Print waviness or wrinkling

Forum dedicated to discussion and technical support centered around the LittleRP affordable, open source 3D resin printer.
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Mattasmack
Posts: 25
Joined: Thu Dec 17, 2015 1:11 pm
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Re: Print waviness or wrinkling

Postby Mattasmack » Thu May 12, 2016 6:53 pm

Ah, that sounds different from what I'm experiencing. Shoot. I don't think I have the setup or print settings for my LittleRP right, so prints aren't quite as I'd like them to be, but at this point I don't know what needs adjusting. I'm using a flexvat from HLocke (projectsinterestsandetcetera.com), and while the FEP sheet has a couple of divots in it, they don't generally show up in the prints. The sheet is slightly old and fogged/scratched.

Here are a couple of photos of recent prints in B9 Emerald.

The first shows the waviness I was mainly referring to. The scale at left is in millimeters, so there are 4-5 waves per millimeter of height. (It's tough to say exactly, since the scale isn't exactly adjacent to the print or perfectly vertical.) Thing is, I'm printing at 40 um layers, so those aren't individual layers; each wave is five or six layers. If they weren't present the print would be much smoother, so I'd really like to eliminate them! I saw a similar features on prints from my FDM printer; there they were caused by a wobbly z axis and the pitch of the waves matched the pitch of the z-axis screw. Here, I don't think there's anything mechanical that has a pitch of 200-250 um. I'm using 40 um layers because that matches the distance travelled by a full step of the z-axis stepper motor.

The second photo shows two jumps, one about 2/3 of the way up the print and the other about 4/5 of the way up. They tend to occur when the area of the layers is growing quickly, but can happen randomly too.

If you have any suggestions or theories I'd love to hear them!

small waves.JPG

jumps.JPG

Mattasmack
Posts: 25
Joined: Thu Dec 17, 2015 1:11 pm
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Re: Print waviness or wrinkling

Postby Mattasmack » Thu May 26, 2016 8:51 pm

Ahh, phooey. Experimentation it is, then! I've been preoccupied for the past couple of weeks but am getting back to the printer now. Starting with some prints with my current settings and paying more attention to where and when the waviness shows up, then I'll get into mechanical checks and adjustments. Unfortunately I don't have a petri dish to try out, this flexvat is the only vat I have. The motion of the vertical guide did seem smooth to me, but I didn't check the rotation of the stepper.

(Full disclosure, this isn't quite a standard LittleRP. I started with the design docs on the website but printed my own FDM printed parts, and first attempted to make my own z axis from parts I had on-hand from an earlier printer. (I was working on the cheap!) The z axis didn't work out and piece by piece I ended up going back to the LittleRP design, and I think I'm now back to the standard design except for a RAMPS board for the controller. But it's possible I've done something else goofy without realizing it that is unique to this machine.)

Mattasmack
Posts: 25
Joined: Thu Dec 17, 2015 1:11 pm
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Re: Print waviness or wrinkling

Postby Mattasmack » Tue Jun 14, 2016 1:22 pm

I haven't followed up here because I had trouble getting anything printed at all for a while. (Turned out I just needed to clean and re-sand the build platform.)

It looks like my problem with the waviness was software rather than hardware. Specifically, Creation Workshop Host (now Photonic3D) running on a Raspberry Pi, which is what I had driving my printer.

Looking closely at the waviness I realized that it was due to some layers being thicker than others, not layers being displaced back and forth. The images of each layer (generated by Creation Workshop) were fine, so I recorded video of the printer in operation and used it to measure the exposure time of each layer. The print I did this for didn't have the consistent waviness like in the photo shown above, but it did have some funny layers. It turns out the exposure times were inconsistent -- most layers were fine, but every ~5-6 layers one might be slightly underexposed or overexposed by almost a second.

I moved the printer back to running directly from my PC using Creation Workshop, and the waviness went away. (Of course, now I'm back to prints being ruined by screen savers, programs opening windows on the projector's screen, someone else using the computer and switching to their account, etc. Which is why I wanted the printer running on a dedicated Raspberry Pi in the first place.)

I might try a Raspberry Pi 3 and see if it does better; the one I have now is a version 1, and it might be underpowered for running a Java application in X Windows that has specific timing needs.


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