Bob,
The fit of the back morse part of the arbor – with or without a tang is less of an issue, as the morse taper is long and a good friction fit can be achieved in the female mating part in the spindle, provided both mating surfaces are clean without dirt or oil.
The issue is more to do with the front end – male Jacobs or B taper which fits into a drill chuck which has a female corresponding fit. The Jacobs or B taper are basically a stub, with a friction fit into the female back of the drill chuck.
The Jacobs/B taper is designed for use in an up/down – in/out movement – so okay for drilling as discussed earlier. Sideways load for light turning, perhaps fine in experienced hands – maybe – but still not recommended as short stubby tapers Jacobs/B were not designed for this purpose. General sideways load – including parting, or holding an end mill in such J/B drill chucks will put on a side force which could dislodge the drill chuck from its mating Jacobs or B taper, leaving the morse part still happily in place in the spindle, with the chuck flying off and creating certain damage.
In the current climate with more new inexperienced people entering the hobby, this is a wrong idea to promote. Some of the new people are unaware that the oil/contamination on arbors/tapers – male and female are to be cleaned off before introducing to each other, to ensure a friction fit. so, if one is to combine the idea of an uncleaned Jacobs/B taper chuck with unclean morse, and then into a headstock, one is asking for trouble.
Similarly, the chances of dislodging the chuck during sideways load are there when working on dirty/or hard materials, especially if such force hits a hard spot in the material it is working on.
If the drill chuck is one which has a threaded female back instead of Jacobs/B, then one could disagree with the above points. Still not recommended in general use on a headstock.
This is my opinion on the matter, based on customer experience over the years.
Ketan at ARC.
Edited By Ketan Swali on 11/07/2018 11:06:52