John
I'm surprised that a wiggler can be made with too little friction. Would have thought that to little would make it impossible to true up before starting. I "milk" mine very close to true first, auto-truing by banging off the workpiece on approach is inelegant bodgery.
Certainly all the issues I've seen are due to too much drag on inexpensive ones.
I find the key is to run around 150 – 200 rpm and watch for it to start to crawl sideways.
If you can get at both sides the 1/2 function on a DRO makes high accuracy much easier. I suspect most folk don't fully exploit it.
Magnetic workpieces are an issue with any uncalibrated revolving probe system using a steel probe. Back to dowel, and fag paper or 1 thou feeler stock. On both sides followed by the 1/2 function on the DRO in my case.
Clive