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Dimensional accuracy  

Dimensional accuracy


How can I choose if the dimensional accuracy of a part is conciderd to be importand on the outside or the inside of a part. 

And yes all the E-steps are set to give a nice cube of 20x20.

Yesterday I designed a bushing that needs to go over a tube of 20mm, I designed it to be 20.2mm so I'm sure it fits over it without to much play. After 5 or so attempts I needed to enlarge it to 20.5mm to fit the tube. 

When placing the part in the slicer it tells me that the part is 20.55x20.55 and the walls are 0.5mm thick. Line width is set to 0.4mm. This will result in a innerdiameter of 19.5mm.  to, smaal to fit the tube. When ussing the Arachne generator the outer dimensions stay the same but only the line width drops to 0.4 also resulting in inner diameter of 19.75mm. 

Any thaughts on how to and what perimeter to adjust to get in my case the inner accuracy?

Part is printed in ASA

This topic was modified 3 months ago by Benovitch
Posted : 09/12/2023 8:10 am
Veteran Member Moderator
RE: Dimensional accuracy

nominally circular holes are usually printed with a series of straight lines, which is likely to make the Bore smaller than the design size, 
Printing without an enclosure, can cause residual stress within the printed model which can lead to warping, or dimensional change
Did you do your e steps and calibration cube with the same material?
printing outer perimeter first can sometimes improve dimensional accuracy. 
For a smooth close fit, you may wish to consider drilling the hoe out or reaming it to size after printing.
printing with the lowest acceptable temperature will minimise internal stress and warping. 
If you are using the latest slicer, have you enabled 'Arc Fitting' this may also help with circles. 
regards Joan

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK

Posted : 09/12/2023 8:43 am
Topic starter answered:
RE: Dimensional accuracy


The printer is in a heated enclosure. E-steps were calibrated with the same material. 

For small holes no problem ro drill them out. This part has a hole of 20mm and one of 16mm to hold a bearing. 

I will try to use arc fitting and see what it gives.

Posted : 09/12/2023 9:02 am
Prominent Member
RE: Dimensional accuracy

You might have caused this when "calibrating" the steps. Except for the extruder it does not make any sense at all to clibrate steps (x,y or z) of a Prusa printer or any reasonably up to date 3d-printer.

If you have deviations in the dimentions of one of the famous calibration cubes they are allmost certainly due to not correctly calibrated extrusion rate (extrusion multiplier, extruder steps...). If you go ahead and correct for this by changing the steps of the respective axis you will get a printer that perfectly prints calibration cubes but will have deviations when printing anything else, because you used the wrong parameter to solve the dimension issue of the cube.

I'd do a factory reset, do the calibration routines from the knowledge base and stay away from the steps on every other axis other than the extruder.

If at first you don't succeed, skydiving is not for you.

Posted : 11/12/2023 3:37 pm