Objects Shrinking in Vase Mode

[ghostguy6 1]

Hello, I am trying to print a traffic wand for some flashlights using vase mode in Cura. When ever I try to print it  using vase mode the item shrinks  by approximately  9% . Taking the wall thickness into account the item should print  with an outside diameter of  41.8mm but in Vase mode in comes out at 38.2mm.  If I print the object in normal mode it prints at the correct dimension of 41.8mm.  The shrink factor compensations are all set at 100%. The scale factor on the model shows as 100% with the correct dimensions so I do not think I did anything to the scaling of the model either.

I am using Cura 5.3.0 and printing on an Ender 3 V2.

 

Does anyone have any ideas how to correct this? I know I could manually upsize the scaling until I get a good print but I would prefer to find out what is causing the problem.

[JohnnyApplesack 2]

I have been experiencing the same issue. I also have an ender 3 v2 and slice with Ultimaker Cura. I am printing a small rotary shaft, about 1/8" diameter. Printing normally presents no issues but the seam creates asymmetries causing mechanical vibration. Printing in vase mode prints perfectly, but then (as you said) shrinks the diameter down for me about 0.1mm. If you print base layers, you will notice the base layers are the proper dimension, but then it shrinks was soon as there is no interior to the printed wall. Moreover, in Cura it is properly dimensioned. I think this might have to do with the fact that we are printing cylinders. Perhaps the melted filament is being "pulled" in because it is only sitting on one previous layer and the print head is moving in a a circle.... but I am not really sure. 

I can't scale the print either because I print base layers as this tiny little rod is superglued to something else. Which is unfortunate because otherwise we could just scale the mesh in Cura in just x and y directions and solve our problem. 

 

Edit: I just did the same exact print (same exact settings) in Prusa slicer instead and had the same issue. I think you quite literally have to scale your entire model except for the first 0.4mm just for those first two layers so the rest of it prints properly. Quite frustrating if I say so 

Edited December 12, 2023 by JohnnyApplesack
Additional info provided to conversation

[GregValiant 1,251]

I don't see any downside to scaling the part up if it gives you a dimensionally acceptable print.  I'll assume that's what you want to end up with.

Some random thoughts...

Cooling of a spiralized model is a lot quicker since there is really no mass around to provide any thermal inertia.  

There is always some shrinkage and certain materials are worse than others.

Could your material have soaked up some moisture?

is the shrinkage all in the XY or is the part getting shorter as well?

Is the print staying on the bed?  If it is well adhered then that portion can't shrink in the XY as the sticking is keeping it where it was extruded.  You could compare a dimension taken near the bottom to a dimension taken up higher.

When designing molds the ballpark shrinkage number we used was 8% so your 9% is right about there for what would normally be expected.  Many production molds are water cooled so they suffer from the "quick cool" thing as well.

[JohnnyApplesack 2]

Scaling up actually works quite well. I bit the bullet, scaled x and y up to 110% (from 100%) and then in my model added a chamfer with variable lengths to both the top and bottom of my cylinder. Messed around with it a few times and got it coming out really clean. The tolerances are now good, Z tolerance never needed to be adjusted thankfully so its all fine and dandy. I think the issue has to do with the print being hollow and specifically with this geometry.

 

The shrinkage (in my experience) also varies with z height (I measured it with a caliper). So where one part of my print tapers, the tolerance gradually fixes itself the more layers it prints. I can provide photos as well if wanted but I think tapering the CAD model and then scaling up XY  in the slicer will work in almost all cases.