Why not a Forstner bit, @opps? They generate a flat bottom hole and the centre point should be less obtrusive than the centre point on a lip and spur twist bit. Axminster used to do decent quality affordable Forstners which are a lot better than those Chinese TCT abominations which you see everywhere
Forstner bits are guided by their rims in the main (the tiny point most of them have is really only there to allow you to start the bit without having it skate across the workpiece). This therefore limits the depth you can drill with them, typically only 10 to 20mm. Go much deeper than the depth of the sidewalls and they start to choke as well as run off line. In fact, below 10 or 12mm diameter I really wouldn't bother with them as the tendency of the smaller sizes to choke is really frustratingAs an aside, and not relevant in this case, isn't a forstner more likely to deviate if drilled deeper? I am thinking of cases when you use dowels.
I think that spade bits are not really designed for accurate working; they are really and truly quick and dirty carpentry tools, so it doesn't surprise me that a so-called 15mm spade might be producing 16mm holes (although it is as likely that the problem results from the centre point being off centre as it is from the the bit body being incorrectly ground). Might I ask what brand of spade bit you were using?The 15mm spade bits ended up cutting 16(?) holes. It may sound silly but it could make the difference of 0.5/1.0 mm at the cam/screw end
Forstner bits are guided by their rims in the main (the tiny point most of them have is really only there to allow you to start the bit without having it skate across the workpiece). This therefore limits the depth you can drill with them, typically only 10 to 20mm. Go much deeper than the depth of the sidewalls and they start to choke as well as run off line. In fact, below 10 or 12mm diameter I really wouldn't bother with them as the tendency of the smaller sizes to choke is really frustrating
I think that spade bits are not really designed for accurate working; they are really and truly quick and dirty carpentry tools, so it doesn't surprise me that a so-called 15mm spade might be producing 16mm holes (although it is as likely that the problem results from the centre point being off centre as it is from the the bit body being incorrectly ground). Might I ask what brand of spade bit you were using?
There is a flip side to this, though. Spade bits (other than those horrible Bosch jobbies with a screw nose) can be reground into all sorts of shapes for special purposes, such as drilling tapered holes, etc. It's as well to remember that they work by a scraping sction, so they do get hot in use, have difficulty coping with knotsand go blunt relatively easily (making them less suitable for drilling in hardwoods). That said they are easily resharpened with a fine file or oolstone slip
The screw nose means that they pull in very quickly. The problem with that is you can end up spelching the fibres around the outside of the hole, which on a coarse grained timber like oak that just creates problems for you. They might be OK when they are new (and sharp), but they aren't new forever. The more traditional spade bit with an (unthreaded) awl point has the advantage (to mind) of having a sharpenabke awl point and sharpenable nickers at the outside of the cutting edge (a spade bit with sharp nickers can be used to score the veneer, before you drill - not all spade bits have nickers). The downside to non screw poi nt bits is that they are harder work because you have to push all the time you are drillingWhy do you dislike the Bosch ones with the screw nose?