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Diagnosing calibration print: Z waviness, bottom thick ripple, mirrored

Hi gang,

I’m on my fourth print so far. I created a 50mm x 50mm Cubert-style block to calibrate. Each step is 10mm. I’ve got some issues to work through. The Z waviness is my biggest concern.

Photos:
4 new photos by Robert Blaske

Issues:
1.) Waviness that runs perpendicular to the Z-axis on the side marked RIGHT. This worries me most because the Z-axis was banged around during shipping (3rd party, not from Kudo3D). I’m wondering if I need to replace the Z-axis which I could claim on the shipping insurance claim.

2.) Thick ripple-effect on the BOTTOM. I’m guessing some kind of light-leak.

3.) The print is mirrored. You can see from the photos that the text is reversed.

4.) The print is 49mm x 49.5mm x 49.8mm instead of 50mm cubed.

Thanks for the help!
-Robert B.

What resin are you using and what are your layer and exposure settings?

My initial thought is that the light bleed on the bottom is related to the XZ and YZ surface plate waviness you’re seeing. Added pigments would definitely reduce the amount of bleed you’re seeing at the bottom, and may help with the side.

What Z layer height are you printing at. Your XY and YZ surface planes looks extremely smooth, despite the ripples. That could mean that you have a focus issue (double-check the focus of the calibration grid) or because there is XY light bleed as well, related to pigmentation or overexposure.

The mirroring of the print is most likely because you didn’t set the “Y-axis flip” option in Creation Workshop.

I had waviness on most of my prints when using both of the soft VATs. I had to switch over to the hard VAT (the one without the squishy silicone layer beneath the sheet of teflon plastic on the inside bottom of the VAT) to get rid of this problem. It’s possible that the problem has to do with lowering the print bed down too low, perhaps causing it to squish into (and deforming) the teflon plastic as it prints.

Switching to the hard VAT brought its own problems, which all appear to be resolved for me now, but now none of my prints have any odd “waviness” on the sides, top, or bottom any longer.

I believe the checkbox James is mentioning in Creation Workshop is on the Config tab -> Configure Slicing Profile subtab -> Reflect Y checkbox. It’s at the center bottom of that screen. My prints have all been mirrored on the Y as well, but I haven’t checked that box to try it out yet. (None of my prints mattered for the Y orientation, so it was merely a curiosity for me.)

Thanks guys, great info. I also noticed that the print’s banding deforms most at the point where the next cube “step” begins.

@James: I’ll need to order some pigment. In the meantime, could it work to just reduce the exposure time? I’m in sharp focus at the bottom surface of the vat because that is where the grid image is visible.

@kevinrau: I’m using the older V1 vat with stiff silicone. I had to peel up the teflon film because it was kinked in the center during shipping. I’m printing on the bare silicone. I think you may be on to something about deforming the print because I was unclear from the instructions about how snug I should zero out the bed.

MakerJuice G+ Black
XY: 50µ
Z: 50µ

Kudo basic settings:
New photo by Robert Blaske

My settings are a lot more conservative than yours on exposure, lift, and up speed, but I’ve had so many issues with the item just sticking to the build plate that I backed everything way off. I’ve been progressively testing more and more aggressive settings, now that I’ve solved that issue.

I thought that printing directly off the bottom of a VAT (without any teflon at all) was very damaging to the VAT?

On the focus issue, my preference is to have the sharp focus be at the inside bottom of the VAT rather than the outside bottom. I want tight resolution exactly where the light will be solidifying the resin…

@jkao in your other posts you use TAP plastics pigment at 0.5% by volume.
http://www.tapplastics.com/product/fiberglass/resin_fillers_dyes/tap_premium_pigments/50

Is that your current recommendation?

@kevinrau You’re right, I hear it’s damaging. But the VAT is otherwise useless because the teflon film was kinked. I bought the materials to pour a new silicone layer and apply a teflon film when this one gives out.

You can try reducing your exposure time somewhat, but it’s a delicate balance between reducing light bleed without reducing part hardness below the threshold necessary to hold the part together during a print.

You can print on the hard silicone bare. Don’t try it on the soft silicone. Hard silicone wears quickly in the areas where resin cures against the vat floor. The photoinitiator & polymerization reaction also reacts a little with the surface of the silicone and causes the silicone to become more opaque to light and UV. It can be a bit tricky to determine the extent of the wear because cloudy to visible light and cloudy to UV/near-UV aren’t the same thing. Autodesk and MadeSolid did some testing of silicone vat wear that they wrote up at:


http://blog.madesolid.com/2014/03/3-things-wrong-vat/

The takeway is that the vat can appear cloudy to visible spectrum and still function fine, or may appear clear to visible spectrum yet become opaque to UV and near-UV as it wears.

This is why for other silicone vat based machines, manufacturers recommend printing in various different parts of the vat and to print at various different rotations to spread out the wear more evenly, rather than risk developing an unprintable spot.

Generally, speaking, I only print on bare silicone when I have huge solid flat parts like these:

http://www.kudo3d.com/forums/topic/epoxy-filled-injection-molds/

In doing so, I’ve found a few tricks:

  • Sweeping the resin every 100 layers or so to exposure the silicone layer to air dramatically reduces adhesion and improves vat life. That huge bottom part would start the print releasing with only 2-3mm of lift. Then as it progresses, the amount of lift necessary gradually increases, but if I pause the print and sweep the bottom, the release lift goes back down to 2-3mm. A print run with sweeping vs. w/o sweeping also results in dramatically less clouding at the end of a print run
  • Be careful of long exposures. The longer your exposure, the more chemical damage will occur on the silicone surface. On teflon film, the main concern about long exposures is light bleed, lift height, and lift speed. On silicone, long exposures will dramatically reduce the life of your vat, and combined with long prints, can cause the vat floor to bond to your part during the print
  • Be very careful of long prints or long e. The failure characteristics of the silicone surface is very different than for the teflon film surface. Generally speaking, when the lift forces max out at some point, but repeated cycles of high lift forces can lift the teflon off the silicone vat floor, creating bubbles or deforming the vat. Long prints with long cumulative exposures increase the chance of having some more catastrophic failure occur

The issue of cure time and overall print duration is not to be underestimated:

If you skip forward towards the middle and end of the video, you’ll see that the silicone bonded so strongly to the part, that it started to bend the part scary high before the silicone ripped out a chunk. I’m pretty lucky that this didn’t cause the to vat to break up and spill resin all over.

Also, 0.5% is a good starting point that won’t overpigment resins that already have pigments in them. Some people have gone even higher in order to achieve higher detail.

Thought I’d add that I Use a triple balance beam and input 1 to 2 percent pigments by weight vs volume. It’s easier IMO to add by weight if you have an accurate weighing mechanism and helps with having to add a bit more resin to an existing mixed solution.

@jkao thanks for all the info and references! Took a while to get through all of it this evening. Much appreciated.

@co3Dprints You reminded me, I have a microgram scale. I crack that out when the pigment arrives.

When the pigment arrives Friday, I’m going to take all of these tips and have another go at the calibration article.