shrinkage compensation prusaslicer 2.91 on XL 5 tool.  

Shrinkage, and by extension shrinkage compensation can vary considerably between different part geometries so tests have to be made with the final version and even then print orientation makes a difference.

Parts with multiple starts on the print sheet may show little overall shrinkage whilst those with long unbroken runs of extrusion may be badly affected.

For example, consider a model table with a stringer half way up the legs - a little like a letter H with a top attached.

If printed standing upright (with masses of support) the legs will print in the correct place and rise vertically until the stringer which will also print OK but begin to shrink as it cools, as it shrinks it pulls the legs inwards slightly and as they continue to print in the calculated place they will overlap outwards slightly for a while then we get to the top which will print OK then contract as it cools.  The result is a marginally undersize top on legs that curve slightly down to the stringer; below that they are straight but may splay slightly so that the footprint is correct...

If printed upside down the top will begin to print as designed and if thin it may complete OK, if thick warping stresses will build as the higher layers which are not constrained by the print sheet begin to contract - it may curve and lift off the print sheet or even bend the sheet.  If it stays attached the legs will print vertically until the stringer which contracts as before.  This time, when turned upright, you finish with a table with vertical lower legs, a short curve at the stringer level and then slightly inwardly bowed legs rising to, perhaps, a slightly domed top.

The job of support is vertical, it usually doesn't matter if it pulls slightly sideways as the horizontal separation is enough; height is controlled by the printer's Z and any Z contraction pulls it away after it has done its job possibly easing the removal process post print.

Cheerio,

RE: shrinkage compensation prusaslicer 2.91 on XL 5 tool.

Thanks Diem. A lot of new things to think about.

What about my questions on using different filaments when they have different shrinkage? How do I print something with PETG  with shrinkage compensation and using PLA as support material. PS tells me it wont use shrinkage compensation because the shrinkage differs between the PETG and PLA. Do I have to fudge the shrinkage on the PLA to match the PETG?

RE: shrinkage compensation prusaslicer 2.91 on XL 5 tool.

Personally I wouldn't bother with shrinkage compensation. Like Diem said the amount of shrinkage is directly affected by part geometry, infill ambient temperature etc etc.  I've been down this road before. 

For example of your calibrate your shrinkage with say a 100mm cube, then your shrinkage compensation is likely only good at that size, if you then print a 200mm cube it'll likely be off 

Your best bet is to design your part in a way that your critical fits can work within the expected accuracy of 3d printing.  This includes providing proper clearance for fasteners etc.

If you have geometry that needs to be exactly a specific for or dimension the only precise way is to print the part, measure it, and then adjust your model accordingly. 

Over time you'll start to get a feel for how much certain things will shrink and you'll be able to compensate in your designs. 

This took me some getting used to as I'm an engineer and I'm used to precision machined parts that often have hole location and size accuracies of +/- .0001". So your can see why there was a learning curve when dealing with fdm printed parts. 

@brian-12 has the essence; I don't bother with shrinkage compensation in the slicer.  If it matters I will trial print, measure, and adjust (ideally a delta gain with a clarifying comment) in the original CAD.  It's rare for a prototype for anything non-trivial to be right first time so I expect to be iterating enough that this becomes just another part of the design flow.

Where it does begin to matter is when the final product is to use an expensive filament but most of the prototyping is done with cheap filaments with differing thermal characteristics.  Here it can help to look up the thermal expansion of both filaments, calculate the difference and apply it to the deltas; it doesn't always work but it's often enough.

Most of the CAD-type functions in the slicer are there as a backstop for those who do not have access to the original files but need to tweak a download to fit.

Cheerio,

w.

RE: shrinkage compensation prusaslicer 2.91 on XL 5 tool.

I'm pretty new to this. I'm working on the EnXLosure for my new XL. https://www.printables.com/model/742864-enxlosure-minimalist-and-printable-prusa-xl-enclos. It is recommened to do shrinkage compensation so custom cut PC panels will fit. Since I don't have the experience I'll follow the recomendation.

RE: shrinkage compensation prusaslicer 2.91 on XL 5 tool.

I have that enclosure on my XL, and yes, for the large parts it requires, figuring out the required shrinkage compensation was useful. Nonetheless, in the end still some parts did fit better than others.