... sorry Rod, I guess from the points he was making, I was figuring Mark would understand ... but to be clearer, since this is a general thread about these machines and not just about answering Mark's questions :tinhat: ...
Although people say 3 or 4 lts per kilogram, and that's fine for "standard" 4-5 kg grain bills, in practice there's space at the bottom of the machine under the bottom of the grain basket which you need to consider separately for "extreme" grain bills (whether small or large)
... the instructions for the Grainfather say to use "3.5 + 2.7xkg" in lts for mashing, that's a 2.7 lts/kg mash thickness and 3.5 lts to fill the bottom of the machine ... so if the Klarstein/Ace/Brewcat/BrewDevil has 6 lts space under the grain basket, then "6 + 2.7xkg" might be an OK rule ... which at around 4.75kgs happens to work out as needing the same amount of strike water as the straight 4 lts/kg calculation
And then for REALLY "extreme" grain bills, the calculation might need to drop to something like "6 + 1.7xkg", just to be able to fit it all in ... but getting dry grain to mix into so little water is quite hard ... but then, to save having to stir HUGE grainbills (perhaps many tons in weight) to dough-in, some very large commercial brewers put the dry grain into the dry mash tun, and let the water in slowly from underneath (underletting) ... water slowly seeps into the grain from underneath, the air is forced out to the top, no dough balls, no need to stir
Hope that's clearer now
Cheers, PhilB