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"Slacking layer" after changing vat

Posted: Tue Dec 09, 2014 11:28 am
by qnzhou
Dear all,

I was able to get some great prints last week until the PDMS became cloudy. However, after I switched to a new vat (I have 2 vats for non-stop printing), I am having trouble printing some models that used to print fine before. In particular, I have noticed some type of "slacking layer/residue" (see image below) floating around and interfering with my model. The same model used to print fine with the previous vat. Any one has a clue about what could have caused it? Thanks a lot!

Image

p.s. The new vat is has not been used before, so I assume the initial PDMS layer is good. I have done both built platform calibration and projector calibration multiple times.

"Slacking layer" after changing vat

Posted: Tue Dec 09, 2014 11:45 am
by behold3d
did you re-calibrate your build table and focus?

"Slacking layer" after changing vat

Posted: Tue Dec 09, 2014 12:34 pm
by qnzhou
Yes, I have calibrated build table and projector multiple times. Is there a way to check if build table is correctly calibrated? My understanding is that if the build table is not correctly calibrated the cured layer would just sit on PDMS instead of attaching to build table. This loose layer would be swept out by the swiper, and in the end you got an empty build table and a lot of floating layer/residue (and maybe a damaged PDMS).

But as shown in the image above, the first couple layers are good and they stick to the build table without problem. It is the intermediate layers that become slack. Could this also be due to incorrectly calibrated build table?

"Slacking layer" after changing vat

Posted: Tue Dec 09, 2014 12:42 pm
by Robert Howle
Post print data.

"Slacking layer" after changing vat

Posted: Tue Dec 09, 2014 12:52 pm
by qnzhou

Code: Select all

Software Version:  Version 1.7.3    Copyright 2014  B9Creations, LLC     www.b9creator.com
   
   Last Comm Port: COM3
   Display Index: 1
   Last Print Attempt Status: Completed
   Configuration: B9Creator v1.2.0, XY at 50 microns
   Job Name: C:/Users/B9Creator/Desktop/To Print/Dec_9_2014_B9/plate_test.b9j
   Job Data
   Name: plate_test
   XY Pixel Size: 30 µm
   Slice Thickness: 30 µm
   Total Layers: 344
   Material Volume: 0.46 ml
   
   Material Settings
     ID: B9R-1-Red, Description: General purpose, lost wax suitable.
     Calc Base: 1.548, Used Base: 1.548
     Calc Over: 0.077, Used Over: 0.077
     Calc Attach Layers: 2, Used Attach Layers: 2
     Calc ABase: 3.56, Used ABase: 3.56
     Calc AOver: 0.177, Used AOver: 0.177
   
   Cycle Settings
     Unsupported Pixel Multiplier: 0.8
     Shutter Open Speed : 70
     Shutter Close Speed : 60
     Pre Exposure Delay (Settle) : 2.5
     Post Exposure Delay (Kick) : 0.2
     Post Release Delay (Breathe) : 1.5
     Overlift Cutoff (mm) : 0.5
     Initial Overlift (mm) : 3
     Subsequent Overlift (mm) : 1
     Dip (mm) : 0
   
   Job Position
     X Offset: 0
     Y Offset: 0
     Mirrored: false
     Show Grid: true

"Slacking layer" after changing vat

Posted: Tue Dec 09, 2014 4:49 pm
by Robert Howle
The red is not meant for the thin slices like 30 z. You should be using cherry or 1:1 mix.

"Slacking layer" after changing vat

Posted: Wed Dec 10, 2014 12:17 am
by mikej
This is a support issue, the unsupported long horizontal layers are breaking when first formed.
You might be able to get away with those large gaps between supports if you increase the settle time and slow the shutter open and close speeds down further.

"Slacking layer" after changing vat

Posted: Wed Dec 10, 2014 1:26 am
by KNSCi
It also looks like configuration is for 50µm xy but the pixel size shows 30µm. You might try angling the pieces about 40 degrees to avoid these droopy parts. It will take longer to prints, but any flat surface like that you try to print that is parallel to the build platform is likely to be a support issue. It's a surprise to hear it has printed well in the past. If you're using a 1:1 mix, try using Mikej's new default Materials settings, they worked well for me on the first try.

"Slacking layer" after changing vat

Posted: Wed Dec 10, 2014 1:35 am
by qnzhou
@robert I have put in an order to cherry resin. With 1:1 mix, I should use the default setting for cherry, right?

@mike Do you have recommendation about what value should I set shutter speeds? The shutter speed felt difference after I swapped vat, but I have not measured it. Could it be possible that shutter speed depends on build platform calibration? I.e. if the build platform is pressing the PDMS harder than previously, the friction could slow down the shutter speed?

As always, thanks a lot for the input!

"Slacking layer" after changing vat

Posted: Wed Dec 10, 2014 1:39 am
by mikej
Shutter speed is set in the Print dialog and defaults to 70% for "Shutter Open Speed" and to 60% for "Shutter Close Speed". You could try setting both to 40%. You could also try setting the "Subsequent Overlift" to 0.5 mm. These changes can help delicate and poorly supported areas to form better, but your best bet is more supports.

"Slacking layer" after changing vat

Posted: Wed Dec 10, 2014 2:47 am
by Robert Howle
Go here and use Mike's test directions and test values.

http://www.b9c.com/support/?mingleforumaction=viewtopic&t=2265

"Slacking layer" after changing vat

Posted: Wed Dec 10, 2014 3:39 am
by qnzhou
I have done a brief test on support density:
Image

It seems 2mm support separation is the only case that has no "floating layers." The test is printed using the default setting shown in my early post. Is 2mm the typical support separation distance?

"Slacking layer" after changing vat

Posted: Wed Dec 10, 2014 3:46 am
by behold3d
I'm not sure there is a "typical"

"Slacking layer" after changing vat

Posted: Wed Dec 10, 2014 5:02 am
by qnzhou
It seems different vat does make a big difference:
Image

With my old vat, I am able to space support much wider without problem. Could the height of PDMS cause this difference?

"Slacking layer" after changing vat

Posted: Wed Dec 10, 2014 5:31 am
by Robert Howle
If your thickness has changed very much (glass thickness, PDMS thickness, vat bottom thickness) then u should recalibrate the projector along with the build table. Remember u are laying the grid pattern on top of the PDMS so the distance from the lens has changed. U should prob check zoom and focus if u want optimal prints.

Robert Howle

"Slacking layer" after changing vat

Posted: Wed Dec 10, 2014 5:46 am
by mikej
Were both factory coated metal/glass vats?

"Slacking layer" after changing vat

Posted: Wed Dec 10, 2014 5:53 am
by behold3d
regarding calibration, that is what I was saying earlier... Each time you switch vats you must recalibrate the focus and the table to account for discrepancies in pdms thicknesses.

"Slacking layer" after changing vat

Posted: Wed Dec 10, 2014 6:12 am
by qnzhou
@robert, @behold3d Yes, I did recalibrate each time I switch vat. However, as a newbie, I am not confident about my calibration skill. :( Is there an easy way to check the quality of the calibration?

@mike Yes, both are factory coated metal vat. The old one is a bit cloudy but still usable. The new vat has more transparent PDMS.

"Slacking layer" after changing vat

Posted: Wed Dec 10, 2014 6:17 am
by behold3d
Ok, well that is good. The process is outlined pretty well in the steps when you select calibration in the settings dialog. Some people use a magnifying glass to ensure good focus but I have not.

your problem does not make sense to me though because the supports would be drooping the other way since the table is inverted.

It seems that something else is at play

edited: try lowering msm by .1 or .2 Maybe the cloudiness of your old vat is helping your cure depth and surface tension may be adding material

"Slacking layer" after changing vat

Posted: Wed Dec 10, 2014 8:33 am
by qnzhou
@behold3d How does a magnifying glass help in calibration?

I have two hypothesis for explaining the difference:
1. The PDMS of the new vat is not as level as the old vat. This could introduce a suction force pulling down the print when sliding it off the PDMS coating. Since the "slacking layer" are the first layer printed of the horizontal bars, it is actually quite fragile, and the suction force would easily damage this layer, thus this layer is "slacking."

Here is my primitive levelness measurement:
Image

2. The PDMS of the new vat is slightly thinner than the PDMS of the old vat. Since at 30 micron XY and 30 micron Z the projector is already at its limit in focal length. So a thinner PDMS coating could move the printing plane outside of the possible focus range of the projector.