I've never worked with these, but accumulated a few i anticipation of 
doing so. I liked the simplicity of them, and their reputation for 
flexibility in use. Over the past few days I've managed a bit of cave 
time, and am rehabbing, sharpening and right-sizing some as per Paul 
Hasluck's Handyman's Book. I found Dunbar of little help, and Lee 
doesn't seem to mention them.

I've made some progress, getting some of the larger bits cutting nice 
clean holes, and adjusting their sizes a little, but the holes they're 
producing aren't flat-bottomed. They have shallow domes in the center. 
This doesn't seem critical at the moment, as I can always pare or rout 
the bottoms if need be, but I was wondering if I should aim for 
flat-bottom holes?  I'm thinking that can be achieved by filing the 
'horizontal' cutter or router edge furthest from the center, to bring 
the edge nearer to square with the center of rotation. Most of them seem 
to droop or angle downwards.

Also I'm wondering about the bevel angle for the upper surface of the 
router. Does30 degrees sound good?

Finally, some of the horizontal cutters have a back bevel, sometimes 
quite large, and it seems to me this is just wrong, because it will 
reduce clearance there. Should I aim to eliminate it completely?

Any comments or advice on any of these points would be welcome. I'm 
hesitant to tackle the smaller bits until I understand these bits 
better, as there's more room for error on the big ones...

Don