Flattening the sole of a cast steel hand plane?

[John C Cox]

Please do the wobble test that Stephen mentions and check it with a flat 0.002" feeler gage on a surface plate (or a clean fresh sheet of notebook paper) before you ever lap it.... I just checked a brand new Stanley block plane on my surface plate - it's better than 0.002" everywhere I could check... There is no need to lap it - and you are likely to cause more problems than you will solve.... (The iron is a different story - but that's not what this thread is about. )

It is useful to lightly "stone" the bottom of a plane with a good flat fine sharpening stone in a figure 8 pattern to knock down burrs that arise before they track up your work...

Be careful about sanding before checking. I have run into quite a few issues with PSA backed sandpaper where it rides up proud a bit on the edges... And can leave you a bit convex... You are better off using wider sheets glued down - and stay away from the edges... Check your progress often against a ground straight edge or surface plate with feeler gages.... Just because an area is not ground by sandpaper doesn't mean it's not flat.. And just because an area is ground by sandpaper doesn't mean it is....