Stringy bottom

[scampa123]

I just printed this raspberrypi case in ABS. The bottom surface, the surface that was actually printed on the glass, came out stringy and I'm wondering if someone can explain why this happens and how I might fix it. In the picture you can see the stringiness...

I'm printing on glass with hairspray. The bed is heated to 110C and the extruder is 245C. Layer height is .15

In the past when I've printed in PLA the bottom surface has been smooth, shiny, like the glass....not stringy. So I'm assuming it is something about the ABS and how I'm printing it...

Thanks!!

[Jules]

Did you re-calibrate the Z-offset for the ABS as opposed to PLA, which is what you had been printing? (Prints at a different temperature, different heat expansion, different gap.)

That looks like the gap is too large, and the threads aren't sticking to the bed or each other. (Got some corner warping going on there too.)

[scampa123]

I may have messed up my Z the other day. I'll print another calibration square and reset...

What feeler gauge do you recommend? I've been using .06 and in the past a 0.1 but I thought I saw on one of your posts a .15 ....What's the recommended one, since I have all three?

Thanks!!

[Jules]

I may have messed up my Z the other day. I'll print another calibration square and reset...

What feeler gauge do you recommend? I've been using .06 and in the past a 0.1 but I thought I saw on one of your posts a .15 ....What's the recommended one, since I have all three?

Thanks!!

I use a 0.15 mm one, but you can go to 0.20 mm. (as long as you remember to do the Z-Offset calibration as well, in either case)

[jimc]

Yes definitely too far away from the bed. The gap is too big. When the 1st layer goes down the extrusions should no be round. Each extrusion should just touch the one beside it

[scampa123]

Update:

I reset my Z, re-calibrated and adjusted my S3D settings and had a much more successful print! I had some stings on the interior, but they were easily removed with an exact knife. The exterior looks much better (except for some white residue from the glass/hairspray I assume..maybe time to clean!!!)....

Here is the before/after shot (bottom set were just printed, top were the originals):

[Jules]

Much better! Almost there.....needs just a touch more adjustment on the Z-Offset. I can still see individual threads in the bottom of the print. It will be a smooth surface, just like you had on the PLA, when you have it set correctly. Bring the bed in a little closer - (maybe a negative -0.04 added to the current Z-Offset that you are using.)

[scampa123]

Much better! Almost there.....needs just a touch more adjustment on the Z-Offset. I can still see individual threads in the bottom of the print. It will be a smooth surface, just like you had on the PLA, when you have it set correctly. Bring the bed in a little closer - (maybe a negative -0.04 added to the current Z-Offset that you are using.)

In all the calibrating I've done over the last few days (more than I've done in 2-3yrs ownership!)...I now question the layer height... The calibration instructions recommended a layer height of 100%, but the standard S3D settings always had the first layer height at 90%....

So the question is, should I revert to 90% first layer height after calibration, or leave it at 100% always? Does this affect the threads at all?

Thanks!!

[Jules]

Much better! Almost there.....needs just a touch more adjustment on the Z-Offset. I can still see individual threads in the bottom of the print. It will be a smooth surface, just like you had on the PLA, when you have it set correctly. Bring the bed in a little closer - (maybe a negative -0.04 added to the current Z-Offset that you are using.)

In all the calibrating I've done over the last few days (more than I've done in 2-3yrs ownership!)...I now question the layer height... The calibration instructions recommended a layer height of 100%, but the standard S3D settings always had the first layer height at 90%....

So the question is, should I revert to 90% first layer height after calibration, or leave it at 100% always? Does this affect the threads at all?

Thanks!!

Some of us actually had this discussion before - what it boils down to is this......S3D gives you multiple ways to adjust for what is essentially an incorrect gap. One method is to use the Z-Offset to move the bed closer or farther away for the start of the first layer. (Essentially you are correcting the gap from the software.)

A different method is to try to fill an overlarge gap by using a first layer height of over 100%. (Or to try to not squeeze out too much filament by using a first layer height of only 90%, if your gap is initially too small.)

Either way works, but not both together. If you set the gap correctly using the Z-Offset, set your first layer height to 100% and leave it that way. The advantage to using that method, IMO, is that you no longer have to make continual adjustments to the multiplier for under and over extrusion, and the Z-Offset stays the same once you have it set for all of that kind of filament. (All ABS, not just that spool.)

The disadvantage is - you do have to determine what the Z-Offset is for each type of filament - it changes between ABS and PLA or PETG. But it usually doesn't take much time to print a few calibration squares and determine that offset. I save the Z-Offsets in the profiles for each type of filament and they are always correct and ready to use when I need them. (I just pull up the PLA profile and it's no further work for me. Win! )

Write-up on the process here, in case you haven't seen it yet - very easy really:

viewtopic.php?f=3&t=3124

But you can skip the Z-Offset adjustment and fiddle with the first layer height. It's going to be harder to get it to adhere sometimes, but it is a valid method if you prefer it, and other people have used it successfully.

[scampa123]

Thanks Jules!

I had used your write-up to set my Z, I just wasn't sure if there was a reason to reset the first layer height to anything but 100%...Based on your response it makes sense to leave it that way..

I will say that at the moment, my Z offset is -24...I know your write-up says anything over 10 you reset the physical Z but I used the .15 feeler gauge to set that already!!