concentric part position

Brianne163 · April 20

I have 4 gears to print and wish to include a reinforcing sleeve in the centre.

I need to make sure that the sleeve is exactly central to each gear rather than judging by eye.

Is there a way to make sure both items are concentric before slicing?

Cura 5.7

Thanks

Brian

CCT_4XSmallGear_Tube_Shaft.3mf

Slashee_the_Cow · April 20

I had a whole bunch of stuff that I wrote up before I dug a bit into your project file and saw that each printed part consists of three model files.

This is, to use the technical term, bad. Cura is clearly slicing them as separate objects:

They should all be combined into one model file (easy, plenty of software that does it, and it guarantees it's in the right place).

But I will do the irresponsible thing and tell you how to do what you're trying to do. You're trying to avoid this, right, where objects aren't quite aligned (on the right)?

Open the Object List at the bottom left. For each part of the same set:

Click each part individually in the object list, so only that is selected:
Open the move tool and input some co-ordinates manually. In this case I'm putting it pretty close to the location it already was on the build plate:
Now repeat the process for the other two parts but make sure you put in the exact same co-ordinates for each one.
Now click the first part in the object list, hold CTRL and click on the other two:

(not a great screenshot because the object list isn't big enough to show them all - I just helped someone with that lol)
Right click one of the selected objects in the list and click Group Models:
Repeat for each other set of models you want to combine. Now if you move one part, the others move with it. If you need to change the settings for one of them, you need to right click the group in the object list and click Ungroup Models:

Then after you've made your changes, group them back together.
Next time, use one model instead of three.

Also I can't help but notice that the centre cylinder especially isn't round:

By my count that's about 32 sides. You can even see it in the preview, instead of being round you can clearly see where it changes angle each time:

The effect isn't as bad on the inside though. Or maybe this could be part of your gear design or something. I don't know.

A couple of other things:

If you're sticking a pre-existing item (like a metal rod) through these, you need to look at Experimental > Slicing Tolerance. This determines which way Cura will round since an object's size is generally a multiple of the line width and minimum line width.
Speaking of which, go set Walls > Minimum Wall Line Width to 0.24mm, that can generally be done on your average printer.
Anyway, when the model isn't the exact size of what Cura can print, it determines how it rounds.
1. Middle means it rounds to nearest combination of lines, but this can mean parts of your print will be bigger than the model.
2. Inclusive makes it always round up, which means the print will always be at least as big as your model, meaning any holes will be the same size or smaller than they are in your model.
3. Exclusive makes it always round down. This means your print will only be at most as big as your model, meaning any holes will be the same size or bigger as the one in your middle.
Go set Mesh Fixes > Maximum Resolution to 0.1mm. This setting is mostly to deal with older printers which can't keep up with a bunch of tiny movements so end up moving slower which resulted in overextrusion. Printers these days can do better. I usually set it to 0.1mm. It's hard to demonstrate the difference graphically, but hopefully I managed to pull it off:

The brightly coloured lines are from the preview with the maximum resolution set to 0.1mm. You can see they follow a rounder path than the others, although it's only going to be so round anyway given your edges aren't exactly round themselves (you can see the individual faces):

Brianne163 · April 20

Thanks so much for your guidance. I will give it a go tomorrow.

Regards

Brian

Brianne163 · April 20

The main reason I went this way was so that I could increase wall thickness on the sleeves without increasing wall thickness of the whole print.

If I redid the model as three separate pieces within the same model, would I then import the 3 models into Cura and then group them together.?

Slashee_the_Cow · April 20

There's a (reasonably) easy way you can increase the wall thickness on the sleeves with the whole piece being a single model.

Here I've combined all the parts into a single STL file:
Now we need a cylinder - you can whip one up in most programs in about five seconds or just use this one I whipped up in OpenSCAD in about five seconds: cylinder.stl
Now add the cylinder to the scene:
These things are the same colour so it's going to be impossible to see which is which... we're turning it into a modifier anyway, so with the cylinder selected open the Per Model Settings tool and click the third button at the top:
Don't worry about all the values there, we'll get to them later. But for now, our cylinder is transparent so we can actually tell the two apart:
Okay, it's a bit big. And in the wrong spot. We need to make sure it's in the same place as the gear, so click the gear and open the move tool:

It's the first object I added to the scene, so it's in the centre by default. So now we just move the cylinder to the same position, click it and in the move tool enter the coordinates 0, 0, 0.
It's still too big, so open the scale tool and turn off Uniform Scaling. Set the X and Y values (in the text box) of the diameter of the area you want to change and and lower the Z to make it a bit shorter (it's alright if it's a bit taller than your gear it doesn't matter):
Now if we look in the preview view the whole model has the same walls:

(and that transparent bit at the top is just the cylinder we're using as a modifier)
Select the cylinder, open Per Model Settings again:

All those 0 values showing in yellow means "this isn't being changed". But we want to increase the wall thickness! Set it to whatever you want. I want 2mm of walls!

Now if we look at the preview... that's one phat centre:
You need to group the gear and the cylinder modifier like I showed earlier. If you want multiple gears in one print, group them first, then multiply the group.