Missed something - Prusa calibration

Hi everyone.

I built my prusa last summer, and had *acceptable* prints in the last october.
It's a non-kit, budget-minded Prusa with a makergear hot end with 0.35mm nozzle for 1.75mm filament.
Controller is RAMPS with a rather old Sprinter firmware (will change as soon as I rescue the config file). Ebay-bought motors moderately overheating drives it (don't have much money for better replacements, for now it's working).

So basically, It's not one of the most top-notch Repraps around.

Anyway, my problem is that this happens, and I never figured out why during the initial calibration. Or any tune-up since now.


This is the first layer. The lines are not compacted together enough, and doesn't melt with the outline. Because of this, flat prints comes out pretty ugly, while this one, without much infill, came out ok!


What could be causing this? I've moved from Skeinforge to Slic3r with Pronterface with better results in general, but this keeps happening. I tried to play with a few parameters in Slic3r, without much success. With Skeinforge, playing with more parameters ended up in abominable plastic aberrations.

So, now, I'm at a loss. And It's frustrating because I'm *this* far from my initial print quality expectations.

Thanks to all for your help!

Dan


EDIT: Material is PLA with temp. of 185 celsius through the print. I don't have a heated printbed (waiting for it).

Edited 1 time(s). Last edit at 05/01/2012 06:03PM by N0M4dIC.

I print on blue tape as well and I find to get good adhesion you need the first layer a little lower so it gets squished. So try moving your Z endstop down a few micron.

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Yes, looks like the first layer is simply too high.

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[www.hydraraptor.blogspot.com]

Thirded. I explain to some of my buddies that have started RepRap is that if you look at the nozzle and plastic being extruded for the first layer and you see the extruded thread "drooping" down and away from the direction of travel, then you are too high for your first layer. I hope that is somewhat clear by what I mean. If not I can draw a picture I guess.

I hope this helps.

bdc
~Stay Calm Out There

I'm still attempting to get the perfect Z height, between scratching the tape and letting the plastic flow everywhere. The printer seem to have overheated since I used it all day, and now it stopped working correctly. I'll try again tomorrow. For now, what do you mean by "drooping"?

I guess a heated printbed would radically improve the quality of the prints and avoid "blobs" on the first layers...

BTW, I used the width of two sheets of printer paper to originally calibrate it.

Thanks to all for your help!

Dan

Make sure your calibrating the gap when the nozzle is at your print temperature.
I use a piece of blue tape folded over then flattened as the guide measure, it doesn't burn like paper does and its the right width for my nozzle (0.5mm).

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My Reprap blog

jds-reprap.blogspot.com

Looks like you are .05-.1mm too high off the print bed.

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www.Fablicator.com

The easiest way to check the Z calibration is to stop the print as soon as it has printed the skirt or the first outline, let the filament cool a little and then peel it off and measure its thickness. It should equal the layer height.

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[www.hydraraptor.blogspot.com]

I agree, if a print is not sticking for somereason or another or just doesnt look right thats the first thing I do is check the thickness of the skirt to make sure its the right thickness and consitant all the way around. But you either need some calipers or micrometers to check this.

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Ryan
Quality Engineer & Hobbyist
thingsandtrains.blogspot.com

You can't really operate a RepRap without a digital calliper or equivalent because you also need to measure the feedstock diameter and the die swell size to be able to print consistently.

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[www.hydraraptor.blogspot.com]

In general, should the zero point on the X axis be the bed itself, or the position at which the first layer is printed?

Also, fixing the Z end switch at just the right position is a little unreliable. Has anyone designed some kind of adjustment mechanism?

ebcdic, you mean Z right?
It should be the first layer height from the print bed.

There are a ton of different designs on thingiverse. Find one which suits you.

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My Reprap blog

jds-reprap.blogspot.com

I had a similar problem with my first prints. My print bed (acrylic) wasn't completely level. It was level corner to corner but there turned out to be to be a bulge in the center. It was slight but it was enough to cause problems. I then used a 3mm glass bed and re-leveled the bed, and the quality increased dramatically.

Wow, the subject became a little hot while I wasn't watching.
Yeah, I had leveling problems with my aluminium bed, at first. Now it's MDF so it's perfectly flat. However, I did not set the Z height at print temp. I will do that. Darn, I should have posted this months ago!

But, how do I know if the first layer height is correct? By printing and comparing with my slic3r setting?
I hope that my cheap caliper will be precise enough...

Thanks for this awesome help!

Dan

NOM4dIC
If you stop as, Nophead suggested, on the first layer and measure that thickness. it should match the thickness you selected in Slic3r or just under.
A cheap set should be fine. I have a $15 dial pair at home that I checked against a digital Mitutoyo $120pair that I use for work, they both give me the same measurement to 3 places in inches, but YMMV.

Edited 1 time(s). Last edit at 05/03/2012 11:15AM by gadman58.

You really don't need the calipers. Just adjust the Z offset until the first layer looks nice and solid.

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www.Fablicator.com

I'm not the one that likes to just take arbitrary measurements, but I ajusted the Z height with trial and error with a layer height parameter of my nozzle size. Damn, this need to be so precise! I just ran out of PLA printing this, and got it pretty nicely flat (with the tape texture) in relation to what I have achieved since now.



Of course, there is still work to do, but I guess I'm on the right track.

I'm getting my first ABS spool (Finally! I'm sick of orange...) this weekend from Voxel Factory. However, I will not receive my heated PCB until next week...

Is there anything particular I should expect concerning calibration from switching from PLA to ABS?

Dan

The temperatures are generally higher for ABS, the steps per mm will be slightly more because being softer it sinks into the hobbed bolt more and sees a lower effective diameter. I don't think is sticks well to blue tape.

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[www.hydraraptor.blogspot.com]

Of course, I won't use blue tape for ABS, but can I just print on the PCB bed, without a Kapton surface? From the pics I have seen, not much people seems to have these.

Anyway, thanks to everybody for the help. Now I'll be able to print more useful things and present better prototypes at demos.

Now I need to find a way to make sure the printer works when somebody else is in the room! The Murphy law is true.

Dan

I don't know if you can print directly on the PCB. I find it isn't flat enough so I put glass on top. That needs PET tape, Kapton or ABS juice to work. PET tap works best I find.

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[www.hydraraptor.blogspot.com]

I had thos same problem but since leveling my bed it is much better. Allthough I have another problem. I can't get the top
Layer to look nice. It kinda looks like a cake that collapsed. The inner filling lays lower than the outlines.

Also the first layer gets printer, then the next layer is about 3mm off.
Anyone know how to get rid of this?