ran few tests to make sure that I do understand joint cuts. Bottom line is wood is forgiving and I will not be using any offsets for the joints, instead will be using a mallet to put the joints together.
second learning is that internal joints already have fillet due to cutter radius but external cuts are sharp (see the cut on the left in the picture) and putting a fillet on the external joint corner (check in this case there were four corners which needed attention) make a decent fit (right cut in the picture).
I was using .25 inch endmill and fillets are .125 radius. i put in this fillet manually, cam do have some limit on external corner fillet. i think i will look for the parameter to change the default in pre-processor or may leave it the way it is for now; i will be using a smaller end mill for final pass to reduce the fillet made by the cutter and may be default is good enough.
next project will be simpler with dado and rabbit (hope this is right terminology) cuts to make sure that i do understand any external edge fillet requirement there as well. stay tuned. In the middle of two med changes in the morphine pump (process will last for six months) and for RA/lupus. cnc hobby is doing intended job of getting me out of bed and keep my mind on positive thinking:-)
cheers