Visible line where wall meets floor edge

[RKAprints 0]

Hi all,

 

We've been having this ongoing issue with printing scale models of our projects. On the print model, the floor slab always seems to extrude outward ever so slightly, creating this visible break where the slab ends and the wall begins (as noted by the arrows). We've tried toggling some of the settings to see if it would help, but no luck. Is this fixable, or does it just need a little sanding? Our project file is attached; please let us know what you think.

 

Thank you,

RPa

2025-01-24 (Print Settings).3mf

[GregValiant 1,454]

I sliced the project and read it into AutoCad.  I used this corner as a reference.

 

This is hard to see and you'll have to zoom in, but it's the Plan View of that corner in AutoCad.

 

The cyan line is the "initial layer" toolpath and shows your "Initial Layer Horizontal Expansion" of -0.86.  The rest of the outer wall lines are exactly colinear, one right on top of the other.  There are 158 layers shown in the view.

 

So the problem isn't in the Gcode as far as the toolpath goes.  It could be flow, it could be the printer, but the machine is being told to go to the correct points in space.

 

[gr5 2,295]

I think the problem is warping/shrinkage.  That slab has a lot of volume of filament all pulling inwards.  Then you get to the more airy-open area (aka rooms) and even no walls in places (aka windows & doors).

 

So one solution is to put lots of holes in the floor - big circles and then cover those with some paper maybe?  It's probably easier to do sanding as you suggested.  If this were a part for a motorcycle the "holes" idea would work really well but it's not - it's architectural so I don't see any easy solutions unfortunately.

 

A heated chamber would help a bit but you already have an S5 which is mostly covered and if you cover the top with anything other than the air manager you will get other problems (assuming this is PLA).

 

Another thing that would help is to use PLA but I assume you already are.  PLA hardens at a lower temp and so there is less shrinkage after it becomes solid.

 

So solutions:

holes in slab

use a low temp filament (PLA is the best)

heat the air in the chamber but no higher than the point where PLA goes solid (52C) and no higher than you damage the printer (so no more than 40C air temp).

 

OH THERE IS A SIMPLER SOLUTION.  You know exactly where the shrinkage occurs now.  So you can fudge it in the CAD model.  You move the slab outwards by the amount it pulls inwards.  This is a common practice.  Especially in injection molding.  The engineers model the part exactly the way they want it and then the company that creates the mold adjusts the cad model to compensate for all the shrinkage related issues - for example if a corner is 90 degrees, the CAD for the mold has it at something like 95 degrees - sounds crazy but those injection molding engineers know exactly what to do.

[RKAprints 0]

Thank you both for the suggestions! I'm eager to see if offsetting the slab just a hair, or if adding holes would fix the issue. If nothing works, we'll resort to sanding. I appreciate the help!

[gr5 2,295]

Sounds good. Don't just guess at the amount to move out.  Measure it on your existing model.  You can use a straight edge and a micrometer perhaps.