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First layer = Crap?

Posted: Tue May 15, 2018 3:06 pm
by BaseZero
Not sure what the issue is here, but figured I'd include some pics to get some input.

Raft goes on fine. First layer looks terrible, but the rest of the print is fine as you can see in the finished pic with exception of the text on the top which my client is aware was too small to reproduce with any accuracy. My noob opinion is that there is some delamination taking place as well as layers not connecting to the "holes". Also, it seems the circular holes aren't true "circles" on that first layer.

Nozzle is running at 215˚ and the bed is heated to 60˚. Running Raise3d PLA for filament.

Any input is appreciated. Thank you.

Re: First layer = Crap?

Posted: Wed May 16, 2018 1:09 pm
by maxamillo
What's your raft air gap set at?

Re: First layer = Crap?

Posted: Wed May 16, 2018 1:14 pm
by Jetguy
So let me get this again, you print a big flat bottom surface print that you care about finish on, and you chose raft and then complained the surface finish was bad?

Don't use raft for a part you want the face to be perfect on.

Since 2 topics were created for the same basic issue here (user needs to learn and understand first layer gap, proper leveling, bed surface prep and not printing with a raft) viewtopic.php?f=4&p=30730#p12750

Again, the 2 are directly related.
User is printing with a raft for reasons unknown but most likely because they are not taking the time to even remotely understand first layer gap and leveling, and then because they use raft on huge parts and with PLA, then they wonder why in some situations likely with smaller parts, since the layer prints rapidly after and heat is retained, the part sticks too well to the raft. So then- we could be looking at they start messing with raft settings leaving a bigger and bigger gap between the part and the object, and then wonder why the bottom of the part looks bad.

It's all related.

Re: First layer = Crap?

Posted: Wed May 16, 2018 8:39 pm
by Casale8
Jetguy wrote:Don't use raft for a part you want the face to be perfect on.

Jet Guy,

I specifically use raft to get better quality prints on the base because I need a guaranteed adhesion to the bed - and I use glue. I'm eight months new to 3D printing though... I get really nice quality prints with raft. I am curious of your thoughts. I also haven't had to re-level my bed.

Re: First layer = Crap?

Posted: Wed May 16, 2018 9:21 pm
by Jetguy
I'm betting, you can still tell the difference between a face printed on a raft and a face printed on buildtack directly or even glass or another hard surface.

By definition, you have to have a gap and so first layer is not squished flat and bonded side by side to adjacent threads when using a raft. Otherwise, you could never remove the raft.

The trick that makes a raft removeable= weak layer bond.
How do you make a weak layer bond? All the same reasons printing without a raft doesn't stick:
#1 you print with a nozzle height higher than the nozzle width, so the round hot noodle of filament is not squished into the previous surface.
#2 you wait a period of time, such that the previous layer has cooled as much as possible, so that when the actual print layer is being placed on the raft fails to melt and bond into the raft top surface because it's not squished and also, there is maximum temperature difference hot layer, vs fully cooled layer.

So where does this go wrong?
Well, on a small object (say something less than 50mm square surface) then the time between the last layer of raft and the first layer of print is a bit shorter, The layer of raft still is just freshly put down and still cooling. Immediately printing a smaller object on top- it sticks to the raft too well. So what does the user do? They follow instructions and increase the first layer gap of the print layer to raft layer in the settings. Fine, that might work for a small object, but now we make that drooling down first layer and adjacent thread bonding just absolutely horrible. You get the exact bad first layer of the print as shown in the photos. On big massive flat area objects, you can have that small gap, and most times- provided your extrusion temp is not too high, your bed temp is not too high, then sure, the time to print a layer is so long, we don't get that hot printing layer over a recently printed raft layer stick.

Re: First layer = Crap?

Posted: Wed May 16, 2018 9:39 pm
by Jetguy
Again, this is why- the side view of a nozzle extruding.
Nozzle diameter VS layer height, in a nutshell.
Nozzle height.jpg

And, the resulting squished side by side layers

Re: First layer = Crap?

Posted: Wed May 16, 2018 9:45 pm
by Jetguy
Good discussion and photos for non raft printing.

Showing different layer height and then first layer gap


Re: First layer = Crap?

Posted: Wed May 16, 2018 9:52 pm
by Jetguy
Again, all I'm trying to say is, I think comparing apples and oranges here.
Can you get a good 3D print using raft? Sure, why not?
Will you have the same bottom surface finish, the same layer bonding, on that bottom layer against the raft as a print that was printed on the actual build surface? No, sorry, in order to be able to remove the raft, some sort of compromise is required in the print settings to create a weak layer bond. That same thing is then what gives potential weakness and defects in the very first layer printed on top of the raft.

If you have an object as shown, that has a large flat face, and that face is somewhat key to the object- no, I would not recommend raft.

Re: First layer = Crap?

Posted: Thu May 17, 2018 4:35 pm
by Jetguy
And just for reference, a friend of mind pointed me at this photo today printed on a Carl Raffle Cone R1 using a Bondtech extruder.
This is what everyone should be striving to achieve.