Adhession verses accuracy on first layers...

[Chuck B]

Here's a newbie question for you: Up until now, my first couple of layers on my ABS parts have been wider than the rest of the wall layers, but I didn't mind that because initially I was having trouble getting good adhesion to the glass plate. I felt/assumed that the wider first layers probably helped compress the plastic and caused greater adhesion. I simply took a hand file or sand paper to the unintended "brim" (is that the right term?) and things worked great. (By the way, I am now using the glue stick with my ABS parts and having great success with adhesion).

But now, I am trying to produce a "lego" type of a part. Naturally printing lego blocks will only work if the stud and the openings are held close to fairly tight tolerances. I see many lego STLs out there so someone must be able to do this, but obviously my "squeezed" or compressed first layers are suddenly NOT going to allow me to accomplish the challenge of keeping thin walls to close tolerances.

If I print the lego block right side up, then the thin walls are too fat at the bottom and the stud will not fit in the cavity produced. If I print the lego block upside down, (which I have not tried yet) then I will have a stud that is too wide to fit into the wall cavity. (Naturally hand filing or sanding round studs or the inside cavity of a small block (to hold closer tolerances) is not going to end with satisfactory results.)

So... a couple of newbie questions:

1) How do I not give up adhesion, but still adjust my Rostack Max V2 (Using Slic3r) to fix my fat first layer problems? (using ABS)
2) If I use thicker paper when calibrating the end stops will that do it? Or will I lose adhesion?
3) How would you layout a lego block (upside down, or right-side up) since there are overhang challenges with both ways?

Can I have both; adhesion and thin wall accuracy?

Thanks ahead of time for your help!

[0110-m-p]

I'll let someone else respond to the adhesion vs. accuracy thing because honestly I have always operated my printer in a similar way to you...fatter first layer for better adhesion. But, the one thing I will add is that I wouldn't try to calibrate the end stops to get the nozzle slightly higher off the bed. Change the EEPROM settings for X,Y, and Z max length by however much you want to move the nozzle off the print bed. Reducing this number reduces the distance the printer will travel off the endstops, which is in turn raising the nozzle at Z0 off the build surface.

Also, just an FYI...most printer paper is ~0.003"-0.004" (0.076mm-0.102mm) and since you squish the paper a bit with the nozzle when setting up the nozzle height, it is likely a little lower than the paper's actual thickness.

[teoman]

There was a setting in mc for overextruding the first layer.

You can use cigarette rolling paper which is thinner.

[Chuck B]

So is my reasoning off? If the paper I am using during calibration is causing the first layer to be squeezed, I don't want "thinner" paper - that would just lower the nozzle closer to the plate, causing the bead of filament to widen out even more, right? I would think I would want to use thicker paper and keep the nozzle further away by a few thousands, wouldn't I? But even so, I will definitely look into the EEPROM settings for X,Y, and Z max length - seems that would be an easyier way to change the distance from the plate.

As to the lego situation? Any advice?

[Jimustanguitar]

http://support.3dverkstan.se/article/23 ... e#elephant

[Chuck B]

"Elephants foot" - never would have come up with that terminology on my own! lol But that's exactly what I'm talking about.

Perhaps the tiny chamfer idea on the bottom of the part will be helpful... I'll have to try that. Thanks!

[geneb]

I put a .25mm radius on the bottom edges of parts that will be in contact with the bed. It's worked pretty well so far.

g.

[Polygonhell]

I actually disagree with the elephants foot diagnosis from Ultimachine.
The predominant cause is running the bed too hot for the plastic, you can never entirely eliminate it, but you can get damn close by turning down the bed temperature.

[Jimustanguitar]

I actually disagree with the elephants foot diagnosis from Ultimachine.
The predominant cause is running the bed too hot for the plastic, you can never entirely eliminate it, but you can get damn close by turning down the bed temperature.

They're both true.

It *can* be caused by squishing your first layer too, though. I learned this when I printed my first gear bearing. All of the gears were stuck together because of that squished first layer, and recalibrating my Z0 height slightly fixed the problem instantly.

[Chuck B]

It never occurred to me that the bed temperature could cause the problem - but I suppose if the first layer or two stays soft (during the duration of the print) because the bed heat is too hot, then the following layers will be constantly pushing down on the bottom layers and creating elephant's foot.

Just out of curiosity, what do you set your bed temperature at when using ABS?

[McSlappy]

Have you tried using a few raft layers? This way you'll get the adhesion you want without the elephants foot. Normally I'm adverse to raft since it does require a cleanup but it might be worth a shot in this case.

[Polygonhell]

I usually run 80C on the bed for ABS with either hairspray or UHU glue sticks.

[geneb]

A brim might work as well. I too run 80C on the bed when printing ABS. I use Elmer's Disappearing Purple glue stick and I've never had an adhesion failure. I print ABS on Blue MAX which is an old v1 machine running the .80 firmware.

g.

[Chuck B]

Wow... I've been running ABS at 90 - so I will try lowering the temperature! I also use the Elmers disappearing purple glue stick - seems to work well. For my latest product prototypes, I have been using rafts with good results too.

Thanks guys for all your assistance.

[lordbinky]

It's a balancing act for sure. I've been able to do small parts in ABS with a bed temp as low as 60-70° when the hairspray/UHU (I alternate between them) was holding well.