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Printing a tube 120 mm diameter - print is undersized  

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Prolle
(@prolle)
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?

 

thanks 

 

Posted : 24/10/2021 6:49 pm
Prolle
(@prolle)
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
(@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
Prolle
(@prolle)
Active Member
Topic starter answered:
My slicer model and actual measurements

dust_port_prusa_forums.3mf

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
towlerg
(@towlerg)
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
Prolle
(@prolle)
Active Member
Topic starter answered:
Print outside first

where can I select the print outside first option?

Posted : 25/10/2021 10:20 am
sylviatrilling
(@sylviatrilling)
Estimable 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
Diem
 Diem
(@diem)
Noble 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.

Cheerio,

Posted : 25/10/2021 11:56 am
Prolle
(@prolle)
Active Member
Topic starter answered:
Prototype

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
sonalford
(@sonalford)
New Member
RE: new

Yes, 'External perimeters first' can be enabled. You must be in 'expert' mode to discover this, which is located at the bottom of the print options page. super mario bros

This post was modified 1 month ago by sonalford
Posted : 29/10/2021 9:49 am
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