Here's a quick and easy way to draw simple counter-sunk screw holes in 3D. I know that a lot of you out there might already know how to draw them or have your own techniques but this is really for anybody who's just beginning in 3D or if your way is just too long-winded.. To demonstrate, I'll use an example of the style I use in my job sometimes..
Things-to-note: 1: I'll be using millimetres in this example.. 2: I'll be explaining using the menus and not the toolbars, as everybody has there own toolbar setup. Please also note that from version to version, the menus might change or be in a different place, so if there are any differences, I apologise.. 3: I use circles (on a 'construction' layer) to use as marker points. This way you can easily snap-to-centre from a distance, without having to keeping zooming in and zooming out again..
COUNTER-SUNK SCREWHOLES IN 3D... 1: Firstly, on a new layer (called 'construction' or something) draw a circle who's centre is at the origin of where you want the top of the screwhole to be..
2: Then on the main layer (the one you want the screwhole to be on), draw two more circles; 1 - the diameter/radius of the shaft and 2 - the diameter/radius of the outer rim of the counter-sunk part..
3: Using the 'Extrude' command (the one found in the Draw >> Solids >> Extrude menu), extrude the 'shaft' circle downwards by however far you require. I use a 10mm deep hole. This will form the cylindrical shaft of the screwhole. You could use the proper 'Cylinder' object but it only if you find it quicker and easier..
4: Now it's time for the counter-sunk section. This is accomplished by 'Extruding' (see above) the outer circle that you drew. Extrude this circle down and at an angle, so it tapers inward. I use 4mm in the -Z direction and an angle of 45 degrees. This will look like a cone with the end chopped off.. Some of you might say that using a cone would be quicker but with a cone, you can't easily calculate the tapering angle without some head-scratching maths - also, the end may stick out past the bottom of the screw 'shaft', which will hamper your effort to 'union' the two solids later..
5: Now with both parts drawn, Modify >> Solids Editing >> Union and select the two new objects. This will form one entity..
6: Now that the object is drawn, use any technique you want to copy the screwhole to any other location(s) that you need..
7: Finally, 'Subtract' the screwhole from the main object (a sheet of steel, for example). Modify >> Solids Editing >> Subtract, then pick the main object to subtract from, then when prompted for the object(s) to subtract, select all the screwholes...and Hey Presto! A lovely sheet of metal (or whatever you drawn), with screwholes drilled out of it..
If you really wanted to, you could add the thread to the screwhole by drawing and using a helix coil...but that's a whole new story..