Hi K....for the record....a machinist of advanced years maybe.........experienced ....OK.........CNC literate.....hardly, but as machinery is machinery and parts of a machine move as good as the components they are made from, what you buy and expect to work is another story.......taking out a mortgage for a hobby is one way to go.
The point I wanted to get across for a person with perhaps little experience of actual machinery build,even though he has 15 years on a machine, is that there are machines that are not all that ideal for conversion and spindle tapers that are not ideal either.....no matter who fits one on a machine.
So....the round column type........2 out of 10 for an ideal machine.
3 Morse taper spindle.....1 out of 10 for an ideal tool retention system.
The main point is, if that's all you have and want to afford....well, a mill is a mill no matter what form it comes in.......that was my experience too, but for choice, it's as I stated.
BTW, back in the 80's Taiwan made mill drills with round columns and flooded the market with them.....theywere called Taiwanese terrors due to the amount of gunge in the bearings and badly fitted dovetails etc.....but they were sought after because they were dirt cheap.....eventually they got better as the importers sent their people to Taiwan to rev them up a bit in the quality control.
The last bad point for mill drills round or square column is that with the quill for the Z axis move you have very little travel and a difficult method for moving it..........making the head the Z axis move is another problem along the way. but that is par for the course with a manual mill retrofit.
It's a leap of gigantic proportions to consider fitting linear rails to the column for Z axis travel........only if it's a square column type, but that's a gigantic leap forward for a CNC retrofit.
As far as the throw away parts are concerned.........everything bar the basic castings is really throw away.......people retrofit for CNC not to go the other way so there is a throw away aspect to consider in the cost.
Ian.