Has anyone ever attempted to reach the lvl cap only using XP gained from combat?

What um, are you asking exactly?

He's talking about not doing any quests and just killing everything i think.

AKA: Grinding.

Pretty sure there is at least one person who stayed near Goodsprings grinding respawning radscorps to hit the level cap.

Yeah, I read a couple posts about that. I meant more along the lines of "normal combat". Exploring the world and killing whatsits and whosies, not doing the Goodsprings exploit.

Why would anyone want to do that . That's like no-life and stupid at the same time.

It seems like a bad idea, just running around shooting stuff. Quests just make you gain levels faster and makes the game much better.

Exactly...300 XP's from a 3 min quest, or 3 hrs shooting 300 geckos...

I don't understand grinding in a single player game. Nobody is going to give you awards for doing it the hard way then.

There are plenty of places with respawning enemies. For example, Black Mountain.

It depends on why one is grinding, although in the general case I happen to agree with you that there's not much point in a SP game.

In this instance it appears the OP is going for a combat-centric character who can't be bothered with the affairs of others; with quests not available as a source of XP gain, grinding is about all that's left. One positive about such an approach: you can pretty much ignore certain skills and perks and concentrate on anything that increases combat effectiveness, which makes SP allocation and perk selection much easier since you don't have to spread points around as much.

While I probably won't do a character like this myself, it's actually eminently practical to level this way; you'll be locked out of the bumper crops of XP available in the DLCs, though, since you have to finish them before you can leave them which involves completing quests.

I do not recommend trying to level this way if you're running an XP-reduction mod, though, as it will quickly get tedious.