Hey all, I’m at the 11th hour for a client and part one of my print job just finished.
It looks like I am going to have some serious sanding in my future. I can feel these lines when I run my finger over the surface. I am not pleased. I foresee hours of sanding a priming, sanding and priming… What happened??
There isn’t much I can do about it now, as my deadline in tomorrow morning. But I’d really like to know what’s going on.
Thanks!
Can you upload your .form file or pictures of your orientation? There could be a few things going on here and the .form file will help to identify whether it’s a matter of orientation and support structures or something going on with the printer itself.
How thin are the walls? Thin parts don’t hold up as well to the print process and they can flex during printing which creates misaligned layers.
Since I can see some thicker lines that are at regular intervals that makes me wonder if there’s something up with the build platform screw
Thanks Frew!
The print is 4.3 x 5.56 x 5.30 inches.
The .form file is a bit meaty (probably could have decimated the mesh, in retrospect), but here’s a link to a .zip of the file.
https://drive.google.com/file/d/0B2H4twRHI48kSno2VEE1UXhsbm8/view?usp=sharing
Thank you for your help!
Hi Zachary,
They walls are .125 inches (3.17mm) thick.
The print is 4.3 x 5.56 x 5.30 inches.
Thanks for your help!
I am torn whether to see if there is anything I can do to prevent this on the second half of the model, or to just go ahead.
Not only do I have a deadline of tomorrow morning (hello all nighter) it occurs to me that I might want to keep the surface quality of both prints similar to maintain consistency.
I am not TERRIBLY concerned about the surface, as this is supposed to look like a clay prototype of the car and I plan to add some fine rake lines via sanding during post anyway… Granted my sanding time has exponentiation, due to these lines.
For hollowed models like these, it’s important to have drain holes towards the bottom of the design to allow resin to escape. While printing, resin can get trapped in these cavities and create outwards pressure that causes these layer artifacts you’re seeing. Adding a drain hole towards the bottom back edge of the model should correct this for you.
I do have two holes, where the headlights would be, as well as one right below the front lip of the hood… Perhaps I misunderstand, but wouldn’t those suffice? I figured they would be the lowest point, and that the model would not close up until the very end…
Thanks again!
If you envision the model printing, the rear of the car is going to print first and create a cavity. When the print descends, resin is going to get trapped in that cavity and can create outwards pressure. To mitigate this, you want to place drain holes towards the lowest point of your model relative to the build platform. For this, that’s going to be the rear of the car near the bumper.
Ah-ha, I understand! It’s not that it’s not draining, it’s that when that cavity comes down, it creates a cupping against the resin, so to speak. Curses upon me! 
I did just notice the bottom was bowing out a bit.
Thank you for schooling me on this and for your fast response!
I will correct the venting on part two. I’m worried now that the two halves will not register properly, but that’s my bad. Wish me luck.
Thank you again, Frew.
I’ve printed quite a few sections of bodies like this and those bands normally show up on mine if the supports aren’t holding the part steady.
I’ve found that the best way to print these is completely vertical (I would print this one bumper away from the build platform). You’ll need a lot of supports on the inside of the body and I add a row of large 1mm supports about every inch or so to keep the part from rocking.
an other trick to smoothen the surface is to use a ip soaked cloth or tissue and wipe the model surface right after washing. Maybe you have to remove the support structure when the model is wet, what is al little bit messy.
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