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skewcrap

Adhesion problems with PLA

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Hi everyone

I'm using an UMO with heated bed and I'm basically printing just PLA. I really had satisfying results, but recently I have trouble with the print not sticking to the glass.

I print with 210°, 65° heated bed, first layer thickness is 0.15mm and bed levelling is fine. There are always smaller spots where the PLA does not stick properly to the glass. If these spots are near the borders, the print is obviously starting to detach. I tried to clean the glass with ethanol or soap and water, but it did not really solve the issue.

Therefore I have a simple question: How do you clean the glass plate? Should I try aceton?

I know that you can use hair spray to improve adhesion, but this is cumbersome and it really should not be necessary for PLA?

Thanks for your help.

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I am cleaning my glass plate with Isopropyl alcohol 70%. I print PLA straight to the glass at 60°C bed temperature. Before each print I'll wipe the plate with a paper towel and a small amount of Isopropyl, plus a more thorough cleaning whenever i feel like it - which ends up being not terribly often.

Don't know if Isopropyl actually is any better than Ethanol however, never used Ethanol and according to Wikipedia both can be used as window cleaner.

PS: Why 70% and not 99%? Well, I've been using Buildtak on my other printer and Buildtaks manufacturer said don't use concentrations higher than 70% for Buildtak, otherwise i'd use 99%.

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I just use soap and water about once per month.

1) Make sure the glass is clean if you haven't cleaned it for a few weeks. You want a very thin coat of PVA glue which is found in hairspray, glue stick, wood glue. If you use glue stick or wood glue you need to dilute it with water - about 5 to 10 parts water to 1 part glue. So for example if you use glue stick, apply only to the outer edge of your model outline then add a tablespoon of water and spread with a tissue such that you thin it so much you can't see it anymore. wood glue is better. hairspray doesn't need to be diluted. When it dries it should be invisible. This glue works well for most plastics.

2) Heat the bed. This helps the plastic fill in completely (no air pockets) so you have better contact with the glass. For PLA any temp above 40C is safe. I often print at 60C bed.

3) heat the bed (didn't I already say that?). Keeping the bottom layers above the glass temp of the material makes it so the bottom layers can flex a bit (very very tiny amount) and relieve the tension/stress. For PLA 60C is better than 50C. 70C is even better but then you get other "warping" like issues at the corners where they move inward but if you are desperate it's worth it. For ABS you want 110C (100C is good enough).

4) rounded corners - having square corners puts all the lifting force on a tiny spot. Rounding the corner spreads the force out more. This is optional if you use brim.

5) Brim - this is the most important of all. Turn on the brim feature in cura and do 10 passes of brim. This is awesome.

6) Squish - make sure the bottom layer is squishing onto the glass with no gaps in the brim. The first trace going down should be flat like a pancake, not rounded like string. don't run the leveling procedure if it is off, just turn the 3 screws the same amount while it is printing the skirt or brim. Counter clockwise from below gets the bed closer to the nozzle. Don't panic, take a breath, think about which way to move the glass, think about how the screw works, then twist. This may take 30 seconds but it's worth it to not rush it. You can always restart the print.

If you do all this you will then ask me "how the hell do I get my part off the glass?". Well first let it cool completely. Or even put it in the freezer. Then use a sharp putty knife under a corner and it should pop off.

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Thanks for your replies. I guess, basically in my case it was a PLA issue. I tried a different brand of PLA which sticks perfectly now. It's just a little bit strange that there are such huge differences for the very same PLA. Is it possible that there are big differences even for the same roll of PLA? I mean, before the sticking issue started, I printed more than 1kg of that particular PLA with good results...

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It's possible that your bed is very slightly out of level and it is getting squished better on one location of the bed but worse in another section. Not squishing the filament (#6 above) is the most common mistake because the leveling procedure by default does not give you enough squish.

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I find different brands of PLA do have different properties. You will notice this even between different colours. Even with a perfectly squished and flat first layer, it could peel off with enough head movement over time.

I notice this especially since I print a lot of small footprint parts. Some PLA absolutely requires a brim, and others are fine without. UM filament sticks really well to glass without anything, clear/natural colour tends to stick more than heavily pigmented ones.

I usually clean my glass with a sprits of some isopropyl alcohol and then a light wipe with a damp cloth.

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@ gr5

I know that bed levelling is very important. I have done it as good as possible. Sometimes there are some spots, where the filament is actually squished to much, but I have just 3 screws to adjust it. If the glass plate itself is uneven, I can't correct it.

The problems I encountered did certainly not come from a bed levelling issue. The filament just did not stick at all. Well, I have to admit that this particular filament is quite cheap, but after I bought the first roll, I made some tests which were fine.

From my experience so far I conclude, that there must be quite big differences for the very same PLA (which means with the same colour). So how do you evaluate which type of PLA to buy? Well, you might get some tendencies, but finally you have to make your own tests.

Edited by Guest

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@skewcrap

It's your hotend assembled as the manual says? Because if so, your nozzle it's tilt.

Try adding small shims / washers. Like @amedee explains on this post

When using the standard umo products the coupler/peek pushes the wood 0.3-0.5mm on the corner of the hotend, that forces the hotend to be slighly tilted, After changing it on my 2 umo+ now I get a little bit better top layers. It should affect the bed adhesion also (I just noticed that it drags much less material close to none when the bed it's perfectly calibrated).

Just droping ideas.

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After cleaning, thoroughly wash the glass several times with pure tap water only. No soap, no detergents, no cleaning aids anymore: they all reduce bonding. Then wipe the glass with very salt water. Yes, salt water. Keep wiping gently and let the water evaporate, until the salt dries into a very thin mist.

To print, heat the glass plate to 60°C. This "salt method" gives a far better bonding of PLA to glass: when hot, it bonds rock solid. But when cold, the models fall off automatically, without any force at all.

Since I started using this "salt method" one year ago, I have printed about 1000 parts in PLA without bonding problems. Often very difficult parts that I could not print with the "glue stick method". No warping, no corners lifting.

See the full manual with pictures at:

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

Let us know if this helps. (But I think it will only work for PLA.)

Geert

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Thanks, sounds great, I will try immediately. I mostly print PLA and sometimes PET, I always use 30 brim lines, but often it is still not enough and corners are lifting. It's always disappointing if the print is affected like this.

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