Creating a sketch on a spherical face

[imtrying123]

Hi, I'm new to FreeCAD and CAD software in general. I'm trying to make a ball marker, a half sphere that goes around a golf ball with a stencil so one can use a sharpie to draw in a design. I've created the half sphere, but what is the best way to create the stencil part? I assume creating a sketch and then subtracting an extrusion of the sketch would work best, but the "create a sketch" function in the part design only likes planes :p
Thanks!
Also, just because of the sticky
OS: Windows
Word size: 32-bit
Version: 0.14.3700 (Git)
Branch: releases/FreeCAD-0-14
Hash: 32f5aae0a64333ec8d5d160dbc46e690510c8fe1
Python version: 2.6.2
Qt version: 4.5.2
Coin version: 3.1.0
SoQt version: 1.4.1
OCC version: 6.5.1

[bejant]

Greetings imtrying123, welcome to FreeCAD and to the forum.

what is the best way to create the stencil part? I assume creating a sketch and then subtracting an extrusion of the sketch would work best, but the "create a sketch" function in the part design only likes planes

Even though Sketcher requires a planar surface in order to create a Pad, you can still make a Pad that extends through the surface of the cover, switch to the Part WB, and Boolean difference it from the hemisphere to create your stencil void using the Part Boolean menu tool:

or by selecting the cover first, then click the Pad stencil, and clicking the Boolean Subtraction tool:
.

If what you have now is a solid half of a sphere with the stencil void removed, you can select the Part WB > Thickness Tool:

to hollow the solid hemisphere.

Edit: If I misunderstood or you need more help, be sure to post back.
Also, maybe these topics will be useful to you:
viewtopic.php?f=3&t=6892
viewtopic.php?f=24&t=6366

[imtrying123]

Thanks bejant! I'm basically a newborn baby in this world and I thought "imtrying" would fit me nicely. I'll try what you suggested tomorrow and post again

[bejant]

Thanks bejant!

You're welcome. Here's something for you to look at, although the work flow is a little different than what I had posted before because I don't think the Thickness Tool will hollow a hemisphere. It's just one solid hemisphere subtracted from another to make the shell, then I Padded a Sketch, Mirrored it, and subtracted that from the shell.

20150125a-Golf-Ball-Stencil.png (27.91 KiB) Viewed 4602 times

Looking at it made me think that a hemisphere may be just a little too big for a stencil; it may fit easier if the stencil shell was less than a hemisphere.

[NormandC]

I don't think the Thickness Tool will hollow a hemisphere.

I had to challenge that so I tried it, and it actually does. You need to select both halves of the planar side. Geometry check reports no error, with or without RunBOPCheck enabled.

I used the development version, but it works too in 0.14.3705 (both with OCC 6.7.1).

Now is it a recommended method? tanderson69's advice to me in another topic kind of started me questioning my modeling practices.

[bejant]

I did select both sides, and thought it had failed. I was suspicious but pressed for time so I'll try again and will post back Monday.

I've been following that other thread too...

[NormandC]

I've been following that other thread too...

I've used 3D parametric CAD for many years now, but I've learned most since hanging around the FreeCAD forum and the FreeCAD developers.

I was given a 32-hour training course on Solid Edge with the reseller when my previous employer purchased licenses of the software, and I took two 32-hour evening courses on SolidWorks at a local college (paid for with my own money). They never mentioned the stuff I've learned here, which is baffling considering how important it is to understand how the software works so you can control the result.

For example, I've been thinking about making a screencast to explain what is boundary representation (B-Rep), maybe compare it to CSG and polygonal modeling. But are people really interested in that? I get the feeling most people only want to know the bare minimum to use the tool. Well I could hardly blame them, considering that's my whole attitude with cars.

[cox]

For example, I've been thinking about making a screencast to explain what is boundary representation (B-Rep), maybe compare it to CSG and polygonal modeling. But are people really interested in that? I get the feeling most people only want to know the bare minimum to use the tool. Well I could hardly blame them, considering that's my whole attitude with cars.

I share your sentiment when it comes to cars, but I cant wait for your exelent screencast