Negative extrusion on a non-planar surface

Hello!

First of all, I have to admit that I don’t have a lot of experience with Rhino just yet. I’ve been plugging along and learning with the use of a lot of youtube tutorials and the like. Fun!

I’ve run into a snag though, and after hours of searching I can’t find anywhere that addresses my problem exactly.

I’m making a medal for a friend of mine. The goal is to get it CNC’ed and presented to him as a birthday gift (the medal is based on this one: Clicky!

I’ve created the medal, and it’s a nice closed polysurface right now (I even merged all the faces after I finished my boolean union, look at me go), however, when trying to add the text I’m running into problems.

I had trouble getting the text to look the way I wanted it to, so I actually created it in Illustrator, where I then converted them to paths which I imported into Rhino as curves. The string of textcurves basically arc around the top of the medal.
I moved the curves above the model, and then used the Project command to project the curves onto the surface, as you can see here:

So far so good. Unfortunately, from there on I ran into problems. The surface they’ve been projected on is at an angle, and because it goes all the way around, it’s also slightly rounded. This makes it non planar. Projecting the curves onto the surface have also made them non-planar.

I’ve tried to extrude the text inwards, and then using a boolean difference to subtract the letter from the model. This actually sort of worked, except that I ended up with a hole at the bottom, looking straight into the insides of my model, instead of a nicely capped hole.

The same thing happens when I try to extrude it outwards, and when I try to cap it, I get the following error.


I want to extrude the text inwards, but the bottom of the inside (if that makes sense) should be at the same angle as the surface is on. If I extrude the letters straight down, one part is much deeper than the other.

Like so, which is what I DON’T want:

Is there any way to do it the way I want?

Full disclosure, I’m currently working on the Mac beta, but I didn’t think this issue was one that was particularly Mac related, which is why I posted it under this category. Unfortunately, this also means I don’t have access to plugins. However, if the solution to my problem lies with a plugin, please let me know anyway!

Hi Rick- if you offset that beveled surface inward, (OffsetSrf Solid=No) to the depth of the letters, you can then extrude the letters through this surfface and then BooleanDifference the offset from the lower ends of the extruded (solid) letters. Make sure the normal direction of the offset (Dir command) is upward. Then your extrusions will all have the correct bottom shape and can be used to BooleanDifference from the original bevel. Shout if you want an example file.

-Pascal

That works! Thanks a lot, that’s definitely not something that I would’ve been able to figure out.

Forever grateful!

I ran into one more snag, but I managed to fix that. I’m posting it here in hopes that it’ll one day help someone else out :smile:

The method described above works wonders on most letters, but it doesn’t work for letters that consist of two curves (R, O, anything with a ‘hole’ in the letter).

What I did, I extrude the letter as described above, and then apply the Boolean Difference from the created offset. As you’ll see, the hole in the letter will still be plugged. To solve this I apply a second Boolean Difference to the letter, subtracting the inside from the outside.
In order for this to work though, you have to make sure you flip the Normals for the inner extrusion to point outward (towards the outside extrusion).

After this step, you can continue with the Boolean Difference from the original bevel, for excellent results.

HI Rick, i am new to this forum and i saw your post and pascal reply. Unfortunately I met the same problem as you now… I am doing a ring and i need text to be extruded on the ring solid surface but the unable to cap. Hope you are able to do a screen shot of hows it is done? Thank you so much.

Hi pascal, i am new to this forum and i saw your reply on rick post two years ago. Unfortunately I met the same problem as you now… I am doing a ring and i need text to be extruded on the ring solid surface but the unable to cap. Hope you are able to do a screen shot of hows it is done? Thank you so much.

@LdotC As you can see from this one, if you want to make sure specific individuals see a particular post, just type @ and a popup list of names (I’m not sure what determines what’s on the list, but it includes those who have posted in the thread) will appear. Just select the ones you want. Then you don’t need to make multiple posts.

(Because you said you were new to the forum).