Creating recess to hold a sphere

[Rick Reese]

A fellow shopbotter has asked for my help in creating a 2-part solid box to house a sphere shaped puzzle. He wants the box split in the middle with the lid held in place by magnets. The sphere is 2.25" in diameter.

I need assistance in modeling the toolpaths in Aspire. I'm assuming it would be as simple as drawing a 2.25" diameter circle and use "Create shape from vector outlines" under the modeling tab? If so, what would the shape profile angle be? I'm also assuming that the depth of the recess would be half of the diameter of the sphere since the recess would have to be machined into both the bottom of the box as well as the lid.

Is there a easier method using a large ball nose cutter and a 2D toolpath?

Thanks for any assistance offered.

Rick

[coryatjohn]

You could probably use a fluting path. Try that. How about concentric circles, each going slightly deeper? Perhaps this method would require a bit of math but should work.

[steve_g]

There are several ways to approach this one… but since you said you’re modeling in Aspire, I think I’d create a 3D dish and cut it out using a 3D toolpath.
Or:
Import and resize a 3D dome from the clipart …
SG

[Brady Watson]

...I'm assuming it would be as simple as drawing a 2.25" diameter circle and use "Create shape from vector outlines" under the modeling tab?

Yes - it's that simple.


If so, what would the shape profile angle be?

-90 - drag the slider all the way down, but there's more than meets the eye. First, you need to create a model with higher resolution. Hold down shift and keep it down while doing a File-New and release when you have the screen that allows you to set the resolution. In the drop down change the resolution to 20x or 50x. This will minimize the amount of jaggedness where the top of the relief meets the zero plane. After you've done this, note how the negative dome is ghosted when you toggle the zero plane on and off...if you generate a toolpath you'll note that the top most rim of the bowl is very jagged if you don't have the zero plane as part of the components to be machined. Try it.


I'm also assuming that the depth of the recess would be half of the diameter of the sphere since the recess would have to be machined into both the bottom of the box as well as the lid.

Correct. When you choose -90 from the shape creator using a 2.25" dia circle as the vector, the height will be equal to the radius, or 1.125" in this case.


Is there a easier method using a large ball nose cutter and a 2D toolpath?
Yes there is, IF you can find a 2.25" core box bit you can nail it in one go by drilling it. However, this is best done on a drill press and not on the CNC. The larger the bit you use with an offset 3D finishing toolpath (preferred) the smaller the stepover needs to be for the bit. I would try a 1/4 or 3/8" dia ball @ 7% stepover and see how that works for you. There's nothing to be gained below 7%.

[Rick Reese]

Thanks to everyone for the helpful information. I'm going to try the 3D modeling approach first.