Bird's nest with PLA

kshanahan · October 2, 2019

I am new to 3D printing and we have an older model Ultimaker 2. I have read some of the forum/expert posts and am a little overwhelmed as to why some of our designs will print find and others will fail after 1 hour of printing. I tested a few small designs, and the PLA and nozzle seem to working fine. When I tried this design, it started loosing its layering after about 1 hour into the 3 hour printing.

Is this something I can prevent with my Cura settings? I think I had them set as the default, with 20% infill.

Smithy · October 2, 2019

Your problem, I think, is adhesion to the glass bed.

For this you should adjust the distance between nozzle and print bed again and make the distance slightly smaller. Furthermore the glass should be clean and free of grease. Additionally I use a UHU stick which I roughly apply to the glass and then spread with a damp cloth to a thin film. Then the object holds firmly on the plate and when the printing bed has cooled down, it can be easily loosened.

kshanahan · October 2, 2019

Thank you for the quick reply! I have been using a regular glue stick, so that may be the issue. I have the nozzle height pretty close, so I am not sure it is the distance.

Can I ask what you recommend cleaning the glass with after printing? We use a scraper to lift the prints - and they come up easily, but there is some residue on the glass. Maybe I should try heating the glassbed and cleaning?

Smithy · October 2, 2019

A lot of glue sticks are working so if you use one, then keep it, no need to change to UHU.

Then I guess your bed leveling is not the best, try to level more closer to the glass. Put a sheet of paper under the nozzle and level until you feel a bit (or a bit more) of resistance when you move the paper.

I don't clean the glass very often, but when I just clean it with soap and water, rub it dry, put some glue stick on it and then I print dozens of prints until I feel I need to clean again.

johnse · October 3, 2019

I print PLA directly on glass on my UM3. I also clean the glass with 90% Isopropyl Alcohol and a paper towel before every print. I also use auto-leveling every print.

If I’m doing a large print, or a tall narrow print I’ll use a brim.

when I print Nylon, that’s when the glue stick comes out 😊

Also... it’s a little hard to tell from your picture, but it looks like your glass plate is upside down. The sticker should be on the top surface.

geert_2 · October 3, 2019

Usually I do the cleaning with desinfection alcohol (I think that is 70% isopropylalcohol + 30% water?), then clean again with pure luke-warm tap water only.

Then prior to printing, I wipe the glass with a tissue moistened with salt water. This leaves a thin, almost invisible mist of salt stuck to the glass. This greatly improves bonding for PLA, compared to printing on bare glass, as long as the glass is warm (60°C). After cooling down, models pop-off by themself, and there is zero bonding. So this method does not damage delicate models.

After that, I just re-wipe the glass with the tissue, without taking it out, and without cleaning. I just clean once every 6 months. The rest is wiping with the tissue moistened with salt water only.

This salt method only works for PLA. For PET, it does not improve bonding, but does reduce the risk of chipping the glass. For ABS it does not work; and I don't know about other materials.

Also, this method works really well for my long and low models. But it is not optimal for thin high models like lantern poles: they tend to get knocked over. Maybe because the salt can not absorb shocks, contrary to a more flexible glue layer?

For me, the "salt method" works better than the gluestick which I tried in the very beginning. But maybe I applied too much glue, and I did not wipe it smooth with water afterwards, which seems to give much better results for others.

For an old manual (and too long, I know), see:

https://www.uantwerpen.be/nl/personeel/geert-keteleer/manuals/

Other bonding methods:

- 10% white wood glue dissolved in water (user gr5),

- hairspray (user neotko),

- glue stick,

- 3DLAC spray (and other similar products),

- very clean bare glass (a bit unpredictable),

- dedicated adhesive foils (for PP, PE,...),

- painter's tape (for non-heated beds),

- others I don't know?

I would suggest you try different methods, and variations within methods, until you find one that works well for your environment, your filament, and your models. As far as I know, there is no perfect method that always works. But there are several methods that are very good for most purposes. Stay with the printer and watch closely when doing these tests, so you can exactly see what happens, and you can abort when necessary.

Also, do the tests with a very hard test model like this below, with a very small contact-area and huge overhangs which tend to curl up and try to warp the model. If the test works for this model, then you have some safety margin for more moderate models.

1. The central round area is to reduce the risk of the model coming off totally.

2. If this model would come off, the area around it prevents it from sliding around.

3. This is the usual effect if bonding is not perfect: edges warp. Notice how much corners of overhangs tend to curl up.

4. Similar model after printing: the edges did warp and lift, but the test could still be completed. In poorer bondings, the model would have fallen off. In better bondings, the ends would not have lifted.