How would you do this?

[jteneyck]

I'm working on the design of a new vanity for my half bath.  The top will look sort of like this.



It's 4" thick and will be made of MDF, then filled, primed, and painted.  I want to put a 1/4" radius on all the edges AND down that internal corner.  The outside edges are simple enough, but how would you go about creating a 1/4" fillet in the internal corner?  As I said, it's going to be painted, so any option that works is fine. 

John

[Phil Thien]

Route a piece of MDF with a cove bit, glue into the corner?

An MDF top for a bath?  That must be some pretty awesome paint!

[cputnam]

Either put some 1/4 round cove molding there or rabbit the edges to receive the molding if it needs to be flush?

[ez-duzit]

For the inside corner fill with thickened epoxy spread using a plastic spreader with a corner cut to the radius you want.

[jteneyck]

Route a piece of MDF with a cove bit, glue into the corner?

An MDF top for a bath?  That must be some pretty awesome paint!

I knew someone, maybe many, would question the use of MDF.  I'm leaning towards using it because it finishes better than any other wood type product I can think of.  Maybe it will be a disaster, but I figure it's a half bath that hardly gets used and a good finish should protect it from typical water splatters.  If it fails, I'll use something else.  

John

[jkjen89]

I'm making an assumption that you are cutting the notch before gluing up the top. If that is the case could you drill a hole on the inside corner
then cut to the edge of the hole?

John

[fredhargis]

The filler piece of cove molding is going to be a lot easier than most of the alternatives.

[Cooler]

Route a piece of MDF with a cove bit, glue into the corner?

An MDF top for a bath?  That must be some pretty awesome paint!

Grain filler + paint + 3 or 4 coats of clear poly on all surfaces and edges might work, though I admit I would not consider MDF for a work surface near water, and, while my saw can cut through two layers of 3/4" MDF, I cannot imagine how to cut a 4" thick stack.

I made a vanity years ago with a breakfront front edge but I made the two side sections about 2" lower as well.  It made for an easy build (three small cabinets instead of one complex large one.  And three smaller pieces of marble.  

In my shop a 4" thick slab would be four pieces 3/4" thick plus two pieces 1/2" thick stacked and glued.  But as I said I would have no way to cut that thickness in a single pass and I don't think you can align the pieces accurately enough to make a seamless edge by stacking after cutting.  And it is going to weigh a ton.

[jteneyck]

Grain filler + paint + 3 or 4 coats of clear poly on all surfaces and edges might work, though I admit I would not consider MDF for a work surface near water, and, while my saw can cut through two layers of 3/4" MDF, I cannot imagine how to cut a 4" thick stack.

I made a vanity years ago with a breakfront front edge but I made the two side sections about 2" lower as well.  It made for an easy build (three small cabinets instead of one complex large one.  And three smaller pieces of marble.  

In my shop a 4" thick slab would be four pieces 3/4" thick plus two pieces 1/2" thick stacked and glued.  But as I said I would have no way to cut that thickness in a single pass and I don't think you can align the pieces accurately enough to make a seamless edge by stacking after cutting.  And it is going to weigh a ton.

I don't plan to make it a solid 4".  I'll use a torsion box type construction with an inset bottom to limit the number of visible seams.  I think the cove piece glued in the corner during assembly, as several of you suggested, is the way to go at this point, but I'm open to more suggestions.  Thanks.

The top won't be a work surface; it's a half bath vanity top in a house not a restaurant so exposure to water will be minimal.  The most abuse will probably be what my wife does cleaning it. 

John

[DieselDennis]

I'd caulk that inside corner before I painted it and then give a nice index finger sized radius to the caulk.

Won't be any worse than anything the vanity top may encounter.