Tree Support Mystery

[mike-truly 3]

 

Cura 3.2.0

 

I'm really liking the new tree support!  (Had one project where just changing to tree support dropped a lot of time off the print time).

 

But there some things I don't understand about it.  I took object above and put it vertically on the print bed and printed several test prints.  On each, the object printed fine and had little tree supports inside the tube near each set of holes (nothing... no tree supports outside the object).  I pulled out the tree supports when done and all was well.  Then when it came to the final print, I put 16 of these objects around the bed and went to print.  This time, rather than printing as before (with the tree supports inside the object), the objects were printed with elaborate tree supports outside the objects.

 

This added lots of time to the print (and material) and was unnecessary as proven by the test prints (as they came out perfect with just the interior tree supports).

 

Any idea why these supports were generated differently just by multiplying the number of objects desired?

 

Thanks!

 

Mike

 

[mike-truly 3]

Here's some images illustrating the problem better:

 

A single object sliced produces only internal tree support for the holes  (as desired).

 

 

Multiply the object so that there are 6 objects instead of one... and a massive tree structure now appears adding time to the print where this structure is not needed.

 

Any way to force NO external tree structure and only have the internal tree support (as in the single object)?

 

Thanks!

 

Mike

 

[mike-truly 3]

When adding the second object... the external tree structure appears.

 

 

(Would be nice to have the option to toggle the tree structure display in solid view prior to slicing the objects).

 

Thanks!

 

Mike

 

[AbeFM 35]

Perhaps something to make the support either per-object or per-print?

 

I noticed that I had to get my objects pretty far apart or change their relative orientation to get independent trees.

[mike-truly 3]

Thanks for the ideas!

 

I tried spacing out the objects but this made no difference... with 2 or more objects, the external trees are generated.

 

Just to be clear... I don't want trees that are external to the objects at all.  I only want the small, internal trees that are present when there is only 1 object on the bed.  If I have 2 or more objects on the bed... the external trees are generated.

 

I think the answer is to make my own supports with little trees inside the object (like what Cura tree support creates when there is only 1 object present).

 

Thanks again.

 

Mike

 

[AbeFM 35]

There are some options for like, infill and supports being relative to the individual object instead of the world. I don't know if the "tree" stuff is tied in there yet.

 

Could you perhaps try "ungrouping" the objects?

 

Huh, well, I did, and no luck. I get one big crazy tree when there's two objects, grouped or not.

 

I've often thought it would be nice to have some post-processing copy, that will stamp the same g-code all over the plate with just an x-y offset (which would do what you want, take one golden object and move it around. I guess that's what you're doing manually. In S3D you put in manual supports then stamp the part all over... but you get the same issue with not quite the same supports generated.

[AbeFM 35]

Question: Wouldn't normal supports work just fine for you? You're not supporting internal structure, just the holes in the outer wall? Just put a push-out piece in each hole. Less material, easier to print, etc?

[mike-truly 3]

Thanks very much for the ideas!

 

I ended up just building my own supports (which were similar to what the tree support was doing when there was just one object.  They had a root which was mounted on an inside wall below the holes and 2 branches which supported the top of each hole).  Worked great.

 

Thanks again.

 

Mike

[ghostkeeper 105]

I know why this could happen, but it still seems a bit glitchy to me.

 

Normally the branches try to connect the surface that needs supporting with the build plate as quickly as possible. And if the build plate is unreachable, it tries to connect the overhang area with the model itself. However when there are multiple branches at the same height, it also wants to merge these branches together, so as they are generated from top to bottom they bend inwards towards each other.

 

So in your print of a single column, each little window created a small branch that would go straight down. But when you have multiple of these they go towards each other and end up in the middle, trying to go straight down from there.

 

What I don't understand, and is probably a bug now, is why it didn't manage to evade the object and go down alongside the column when there was one object, but it did manage to evade the object when there were multiple.

[AbeFM 35]

An option for "tree supports per object" might be useful here.

 

From what you're saying, he could print one object upsidedown or 1 mm off the bed, and avoid the tree issues?