I have tried to follow the guides to countersink holes - but they end up like this - what am I doing wrong?
What guides? There are probably hundreds.
Since you didn’t tell us what you did, how would anyone know what you did wrong?
Here’s the procedure in a nutshell (and there are lots of variations):
Push/pull your through hole all the way through.
Select the circle at the top of the hole. Now hit Ctrl (to leave a copy) and use the Move tool to copy the circle straight down to the depth of the countersink.
Select the circle remaining at the top of the hole, and use the Scale tool to scale it uniformly about the center (Shift+Ctrl+Scale) to the diameter of the countersink.
-Gully
Or, try it this way instead.
- Draw the circle for the through hole and another centered on it for the limit of the countersink. Select the face for the through hole and its bounding edge. Use a double click with Select on the face.
- Get the Move tool and while holding Alt on the PC or Command on the Mac to invoke Autofold, move the selection down to the depth of the countersink.
- Push/Pull the hole the rest of the way through.
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sorry for my bad explanation - i’m trying to do as “Box” describes here: Countersinking an existing hole, or subdivide the hole ,any videos ..sorry still learning
“How you do it depends on the hole, it best to show us an image to get a more correct answer.
One simple way is to use the scale tool.
First use ctrl+move to copy an edge down the hole then ctrl+scale on the top edge to enlarge it around it’s own center.”
How big is the hole, very small I bet. Sketchup has problems forming faces when they are less than 1mm. If the radius of your hole is so small that the segments of the circle fall below that threshold the faces will fail to form.
Scale it up and try again.
The hole is 2 mm diameter and the material is also 2 mm. Do I need to scale up the whole project - create the countersink and scale down again?
Yes, even scaling by 10 should solve it.
I’m a Sketchup rookie … do I have to convert my model in to a group - scale up - explode group - create the countersink - create group - scale down?
You can make it a group but you don’t need to. If you do make it a group you don’t have to explode it, only open it for editing.
Either way, select the raw geometry or the group, hit s on the keyboard for scale, grab one corner and drag a bit then type in mid air 10 and hit enter.
Do the countersink.
Select all of it again, hit s, grab the same corner, drag a bit and type in mid air 0.1 and hit enter.
Perfect - thanx !!! 
So you have that method sorted out and it’s good to understand how to deal with small geometry. It’s also useful to understand the first method Gully described and the one I described. They don’t require scaling up.
Yes Dave your method will work without scaling, but the one Gully described is the one I used in the link. If you try that method on a 2mm radius hole it will fail.
Oops. OK. Well, mine works without scaling. 
And I was about to share this as well. My method can work on multiple holes at the same time.
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Ah so many ways, so little time.
The P/P Cardinal point method.
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True that. At least for metric screws with 90° countersink angles, the method you show is easier than scaling because the move distance is the same as the Push/Pull depth.
Nice work fellas, should the title be changed to Countersink problems and solutions?
We covered much of this and perhaps more not that long ago didn’t we?
Shep
Many many times and many many more to come.
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And I mean that in the nicest possible way. When the day comes that I don’t want to answer questions I will stop answering. If it ever seems that I am answering after that time please let me know!
Oh and as for a thread title change… how about, Countersunk.
If I may interjet here.
There is an extension called “Drill” by WudWorx.
You can select a number of different hole including countersunk.
In addition, you can select the depth, diameter and angle of your countersink.
All you have to do is layout where and the number of hole you want and click each one.
Or you can simply select multiple holes in sketchup.
Ther are a few more extensions offered by WudWorx. I have them all and find them invaluable.
Website: wudworx
I hope this works for you.