How to scale from 40 mm to 23 mm diameter properly?

I imported a round vector design (like a coin) from Adobe Illustrator into Rhino. In original .ai file the coin was 23 mm in diameter, but after the import it shows 40 mm (accordingly to grid). And the 3D printer it printed 40 mm as well…
Which is the correct way to downscale to 23 mm? There are letters inside the logo - so I need to downsize it altogether not just a diameter. This is my first 3D model, thanks in advance for your patience!

P.S. Or may be the way I imported it into Rhino is not correct?

When I import with this parameters - it imports it 23 mm in diameter (same size as in illustrator).
But still I will love to hear the professional opinion of the correct workflow. Thanks again!

if you at any moment have something that is 40 mm and u want it to be 23 mm,

I personally use the scale command.

For a cylinder I use the radius because then I can scale it the the center.

You would use either scale 2D (if you only want the radius to change) or scale if you want the height of the object also to change.

Select the center ot the object as first point, then a knot/mid point on the side, now you have the radius so that would be 20mm (of your 40 mm diameter) now you can type in the length you want that radius to be, so that would be 11.5 (of your 23 mm diamter). press enter and voila

You could also instead of selecting the seccond point, use a scaling factor, for example if u want your 40mm to go to 20mm? you could:
Scale: center point: 0.5 enter

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Peter, thanks for your explanation! Will try to figure out the SCALE command.
So far as I explored the subject - there must be some way to already import it 23 mm (the same size as the original .ai)
Meantime I found this tutorial (but it doesn’t refer to sizes):

Hi Eva,
In Rhino, the first stop should be the Help, it’s very good and complete.
You’ll learn a lot there about Import and the three available Scale commands.
Start a command and, without completing it, hit F1 on the keyboard.

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Thanks, Marc! Already using the Help option. The thing is - I haven’t found yet how to deal with the exact sizes yet. And the work I do is urgent for the 3D printing on Saturday. I just downloaded the Rhino couple of days ago and even being a quick learner, don’t believe to nail all Rhino till Saturday… So I need some HUMAN HELP:) And thanks again…
P.S. I already managed alone to import it 23 mm as I wanted. See the first screenshot above. But still wanna be on the safe side. Besides, may be this will help other beginners as well.

It seems the standard scaling is not in real sizes, I would not know why though.

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Scaling can be in real sizes. Set your model units to mm.
Now, use the Distance command to check the size of your object. Pick two points where you know what size the object should be. Does the distance read 23m? This is a better way of determining the size than looking at the grid.

If not, select all of the objects and start the Scale command.

At the Origin point prompt, snap to a point where you want to start (use the same points as you used on the Distance command.

At the Scale factor or reference point prompt, pick the second point you used for the Distance command.

At the Second reference point prompt, pick the second point you used for the distance command and type 23.
Check the Distance again.

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@margaret, thank you so much! Will practice it on my coin.

What I learned from this - besides all scaling stuff (still trying to nail it - I’m on Mac, and I don’t have the fancy “HTML style” code bar - or at least I can not find it) - the important thing - ODD numbers (like 23 mm) are not good to grid, because I can not snap it to the Zero point. Or there was smth like “snap to 0.5 mm” and I missed it…??

Yes, of course Eva, you can change all the grid’s properties. Go look in the menu for Tools->Options and look for Grid in the Document Properties.
I recommend that you don’t rely on the grid for modelling, you should familiarize yourself with numeric entry. And find where is your command prompt, it’s essential!

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Thanks @Marc! I do have a prompt command window and I do it, just it looks different from Rhino tutorials I see online (the ones done in PC). And I will explore the Rhino grid options.

As Marc says, don’t rely on the grid for accurate modeling. The grid is just a visual reference. It is much better to use numeric input and object snaps when you are modeling. Using grid snap unless you are just eyeballing distances, leaves you very prone to making little mistakes that will haunt you later.

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