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industrialdesigner-uk

Help! UM2 - Print keeps coming off the heated bed - solved

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Hi,

Is there anyone out there who has some experience with overcoming aborted prints due to the print coming away from the heated bed?

I am trying to print in black ABS. using Cura 14.01 & UM2 standard settings for ABS.

I have tried a plain glass bed, glue stick, and hair spray. On all occasions the print has got to about 3mm high of the bed and shown signs of lifting at the edges.

Eventually the print has parted from the bed completely after 5mm height.

I have tried to help anchor the areas that are starting to lift using a small squirt from my hot glue gun. This has saved the day once or twice before when I was printing in PLA recently, but I think in the case of ABS, the heated bed is a little too hot for the glue gun glue to help me.

I have tried different rafts but that doesn't seem to help in this case.

The footprint of the part is approximately 170 x 100mm and I was wondering if the ABS is shrinking too much before there is enough height in the part to stablize it, so stopping it from peeling at the extreme edges.

The room is normal room temperature...ie..not really cold or extremely hot, but I was thinking maybe I should try to close up the openings in the printer housing just to try to maintain a slightly higher air temperature??

Should I run the bed at a lower or higher temp?

I am printing at a resolution of 0.1mm will changing the resolution or print speed do anything to help??

Thanks,

David

 

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Hi Nuno,

Thanks for your suggestion.

Just before you posted I set the printer going again on the same part.

I've used hairspray this time, but I have turned up the bed temperature to 100*C as you suggest. Fingers crossed.

6th time lucky :smile:

PS. Is it best to put the glue (from a stick) on to a completely cold bed or is it ok to put it on when the bed is hot? I can't seem to get a nice tidy looking coating on the glass surface. It always go's on a bit lumpy. That's why I prefer to use a spray type application.

I am new to 3D printing...maybe i'm doing it wrong(?)

 

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Bed temp can be crucial. Also you might want to check the actual temp in the tune menu as the UM2 will struggle to keep up the high temp especially if the fan turns on. Set the fan to anywhere between 0 and 50% might help. Also, check the glass transition temp of your particular ABS, they vary a bit but usually 90C or lower.

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Did you enable brim? It helps quite a bit - it's in the "adhesion" drop down on the first basic settings page.

The shrinking is happening because each upper layer shrinks and pulls hard against the lower layers. While still above the glass temp (around 100C) you don't care about the shrinkage because it is laid down as a liquid and will only contract in the shortest dimension (get thinner/skinnier). But once it gets below 100C or so, it pulls in all directions until it cools to air temperature.

Because of this:

1) Nozzle temp does not matter (for lifting/curling) - as we only care about temps below 110C.

2) Keeping air temp warm helps quite a bit. The shrinkage from 100C to 20C is double the shrinkage from 100C to 60C.

3) Keeping the lower 5mm above glass temp sometimes helps as it will deform slightly instead of lifting but on the other hand it might not look so good (kind of half melted).

4) Turning off the fan can be very helpful. Some people who print ABS never use the fan. You don't get very good overhangs but also it is less likely to lift.

5) Print speed does not matter.

ABS juice is a great thing to try - stick a bunch of leftover ABS filament into a glass jar, fill the rest up with acetone, let it soak for hours and shake it up. Paint this on with a junky paintbrush. Let it dry before printing.

Having square corners on your part is a problem - all the force is at one tiny .4mm corner. Brim converts this into a rounded corner and helps hugely. You need perfect brim though - it needs to be squished down onto the glass flat. No gaps in the brim and especialy no gap between the brim and the part. Rounding the corners in CAD might help but brim is even better.

Having no bottom surface helps. or running large holes from top to bottom of your part - especially the bottom 10mm helps a lot. This is because there is less shrinking force.

Temperature is ciritcal - try 5 and 10C lower and higher than what you've tried before.

Personally I would do an experiment where you print the bottom 1mm of the UM robot with different surfaces and different temp. Abort the print after 1mm and try to pry it off.

 

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Hi David,

I am not sure about the hairspray, never used.

I noticed in my prints if you put the stick glue on a hot bed doesn't stick so good as on a cold one

I forgot to mention, but others already did, enable the Brim that will help a lot

Note: I never use more than 50% fan with ABS and some times I even set to 0

I also have the feeling that Black ABS needs more temp than others, since you can't go over 260ºC you can lower the fans % (gr5 quote: You don't get very good overhangs but also it is less likely to lift.)

 

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Hey, Folks!

Thanks a lot for your advice...

I have hollowed out the centre area of the footprint on the part and then added a 0.2mm in-fill...as a kind of internal 'brim'.

Then I have also added a 0.2mm high brim thats about 15mm wide, all around the footprint.

I have applied the gluestick on a cold glass surface before heating the bed up to 100*c.

I have put cardboard over the openings of the printer housing in an attempt to keep as much of the heat into the air around the model as it builds. It's going to be a cold night tonight so every little helps I guess.

On the 'tune' settings the fan speed is set at 0% (not sure what that means, if i'm honest, but it sounds right :-)

We are now about 14mm high and so far all looks good !!

19 hours to go.....fingers crossed !

 

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Hello everyone,

Ok I just got around to put a photo up here, so you can see the model that was giving me the problems.

And now I can't seem to work out how to upload a photo directly from my computer to the forum....hmm?

Aha! It seems that I have to get authorisation from the administrator..hmm..(?)

 

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Ok.....here are a couple of images of the part.

I am in the process of printing the other half of this large component. I plan to bond them together. The parts also interlock.....It will be interesting to see if the parts are accurate enough to fit together. I made a 0.2mm clearance between the interlocking surfaces.

Fingers crossed !

Resize Of IMG 1369Resize Of IMG 1370Resize Of IMG 1394Resize Of IMG 1398Resize Of IMG 1403Resize Of IMG 1376Resize Of IMG 1377

 

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Hello

gr5 - that's an inspiring concentration of the exact info i was looking for about curling / bending / separating prints... i can't thank you enough! also can't wait to try the abs juice, once i get to abs prints... also, any chance that a thicker infill could have an effect on curling?

 

ind-des-uk - i'm very glad to see you managed to get the thing printed.

as for clearance - not sure which snaps u mean, but 0.2mm sounds ok. i usually use 0.2 or 0.1, but only if the slots are printed in x/y. anyway, didn't u do small tests for the snaps, before printing a multi-hour part?

also, a tip - if you use painter's sticky tape (the white-ish paper stuff that usually has weak glue and can be easily removed without leaving marks) to cover the glass (or just the area to be printed over) the PLA sticks really well to it, especially if you calibrate the first layer to smear or semi-smear.

it holds so well that i don't even need brim when i use it. when heated this "weak" glue becomes much stronger.

but, there are drawbacks - large flat things sometimes stick so well that even after cooling i had to struggle with them for a while, inserting a thin metal scraper under the tape around the edges... so i've actually proffered it for prints with a small base that i want to stick really well. also there's some residue on the base, which washes off quite easily with warm water, and a bit of residue on the glass, which is quite easy to remove by dabbing it with a fresh piece of this same tape...

more testing is required.

(haven't even tried with ABS yet)

continued good luck!

 

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