So, I got a Ork nob, 20 orkboys and about 30 gretchins.The explorers standing with 10 troops and themselves at a big door leading to a deposit with plenty space for combat. As usually happens they killed all in about 30 sec, because i deployed the orks way too far and by the time they charge into melee there where only 3 orkboys standing half dead. How would you play this combat?

If players are breezing through your combat perhaps you should look to upping the arsenals of your enemies. Orks have heavy weapons same as everyone else, in fact they might have the most dakka around considering most in the Expanse are Freebootas.

Put some Flash Gitz in there with Snazzguns and grenades, Lootas in the back cackling wildly as they suppress them. Drop some Squigs that bound ahead of the Orks to tie up the Explorers, put a Mek with a Kustom Blasta and a Force Field in a group of Shootas and start targeting the heaviest PC.

Never forget to use a faction to its fullest, don't get caught in the trap that you only have a few units to represent the enemy. Variety provides both a challenge and a more memorable experience.

Excellent advise, many thanks.

You could also take a leaf out of the Dawn of War book and have a Big Mek teleport himself and his best burna boys up close and personal. The fluff generally supports Orks having access to teleportation technology and it has the added bonus that most sane players won't touch it even if they manage to keep it intact after the fight.

Just to toss some fluff, if the group hasn't already been identified by your party, your needs, or whatnot, you might have the Orks be Blood Axes, who are known for being sneaky, and for thinking sneaky. Not to say most Orks don't think/plan, at least a little, but many of them favor a straight-up fight, and recklessly engage, thinking that their toughness, durability, size, and innate "Orkiness" will keep them safe, which can be totally taken advantage of by cagey players. Blood Axes, though, seem willing to hide, and leap out on your backsides, when you didn't even plan on them being there. The above porting Big Mek, with his kustom force field, and hand-picked burna/close combat boyz could easily fit in with a group of Orks renowned for not playing "Orky fair", and if your players think they know Orks so well, being one of the primary antagonists of the 40k setting, it might be a rude awakening when they meet Orks who totally behave differently then the norm. This is my take on the Blood Axes, anyway. Your view might differ.

Blood Axes are good. Kommandos also favour the use of high explosives so setting traps isn't unusual.

In fact any Oddboyz are likely to make things tricky for the players.

Weirdboyz = psychic artillery/support

Runtherds = Squigs, squigs, squigs... Or even the occasional squad of Gretchen marksmen/mobile cover

Bad Doks = Cyborks and patching Orks up on the fly... don't forget Orks have their own range of drugs (Fightin' juice) that can make them even more horrifically resilient

Meks = Guns or even just the humble trukk can mean a lot more Orks reach close combat.

Uh! More excellent advice, thanks guys!