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Printing a tube 120 mm diameter - print is undersized  

Active Member
Printing a tube 120 mm diameter - print is undersized

Hi all

very happy with my mk3s+ after first 3 days of use and a relatively trouble free kit build. However, I have tried to print a tube of 120mm outside diameter, 3mm wall thickness.

unfortunately the print measures undersize at 119.15, I would have hoped for less than 0.5mm error

my first 3D printer, so are my expectations too high for this tolerance or are there some settings I should tweak?




Posted : 24/10/2021 6:49 pm
Active Member
Topic starter answered:
Cube 20mm

If it helps, I have printed the measurement cube. x measures 20mm, y measures 20.1mm and z measures 20.2mm


Posted : 24/10/2021 9:26 pm
Dan Rogers
Noble Member
You could slice your model, use file/save project as/ and upload that file here after zipping it

We could see if you did something to get unusual results if you uploaded your post-slice project from prusa slicer.  Dimensional accuracy is something that you may have to do some scaling if you are looking to get a different result.  Suggest you look at the dimensions in the slicer after slicing the model - it may be you didn't model what you think you modeled.  Hard to tell

Posted : 25/10/2021 6:46 am
Active Member
Topic starter answered:
My slicer model and actual measurements


Thanks Dan, see attached. Correction to initial post.

Bottom of model, diameter, as drawn, == 123.5mm

as measured == 122.8mm


At the top of model, as drawn == 121.5mm

As measured == 120.7mm

Posted : 25/10/2021 9:21 am
Noble Member
Print outside first

I seem to remember that the print outside first is intended to help with dimensional accuracy.

Of course you could play with scale factors.

Posted : 25/10/2021 10:05 am
Active Member
Topic starter answered:
Print outside first

where can I select the print outside first option?

Posted : 25/10/2021 10:20 am
Honorable Member
External perimeters first

You can enable 'external perimeters first'. You need to be in 'expert' mode and then you will find this towards the bottom of the print settings page. 


Posted : 25/10/2021 10:57 am
Famed Member

Remember you are printing hot but measuring cold.  There will be thermal contraction It varies with different filaments. Cylinders have all strain vectors pulling to the centre, there will be stress contraction.

The answer is to print a test part and calibrate.  FDM is very repeatable so you only need do so once per part/filament combination.


Posted : 25/10/2021 11:56 am
Active Member
Topic starter answered:

Thanks all, I have applied the advice from Diem, and decided to print a shorter / smaller prototype for sizing and adjusting from there. Although i haven't got the accuracy from the 3d CAD model to the print, I am reasonably happy with the initial prototype method!

Posted : 26/10/2021 8:08 pm
Mary Rose Solero
New Member

It is possible that your expectations are too high for the tolerance of your first 3D printer. However, there are several settings that can affect the accuracy of your prints, such as the nozzle size, the layer height, and the print speed. Additionally, factors such as the type of filament and the quality of the build surface can also affect the accuracy of your prints. You can try adjusting these settings and experimenting with different materials to see if it improves the accuracy of your prints. Also, you can check the calibration, bed leveling and the extrusion rate of your printer. it will help to get accurate prints. 





Posted : 27/01/2023 4:34 pm
SG Newb Rider
Eminent Member
RE: Printing a tube 120 mm diameter - print is undersized

If you're slicing using Cura, you can try the experimental mode called 'slicing tolerance', the slicer usually takes some liberty with the 3D model when slicing them into layers. Use the 'Inclusive' setting if your print is undersized. 

Here's a video that explains slicing tolerance, and why it's an issue sometimes


Posted : 01/02/2023 2:56 pm