Bob, thank you for sharing the link (and thank you to Robin for the content he is sharing) - I really enjoyed Robin's video. Now I have something else I didn't know I needed, that I now know I need!
I have fairly sturdy machines and I don't think I have a problem with the performance of the compound. Maybe I do and now I know and so I do? I certainly get it that all metal moves and when you get right down to it, nothing is really and truely solid. Every additional element in a mechanical system will add flexibility. The machine I am looking at is my 15" Enterprise - not a heavy pattern machine (D1-4 spindle and MT3 tailstock) and I am using a Phase II CXA (I have a center relieved washer underneath so the clamp force is out from the center bolt). By in large I am happy with the result. Sure, I have shifted the tool post on occasion - but usually I have done something extreme.
I find I don't use the compound very often (I leave it pulled back to just cover the nose, with the dial set on zero). I leave mine mostly at 45° for doing little bevels. I do use it for threading, set at 29°. I acknowledge that the 29° thing is not necessary - but it is no big deal so that is usually the approach I take for threading. If the compound was gone, I would not go to the trouble of installing it just for threading. Going to a solid block would be quite a bit stiffer.
Robin pointed out he is using a better than average machine and it has a really good compound (an HVLH - no kidding). In spite of that, Robin sees real value in a solid post. I'm a hobby guy - I'm going to believe him.
Robin presents that a big part of the reason for a solid tool post is to maintain the DRO tool offsets in 50+ tool holders!!
I don't have a DRO and only a dozen holders (so I do some switching of tools in the holders). Still, it seems a solid tool post would be a good deal.
I use a solid rear post for part off - it works great (blade inverted). Parting off from the front worked fine, but the rear post saves one holder and only takes a few extra seconds to set up (once set it is always dead on square and at center height).
Right now I commonly drill from the tool post (depending on the size of drill). For even larger drills, I'd rather be right off the cross slide. Likewise for good sized boring bars, I think a solid post would be an improvement.
Clearly Robin's solution is good (very good). I'm thinking a lesser effort would provide most of the benefit. I'm one of those guys that rarely actually makes anything that leaves the building. I'm usually fixing or adding to the machines or related tooling!
The lathe in question has a flat cross slide with 2 long t-slots and the round T-slot for the existing compound. I'm thinking of a sub-plate bolted into the existing T-slots, with several T-slots parallel to the axis of the lathe. Granted I'd lose a little swing over the cross slide, but I rarely have a job that big between centers (either large and hanging off the spindle, or long and thin supported at the tail stock). Then one could bolt on any number of different posts key'd into the T-slot: my existing rear post (which is presently mounted on its' own little block), a center mounted post for larger boring bars (sleeved as needed) or larger MT drills (with adapter sleeve), also a post similar to Robin's for the CXA locked against rotation but with a couple mounting positions (maybe a dowel pin pressed into the bottom of the post that could register into reamed holes in the lower post?).
Has anyone heard of solid posts (a selection of them) on the cross slide of a conventional lathe?