Contour lines, from a mesh surface

Hi all,

First post, and first question. I’ve searched all over, but the closest I’ve come to what I need to do is this (which is the opposite of what I’d like to do).

I’d like to take a 3d surface mesh, and create from it contour lines. The reason is that I’ve made a blender shape and will machine it from wood. There is a lot of wood to machine away, so rather than start from a rectangular block I’d like to laminate some “contour slices” together to start from a rough approximation of the final shape. Say 15 or so 6mm thick slices.

This is what the machined wooden form will eventually be used to make - a strip built bowl (as a wedding present).

I’ve a attached a couple of screenshots of the shape so far in blender. It’s a subdivided plane, with subsurf added to smooth things out. THis one isn’t sacred though - if there’s a better way to approach this problem I can re-build a shape…

Thanks for any help you can give! I’m really excited about this project! :smiley:


NOT a free or open source solution, but depending on where you’re going to get the bowl machined they may already have it, especially if they’re running a ShopBot: Cut 3D

I’ve used it to slice up large Blender creations and cut them from thick sheets of pink foam.

For that number of slices, you can just cut the contour lines by hand with the knife tool. Add a vertical line subdivided at the spacing you want the contours:

Go to a side view, select the entire surface, and choose the Knife (K) - Exact. Ctl-click on on of your contour reference vertices to start the cut, and MMB-drag to constrain the cut to be horizontal.

Repeat for each contour line.

Best wishes,

You could use a wood texture projected only along the z axis (x and y are disabled in the texture panel). If you use a color ramp in the texture with two colors and constant interpolation you will get bands with sharp edges. Then you would place an orthogonal camera viewing along the z axis to render the contours. Adjusting the z scale of the texture will allow you to control the number of contour lines.

Thanks for all your help.
Matthew, your method is what i’d already been trying to do. I like it because I can export the resulting wireframe to a CAD program as DXF, then tidy it up and machine it.

I’m quite new to blender, and I’m struggling to get it to work.

I’ve drawn the subdivided line (should this be in the same object as the mesh, or separate? I’ve tried both).

I can’t get ctrl-click to constrain the first part of the cut to a vertex (not visibly anyway).
Also, I can’t find a way to constrain the cut to horizontal using the middle mouse button.
The good news is I CAN do an exact cut using the knife tool! :yes: I just need to constrain them somehow.

These problems are probably me, but if not, I’m using 2.49b if that makes any difference?

Thanks so much for your help!

OK, think I’m making progress,

The magnet on the toolbar must be activated

Hold down ctrl, and select a point near to the chosen vertex (single LMB click). Release Ctrl.
You can move the mouse, but next click the MMB (single click)
Move the mouse to where you need to go, then single LMB click again
Hit return to finish the knife cut, and hopefully see new vertices where you need them.

The tricky thing is there are no visual clues that the constraints are happening. No white circle on the ctrl snap (as you get when moving a vertex). No orthogonal line when you click MMB.

Still, it seems to work. More news soon… :slight_smile:

I suppose you can cut them layer by layer. But you can do the same by using Boolean. I just used sliced up plane as a cutter, extruded over the surface than used Union. It looks like hell, but if you erase all the vertexes on 4 corners most of mess gets erased all at once! Still some clean up required. Solid view mode helps here a lot.


Hi ridix,

Thanks for the alternative method, but I’m not sure I understand. Did you do all the cuts in one go?

Matthew’s method has worked - just some cleaning up to do to get the section contours I need into cad. Thanks…


I’m glad it worked for you in the end. To address some unanswered questions:

My example was in the same mesh, but it should work either way.

These problems are probably me, but if not, I’m using 2.49b if that makes any difference?

This method won’t work at all in 2.53, since snapping the knife to a vertex hasn’t been implemented there yet. For me it’s one of the two or three most important pieces of missing functionality in the current beta; together with nonproportional edge slide it is a persuasive reason to keep 2.49 on hand for precision mesh modelling.

I’m fairly sure you don’t need the magnet on, but I almost always have it on anyway.

Best wishes,

Thanks Matthew,

Just to close the thread - it’s not in the computer anymore! :smiley:

At the time I’m writing this thread has had 9 views, and 8 replies… One of the most helpful forums I’ve ever been involved in. Thanks everyone for your help!