OK, where are my molding people...

I have to cut into my sheetrock and remove a 2x3 piece that will include my nice new baseboard.

Is there a way to cut through the molding that's already on the wall without wrecking it?

It is MDF, and I really don't want to take it down because I won't be able to get it back up, me thinks.

My own thoughts: some low-duty reciprocator? A rotary (dremel) saw? Remove the sheetrock from behind the molding, then cope the molding cut?

Any ideas cheerfully entertained...

You can cut out the dry wall above the baseboard. Then pick out what remains behind the base board with a screwdriver but I don't understand why you would want to do that. Are you leaving the baseboard in place or are you make changes to it. You can't cope the base board without removing it. What's your inhibition about removing it? Reinstalling is a piece of cake.

Why not put you project in more context, maybe someone will be able to assist you.

OK, so let me clarify:

I have two dining room walls -- A and B. "A" currently has a hot water heating convector cabinet built into the wall.

We are going to build French doors into that wall, so we need to move the heating convector to wall "B".

In building that convector into the wall (it sits about 5 inches into the wall), I will have to cut a hole in the sheetrock and into the existing molding.

If I pull the base molding off (it's MDF), I'm afraid it will be destroyed (cracking, large holes pulled out from the nails, etc.).

Sooo, I'm looking for a way to simply cut that molding without ripping the entire plank off the wall.

Did that make much sense?

The Fein Multimaster will do it. Fein Power Tools USA Quality Precision Power Tools. Warning - it's not cheap.

First MDF baseboard is probably one of the cheapest things you will find at the lumber yard or home center. Second if you cut the paint, caulking along the top edge with a utility knife you will most likely be able to pry it off with out damage. The nails will pull through the MDF and remain in the wall. Since the ends are probably mitered in the corners with the adjoining molding, start in the middle of the wall so it can bow out as you pry it off. Nail holes are easily filled. You will probably have to repaint.
I take it that you heat convector is a rectangular unit that sits in the wall between studs and projects out beyound the wall surface. If that is correct you would want to simply cut the recess in the wall and the molding. The remaining molding would have a square cut end and would butt up against the heat convector. If that is correct remove a little of the drywall to determine where the studs are and exactly where the heating convestor will sit. Mark the outline of the dry wall to be removed. Then using either a utility knife or a dry wall saw remove the drywall. Cut the molding in the center of that opening. Just about anything will cut the MDF. You probably could use the drywall saw. Use a hammer and chisel if you want. MDF is quite soft and pliable. If you cut the molding in the center, then pull it away from wall a few inches you should be able to easily cut it at the mark with a hand saw.

Is this what you have to do?

Harold has the right idea if what he is suggesting is your project then don't fear the mdf . If it were me I would just remove it and repaint the base. Mdf is one of the most forgiving trim materials you can work with. In my experience it comes down easily with careful cutting of the caulk line a and a little gentle prying. GOOD LUCK, AC

Yes, that's exactly what's going on. (And yes, the molding butts right up to the convector's edge.)

Since you folks seem confident that the MDF will survive, I'll give it a (gentle) spin.

I'm only worried about the MDF because it was a custom profile that was shipped to us, so to get another board would be a hassle.

What I'll do is use the jab saw on the sheetrock, and cut the molding with the coping saw. (I'm looking for a clean cut.)

PS. Harold, that is a masterpiece picture!

@KISS: I secretly lust for the MultiMaster whenever I see the ad on late-night TV... and I'm only half-kidding. Especially at the low low price of $400.

Beginning to see the light. Cut the molding in the center of the opening. Pull each piece gently away from the wall and make your finish cut. I'd use something other than a coping saw. I'd get a better (straighter) cut with a hand saw. Coping saw's blade too narrow. Try a mini hack saw, one of those handles that holds a the blade with the end sticking out. Or wrap a hack saw blade with tape on one end for a handle. After cutting in the center of the opening you should be able to pull the molding away from the wall about 6" if the closest nails is any distance away. It's that flexible. Main thing is to cut the paint/caulking line.

Epilogue:

The drywall saw went through the molding cleanly and easily.

I now have a nice square hole in my wall.

Thanks.

Good job !