What causes flat botton finishing?

Hi everyone,

what causes this finishing?

This has been printed with ABS 1.75mm, MKII heated bed at 60C and 3mm glass with Kapton tape. Also, I tried with other 3 filaments and the result is the same.
It seems like the bed is too hot and melting the plastic, but everyone else mentions printing ABS with the bed at 110C. I initially though that my thermistor could not be working properly, then I printed a few parts with 55C to check and it turn out that it didn't stick to the bed.


Any tips?

Franklin Dattein

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Cheers,
Franklin Dattein

Are you sure it is not PLA? Put some in near boiling water and if it goes soft it is not ABS.

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[www.hydraraptor.blogspot.com]

The melting point is 235 and I tried melting it at 225 without success, so I would say it is ABS. Anyway, I will make the hot water test tonight.

Assuming that it really is ABS, any other idea?

Cheers,
Franklin Dattein

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Cheers,
Franklin Dattein

Well if it ABS the bed temperature is too low so I would expect it not to stick well and it certainly won't melt the plastic.

If you asking why it is a smooth finish, that will always be the case if you extrude it onto a smooth surface and have the first layer height low enough to leave no gaps between the filaments.

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[www.hydraraptor.blogspot.com]

Tha makes sence. How do you suggest I should configure Slic3r to make a taller first layer, in order to have the same finishing on all sides of the part?

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Cheers,
Franklin Dattein

Is that just the first layer?

Yes, just the first layer.

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Cheers,
Franklin Dattein

That looks like you have skirt/brim turned on then.

I do use skirt and no brim (3 skirt loops at 0mm of distance have proven to effective against warping).
However, I don't see how it is helping to cause a flat/melted bottom. Can you shed some light on this?

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Cheers,
Franklin Dattein

Hi Franklin,

the bottom layer 'represents' the surface structure of the bed - if it's plain/smooth, the bottom tracks will be plain/smooth too ...

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

It is normal to have a fairly smooth bottom. You won't ever get the same finish as the other sides because they aren't pressed against a smooth surface.

To make it gappy make the first layer higher by calibrating so that Z = 0 is higher. You might have problems with it sticking then as the contact area of squashed cylinders tends to zero as you squash them less.

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[www.hydraraptor.blogspot.com]

That is good and bad news. Good because it means my printer is finally fully calibrated. Bad because I wish I could print it with the same finishing.

I got a prusa kit from Makergear, the plastic parts are white ABS and they have no flat/smooth finishing. Any idea on how they achieve that?

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Cheers,
Franklin Dattein

... most common are some breakaway 'raft' layers first, on which the part is printed - then you'll get the 3D-structure of the topmost raft-layer ... but it could be a piece of work to remove all the bits of the raft.

It's something tricky, if you want easier removable bottom layers with gap-width betweeen the tracks and different temperatures for raft and object layers ...

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Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

you can also try to make the printing surface different with tape eg

you could sandblast your piece of glass ofcourse aswell

wow!? sandblast? that seems like it would bring in a host of other problems? possible that the parts would not stick as well, or that the glass bed would be very hard to clean since there would be a lot of 'pitted' area for the plastic to get into, which may be hard to get out?

Anyone done this? any experiences? could be cool! since u can sandblast one side only and leave the other smooth you could potentially have one glass bed that you can flip over for different finishes!

Just to close the case, the reason for tha surface finishing was because the nothend was too close of the heated bed.
I was measuring the distance with a business card, very tide, between the hotend and the heated bed.
Fixed the problem by adding an extra 0.2mm distance and now the business card slides without any effort.

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Cheers,
Franklin Dattein

Hi there, I've worked profesionally with 3D printers for about 3 years.

What you're talking about the flat bottom is completely normal when you print without a raised raft. Because you're printing with a thermoset that is a liquid that turns to a solid, it naturally takes and saves the physical imperfections/structure of the surface beneath it.

In order to prevent physical imperfections from what is known as the "interface layer", that is to say the first layer of plastic that touches your model that is not the model itself, you have choices;

This assumes you are using a raft that raises the object off the "imperfect platform" that is usually your print bed / tray / glass / etc.
1. Use a slicer program like replicatorG with a custom slicing profile to adjust the exact temperature of the interface layer. This allows the plastic that bonds with your model to be at a different point of crystallization so its' bond strength isn't as high, but still does what it needs to (supports.) This will allow for much easier removal of the model, and can even allow you to use the same material as a support structure (though I wouldn't recommend it, it is not as pretty.)

2. Build in a removable platform that connects to your model that is made to be tossed. This will establish your model layers and model material before your actual object is started, causing the interface layer imperfections to only be visible on your 'pedstal' if you will.

3. If you're having trouble with actual damage from the raft material being removed due to its' bond strength being too great and taking some bits of base model material with it, you're going to need to a soluble support structure. I would suggest pva (polyvinyl alcohol) which is water soluble. You can also get some ABS based solubles but you need to use hydroxide (lye) in a very high concentration.