How te select the middle of an object in space


#1

This is certainly a really basic question, but to explain myself I am certainly going to make this more complex than I need too.

I wanted to 3D print a ‘nut’ with a thread which I have no skills to draw… But I found a design that had the thread I need which looked like this:

I cropped off the bottom, giving me the thread I need:

And my plan was to ‘wrap’ it in hexagonal cylinder to make the walls, like this:

And as you can see, I did it… Except tly the hex the thread isn’t exactly in the middle of the cylinder, because couldn’t work out how to ‘click’ the mid point… Instead I just had to pick a point which was near the centre… It i will do for this application, but I would like to learn how to do it accurately.

When I imported the model, the Blue axis passed through the centre… So I just need to click on that line at the height of the model, and I can’t work out how to do it… Like this:

The crude red arrow should show where I am trying to click… But I can’t find a way… How do I draw something from that very point?

I hope you understand what I am asking and look forwards to your thoughts

Jon


#2

If it’s already centered, you can use the line tool, start to draw it from 0,0,0 and then keep shift key to lock the movement just vertically.

You will have a point in the middle for grip.


#3

But it’s also easy to model it from 0.

  • Draw a circle;
  • Offset inside;
  • Change the number o segments for exterior circle;
  • Delete interior face;
  • Push pull;
  • Make it a group.


#4

I’m going to assume you have a circle you can use to centre your object. Then you can use simple geometry to find the focus, as below. This is useful if you have no other way of determining the focus.


#5

Try this extension CenterPoint all.


#6

Hi… Of course…a line… Why do I keep forgetting the obvious… That was exactly what I was looking for.

Not sure I follow your example of how to do this from 0… I can see how to create the outer hex and the inner circle… But the whole point of this was to use the ‘thread’ that I stole from the other design.

Jon


#7

@jweaver, do your own “thread” :wink:


#8

right click circle and in the context drop down there should be a “find centre” option, select it and it will put a mark in the centre. Make sure you have “guides” turned on for it to be visible. use that for aligning your hex.


#9

Thanks all for your help… There is a lot of info to digest… But what has been a huge help is the “Centre Point” extension. Thats REALLY helpful

The video of how to make a ‘thread’ is very interesting and something I am going to look at.

Can I ask one question… In one of the vidoes, i am sure I saw someone take an existing circle and convert it to a hex.

I know you can do this at the time you create the circle (by typing 6s), but is to possible to do this after the fact… This is something I have often wondered, as I generally make my circles 96s to make them more round for 3d printing and sometimes forget and I wondered if it was possible to do it after the fact.

Thanks again all… I really appreciate you taking the time

Jon


#10

if you select the circle and look in “entity info” you will see the amount of faces it has, if you type your new amount the circle will update. This will only work on an isolated circle, once it is connected to other geometry it wont do this.
BTW, the right context click “find center” is a native tool and shouldn’t need a plugin, but maybe the plugin has more options?


#11

Subsequent modeling operations often destroy Arc and Circle entities.
That means they no longer display a center inference and the Find Center command is useless.

There’s no faster, easy to use tool for such situations than this one:

CLF Arc Centerpoint Finder by @ChrisFullmer
Add a Construction Point to the “should-be” centerpoint of an exploded arc or circle.
https://extensions.sketchup.com/en/content/clf-arc-centerpoint-finder


#12

Precisely. That’s why I suggested using geometry. Any plugin or even the native inference point will only work with something SU recognizes as a circle.


#13

Fullmer’s elegant Arc Centerpoint Finder finds the center of exploded Arcs and Circles.
It eliminates drawing reference geometry to find center.


#14

Cool.


#15

Hi All… Sorry to drag this up again, but I have a similar question but its subtly different.

I have imported an STL, and have a circle which is now made up of faces…

Typically, I draw guidlines across the circle, from an intersection to the opposite side, looking for the point where the line is the longest… But in this case, there are 2 opposite points which are the same distance.

So I end up with this.

I know the centre is in the middle of the hexagox in the middle… And to be fair, this is accurate enough for what I want… But I am sure there is a better way.

I did try highlighting the circle in the hope that “find center” would help, but the option doesn’t appear when I click the right mouse.

Can anyone give me some pointers/tips?


#16

draw those lines like this?

or with exploded curves, select two edges and use Chris Fulmer’s “arc centerpoint finder”


#17

This solution was presented to you by @simoncbevans in a post above and is very simple to apply for what you want.


#18

Thats pretty much exactly the same method I used… But if you click on one side of the circle, how do you know which point on the other side is directly opposite? I normally look at the distance between the 2 points and find the longest… But in the circle I have, 2 points opposite are EXACTLY the same distance (down to 0.00000mm)… So I have to draw 2 lines… Which then leaves me with a hexagon in the middle.

I am keen to try the “arc centerpoint finder”. Will it work with a curve thats made of of little straight lines like this?


#19

**[quote=“mihai.s, post:17, topic:74323, full:true”]
This solution was presented to you by @simoncbevans in a post above and is very simple to apply for what you want.

[/quote]

That is perfect… Thanks to Simon for the tip, it seems I missed this.

Its takes me back to school with some basic geometry that I had forgotten all about… That is a really nice solution which will do exactly what I want.

One questions… What it is that you do right at the end of your animation? You go around the circle in segments… I guess its to prove that the circle matches perfectly from the new centerpoint… But it doesn’t look like the circle tool as there just appears to be a radius line shown…

Thanks all… Jon


#20

yes the chris fulmer tool will work. All sketchup circles are made of flat lines, they only appear rounder with a higher count of edges. THE CF plugin is suited to curves that are exploded or partial (arcs).