Loose Tenon Size for Door Construction

Thoughts on a practical size for loose tenons and mortises in man door construction. October 13, 2009

I have a job to do - 15 white pine interior doors with cope and stick pattern. I plan on using either loose tenon or dowels machined prior to running the copes. I already have 5" cutters yielding 1/4" x 1/2" stub tenons so buying new tooling is out.

Doors will use:
11" bottom rail with 2x 2-1/2" wide tenons
7" latch rail with 2x 2" wide tenons
6" top rail with 1x 2-1/2" wide tenon
Tenons centered in stock.

I have 3 questions:

1. Are 1/4" thick tenons sufficient?

2. Is a 3" overall length (1.5" each mating part) enough?

3. I was also thinking of trying a Dowelmax jig with a number of 3/8" x 2" dowels but am concerned with the relatively short dowel length. Could also use dowel rod and cut my own longer dowels too, 3", 4", 5"? Is anyone using dowels with success and would 2" standard compressed dowels be long enough?

Forum Responses
(Architectural Woodworking Forum)

From contributor G:
I make interior doors at 1 3/8" thick using my cabinet door setup. The profile is not the standard 1/4" bead but has a 1/2" bead that is slightly flattened - it is a 18th century reproduction. I use 3/8" x 3" dowels in them and have never had a problem, no call backs in 15 years. Your 1/2" tenon should work fine.

From contributor D:
A guideline for tenon thickness is 1/3 the thickness of the stock. Doesn't translate to well in inch, but 1/2" to 5/8" is good for 1-3/4" doors.

From the original questioner:
To clarify: the tenon's I was going to use are 1/4" thick not 1/2". In speaking with the folks at Dowelmax they were quite convinced that a number of 3/8" x 2" dowels would be more than sufficient and that any failure would manifest in the material not in the glue joint. It seems there is no decisive guidance for this topic. Everyone has their own way and their own opinion. I wonder, is there any benefit to extending dowels or tenons deep into the stiles to strengthen them? For example, 4" of mortise or dowels into a 5" stile. Might this cause more problems by restricting the movement of the stile due to the cross grain glue bond of the tenon/dowels?

From contributor J:
I use thicker tenons than that on a 3/4" cabinet door. I wouldn't trust it for a full size man door. If you have an order for 15 doors and plan to do others in the future, I'd invest in the proper tooling or think outside the box. How about square sticking, you can do that with just a rebate head or a dado set and make the tenon any thickness and length you want.

From the original questioner:
It seems loose tenons are pretty in favor so I'm leaning that way. I'm seeing that 1/4" is probably a little thin and 1/2" is more the norm so that would be a wise revision to the plan. Any suggestion on an appropriate length of tenon? 1.5 to 2" (3"-4" overall length) was what I had in mind.

From contributor K:
I don't think 1/4" bits clear their chips very well, especially in deep mortises, and deflection is an even bigger problem. Half inch is a lot better, but I think 5/8" is even about twice as stiff, and moves more air/chips. I don't see any down side in going larger, do you?

From contributor F:
I like the loose tenons as you have more surface area for glue, and a bit more play for alignment. With dowels you have to have every one of them dead on or you’re stuck. I just recently picked up a slot tenoning machine to increase my production, (have 15 doors and 6 panels to do), and it's a heck of a machine. I'm using 2 - 3/8" thick x 1-1/2" wide x 3" long tenons for each joint (my stiles are only 3" wide). I don't think the short length will be a detriment at all, but these doors are fairly light and made up of hard maple and rift sawn oak. If I was doing heavier hinged doors and/or using a softer wood, I'd probably make the tenons a bit longer.

From contributor H:
I use a 1/2 inch thick tenon because it is relatively easy to get a spiral bit with a two inch cutter length. That means a two inch deep mortise in rail and stile for loose tenons. I have never had any separation problems. A two inch long tenon that is three inches wide has a lot of glue surface. Be careful if you sharpen the cutter during the job. You will lose a few thousand in the sharpening process and will have to adjust your tenon stock accordingly.

From the original questioner:
The deflection of the 1/4" spiral bit had not occurred to be but indeed I can see how that could present a problem. I will up the tenon size to 1/2". Now that I have a mock up milled with cope and stick there will be no problem mortising in 1/2" slots. Thanks to all for the input.

From contributor G:
We use 1/2¨ x 4¨ fluted dowels for interior doors regardless of the cope/stick profile. Using a horizontal borer for this task makes it fast and accurate. You can buy both fluted and spiral dowels from this link.

From contributor L:
We’ve made lots of doors with ½”x 4” loose tenons over the last 20 years with no problems. Make the tenons fit the mortises so you can push them in by hand dry as a test and use glue on both surfaces. I wouldn’t try doweling without a multiple spindle drill, a horizontal boring machine with stops or a CNC machine. I think 5/8” dowels are the common size for doors.