Posted by JA on 20/06/2022 12:50:15:
I now use a simple edge finder without any lubrication. However I am aware that it is not as accurate as a small length of silver steel bar and fag paper, previously used. Since I do not smoke (anything) ordinary printer paper was used as a substitute. It was always 0.004" thick.
I wonder how accurate a simple electrical edge finder is. It must be affected by oil etc hindering the conduction of the current.
One trades accuracy for speed which is never wise.
JA
In another recent thread I posted this:
One of my books gives figures for some locating methods, unfortunately not all of them.
From worst to best:
Cone into hole (how I do my rotary table) – ±0.005"
Wiggler needle – ±0.003"
Laser pointer – ±0.002"
Electronic Edge Finder – ±0.0005"
Mechanical Edge Finder – ±0.0002"
Interesting how good a mechanical edge finder is, ten times more accurate than a laser pointer! But laser pointers are designed to find cross-hair markings or centre-punch holes, which an edge finder can't do, and a laser pointer is quicker and more accurate than a wiggler needle, which I also depend on.
Note how difficult location inaccuracies make it to work accurately in tenths!
Somewhere else I hypothesised fag paper is better than might be expected because it compensates for the operators slow reactions. The operator winds the cutter in until he notices it's hit the paper. As human reactions are surprisingly slow, any measure based on a visual cue will be late, ie when the surface is detected by your 0.004" printer paper, the cutter is closer to the metal than 0.004". I think how close depends on the thickness of the paper, how slowly the operator moves the cutter, and how quickly he reacts.
All in all, I think cigarette paper is a good way of getting the edge of a cutter very close to the work. I get good repeatability from Rizla Grey Paper which I believe is their thinnest. It's a little under 0.02mm ( 0.0008" ) thick. Ordinary kitchen Aluminium foil is thinner again, but I've never tried it.
Dave