Text on a Sphere

[wtbaker69]

I have an application where I draw letters and symbols in AutoCAD and machine them from a flat board approximately 1" thick. The letters have uniform face thickness and tapered sides. I get .the taper on the side (7 degrees) by using a tapered cutting tool. It's a simple application. I use vcarve software to cut the profiles simply to get the tapered cutter to move up in Z at the corners and to move up in Z to get the cutter tip to fit through areas where the whole cutter won't fit.

What I want to achieve to do some prototyping is to machine these letters from pre-cut sections that are like the tip top of a sphere. I need the toolpath to follow the contour of the pre-cut sphere section with respect to Z.

I've seen 3d tool-path generation from 3d models where a ball nose cutter passes back an forth over the part with tiny offsets and achieves a near smooth surface. I don't want to do that. Too much machine time and tool wear.

I want my cuters to follow the profile of the letters and shapes with respect to X and Y and follow the pre-cut sphere section with respect to Z.

Just like if you were to take a v-carve toolpath that was intended for a flat board and project it down onto the top of a basket ball.

Ideas?

I'm familiar with -- and have access to -- AutoCAD, BobCAD, ArtCAM.

[mcphill]

Not sure I follow. Are just the letters "raised" off the main flat surface, or are they just "outlined" with the V-bit and most everything is on the same plane?

[CNCRim]

Hmmmm, it's sound and look simple to engrave raise letter on the sphere, but it not that's easy. Whatever you try to do and try to save cycle time, I don't see it happening unless you have full 5 axis machine.

[ger21]

Aspire can do what you want (project the toolpath on a sphere), so I'd think that ArtCAM may be able to as well. But you may need to import a 3D sphere of the correct size.

[wtbaker69]

Well let me try to explain the original post better.

I use v carving software to generate toolpath to cut a letter out of a flat board. It would be similar to raising a letter, but in this case, I make through cuts and get a profile shape of a letter. I generally want a constant face width on a simple font letter.

Let's imagine a 3" tall "+" sign. Currently I would CNC route it from a 1" thick board. The tool paths would go around the profile and step down in Z until it cut through the board and created a "+".

The front face of the + would be in a flat plane. So would the back. The sides would have a 7 degree draft angle that they inherited from a 7 degree cutter.

Now what I want to do is cut this shape from a sphere like section. I want to prepare little blanks on a lathe that are like round disks with a raised spherical center. Similar to what you would have if you took a shallow bowl and turned it upside down.

I want the toolpath generated to follow that spherical contour and create a + sign with uniform face width and the 7 degree draft (from the cutter) but the front face would not be in a flat plane. The back face would be flat. The front face would be maybe 1-1/8 or 1-1/4 thick near the center of the + and only 1" thick near the four ends of the lines on the + sign.

[mcphill]

Well let me try to explain the original post better.

I think I follow you for the most part, but still need a little help.

When you state that the cutout has a 7 degree taper "from the tool", how big is your endmill? If it is a normal "V-Carve" bit, then it only has a cutting edge about 1/8" long - no way that makes a 7 degree taper on your whole cut out letter...

It sounds like you want to follow a perimeter path in X and Y, while plunging Z to keep up with the spherical surface, all being cut by a rather large diameter (0.5"?) V-ground endmill. Close?

You can do this with BobCAD. If you confirm that is what you are looking to do, I should be able to help you get there.

[wtbaker69]

Cutter diameter is 1/2".

The tools goes around the perimeter of the letter while "plunging" up and down in Z to follow the sphere. The cutter can't cut it all in one pass so the software calculates the offsets and moves the centerline away from the letter perimeter on each progressively deeper pass.