We have been faced with almost weekly requests to manufacture (glass) mullion doors with the mullions forming an 'X' pattern in the framed door opening. Our only method, given tooling and machinery on-hand, is to make the door frame and mullions with a square-edged profile (i.e. no framing bead), and simply angle cut and butt-joint the mulls against the rails, and one-another in the center of the X where they meet. Obviously, not a quality joint, and very limited on style. Our regular setup for coping mullions will not allow for the mullion to be coped with an angled end. We feel like we're going to have to 'invent' some method in order to expand our capabilities, and provide profiled and matching coped X mullions. My first thought would be to rely on some type of router table set up, due to higher rotation/reduced cutting pressures while dealing with what I cant imagine to be a very robust setup. The primary challenge being able to cope at a variety of angles (the X's are rarely in a SQUARE door frame, and nor are they perpendicular to one-another). We see photos and examples of these doors all the time...HOW IS IT BEING DONE?!

You need a sliding shaper. Simply use a fences set at 45 degrees to the cutter head. How are you currently coping your square cut rails?

Thanks for the reply...
Currently, we are not coping them. They are just a butt joint, glued and stapled at back side.
On the basis of your reply, I quickly searched and found an adjustable angle coping sled (DELTA 43-188 Sliding Shaper Jig), which is unfortunately no longer available. I imagine we could repurpose a sliding miter jig, and build something like this ourselves. This method will still take a fair bit of time and careful attention with cut/trial, but I suppose that is to be expected. Also, as the angle can sometimes be very steep, that causes the coped end of the mullion to be extended quite a bit beyond the sled clamps...especially not good for coping the portion that requires the mullion end to be 'leading' into the cut. I see some other coping sleds out there, but all others I'm finding are fixed, with no angle adjustment.

We used to make these for a cabinet shop almost every month. I made a custom sled that held the part at the correct angle to go thru the coping cuts. When coped, the parts were left 1/8" wider on each face to enable cleaning up and blow out. Then we sized to final width, then profiled and assembled.

I would charge about $250 per door, usually doing 2 to 4 to 6, but sometimes it was 20 doors! Eventually, they learned how to make these themselves, but they had a struggle.

You don't need anything special - make a slide out of good 1/2" ply or 3/4" mdf or solid wood. Get your angle and test it with scraps.

We were supposed to do a set recently, but the customer decided to do a regular vertical/horizontal.

My plan was to run a pocket in the cnc the size I needed to hold all of the mullions in a piece of mdf and use a bearing to ride against it. Put the whole X together and do all eight outside copes with the X assembled.

Leave my perimeter sticking oversized to fudge anything with overall door size I needed to after assembly, since getting everything right on the inside is more important than getting the overall size perfect right off the bat. Or, if I REALLY screw up, I can make my template just a freckle bigger if need be easily, and run ne parts.

Not that I'd ever do anything wrong....

People generally ask for those X mullions and learn they need a second mortgage to afford them. If you offer them, send out the specs to one of the door companies that make them and get a quote and charge that much or more even if you make them in house.

The thing is, door width changes, so does the templating to make the darned things.