Cabinetman
A strange assumption to make from my accent.
I'm on the shamrock shore as it happens.
Amongst many other things, I have failed to lap four planes I can remember that ended up in a not so flat state afterwards.
Two of the first were shoddy adjustable mouth planes, when the shoe was adjusted it would lift the plane off the work.
This should have taught me the lesson I know now, which I describe in detail about keeping the edges of the plane from getting dubbed leading to a convex profile, and movable mouths need to be on the same plane as the sole.
Wait I'm mistaken, I had an old welded Record no.5 plane that was really thin, before I made it worse and the ends ended up being about as thick as a soggy wafer.
These were when I used to do the same thing demonstrated by nearly everyone...
having a super clean abrasive roll clamped down taught, on a long lap that wouldn't deflect.
I can remember some more things also if one wants to know.
That no.8 plane I done the same thing to aswell!
I ended up scraping that one which was really vicious.
I have another no.5 scraped a bit better at the folks, it came in the same state as Dave's Bedrock.
What about some more numpty mistakes?
Incorrectly lapped a grinder tool rest plate and it's still there, I presume it might help in this case with stiction.
That's only a bit o steel though.
What about making and lapping a keyway?
whilst doing it as carefully as you can, tapping firmly into the pulley and the motor shaft,
and exactly half way, it blowing out a section of the aluminium pulley where the grub screw was?
This was when I was just completely under the illusion by copying all the woodworking pros.
Is that enough instances of me being a numpty to take flatness into consideration?
I ain't saying that all planes should be lapped,
I'm just saying the general consensus on t'internet advocates the wrong way to do it.
Most folks who go as far as Dave cleaning the plane, and dressing it up,
or just stumble on one with a good rust patina, its safe to say they
probably would want to lap the plane, whilst putting full trust in the master of the craft.
Woodworking that is!
You'll get away with it on a no.4, but when you've got anything longer and out of flat, and the plane is definatly not behaving nicely in use as other planes one has..
then the principal of lapping must be adhered to, for the sake of the tool.
Might not be a good idea to do atall, if the casting is thin, there could be a pocket that you might "discover" and have to look at it!
Hope ye all had a good chuckle at my expense.
All the best
Tom