is it legal to use a seperate board?

I should think so. Why not? At Daily chess of course it's legal. In live chess, so far as I know, the only criteria are that you don't take advice from another player or use a computer. Regarding moving pieces around on your own physical board, I expect there are different opinions about that. I have no trouble visualising but if you do have trouble then why not? Perhaps someone knows the answer!

For What it's Worth.

This is an excerpt from Chess.com on Fair Play.  Here is the link to the rest of the info.  https://support.chess.com/customer/portal/articles/1444879 

Jeff2e16 clears that one up !

Ok in 2 day (correspondence) chess.

Absolutely not allowed in 3- min ( live} chess.

Good luck busting anyone using a physical board during a rapid game. I mean seriously, how on earth would you enforce, much less have evidence of that?

"Outside assistance of any kind" is up for interpretation. I'd say that outside assistance simply refers to other players or to computers and to books but not to boards. Not that I've ever played live chess with a second board set up. It probably wouldn't be worth the time it takes to move the pieces on a second board. But "outside assistance of any kind" doesn't seem to refer to boards. The writing in red seems to be someone's addition to the rules and not part of the rules.

The comment in red is mine.  You can refer to USCF or FIDE rules for all the particulars of OTB play.  Most would agree it would not be fair if your opponent in an OTB match were using chess software on a phone or pad during play for whatever reason (or physical analysis board, books, notes etc.).   We agree to certain parameters to insure online Live chess is Fair and what is allowed in OTB play seems like a good place to start.  I agree "outside assistance of any kind" is vague and clarification by Chess.com would be helpful.  For the results of a game to be meaningful play should be fair.  That's all I meant to say.  I just wanted to insert what Chess.com had to say and an observation of my own into the discussion.  I was not trying to invalidate the points of the other posts.

We agree to certain parameters to insure online Live chess is Fair and what is allowed in OTB play seems like a good place to start>>

Fair comment although I'd suggest it may be a matter of personal taste if people use a separate board in online live chess. It doesn't obviously break the "no outside assistance" rule. I wouldn't do so because it would slow me right down having to move the pieces. I think it would break my concentration.

This is about the tenth time I've seen this discussed in the forums.  We always seem to come to the same conclusion.  Yes it's technically illegal in live chess since a second board would not be allowed OTB.  However since there is no way to enforce the rule it seems OK unless you are using that board to move pieces around and do analysis on.  That would be cheating, and although there is no way to detect it, you should at least feel a little ashamed of yourself.   I suspect though that it's more trouble than it's worth for most time controls and folks who are playing longer games know better. 

Now I understand why Chess.com does not allow the utilization of the DGT autosensory boards to their playing site.

Analysing on a separate board in live chess must be against the rules.

I don't see how you can justify having a separate board at all, you are not allowed two boards OTB. Unless you guarantee not to use an on-screen board at all, and have the moves transmitted in notation.

I wouldn’t feel cheated at all if my opponent was just replicating the board. Using it as an analysis board is a different story.

I can't speak for Chess.com's official rules (as stated above) but personally I would not consider my opponent to have cheated for having a physical board going during a daily chess game - unless they had outside help (another person or thing help) with the position. if a "separate board" is an engine, or some kind of assisted analysis, that for sure is cheating.

But as long as all of someone's ideas are honesty their own, I don't care if my opponent has a physical board going during a Daily Chess game. it's like correspondence chess, and haven't people worked that out OTB for centuries?

Live chess is different - there I think you inherently agree to play with what's in front of you. Plus, watch GMs, they calculate in their head, and I don't think you can get better at that unless you do it. 

In Daily yes.

In live chess only if don't move around your pieces and just use the board because you prefer 3D.

I had to use a separate board when I started playing on chess.com because  it took a while to get used to the screen. So I think using a separate board makes it more like over the board, not less. If using a separate board is not allowed, then lots of other things shouldn't be allowed either, like different style pieces, or different colored boards.

By the way... Chess.com offers an "analysis board" that's a simple click off of Daily Chess, and sets up your current position with the ability to move pieces around. How could that "second board" not be not allowed when chess.com takes you to it? 

The discussion is primarily about live games,  No one is disputing your right to use as many boards as you want in correspondence chess ("Daily Chess").

Fair enough, but the original question was: "Either in 30 min or 2 day chess are you allowed to recreate positions on your own board to help with visualization". Just responding to the question as the OP asked it.

Cheers