Uneven/"mountainous" bottom of the prints around support connections


#1

Hi,

I just printed a test cube on a Form 3 and found the bottom of the print to be quite rough after removing the support. I’m not talking about the left overs from bearking/cutting off the support connections but more some sort of goose bumps like elevations which formed around the support connection.
My process was:

  • Printing on Form 3
  • Form Wash for 25 minutes and spraying isopropyl alcohol on more difficult to clean features with a hand spray bottle with a hard jet
  • Curing in Form Cure
  • Removing Support.

I normally remove support only after curing so that the part could not possibly warp on me during cure - not sure if that is an actual problem but I recall reading/hearing about it at some point so I adopted it.

I remember having a similar Problem once when I printed a flat object parallel to the build platform with support. I guess the problem back then was that the support pulled too hard on the first super thin layer which then deformed (since the part was not rotated to allow for a continuous build and relatively low pulling forces per area). In this case I had the object printed at an angle though to avoid this.
Except for that problem, the only other thing which comes to my mind is that there might have been uncured resin attached to the support left, which cured in the Form Cure cycle. Allthough I would be surprised because I cleaned it as good as I possibly could.
Anyone have experience with those kinds of issues?

[BTW: on the second picture you can see three holes. The biggest one at diameter 8, depth 5mm printed nicely, the middle one (diameter 4, depth 10mm) almost nicely, just clogged at the very end, the smallest one (diameter 2, depth 10mm) doesn’t go in for more than 3.5mm. I tried to lean them with a toothpick before curing but the clogged resin was already cured out of the printer. Possible fixes?]

https://drive.google.com/open?id=1-_MX0uk-KEnam2qKHZBmdg3BCVtrkEcx
https://drive.google.com/open?id=1X6qglgc7I2MMTndrFSbdPYpZon96RC1Q
https://drive.google.com/open?id=1-eIo_Wpk6HVVePVg24AghrOp2Jwgiy9y


#2

Hey @Tommy!

Thanks so much for taking the time to post. I’m sorry to hear about your troublesome print results, but I’m confident we can sort it out for you!

Based on what I’m seeing here, this should be a pretty quick fix! Feel free to correct me, but it appears this print was done with the “bottom” of the cube basically parallel to the build platform. When a flat side is printed with this orientation, you got exactly the sort of results we’re seeing here.

Apologies for the strained metaphor, but imagine I’ve got a bunch of supports in an orientation that look like table legs and the printer has printed those supports just fine and now you’ve finally gotten to the first layer of your actual object(where the surface of a table would be). Now imagine instead of a hard wooden surface, we drape a very thin wet towel on top of those table legs. Obviously the towel is going to bow down in the middle simple because gravity is pulling on it, but it would only sag where there aren’t supports.

That’s essentially what’s happened here. When you print a 25/50/100 micron thin layer of still wet resin, and the only thing holding it up is some pin-head sized support touchpoints, you’re bound to get some sagging between those areas.

Long story short, the easiest way to correct this issue is just to print your part at an angle. Typically we recommend printing at 45 degrees of lean in 2 axis, so for a cube, you basically want to print off of one corner. That way as it builds, the whole part supports itself the entire way up the object.

Hopefully my explanation helped a bit, but please don’t hesitate to ask if I can help in any other way! More reading on this subject specifically can be found here: https://support.formlabs.com/s/article/Model-Orientation?language=en_US


#3

Hi,

This is parasitic curing of residual resin effect - surface facing toward build plate can be strongly affected when the resin can’t flow out and stays for long in one place

Change object orientation to mitigate it,


#4

Since you’re printing a cube, start on one corner and have it angled at 45 degrees in the other directions so that its’ building up like a pyramid.


#5

thx for the detailed description, DKirch, however I actually did arrange it at an angle to avoid this known problem. I think the “parasitic curing” mentioned by luben111 could be the best explanation and might be fixed with zachary_brackins suggestion of orienting at an even steeper angle - which in turn also decreases the forces you mentioned so it should play out whell. I’ll try all of it, thx for the input!