Panels for Railroad Roundhouse Doors

A discussion of technical assembly details for some huge architectural doors to be made of sawn wood. June 28, 2013

We are building doors for a railroad roundhouse. Each panel of the double doors is 6' 6 1/2" x 17'. The panels are specified to be tongue and groove construction. The architect would like us to screw the tongue and groove boards in the panel together along each edge. Due to the size of the panels we are concerned with warp. Do you have any concerns with this construction?

Forum Responses
(Architectural Woodworking Forum)
From contributor J:
It does not sound like the architect knows much about woodworking, but your description isn't clear enough to be sure. Do you mean that the panels are made up of several boards T&G'd together, and he wants to put rows of screws through the tongues and grooves?

Railroad roundhouses are not structures we see every day. What sort of wood is specified? Where will these doors be used? There could be a lot of movement in panels that large.

From the original questioner:
You described it better than me. That is correct - the panels are made up of several boards T&G'd together, and he wants to put rows of screws through the tongues and grooves. I think the architect may have seen this done by another company. The doors are being made out of mahogany and will be operable. Do you think the screws will make the panel more rigid or do you think the panel will not be able to expand and contract due to the screws?

From contributor D:
Please put your architect in touch with someone that knows about large doors and has a good track record of this type of work. He does not have to reinvent this type of wheel. What is being proposed is not correct or worthwhile - as you describe it. He may have seen this somewhere, but that does not mean it is successful. Wood is wood, and there are good and proper precedents for this type of work. Are these to be swinging operable or sliding operable?

From contributor N:
Leave space in the groove; assembly with spacer balls helps. Bore slightly oversize for through bolts (not screws) so they don't split the planks. Use absolutely vertical grain wood for the planks. As they expand, they'll do so in width yet remain in alignment. Flat sawn pieces will expand in thickness and/or cup, and get tight in some spots and not others, leaving S-curved and bowed spots, possibly even cracking apart the grooves. Generally speaking, panels that big, like on gates, need crossbuck support. There was an article in Woodwork Magazine awhile back worth looking up that featured the English 5-bar gate. Not much technical info that I remember but the pictures of old and still operable gates gives one a good idea the kind of joinery needed to support such wide doors.

From contributor N:
I just re-read your post, and I want to specify I mean through bolts only at the ends of the planks, top and bottom, and at rails or crossbucks. Not planks screwed/bolted together.

From the original questioner:
Thanks for the feedback. The doors swing.

1. How do the panels expand if they have through bolts?
2. I am gathering we do not use any glue when putting the tongue and groove together.
3. We are thinking of incorporating a cross buck on the interior. How do you suggest we attach it to the door?
4. The door will be primed and painted. We are planning to prime the panels to prevent expansion/contraction.
5. Is vertical grain wood the only way to go?

From contributor N:
The individual planks need to be fastened, not the panel as a whole. The reason I said space balls help is you want no tongue to bottom out in any groove. Each plank will shrink and swell and the extra space is needed to accommodate that. No glue will hold a panel that size together. Think of each plank as an individual panel.

You need to read up on wood movement. It expands and contracts mostly across growth lines. Vertical grain is absolutely necessary - I'd use VG Douglas fir if given a choice. The oversize bore (centered in width) is for when a plank shrinks and tightens onto the bolt. The extra space accommodates this so it won't split from the pressure. The crossbuck needs to be able to keep the door from racking out of square, as this will be immensely heavy. I cited examples from a magazine article you should check, as well as search the web for photos of large gates/doors. You need to be able to cut huge precise mortise and tenon joinery, and without proper machinery this can get to be a bear.

I gotta say, some of your questions sound a little basic and this is not a project for the feint of heart. This is a very advanced door in my opinion, and I have built several thousand of them. I don't really have time to go over all the things you need to know on this forum, as nothing teaches years of experience like experience itself.

From contributor D:
I agree that this is a very advanced door that requires a builder with experience and competence. I am sure you are conscientious and willing, but that will not make a door that will last, or justify its cost. Please consider consulting professional doors builders or send your architect to them.

There are two basic types, and I am unsure of what is needed.

A plank door will show only vertical boards on one or both sides. It must have a structure that will hold it rigid, to keep it from racking, or the t&g from shifting. This could be a z brace or x brace or some other affair.

A frame and panel door will have a stout and stiff mortise and tenoned frame that carries the weight, hinges and panels, and the panels - in this case vertical boards - and allows them to each move.

Painting will not stop wood movement. Screwing t and g together will do nothing but give false hope.

From contributor N:
I wonder if anyone has ever built any of those that were truly bowed in, matching the radius of the building. I find this truly interesting as I have one right now with a slight bow, 330" radius on a 40" wide door. No, I won't be using a CNC, except for making the sill.

From contributor D:
I'm pretty sure those roundhouse doors are large enough that one would have figure in the curvature of the Earth. Seriously, I think one could easily make them flat and let the jamb fit within the curved building face.

I see a three ply affair; two m&t frames, one on either side and the T&G in the center, with those big bolts or rivets through the 3 parts. Or maybe just a two ply, with a m&t frame on the outer side and the T&G on the inner side. The hardware is definitely a serious component, but easily made in such a place as a rail yard.