... not so sure about persistent - more anal
Well when I re-fitted the labels i'd removed before grit blasting, I realised that one was missing - probably fell off years ago, but it left four irritating holes that annoyed me !
... so google research - what was it. Well some of these flails had a label there that was the original selling distributor, and others just bore the name of the flail 'Turner Turbomower 72HD in rather florid handwriting. Having now repaired the chiller on my laser engraver hopefully I could make something similar.
The eventual label was on 1 mm stainless sheet using the 'Dry Molybdenum Di-sulphide' process that I detailed in my 'Laser Marking Steel' thread. However it wasn't without it's problems. First try was on aluminium (like the originals) but it just rubbed off. Then I tried galvanised steel with the same result. I was beginning to doubt the process, and even dug out the original form tool I'd previously marked, and marked another face of it successfully. Hence moving to stainless steel.
Another issue I had was the scanning speed of the laser. It should go at a controlled speed while the laser fires, and faster when not firing. However with the program speed set to 3 mm / Sec it was actually doing 15 mm / sec firing and 3 mm /sec when not, the result being that that label took 6 1/2 hours to produce
Another issue was that the 1 mm stainless ended up dished from heat of the laser but I reasoned that as the corners were raised, they would pull down flat when riveted, and this proved to be the case.
... more investigation needed but at least those holes are now filled