How often do you flatten your stone?

[MadMel]

I'd say if i had to, it would be before use.

[Vertigo]

When they need it.

This. I've found that "when they need it" can mean every few sessions, or multiple times during one session. Just comes down to how much work is being done. When I'm thinning a knife on my coarse stones, I clean and flatten them every five minutes or so; my Rika, on the other hand, hasn't been flattened in months.

[jason]

Not often - I haven't in a year and a half.

[Potato42]

I guess I'm kinda OCD about flattening. If I see swarf building up in a certain spot I'll usually give a quick rub down with the plate. I also happen to use a Shapton DGLP which is super flat, and that may make a difference.

[euphorbioid]

Always before, and sometimes during, every sharpening session. I make sure the swarf is off the stone and the color is uniform across each stone. This way I know the stones are flat. For those who aren't this anal, how do you know your stones are flat? Especially when thinning and flattening a bevel, flat stones are absolutely needed, IMHO. The knives themselves are rarely perfectly flat so a level stone will give me a shot at a flat bevel.

Jan

[Lefty]

I work my stones in sections, and level them out this way.
It really depends on your sharpening type, whether or not a perfectly flat stone is essential, or not.

[aaronsgibson]

For me it depends. On my coarser stones after one or two knives depending on how long I stay on them. 6k and up not so much maybe after five or so uses. I try to use the whole stone so I really minimize the use of having to flatten it. As for my natural, I've never had to flatten it and odds are I probably won't. But stranger things have happened.

[Miles]

I flatten as often as I need to. I did seven knives a couple nights ago. I was flattening usually after each knife or two, and in the case of a couple of unusually neglected knives I was doing for a coworker, even DURING sharpening.