Pop quiz, spot what the issue is... and the fix

[okeydokey]

I'm a bit confused so I need to read it again again - could you have got the same result by filling the previously drilled holes with a some dowel then just re drill with the flat bit to get the countersunk portion then drill the rest through with a standard drill bit?

 

[Ttrees]

Only possibly so if it were timber and in this particular case.
Say one wants a really clean hole, likely would be better getting a forstner bit rather than afancy spade.
and then you have a peck hole, which if not using an M10 bolt and an M6 or M8 would be a sloppy affair, and on thin material a bit weaker.
If I wasn't so close to the edge, I might have chosen a wider spade bit to make the job look more proportional.
(I was toying with the idea of making these bolts into cheese heads, but I don't think it's possible to make them round and not be too small looking)
The beauty of this method is that it is guided, so some cheap spade bits make sense to have around.
Ps I tried hammering the shank flat, but this stuff is rather tough compared to mild steel.

Tom

 

[Ttrees]

This might explain better about the sloppy hole from the pecking if using for narrower fixings.
Here's another spade bit I ground and filed down to what I think is possibly an M6 thread,
(if so, illustrates the point of the guided element of the tool, should one need be grinding one of these in somewhat of a hurry)

Looking back, I see that I have a little missing of the edge of one side, and yet it still worked very well.
Nice to have something which in my opinion is rather dependable, should you not drill too deep!
You get pretty fast at taking the bit out to check the fit of the bolt head,
and I've never had an any issue starting the cut again.

Works well in timber also, having done this with bolt on guitar neck conversion,
didn't have a lot of tools back then, and not even sure if I filed bevels onto the bottom,
I do recall some light burning, so am guessing I didn't have any bevels filed onto them.
They must play a good part in regards to timber, as every spade bit I've seen has them.