Casing a Double-Curved Door Arch
From contributor R:
Yes, there is a way, but it is called three dimensional descriptive geometry and it is not for the weak of heart. The above book suggestion is the most practical solution. Go buy two (at least) sets of trammel points while you are at it and have fun!
From contributor J:
Fiber reinforced plaster or epoxy done in place?
From the original questioner:
Thanks for the tips. I'll find that book. My first thought was to use flexible mouldings, but the architect wants real wood with a boat finish.
From contributor D:
We do this once or twice a year, usually for an arch head door in a curved wall. We do not use computers, software, or obtuse methods, but to explain it would take a book. The shop I learned this in called it "straight up" and it was simply a full size plan and a full size elevation, and stack laminated stock for strength, with cold bent laminations for show. Profiling the casing is usually the biggest challenge.
Visualize it all as mere radii, all in one dimension, and then the other dimension. Very difficult to describe, but once you see it, it is just a matter of doing it. I consider this probably the highest form of an advanced millworker's skills, and certainly not for the weak of heart or inexperienced.
From contributor P:
This is about as tough as it gets. It is, however, doable in a small shop using lots of ingenuity, jigs and planning. The level of detail in the profile can be a real deal breaker as well. You may have to break the total profile down to some simpler detail, then glue them all together. No fun. I have done it with a shaper, curved fence and guide shoes on the table, but I favor the W & M moulder most of the time.
Depending on the curve and the volume of wood needed, your glue up options vary. Laminations work, but you have to deal with the visual affect of the glue up after machining. This may be undesirable when finishing real wood. I have also experimented with gluing up several steam bent pieces, then bandsawing the arch curve after. I found it easier to leave excess stock on the rough piece prior to milling the profile, then trimming that off later.
One thing to watch for - the wall radius and the arch radius must be a true radius. If the arch radius is actually something else, say an ellipse, things get much more difficult.
From contributor B:
First of all, you may want to consider outsourcing this. There are many shops such as ours that can produce such an item. Cost will be high, so hopefully you haven't committed to a price with the customer. Either curved specialty shops or 5-axis CNC shops can handle the job.
If this is an eyebrow arch with a low springline height, here is how you can make it. If it is a taller eyebrow, a half round or non-true radius, then this is only a beginning point, as it becomes much more difficult.
So, for a low springline eyebrow, you need to resaw boards that are as wide as the final overall height of the eyebrow. For example, if your arch height in elevation view is 8" and your moulding is 4", you would need to resaw at least 12" wide boards. After resawing enough material at about 1/8" thick x 12" wide, you need to laminate these layers at the wall radius on a form. A vacuum press is very good for this.
Once the curved 12" wide blank has dried, you can bandsaw out the 4" casing. To create the casing line, cut the casing first out of bending ply such as wacky wood. You can then lay that piece of bending ply over the laminated blank and trace its outline. This will give you a bandsaw line to follow. When done bandsawing, you have an S4S casing. If no profile is needed, you are done except for sanding.
To profile this "safely," I'd suggest a moulder such as the Williams and Hussey. Even with this machine, though, a good deal of curved work experience will be required because you are going to be guiding the S4S blank through with fixed point fences, a curved bed and a lot of free hand guidance. Not for the faint of heart. That's how we make them. We've done everything from casings to crowns using this method.
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