I've recently been looking at trying to reduce the friction in the ways of my CNC'd Sieg SX3, as the high force required to move the table with the gibs tightened is resulting in high backlash (~0.1mm / 0.004"), I ultimately intend on scraping the ways but for the time being I'm thinking about lapping them. Now I'm sure lots of people reading this are screaming "don't do it!", mostly down the understanding that the abrasive will become embedded in the ways, which is a fair point, but why don't we try and remove it? Most lapping compounds seem to be made of aluminium oxide, silicone carbide or diamond particles, the latter two seem pretty impervious but aluminium oxide is readily attacked by hydroflouric acid (nasty stuff) and phosphoric acid (not so nasty stuff), so why don't people lap with an aluminium oxide compound and clean it up with phosphoric acid?

Phosphoric acid is easy to get hold of and relatively safe, it's regularly used to remove oxide films too so shouldn't damage the base metal. I'm thinking of trying it out on some cast iron scraps, just to check there's no nasty chemical reactions that could damage it. Can anyone think why this might be a bad idea? It would seem to make sense for those who would rather lap their ways...