Before I show you how - anyone know how to get patterns for curved joints?

[Jim Underwood]

I needed to cut out some parts for a curved hood cabinet, but I didn't know how to figured the cutout for that. So I asked around various places, but got very little information.
So before I show you how I did it, let me ask you all how you might figure part cutout in your CAD program for a hood that looks something like this:

Curved_Hood.jpg

[George Brown]

I might be missing the point, but the curve is easy to program. The joint is still a 45 degree angle. So cut the curve with a 45 degree v-bit. Unless I'm missing something, that is how I would start.

EDIT: Sorry, I see your point, never mind

[Jim Underwood]

You are correct of course. You can cut that corner with a 45 V-bit. And that's exactly what I did.

But yep, that's missing the point. Let me see if I can be more clear.

How do you create the pattern for the sides and front curved parts? What's the radius of that curve you'll cut with that 45 bit? It's not the same as the radius of the curve as viewed from the front or side ortho views. The distance is also greater...

So how does one generate the cad for these parts: The front curved part, and both of the curved sides?

[George Brown]

The curve has to lie on the plane defined by the 45 degree bevel, because that is where the two parts will touch. I have to think about how to program that in.

Maybe:

1. Draw the curve that you want it to look like on the XY plane.
2. Create a new plane, intersecting the XY plane at a 45 degree angle.
3. Create a projection of the curve onto the new plane.

How does that sound?

[Jim Underwood]

I think you've got it actually... And you could get the length of the back side by using chord and radius formulas.

Great feedback.

The way I did it was to use Sketchup to draw the shell, and a free plugin to "unfold" it, then import that pattern into Cabinet Vision, then edit the shape of the parts around that pattern. I then output those parts with kerfs and 45 V-bit cuts to our Komo. I can post pix later.

Well I gotta go, my commanding officer just told me to get ready for bed...

[Jim Underwood]

Ok. So we could draw in a 3D CAD program, the XY co-ordinates of the curve we wanted, draw a diagonal plane, then project points on that XY curve to the diagonal plane. Then we could draw arcs along those points to get the curve we wanted in the diagonal plane. For a couple of days I tried a similar thing in AlphaCAM with intersecting surfaces and "project to flat" that SHOULD have worked, but AlphaCAM gave inconsistent and highly inaccurate results. Suffice to say I gave up, and went with a freeware program - Sketchup - that did it a lot quicker, and more accurately. If I had figured out how to do what George suggested at the time I probably would have done it that way. But I'd never have tried it in Sketchup and found how easy it was...

Here's a video of the process using a free unfolding plug-in:

http://screencast.com/t/LzMP67ZnZGZm

The free version of Sketchup can be downloaded here:
http://www.sketchup.com/intl/en/download/gsu.html
To unfold the model you create, you'll need to download the unfolder plugin, and put the extracted file in the Sketchup plugin folder.
http://sketchuptips.blogspot.com/200...-unfoldrb.html

Once I had model unfolded, I imported the skp file directly into Cabinet Vision Solid. I then shaped my parts around the unfolded model as a pattern.
It took several days of messing with this, but I could do this in about 15 minutes now.

[Jim Underwood]

Here is what has been assembled so far. It's actually a little farther than this since the last side was put on and the thing patched with bondo ready to be sanded. Good job this is a painted set!
A_HoodRibsBottom.jpgB_HoodRibsTop.jpgC_HoodRibsRight.jpgD_CurvedSidesKerfed.jpgE_FrontKerfedandCorbels.jpgG_HoodBack.jpgH_HoodLeftRibsSkinnedFront.jpgI_HoodFrontSkinned.jpg

[Albert Nix]

Very nice work!!!

[Michael Kowalczyk]

Nice work Jim. Thanks for the video on unfolding. It is amazing on what some of these free apps can do these days.

[George Brown]

That is an AWESOME unfolder plugin, makes things too easy! Thanks for sharing the video.

Great job!

[Jim Underwood]

You are quite welcome. I'll post more pictures as the job progresses.

[Paul Grothouse]

This is one of those jobs that to do without 3D design is a a real challenge. In the past I have built jigs, bent the plywood to the shape and cut the shape on a sliding table saw or bandsaw.

If you have software like Solidworks, Inventor, Rhino or even MasterCam you can use the surface/sheetmetal functions to calculate this design. You build the shape, as a surface, thicken it as sheetmetal and flatten it out, off to the CNC. It's so easy, it's not even fair, I think of all the hours I wasted in my life doing jobs like this the old school way.

[Jim Underwood]

Well you would have thought AlphaCAM would have handled it easy peasy. But NOOoooo... It has the right features, but they are glitchy. That's what chaps me.