T&G cabinet door frames: tongue and panel dimensions

[mark mcfarlane]

I'm building a set of mission/shaker style doors with simple T&G rail/stile connections and rebated, glued in 1/2 MDF panels.

I'm thinking I should make the rail tenons 1mm shorter than the 7mm depth of the grooves in the stiles, and similarly, make the MDF door panels 2mm shorter than the groove-to groove distance, to allow for a tight fit.

Is this a reasonable / common approach?

Another option I've considered is to ease all of the edges of the rails and stiles to show an intentional reveal. This has an advantage that one of the mating surfaces at the rail/stile joint can be slightly proud and it wouldn't show, i.e. less sanding.

Edit: I have changed my approach from above. The tongues shall be exactly the same as the grooves, the panels will be 1mm 'small'. I'll hand sand the tongues if I need to pull the shoulders tighter.

[Jim Becker]

For the panels, I always leave a "proverbial hair" of available space so that the panel doesn't interfere with being able to glue up the frame square. For the tenons, I'd be less inclined to leave them short because of how glue operates.

[Jim Morgan]

Rail and stile cutters make joints without gaps; not sure why you would need them here. As Jim says, leaving the panel a wee bit smaller helps ensure that the r&s joints fully seat.

[mark mcfarlane]

Here's my thought process: If I cut the tongue and grooves to the same length, but for whatever tolerance reason, or wood movement prior to glue up,... the tongue on the rail is a few thousandths of an inch longer than the depth of the groove in the stile, then the joint won't close up.

If I intentionally cut the tongue short I can pull the rail shoulder tight against the stile. Its the same rationale as making the panel a tad too small.

I thought this was a common technique for mortise and tenon joints, to cut the tenon a tad shorter than the mortise depth.

Jim, what property of glue are you thinking of?

[Mike Cutler]

Mark

I don't know how important everything is to you, but if you do it this way, you will have gaps showing on the top and bottom of the doors. Not a problem for uppers, but any lowers would be very obvious.
One thing also to remember is that when you clamp up the joint, the end grain of the tenon/tongue, will compress the fibers of the long grain at the bottom of the groove.
I think you should just leave it the way it comes off the cutters. Zillions of doors have been made with this dimensional tolerance.

I'm making some Arts & Crafts style doors for our kitchen that are basically T&G joints, but the tongues on mine are deeper. 5/8"-3/4".

[Bob Grier]

If you leave the tenon short you can fill the gaps with filler. I think it looks better to make them tight fit.

[Kevin Jenness]

A 1 mm gap at the tenon end is excessive. .005" is sufficient to keep from bottoming out and preventing the shoulders from closing. The panels should have a greater clearance in case of high moisture expanding the panel and blowing the door apart- mdf is fairly stable and you are gluing the panels, so 2mm (.080") clearance should be enough insurance.

When I make doors like this 3/4" thick I mill a 1/4" x 1/2" groove and use 3/8" mdf rabbeted to fit the groove and leave a 3/32" reveal to the frame at the back. The groove is offset to the front of the door to leave the panel slightly recessed at the back. I leave 3/16" clearance at the bottom of the groove and use 1/4" spaceballs to center the panel. The extra panel thickness makes the door more solid than using 1/4" material.

[scott vroom]

You can certainly do as you suggest and cut the tenons shorter than the grooves, however as Mike pointed out the gap will be visible on base cabinet doors, something that I find unattractive. You can fill the gap but it will be noticeable.

Easing the edges of the rails and stiles to show an intentional reveal just to avoid sanding a mismatch of the mating surfaces falls into the category of "cheap tricks" IMO.

You mentioned rebating the panel. An alternative would be to run the groove the entire length of the stiles to accommodate both rails and panel.

On all of my doors I take the easy way out and use a router bit set. Sets can be had for <$50 up to $100 for top quality Whiteside. You can make dozens of doors without having to resharpen, a good investment when time is more important than technique.

[Bill Adamsen]

I tend to make full mortise and tenons ... but the principle is the same. Dry fit first to make sure it will glue up tight. As everyone else has pointed out ... cutting it short with the T&G style will leave a gap. Of course it is easy to go back and plug that hole with a wedge of the same wood (what I do on box joints).

[mark mcfarlane]

Thanks everyone for catching my error, I didn't think about the visible gap on the top and bottom of the door.

Scott, the groove will be the full length of the stiles. The rebate on the back of the panel is necessary because I am fitting a 1/2 MDF panel into a 1/4" (6mm) groove. I want the extra weight of a thicker panel, just for the 'feel' of the door.

[brent stanley]

Thanks everyone for catching my error, I didn't think about the visible gap on the top and bottom of the door.

Scott, the groove will be the full length of the stiles. The rebate on the back of the panel is necessary because I am fitting a 1/2 MDF panel into a 1/4" (6mm) groove. I want the extra weight of a thicker panel, just for the 'feel' of the door.

I typically do as you suggest with the panel itself, but for the rails and stiles, the difference between the tongue and groove should be very very small. You'll never see a few thou at each joint, and it ought to serve the role of simplifying glue up.

One concern is if you paint them after assembly, there's a chance that the panel will shift at some point (and or expansion/contraction of frame stock), revealing an unpainted strip. You can deal with this by painting the panels before assembly but you need to count on the thickness of a few coats of paint on each side when deciding on the leave thickness when machining the edges of the panel.

B

[scott vroom]

Thanks everyone for catching my error, I didn't think about the visible gap on the top and bottom of the door.

Scott, the groove will be the full length of the stiles. The rebate on the back of the panel is necessary because I am fitting a 1/2 MDF panel into a 1/4" (6mm) groove. I want the extra weight of a thicker panel, just for the 'feel' of the door.

I too prefer a meatier panel, but I take a different approach. My shaker panels are milled to 5/8" and then I use this Lee Valley back cutter bit to give it a 1/4" edge. This allows me to insert the panel into the stile groove and still have the mass of a thicker panel.

[Jim Becker]

Here's my thought process: If I cut the tongue and grooves to the same length, but for whatever tolerance reason, or wood movement prior to glue up,... the tongue on the rail is a few thousandths of an inch longer than the depth of the groove in the stile, then the joint won't close up.

But that's something that is very easy to deal with as you dry-fit just prior to slathering on the glue. Taking off a whisker is a lot easier than putting a whisker back on!

[mark mcfarlane]

But that's something that is very easy to deal with as you dry-fit just prior to slathering on the glue. Taking off a whisker is a lot easier than putting a whisker back on!

Yep, I have changed from my initial approach from.

The tongues shall be exactly the same as the grooves, the panels will be 1mm 'small'. I'll hand sand the tongues if I need to pull the shoulders tighter.

Thanks everyone for the help.

[Jim Becker]

The reason that I suggested keeping those tongues at full length is that the tenons are the entire non-end-grain glue surface that's going to be the strength of the frame, so other than adjusting for that "whisker" for fit, you maximize glue surface that way. For more strength, you'd need haunched tenons with traditional mortises in addition to the T&G coped edges.