Making an arch

We removed a full length closet in our bathroom to make room for a tub. No problem, I thought; just take out the sliding doors and stick the tub in the space that used to be the closet. But the Wife wants me to build a graceful wooden arch between the two stubby end walls of the original closet. Basically there remains a pair of 9" walls floor to ceiling where the closet doors used to be; she wants the arch to start 3/4 of the way up those walls and meet in the center at ceiling height. I've never worked with arches before. How does one design and build such a thing?

Pete

Pete:

Maybe try a long thin piece of wood that you can bend in place to see where all should go and get some measurments. Transfer to flat surface and make a laminated beam to span.

You could also lay it out on a flat surface by bending a piece of wood or drawing an arc. One way to draw an arc is to place two pegs at the same distance apart as the walls. Take a loop of string with a pencil tied onto it. Then move the pencil from one peg to the other keeping the string tight. It will make an arc. Changing the length ot the string loop will change the depth of the arc.

Laminate a beam that matches the arc you pick.

Hope this helps. I've never done it this way but did laminate a roof form for a bird house using pegs and clamps.

There are also Mathmatical formulas that would render dimensions but those are far far in my forgotten misspent past.

Egon

Home Depot has kits to do it. At least that is where I thought I saw them.

Take two pieces 1/2" plywood and cut the arch out with a jig saw and mount it flush with the studs, on either side of the doorway. Cut both sides at the same time, or all four in your case. Then make some short blocks to join the sides. That's the base.

For drywall, it's pretty easy. Cut out drywall, metal corner tape and mud til smooth.

Wood is gonna be harder I'm thinkin. This is just an idea. Take some 1/4" hard board (masonite) and rip the width of stud facing. Then cover with 1/4" veneer plywood. You may have to kerf the back side to bend the ply. Special bending ply may be required. (all the ply are aligned the same direction) The curved molding you are on your own. [img]/forums/images/icons/shocked.gif[/img] [img]/forums/images/icons/crazy.gif[/img]

There are lots of techniques for making the arch itself, and you already have good suggestions.

To premake it out of wood, lay out the radius on a sheet of plywood and build a form on the inside of the radius; then laminate your wood around the form, leaving clamped overnight (wood handscrews are best for clamping this). Rip the wood 1" wider before forming, because it is very hard to hold the layers even while bending. After it is cured, scrape the glue off of one edge, rip to 1/2" wider using that edge, and then turn it around and rip to final width using the just-ripped edge.

For the moldings to trim out the arch, your best (and safest) bet would be to seek out a custom millwork shop that has a radius molder, if your profile is at all complex.

In the days before our shop had such a molder, I used to shape radius moldings using a shaper. This is a freehand-feed operation, and can be dangerous due to kick-back. Also, any slight "wobble" in your feed, and the result is some hand carving needed in your finished product. [img]/forums/images/icons/shocked.gif[/img]

One type of molding that would be easy to hand work on the radius is just a flat board with a bead on the inside edge (1x3,e.g.) (see attached). For the radius part, after bandsawing the wood, you can begin the bead cut with a simple scribing guage type of set up, with the face of the scribing guage rounded slightly to accomodate the radius. Then finish up with a rabbet plane and chisel.

Pete:

Scanned this page from a Xmas present. It may be of interest to you.

Egon

Thanks all. Got some great ideas and lord knows with my land all tied up in snow and ice I have plenty of time to try variations!

Pete

Interesting Christmas present you got there Egon.

try www.easy-arch.com if you need more let me know

My previous house had what you are trying to make. The bathtub of one of the bathrooms was set in an alcove with an arch over the side of the tub toward the center of the room. I always just sort of took it for granted till I got a look at the OTHER SIDE when I was up in the attic. This was 1928 lath and plaster construction. The arch was bent from wood with multiple cuts on the backside to facilitate bending. The arch looked to be eliptical and in character with the rest of the Spanish Mediteranean architecture.

Egon has given you a good suggestion as regards generating trial elipses. As you move the two "foci" closer to one another your elipse degenerates into a circle. As the string is shortened toward being stretched between the two foci, the elipse degenerates into a straight line from one focus to the other. By varying the separation between the foci and the length of the string, you will be abole to generate a family of elipses that spans the available variations.

You want to adjust the length of the loop of string and separation of the foci such that at the widest you can make an elipse that just fits the width of your opening. You then change the distance between foci and adjust the string length to again fit the opening. These two adjustments, distance between foci and loop length, allow you to create solutions that fit your opening width. A you try different pairs of adjustments you get different shapes of elipses varying across different values of eccentricity. You just need to pick the shape yoiu guys want.

Hope this isn't too terribly unclear and confusing.

[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]