All, I have searched everywhere and cannot find a clear answer to this issue:

My latest project is refacing my kitchen cabinet doors and drawers. I'm using poplar for the rails and stiles and went with 3/8" mdf for the panel. The particular cope and stile bits I'm using leave around 1/8" reveal to the panel on the back of the door. For a sturdier door, I want to go with the 3/8" mdf and my plan was to route a rabbet on the panel such that it fits the 1/4" grove and also then the back sits flush with the rail and stile.

Problem is this: how do I center the door panel such that the back of the door has the same gap to the rail/stiles all around? Maybe it wouldn't matter to some, but it will to me. I thought about space balls and not gluing in the panel. Is this the best option? In this case, do I need to pre-finish the panel? I'm a bit worried that the space balls compress over time and an unfinished gap will appear unless I pre-finish.

I'm planning on spraying finishing the doors with primer and then latex. How would I pre-finish the panel and still spray the final door. I'm also worried about the additional paint thickness preventing the panel from fitting in the groove.

If I instead glue the mdf panel in place, I think I can avoid pre-painting the panel, but how do I keep it centered? If I make it too tight in the groves, I would that the rails/stiles will be difficult to assemble, square, etc.

Appreciate your comments and input. Thanks in advance.

A stable panel can be glued into the stiles and rails with no problems down the road.

At assembly, pull the top and bottom rails tight to the panel. Face down, center the panel by sight. Leave the panel 1/32" or so shy on the width so the panel cannot interfere with glue-up - it does not need to bottom out. The reveals on the back are easily seen and you can adjust as things go together. You are the one sizing the panels, so you get control over those reveals.

You can use what is called a back cutter which is basically a cove like a miniature raised panel detail . Perhaps prime the panel before assembly .Maybe a drop of glue near each corner to keep them centered. Good luck

Based on my experience if everything is cut accurately space balls will center the panel.

The fit of the panel in the groove is important. It has to be just right.

I would prime the panel before you assemble if it is an option.

An old technique is to center the panel and then drill from the back on the centerline of the panel, to pin it with a round toothpick through the rail.

If you're going to go to all this work, you might want to rethink using latex on your kitchen cabinets. Unless you want to redo them in a few years.

We always use 3/8 MDF, back cut the panel with a raised panel cutter, and use space balls just like our solid wood panels. with flat panel doors we never pre-prime the panels. No need to as they will not change dimensions. With painted raised panel we always pre-prime and sand the machined area before assembling the doors.

Been doing it this way for years with no problems.

Don’t use poplar. Soft maple is the better choice.

3/8” mdf for flat panels. 5/8” for raised.

Make the panel so it is 1/32 smaller than the groove. You can make it 1/16” less than the overall length of the rail, then do the math.

This is best accomplished with a back cutter. You can also use a dado set in a table saw.

You are basically squeezing the panel without bothering the stile/rail joint.

Glue them in with TB1.

Finish them with 100% acrylic trim paint. It’s got to be hard enough you can sand it. Do not use latex.

I assume you’re cutting your back cut square , we use a small cove type raised panel cutter for our back cuts , or even Freeborns back cut shaper cutter would work . Plus it looks much better than the square cuts , and they don’t have to be perfectly centered . No way anyone can see the difference