surface.

I noticed that some of my filaments are more likely than others to do this. The effect seems to be reduced if you print a very thin initial layer, I like 0.1mm (this requires a very flat bed when printing on glass, ye olde blue tape was more forgiving). I also tried putting on a VERY thin layer of glue, barely putting any pressure on the glue and spreading it super thin worked well for me while keeping a shiny bottom surface.

As for bed leveling. Make sure that the head of the printer (the fan shroud more specifically) isn't hitting the metal clips holding the glass in place as that will screw up your bed leveling.

 

[yellowshark 135]

I use extra strength hair spray on my glass which I have found to be very good for both PLA and PLA/PHA. Temp. set to 60 degrees as measured with a digital thermometer

 

[joergen 1]

If the print head is too close to the glass, and the glass is too hot/cold, and the print temp is too low, the friction from the printer movement will tear off parts of the print. print the first layer 5-10C hotter, and lever your bed properly.

 

[mikey 0]

It actually seems like the problem I was having was oils from my skin preventing adhesion in some spots.