There's obviously multiple methods of setting tool height, some either faster, easier or more accurate than others. I also use a combination of the OEM 4 way or a QCTP. There's quite a few fixed dimensions on a lathe that each owner ought to have written down. Even G. H. Thomas mentions there importance. I machined a couple of pieces of scrap bar stock once I had the measured dimensions from both my lathes flat surfaced cross slides to there head stocks C/L. But other areas can be used as well if your cross slide isn't already machined. Both those gauges are kept protected and safe from damage, I then bought a cheap off shore magnetic base and .001" reading dial indicator and added what's known as an Elephants Foot indicator tip. That enlarge flat tip makes finding the exact cutting tip height a whole lot easier on neutral or positive rake tools. It obviously couldn't be used with negative rake tools, but few at the hobby level would be using them. A heavy lump of steel bar stock and vertical rod to fit the snugs used with those magnetic indicator stands would do as well if you don't want to dedicate a magnetic base to this. I used those setting gauges I machined as my indicator zero point when switching between lathes or just as a quick recheck the indicator is in fact still zeroed. Most lathe tools work as well as there going to at that true spindle C/L. For whatever reason you happen to believe, boring bars may or may not in all conditions and materials. So I've found setting the tool point on them .003"- as much as .005" high will sometimes work better. Without a fairly accurate way to measure exactly where the actual tool point is, you can't easily duplicate where you want it. No doubt others will disagree with my method, but this has proven itself to work well for me, so I'm not about to change how I set my tool heights since its fairly quick, accurate enough, repeatable, and the forces involved are very light, it won't chip that delicate carbide tipped tooling.
Using a dead or live center in the tail stock as your tool point height position might only get you fairly close for the lathes in decent or highly used condition that most of us would be using. Even the best tool room lathes in the world will come with the tail stock C/L purposely set high by a few thou. A highly worn lathe will almost always show the tail stock quill pointing down by a little or a whole lot depending on the amount of wear it has. In general, and as long as its not excessive, that vertical misalignment has almost zero measurable effect on the part diameter when supported with the tail stock. Used to set your tool height it just might. And there's a great many off shore lathes where that tail stock quill is anything but correct or even close enough to be used to set that tool tip. I had one that was pointing up and over .009" high with just 2" of tail stock quill extension. In theory, the trick of using a machinist's scale and eyeballing its vertical alignment works well. Sometimes it does, I've also double checked it using that indicator and have seen a few thou variation at times. It could also crack or chip carbide if your not using a very light and gentle touch. And the larger the diameter of the shaft, chuck body or face plate rim your using that scale against, the less accurate it might be. And that's something that seems to be rarely even mentioned.
. FYI the lathe is a Myford 254, with an early Myford QCTP.
