Jump to content
Ultimaker Community of 3D Printing Experts

Terms are not clear to me

Recommended Posts


I have started working on a 3d Printer. I am not able to comprehend various parameters i-e what are they.

Firstly, what is meant by outer shell and inner shell?

What is the difference between infill speed and inner shell speed?

Does changing the density changes the air gap?

Share this post

Link to post
Share on other sites

It's best to ask Cura what the terms mean as it will never give you a false answer.  It will never lie to you.

To do this put your object into cura and look at it with "slice view".  Pick an inner layer with the slider on the bottom right.  You can use shift+up arrow to move one layer at a time.   The "shell" is the outer perimeters.  So the red line is the outer most shell, the green lines are more shell (if you have more than 2 passes) and the yellow lines are "fill".

Experiment with settings.

ALWAYS make sure shell is a multiple of nozzle diameter.

Changing density changes how much yellow infill there is on areas that are not "top/bottom".  Top/bottom areas are yellow but they are always 100% fill.  top/bottom might not be at the top of your print - it might be in the middle if you have for example a shelf.

Don't mess with infill speed - I strongly recommend you set this to 0.

I don't know what an "air gap" is.  Maybe the space between the yellow fill grid?

But change these cura settings and look what happens in slice view.

Edited by Guest

Share this post

Link to post
Share on other sites

Ok, let us assume you have a 0.4mm nozzle and that is the measurement in Cura, under the Basic tab; if you have not touched it, it will be because that is the Cura default.

Everything the printer prints/draws is a line, even curves as these are made from miniscule straight lines which you will never see. So when a line is printed its width is 0.4mm.

If we take a simple piece of geometry, a circular column, and look at the cross section, the outer part is a wall and the inner part is infill. The wall is made of a number of shells. In Cura there is a parameter under the basic tab called “Shell thickness”. This should be set to a multiple of your nozzle size, many people use 0.8mm most of the time; I suspect that is the Cura default.

With that setting the outside wall will comprise two shells, each 0.4mm wide. The outside circle is the outer shell and the inside circle next to it is the inner shell. If you set the shell width to 1.2mm you will have one outer shell and two inner shells. If the xolumn has been designes as solid, the the rest of the inside will be infill.

Another example: you are printing a model of a house with real walls that are 2.4mm thick. If you specify the shell thickness as width 0.4mm Cura will print one 0.4mm wide line (shell). If you have infill % set to 0 then the wall will have a gap in the middle measuring 1.6mm. If you change the shell thickness to 0.8mm then you will have two lines printed and the gap will be 0.8mm. If you set the shell thickness to 1.2mm you will have three lines printed and the wall will be solid with no gap.

Speeds – you can print the outer shell, the inner shell (could be multiples) and infill all at different speeds – but DON’T. Although I think the Cura default is to use different speeds as default (BAD). To change the default speeds you will need to go to the manual menu tabs and change the relevant parameters. But if you are nervous with that at the moment do not worry, just leave the defaults as they are.

When you are more confident, you can set the print speed on the Basic tab to what appropriate speed you want and then go to the Advanced tab and set the Infill, Top/Bottom, Outer Shell and Inner Shell speeds to zero – they will then all print at the print speed you set on the Basic tab. I think that will answer your question; I do not know what the Cura defaults are for the inner shell and infill speeds, they could be the same or different.

Using different speeds will increase the risk of surface imperfections (i.e. the outer shell) and really only gives you a distinct advantage if printing a very large model.

Air gaps – not quite sure what you are referring to but if you use 100% infill the infill will be solid. If you use 50% infill then theoretically there should be a 0.4mm gap between every line of infill.

Share this post

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Our picks

    • Ultimaker Cura | a new interface
      We're not only trying to always make Ultimaker Cura better with the usual new features and improvements we build, but we're also trying to make it more pleasant to operate. The interface was the focus for the upcoming release, from which we would already like to present you the first glance. 
        • Like
      • 130 replies
    • "Back To The Future" using Generative Design & Investment Casting
      Designing for light-weight parts is becoming more important, and I’m a firm believer in the need to produce lighter weight, less over-engineered parts for the future. This is for sustainability reasons because we need to be using less raw materials and, in things like transportation, it impacts the energy usage of the product during it’s service life.
        • Like
      • 12 replies

Important Information

Welcome to the Ultimaker Community of 3D printing experts. Visit the following links to read more about our Terms of Use or our Privacy Policy. Thank you!