adhesion to bed issues

Hi,
Using PLA I managed to print with great results the android sample using no raft with a 0.3 and 0.2 layer height without any detachment from bed. I suspect that the flat surface area of the android makes the adhesion to the bed more reliable.
Now it was time to print something more advanced that is not flat like the android so I used the skeinforge raft option (makes rectilinear lines between bed and object for support) . However I`m having problems with prints getting of bed after the very few layers. I also noticed that if I switch off the fan there is a slight improvement, but I don`t think it is the way to go as the print seems to collapse due to heat.
How can I sort out this problem?
should increase bed temperature to say about 80deg cel ? and how can I do this?
Is it possible to print a flat surface pad on the first layers underneath the raft so to improve adhesion to the bed ?

Leander

Edited 1 time(s). Last edit at 01/14/2014 04:20AM by leanderborg.

please help

Hi,

Here are a few good threads on this topic:

[forums.reprap.org]
[forums.reprap.org]
[forums.reprap.org]
[forums.reprap.org]

I get all my PLA prints to stick on glass cleaned with household vinegar. Give it a good scrub with a normal paper towel till you hear it squeak. Every once in a while I clean it with a brush and some dish soap.

Regards,

Niels

Thanks Nilez,

I forgot to mention that I was using acetone in the above post. Before changing any settings I will try vinegar and then will see from there.

Acetone (and other solvents) give mixed results depending on the item you wipe the glass with. It tends to solve material from your towel or cloth and that leaves a bad residue on the glass.

I was using plain toiletpaper

Toiletpaper was giving me trouble also I believe. At least in combination with the acetone. The plain paper towels are my preferred choice right now.

You shouldn't turn on the fan for the first layer. If the object has lots of small tricky geometry slowing down the first layer even more than 50% (Standard Gcode settings) helps. Raising the bed temp to 80C probably won't help 75C is adequate. The hotend temp may need to be hotter for the first layer for certain PLAs but if it's the green PLA that comes with the kit you won't need to raise the temp.

Depending on the PLA it will require different "tricks" to get it to stick correctly. I have heard people use blue tape, PVA glue, glue sticks, hair spray, lemon juice, sugar juice to get PLA to stick. Most people use blue tape and some use hair spray, I personally use a glue stick (the one that starts purple and turns clear) on glass.

Good luck.

I retried the same print(with raft) using white vinegar(5% Acetic acid) , little improvement but still raft base getting loose from bed.
I checked the bed surface temperature using an infrared temp probe and it is indicating 50 at start and goes up to about 60 after 10 minutes into the print

I have my printer in a cold room 16deg cel. And I suspect that this is the problem.

modified temperatures on the start_pla.gcode file:
bed ----> 70 to 75
hotend----> 185 to 190
I got good results and managed to finish the print without warping.
I rechecked the bed surface temperature and now it is 55 at start and goes up to about 68 after 10 minutes into the print

How can I set these temperatures to the first layer only and not for the whole print?

Hi,

I think you have to set it using some custom gcode lines in the start_PLA.gcode file. Otherwise I think the temperature tab in Skeinforge maybe offers some settings.
Here is some good info on the gcode editing (in this case intended for use with Slic3r):

[forums.reprap.org]

M83 ; use relative distances for extrusion
G28 ; home
G1 X0 Y98 F9000 ; Go to the middle of the front
G1Z0.05 ; close to the bed
M104 S185 ; set extruder temp
M190 S70 ; set bed temp & wait
M109 S190 ; wait for extruder temp [first_layer_temperature]
G92 E0
G1 X50 E5 F200 ; make a thick line to prime extruder
G1 E-1 F1200
G1Z0.3 ;lift Z


should this set the temperature to 190 for the first layer then revert to 185 ?
Sorry but i`m newbie to gcode !

Hi Leanderborg,

Well, I'm a total newb as well so I haven't played with this with the use of Skeinforge (In Slic3r these options are a little more obvious btw). Maybe an expert can chime in at this point ....

Also you shouldn't normally need to use a raft if you have a heated bed (at least in my experience)...

Quote
leanderborg
M83 ; use relative distances for extrusion
G28 ; home
G1 X0 Y98 F9000 ; Go to the middle of the front
G1Z0.05 ; close to the bed
M104 S185 ; set extruder temp
M190 S70 ; set bed temp & wait
M109 S190 ; wait for extruder temp [first_layer_temperature]
G92 E0
G1 X50 E5 F200 ; make a thick line to prime extruder
G1 E-1 F1200
G1Z0.3 ;lift Z


should this set the temperature to 190 for the first layer then revert to 185 ?
Sorry but i`m newbie to gcode !

gcode is run sequentially - it's just a list of instructions that tells the printer to do a bunch of things one after the other.

It's not a good idea to leave the extruder at extrusion temperatures for long periods as the filament can burn and oxidise inside the nozzle so that's why most people heat the bed first (which takes longer) before heating the extruder (which takes about 3 minutes for ABS temperatures on mine).
The various heat/heat-and-wait commands allow you to do this without having to wait an extra 3 whole minutes (I bet you guys are the same impatient guys who use activator on super glue ) by allowing you to start heating the bed whilst the extruder is still warming up.

Slic3r has the ability to set different temperatures for first and subsequent layers and as Nilez says the settings are pretty obvious in the dialogs.

I'm not sure how Skeinforge does it but unless there's a setting that overrides your start gcode AFTER the first layer then I don't think this will do what you think it does. I think you may need to wait for someone with Skeinforge knowledge.

There's a good gcode reference here by the way.

I use PVA-based wood glue dissolved in water in a 1/10 solution. Seems to work everytime. It still leaves a shiny bottom.

Did some some more testing with 10%PVA solution. Wow this stuff is great ! Now the print got so stuck to the glass that it`s a little difficult to release when cold !
Problem solved. Thanks everyone !

Edited 1 time(s). Last edit at 01/20/2014 04:23AM by leanderborg.

I would actually say that 10% solution might be in the high end. I ended up taking a flint of the glass plate when peeling of a piece, but that was with a 20%-30% solution. I haven't experienced a to weak solution yet. I think i'm down to 6-8%.