Mortising opinion?

[David Kenagy]

Looking for opinions on construction of two panels, 50” wide, 80” tall. These will be secured in a residential elevator, forming two of the walls. (The other two faces are “X” style doors that fold out of the way).

The two wood assemblies will be quarter-sawn white oak in the “Shaker” style. That is, 3 stiles from floor to ceiling (6 x 3/4) and 5 rails (5 x 3/4 at top and bottom, 2.5 x 3/4 between). Between the full-length stiles are smaller stiles and between all the rails/stiles are flat panels of 1/4 inch white oak. The rails & stiles will be glued but panels will float.

So essentially there will be wall-sized grids of white oak. But more detail about the way these are secured: I will mill the stiles with 1/4” dadoes on the internal edges. These will accept the panels (no glue) and can accept the glued tongues of the rails. That choice is easiest, but only 1/4” tongue and groove connection.
Or I can make much longer tongues and cut deeper mortises in the stiles. Since I don’t have a drill mortiser, that’s either another purchase or a lot of chisel work.

In cabinets, I’ve had great stability with similar assemblies done in the simpler way. But panel sizes were only 30-40” tall, and had side walls. The elevator panels will be secured to a steel structure. It won’t get the abuse that a door gets, but it’s in an elevator.

Would experienced folks tolerate the 1/4” tongues, or is that courting disaster?

[Kent A Bathurst]

I'm mid-range on the pucker factor here, to be honest.

Are the full-size panels made and then installed? If so, then the back side will never be seen.

I'd go with the 1/4" M&T. And on the back, I'd use something like a butterfly key to reinforce the main/primary joints.

Not a true "look at this!" butterfly, but something that can be shaped to fit in a router-cut slot [?] without any screwing around for exact fitting.

Maybe not even a butterfly shape - just a rectangular 1/8" thick flat piece kinda 1.5" x 3"-4" spanning the joint in a routed slot [don't know the right word? ]. Glued in place, and maybe some 1/2" 23ga pins to reinforce.

No callbacks on that version.

[John TenEyck]

If they are load bearing, I would never get in that elevator if I knew how it was made. Mortise/tenon joint depth should be at least 3X the thickness of the tenon. If using a stub tenon, a cope and stick stile/rail joint makes up for some of the shortcomings of the stubby tenon, but I wouldn't bet my life on it.

At a minimum, I'd be using 3/8" tenons, 1-1/4" deep, and 3/8" panels. I'd use veneered plywood panels and I'd glue them into the frames. That construction will give you a very stable construction with no rattles that can support very high loads.

John

[Jim Becker]

John, I hear you, but it's likely that these are "finish" panels that are just adhered to the elevator structure to make it look nice. That's a guess on my part, of course.

David, it would be very helpful if you can clarify the details of the project because the structural expectations do matter.

[Kevin Jenness]

If these panels are just decorative and hanging on a solid steel frame stub tenons should be fine, but if they have any structural significance they should be thicker with more substantial joints. If this is a manufactured elevator there should be some guidelines available for liner panels, otherwise there should be an engineer involved. You don't want to wing it on an elevator, so to speak.

[David Kenagy]

This is great feedback.

The panels are not structural. Think of a box, riding on (secured to) a forklift. The manufacturer’s “base” model offers two sheets of MDF coated with a wood-colored paper. The steel beneath the floor and behind one of the panels carries the weight, but pieces of plywood above the box maintain the correct orientation of the ceiling and opposite wall. As mentioned, the backs are never seen. For $5k they make something similar to what I’m describing, but the 1/4 panels are (again) MDF with a thin image. I’m replacing those with the assemblies described, but (admittedly) I don’t know whether they make mortises as robust as the ones John mentioned.

Since John’s also a CNC craftsman, I’ll mention that I planned to carve two of the 1/4” panels from 3/4” stock to produce bas reliefs. The others would remain simple, Shaker-style.

[William Hodge]

The worst stress for these panels is wood movement when secured to a metal wall.
Mortise and tenon joints are a great way to join solid wood parts. A Grizzley bench top mortiser is $360. delivered, and would pay for itself in time saved, and deliverable quality. Shim the post off the base to get 6" wide wood under the chisel.
Drawbore and peg the tenons, you will feel like a craftsman of old.

[Mark Wooden]

I feel a 1/4" is too short for use in an elevator that will be moving and also vibrating- no matter how slight- in use
I don't know what machines you're using to mill your stile and rails with; but I do know that several of my cope and pattern sets for my shapers have a 3/8" deep groove and they all can be used to cut a plain T&G joint. I also have a few that will do a 5/8" depth, but these are custom ground. Either can be pinned from the back after glue up
If you are using a square edge shaker profile, and you're only making the two panels, the work can be done on just a tablesaw and you can make the depth/ size of your tenons larger to suit the size of your panels. I also would'nt spend the time to cut the back out of the frame to install the ply panels but would cut them to fit as with a cabinet door and put them in during assembly, putting a 23 ga. pint centered on each side to keep them from moving around. A small bead of silicone in the back might not be a bad idea to keep them quiet either.....
Quick edit-
I just realized that what I've described might not provide the depth of the face of the frame to the panel desired- my solution to that would be to increase the frame thickness, but I don't know if that would work in your situation

[David Kenagy]

If I'm reading folks correctly, the consensus calls for tenons with a thickness of 3/8". I presume a tenon length of the same.

While a mortiser would be easier, I haven't needed one before, so I'm thoughtful about buying one for a solitary project. Some years ago I made a mortising jig for my router, though it's been idle for some time. But putting centered 3/8" mortises into the stiles, and leaving tongues of that size on the rails should only take a bit more time (and less time than hand-chiseling). The jig for the router also enables longer tenons than 3/8" if that's necessary.

Given that I might have mis-read the opinions, please give me a "yep" or a re-direct!

[Kevin Jenness]

1/4" thick, 1/2" long stub tenons glued in the panel groove are reasonable/normal for a 3/4" frame. Many kitchen cabinet doors are made that way. Nothing will be gained by using 3/8" thick tenons unless the frame is thicker. For more glue area/strength use a longer haunched tenon or add spline tenons or dowels.

[Jim OConnor]

Think about how much weight this adds to the elevator. I’d think you would want to be a little careful about “permanently” reducing the passenger capacity……

[David Kenagy]

Weight has been a consideration. The "stock" products are slabs of MDF. One manufacturer's option is a pair of panels made with 3/4" raised panels (oak). My plan is 1/4" flat panels. Rails and stiles being similar, my panels will have 1/3rd the weight of theirs.
The adjacent room (a kitchen) is made in the same style, which was the first factor. The second concern is that the manufacturer's flat panels are just printed paper on 1/4" MDF (no way to repair, if damaged). But low on the list of 'wants' is my plan to use a CNC machine to make a bas relief image on four of the lower panels. Each will have just part of the overall image: our dog. The result is supposed to look as if he's just on the other side of those (undecorated) rails and stiles.

[Dave Sabo]

Not sure why your apprehensive about buying the tooling you need for this job?

The customer is paying anyway.